MSK 3

Question 1

End stage SLAC

Answer 1

In end stage SLAC, the midcarpal joint collapses under compression and the lunate assumes an extended or dursiflexed position - DISI

Question 2

synovial thickening

ddx

Answer 2

• synovial thickening
  
  • lipoma aborescence
  • PVNS
  • rheumatoid
    *

Question 3

dDx of ABC

Question 4

Answer 4

Gorham disease

Dr Francis Deng and Dr Yuranga Weerakkody◉ et al.

Gorham disease or vanishing bone disease is a poorly understood rare skeletal condition which manifests with massive progressive osteolysis along with a proliferation of thin walled vascular channels. The disease starts in one bone but may spread to involve adjacent bony and soft tissue structures.

Terminology

Other names for this condition include progressive massive osteolysis, Gorham-Stout disease, and phantom bone disease.

Epidemiology

Gorham disease is thought to be non-hereditary and there is no recognised gender predilection. It can potentially occur in any age group although most reported cases have been in young adults 2.

Clinical presentation

Signs and symptoms are incredibly varied depending on the bones involved, and may only become apparent after a fracture.

Pathology

The osteolysis is thought to be due to an increased number of stimulated osteoclasts 3, which is likely secondary to abundant non-neoplastic vascular and lymphatic proliferation in the affected region 9. The bone is subsequently replaced by variable amounts of fibrous connective tissue that is hypervascular10.

Location

Gorham disease can potentially involve any bone. Reported sites include:

humerus (first reported case)

shoulder girdle

pelvis

skull 2

mandible

Splenic lesions (cysts) and soft-tissue involvement underlying skeletal disease represent characteristic extraskeletal manifestations supporting the diagnosis 6.

Radiographic features

Plain radiograph and CT

intramedullary or subcortical lucent foci may be the earliest manifestation 1

this progresses to profound osteolysis with resorption of affected bone and lack of compensatory osteoblastic activity or periosteal reaction

Scintigraphy

99mTc bone scan may initially be positive but later becomes negative with ongoing bone resorption

History and etymology

It was first reported by Jackson in 1838 12 and later defined by Gorham and Stout in 1955 13.

Differential diagnosis

Imaging differential considerations include:

generalised lymphatic anomaly

multifocal lymphatic malformations, including intramedullary bone lesions

does not classically cause progressive osteolysis 11

osteolytic metastases

osteolytic primary bone lesion

multiple myeloma

osteomyelitis

rapidly progressive osteoarthritis

Milwaukee shoulder

multicentric carpal tarsal osteolysis

Question 5

Answer 5

Osteochondritis dissecans

Dr Mostafa El-Feky◉ and Assoc Prof Frank Gaillard◉◈ et al.

Osteochondritis dissecans (OCD) is the end result of the aseptic separation of an osteochondral fragment with the gradual fragmentation of the articular surface and results in an osteochondral defect. It is often associated with intraarticular loose bodies.

Epidemiology

Onset is between childhood and young adults age, with the majority of patients being between 10 and 40 years of age, with approximately a 2:1 male to female ratio 3.

Risk factors

repetitive throwing / valgus stress and gymnastics / weight bearing on upper extremity

valgus stress / compressive force on the vulnerable chondroepiphysis of the radiocapitellar joint in skeletally immature patients is supported as the aetiology for OCD of the capitellum 8

ankle sprain/instability

In the talus, 96% of lateral lesions and 62% of medial lesions were associated with direct trauma 9

competitive athletics 10

family history: epiphyseal dysplasia has been postulated as a subset of OCD 11

Clinical presentation

Symptoms are variable and range from asymptomatic to significant pain and locking (suggesting loose body formation). Joint effusions and synovitis are often present.

Pathology

The exact aetiology is uncertain and controversial, with the majority of cases thought to be the result of trauma 4. In up to 40% of cases, patients give a history of trauma as the inciting event 3. Other postulated causes include 4:

avascular necrosis (AVN)

fat emboli

microtrauma

familial dysplasia

Location

Many joints can be affected, but typical locations include:

femoral condyles are most common site accounting for ~95% of all cases: osteochondritis dissecans of the knee

talus: osteochondritis dissecans of the ankle
capitellum: osteochondritis dissecans of the elbow

glenoid 7

Staging

See osteochondral injury staging and osteochondritis dissecans surgical staging.

Radiographic features

Plain radiograph

Plain radiographs should be the first step in the evaluation of knee pain, however, unless advanced changes are present and/or a meticulous technique employed, early findings of osteochondritis dissecans may be occult. The intercondylar “notch” view is very helpful.

Early findings include subtle flattening or indistinct radiolucency about the cortical surface. As the process progresses, more pronounced contour abnormalities, fragmentation and density changes (both lucency and sclerosis) become evident. If an osteochondral fragment becomes unstable and displaced, then donor site and intra-articular fragment may be seen.

CT

CT has the advantage of sectional imaging through the joint and multiplanar reformats. Findings are similar to those seen on plain radiographs.

MRI

MRI is the modality of choice, with high sensitivity (92%) and specificity (90%) 4 in the detection of separation of the osteochondral fragment. This is essential in determining management.

T1:

variable signal overall with intermediate to low signal adjacent to fragment and variable fragment signal

T2:

the high signal line demarcating fragment from bone usually indicates an unstable lesion however false positives can result from oedema 6

low signal loose bodies, outlined by high signal fluid

donor defect filled with high signal fluid

high signal subchondral cysts

T1+gad:

enhancement indicates the viability of the lesion

The four classic signs of instability described at MRI include 14 :

high signal intensity rim at the interface between the fragment and the adjacent bone on T2-weighted MR image

fluid-filled cysts beneath the lesion

high signal intensity line extending through the articular cartilage overlying the lesion

focal osteochondral defect filled with joint fluid, indicating complete detachment of the fragment

Complications

persistent pain with activity: ~ 2/3 following surgical management of knee and 40% following surgical management of elbow 12,13

articular incongruity 13

early degenerative joint disease 13

Treatment and prognosis

Spontaneous healing is usual unless there is an unstable fragment, and treatment revolves around rest and immobilisation for up to a year 5.

When the fragment is unstable or displaced, without treatment patients are susceptible to premature secondary osteoarthritis. Numerous surgical approaches have been tried, including drilling, bone grafting, replacement of bone fragment and pinning 5.

When surgery is performed, the results in most cases are only “fair”. ~50% (range 35-70%) of patients achieve a “good to excellent” clinical outcome 3 but even in these cases, the majority develop osteoarthritis.

History and etymology

It was first described by the German surgeon Franz Konig in 1888.

Differential diagnosis

normal irregular distal femoral epiphyseal ossification

avascular necrosis

osteochondral impaction fracture

stress/insufficiency fracture

See also

differential diagnosis of erosive arthritis

Question 6

Answer 6

Unicameral bone cyst

Dr Henry Knipe◉◈ and Assoc Prof Frank Gaillard◉◈ et al.

Unicameral bone cysts (UBC), also known as simple bone cysts, are common benign non-neoplastic lucent bony lesions that are seen mainly in childhood and typically remain asymptomatic. They account for the S (simple bone cyst) in FEGNOMASHIC, the commonly used mnemonic for lytic bone lesions.

Epidemiology

They are usually found in children in the 1st and 2nd decades (65% in teenagers) and are more common in males (M:F ~ 2-3:1) 2,6.

Clinical presentation

These lesions are usually asymptomatic and found incidentally, although pain, swelling and stiffness of the adjacent joint also occur. The most frequent complication is a pathological fracture, and this is frequently the cause of presentation 1,2,6.

Pathology

When uncomplicated by fracture the cysts contain clear serosanguineous fluid surrounded by a fibrous membranous lining. It is thought to arise as a defect during bone growth which fills with fluid, resulting in expansion and thinning of the overlying bone.

During the active phase, the cyst remains adjacent to the growth plate. As the lesion becomes inactive it migrates away from the growth plate (normal bone is formed between it and the growth plate) and it gradually resolves 3,5.

Location

They are typically intramedullary and are most frequently found in the metaphysis of long bones, abutting the growth plate 1. Locations include 1,2,5:

proximal humerus: most common 50-60%

proximal femur: 30%

other long bones

occurrence elsewhere is relatively uncommon, and usually occurs in adults

spine: usually posterior elements
pelvis: only 2% of UBC 1

UBCs can be rarely seen in adults in unusual locations such as in the talus, calcaneus, or the iliac wing.

Radiographic features

Plain radiograph

UBCs are well defined geographic lucent lesions with a narrow zone of transition, mostly seen in skeletally immature patients, which are centrally located and show a sclerotic margin in the majority of cases with no periosteal reaction or soft tissue component. They sometimes expand the bone with thinning of the endosteum without any breach of the cortex unless there is a pathologic fracture. Prominent ridges of bone can appear as pseudotrabeculation on x-ray but in fact, UBC is made of one contiguous cystic space. Rarely, they are truly multiloculated 3.

If there is fracture through this lesion a dependant bony fragment may be seen, and this is known as the fallen fragment sign.

CT and MRI

CT and MRI add little to the diagnosis, however, can be helpful in eliminating other entities that can potentially mimic a simple bone cyst (see differential diagnosis below).

MR signal characteristics for an uncomplicated lesion include:

T1: low signal

T2: high signal

Usually there no fluid-fluid levels unless there has been a complication with haemorrhage.

Scintigraphy

Unicameral bone cyst on bone scintigraphy tends to appear as foci of photopenia (cold spot). However, a pathological fracture would cause an increased radioisotope activity.

Treatment and prognosis

Intervention is usually not required for an asymptomatic lesion. If large and threatening to fracture, or causing deformity then an intralesional steroid injection can be performed 3-5. If fractured the bone usually heals normally 5. In some instances, surgery with curettage and bone grafting is required.

Differential diagnosis

General imaging differential considerations include

intraosseous lipoma

fibrous dysplasia

eosinophilic granuloma (EG)

giant cell tumour of bone: usually older, extending to articular surface

non ossifying fibroma: eccentric, cortical base

haemophilic pseudotumour (intraosseous)

aneurysmal bone cyst (ABC): usually eccentric

Question 7

Answer 7

runners and cyclists

oedema between ITB and Lat fem condyle

Hx may be ? lat meniscus tear

this is the next cause for lat knee pain.

Iliotibial band syndrome

Dr Yuranga Weerakkody◉ and Dr Saqba Farooq et al.

Iliotibial band (friction) syndrome is a common cause of lateral knee pain related to intense physical activity resulting in chronic inflammation. Alternatively, the same pathology can occur over the greater trochanter and is considered the same diagnosis.

Epidemiology

Commonly affect young patients who are physically active, most often long-distance runners or cyclists. The exact prevalence is unknown, but one study has found the prevalence among actively training marines to be higher than 20% 5. Iliotibial band syndrome accounts for 12% of running-related overuse injuries 4.

Clinical presentation

Classically, iliotibial band syndrome is diagnosed by history and physical examination. Pain over the greater trochanter or at the lateral knee joint is the presenting symptom with point tenderness 1-2 cm above the lateral joint line. Pain is usually worse with downhill running and increases throughout an episode of activity 4.

Pathology

When the knee flexes, the iliotibial band (ITB) moves posteriorly over the lateral femoral epicondyle. When the band is excessively tight or stressed, the ITB rubs against the epicondyle irritating the lateral synovial recess.

WIth hip flexion, the ITB slides anteriorly over the greater trochanter and may cause a painful clunking sensation or audible snap.

Aetiology

The following physical factors are reported to be associated with the development of the syndrome 4:

limb length discrepancy

genu varum

overpronation

hip adductor weakness

myofascial restriction

Microscopic appearance

The histologic analysis demonstrates inflammation and hyperplasia in the synovium.

Radiographic features

Ultrasound

Allows visualisation of the impingement by assessing dynamic motion of the ITB through knee flexion and extension.

MRI

MRI is reserved for when the diagnosis is unclear and to exclude other aetiologies of lateral knee pain such as a meniscal tear or lateral collateral ligament injury.

MR findings of ITB syndrome include ill-defined signal abnormality within the fatty soft tissues interposed between the ITB and bone. In the knee, the soft tissues lateral to the lateral femoral condyle show low T1 and high on T2 signal, in keeping with oedema/fluid. In the hip, similar soft tissue changes are present and there may also be tendinopathy or tear of the gluteus medius or minimus tendons. There may also be marrow oedema in the affected bone.

Cystic areas representing primary or secondary (adventitious) bursae may be identified.

Chronic MR findings include thickening of the ITB and increased T2 signal intensity superficial to the ITB are occasionally seen. Soft tissue fibrosis and bony proliferation may be present.

Treatment and prognosis

Initial treatment is conservative, consisting of physical therapy, anti-inflammatory medication, and steroid injections 3.

Surgical treatment is reserved only for those who fail conservative treatment and includes resection of the posterior aspect of the ITB 3.

Differential diagnosis

General imaging differential considerations include:

lateral meniscal tear

lateral collateral ligament injury

See also

proximal iliotibial band syndrome

Question 8

Answer 8

Fibrous Dysplasia

Polyostotic

Question 9

Answer 9

• Basion Dens Interval discociaterval
  
  • Kids < 8 year have different injury pattern and have high risk of ligamentous injury
  • Kids < 8 years have an adult injury pattern.
• don’t miss bilateral injury.
• Used to evaluate Atlanto-occipital discociation injuries.
• Distance from the basion to the tip of the dens should be < 12mm on x-ray or <8.5mm on Ct.

Question 10

What are the main differences in characteristics of Primary bone tumours VS primary Soft tissue tumours (that are near bone).

Answer 10

• Primary Bone tumours
  
  • Epicentre centered on bone.
  • Beveling away from bone (ie inside to out)
  • Periosteal Reaction present
  • Large boney component, small soft tissue component.
• Primary Soft tissue Tumours
  
  • Epicentre in soft tissues adjacent to bone
  • Bevelling towards bone (ie Outside in)
  • Periosteal reaction absent
  • Large soft tissue component, small boney component.

Question 11

Describe the FiCAT Classification

2019 Aug Q100

Answer 11

Ficat and Arlet classification of avascular necrosis of femoral head

Dr Mostafa El-Feky◉ and Assoc Prof Frank Gaillard◉◈ et al.

The Ficat and Arlet classification uses a combination of plain radiographs, MRI, and clinical features to stage avascular necrosis of the femoral head.

Classification

stage 0

plain radiograph: normal

MRI: normal

clinical symptoms: nil

stage I

plain radiograph: normal or minor osteopenia

MRI: oedema

bone scan: increased uptake

clinical symptoms: pain typically in the groin

stage II

plain radiograph: mixed osteopenia and/or sclerosis and/or subchondral cysts, without any subchondral lucency (crescent sign: see below)

MRI: geographic defect

bone scan: increased uptake

clinical symptoms: pain and stiffness

stage III

plain radiograph: crescent sign and eventual cortical collapse

MRI: same as plain radiograph

clinical symptoms: pain and stiffness +/- radiation to knee and limp

stage IV

plain radiograph: end-stage with evidence of secondary degenerative change

MRI: same as plain radiograph

clinical symptoms: pain and limp

History and etymology

The French orthopaedic surgeon Paul (RP) Ficat (1917-1986) 4 in association with Professor Jacques Arlet devised a system of staging idiopathic avascular necrosis of femoral head in the late 1970s based on two fundamental concepts 2:

a standard radiograph shows only the shadow of the mineralised portion of a bone

bone necrosis is the end result of severe and prolonged ischaemia

See also

avascular necrosis

avascular necrosis of the hip

Steinberg staging

ARCO classification

Question 12

Segond fracture

Answer 12

Avulsion of middle third of lateral capsular ligs

VERY HIGH ASSCOIATION WITH ACL tears

Internal rotation and varus with internal rotation

look for posterolateral corner injuries

Question 13

Answer 13

LCH

Question 14

Osteopathia striata

Answer 14

AKA: Voorhoeve Disease

• Linear longitudinal striations in metaphyses
• A/W focal dermal hypoplasia (Goltz syndrome)
• “Celery Stalk metaphysis”

Question 15

Meniscocapsular separation

Answer 15

Meniscocapsular separation

Meniscocapsular separation refers to detachment of the meniscus from its capsular attachments. It is an uncommon injury.

Clinical presentation

Clinical findings are nonspecific and can include pain, instability, and joint effusion.

Pathology

Location

it is more common in the medial (more frequently posterior horn region 5) than in the lateral compartment of the knee

ramp lesions are a specific type of meniscocapsular injury associated with ACL-deficient knees 6

meniscofemoral detachment is more common than meniscotibial detachment 4

Associations

While it can uncommonly occur in isolation, it is more often associated with other ligamentous injuries.

Radiographic features

MRI

Meniscocapsular separation is usually diagnosed arthroscopically and the positive predictive value (PPV) of MRI has been traditionally described as being low 3 (as low as 9% medially and 13% laterally).

Low predictive value MRI findings that have been correlated with meniscocapsular separation include 1-2:

interposition of fluid between the meniscus and the medial collateral ligament

meniscal corner tears: according to one study had a PPV of 0% medially and 50% laterally 3

perimeniscal fluid

meniscofemoral and meniscotibial extension tears

irregular meniscal outline

increased distance between the meniscus and the medial collateral ligament

visualisation of fluid from the superior all the way to the inferior end of the meniscus has been described as a more suggestive feature 5 (PPV unknown)

On MR arthrography meniscocapsular separations have been correlated with interposition of contrast medium between the meniscus and the medial collateral ligament.

Treatment and prognosis

It may heal after conservative treatment or after re-suturing the meniscus into the capsule.

Complications

Potential complications include:

increased meniscal mobility and resultant meniscal tears 5

Differential diagnosis

On MRI consider a normal menisco-synovial recess / perimeniscal recess 4.

Question 16

SLAC Wrist

Answer 16

OA and CPPD and Rheumatoid

Question 17

Answer 17

adamantimoma

anterior tibial cortex is typical

ddx is OM and FCD

Question 18

dash board injury

Answer 18

forse is applied to an aspect of prox tib with flex knee

Puture PCL

Check PCL, POp art and nervers

Question 19

Describing the epicenter of the lesion

Answer 19

Intra-articular

central

eccentric

cortical

paraosteal

Question 20

Answer 20

Mazabraud syndrome + ABC

Question 21

Erosive OA

Answer 21

• gull wing
• joint space narrowing
• central erosions
• PIP and DIP
• Ankylosis
• Undulating osseus contours
• F > M
• Subluxations on ulnar side
• does not effect MCP/intercarpals/proximal zones
• if you see it proximally, may be psoriasis

Question 22

popliteaus pseudotear

Answer 22

mimics posterior tear

Question 23

Answer 23

Volar plate avulsion injury

Dr Mohamed Saber and Dr Charlie Chia-Tsong Hsu et al.

Volar plate avulsion injuries are a type of avulsion injury. The volar plate of the proximal interphalangeal (PIP) joint is vulnerable to hyperextension injury, in the form of either a ligament tear or an intra-articular fracture.

Gross anatomy

The volar plate forms the floor of the PIP joint separating the joint space from the flexor tendon sheath. The volar plate has a ligamentous origin on the proximal phalanx with a capsular insertion onto the middle phalanx.

Pathology

Hyperextension injury involving the PIP of the finger can avulse the volar plate which is commonly associated with a volar avulsion fracture at the base of the middle phalanx.

When the volar avulsion fracture involves a significant portion of the articular surface, instability and dorsal dislocation of middle phalanx can occur. This is because a greater portion of the stabilizing collateral ligaments is attached to the avulsed fragment.

Classification

Knowledge of the orthopedic Eaton classification is practical when reporting volar plate injury as it influences the decision on management 3. Treatment is dependent on the following factors:

size of the fragment (<40% of articular segment)

degree of impaction

direction of the dislocation

Another classification which is considered useful for management is the Keifhaber-Stern classification.

Radiographic features

A small fragment of bone is avulsed from the volar base of the middle phalanx. If there is significant involvement of the articular surface, this may be associated with dorsal dislocation of the middle phalanx.

Treatment and prognosis

Overall, a small fragment involving <40% of the articular segment and/or reducible fracture with < 30 degrees of flexion is usually managed conservatively with finger splinting. A large fragment or > 30 degrees of flexion to reduce the fragment and malalignment post-closed reduction are indicators for operative treatment.

Question 24

Answer 24

Giant Cell Tumour

Case courtesy of Radswiki, Radiopaedia.org, rID: 11454

Question 25

Hoffas fat pad inpingement

Answer 25

• Hoffas fat pad inpingement
• cause of anterior knee pain

Question 26

Answer 26

There is a well-circumscribed anterior paraarticular oval mass within the infrapatellar (Hoffa’s) fat pad. It appears isointense to the muscles on T1WI with a central area of high signal (isointense to the articular cartilage), heterogeneous high signal on PD fat sat sequences with a central area also isointense to the articular cartilage and peripheral hypointense rim (calcification). No enhancement is seen following IV contrast administration. Note mild oedema of high signal within of the infrapatellar fat pad with no lesion of the adjacent bone. An intraarticular effusion is noted. Grade 3 vertical oblique tear of the posterior horn of the medial meniscus.

Case Discussion

Intracapsular (osteo-)chondroma of the knee is a rare benign tumour of cartilaginous origin due to an extrasynovial metaplasia, usually located within the infrapatellar fat pad.

The main differential diagnoses include localised pigmented villonodular synovitis (also known as intraarticular giant cell tumour of the tendon sheath), calcified synovial sarcomas, calcifying bursitis, primary synovial chondromatosis, periosteal chondromas, and soft tissue chondrosarcoma.

Localised pigmented villonodular synovitis typically appears as a soft tissue mass of midline location within the infrapatellar fat pad in contact with the patellar tendon. Its signal intensity is variable; however, the presence of low signal intensity on all sequences is a typical feature, indicating haemosiderin deposition.

Question 27

Answer 27

Question 28

Answer 28

calvarlia haemangioma

Question 29

Radiographic features

Five classic bone contusion patterns have been described 1-4:

pivot-shift injury

Answer 29

valgus stress to flexed and externally rotated knee

contusion pattern: posterolateral tibial plateau and mid part of lateral femoral condyle

associated with anterior cruciate ligament (ACL) tears

see also: contrecoup injury of the knee, O’Donoghue unhappy triad

Question 30

Answer 30

Haemophilic arthropathy refers to permanent joint disease occurring in haemophilia sufferers as a long-term consequence of repeated haemarthrosis.

EpidemiologyCut

Around 50% of patients with haemophilia will develop a severe arthropathy.

Clinical presentation

Presents similarly to osteoarthritis, with chronic joint pain, reduced range of motion and function, and reduced quality of life.

Pathology

Haemophilia is an X-linked recessive disease affecting mainly males. Haemarthroses may be spontaneous or result from minor trauma and typically first occurs before the age of two and continues to occur into adolescence. It is usual for the same joint to be repeatedly involved. In adulthood, haemarthroses are uncommon. However, proliferative chronically-inflamed synovium results in the development of haemophilic arthropathy.

The haemarthroses results in the deposit of iron in the intraarticular region, which then leads to the proliferation of the synovium, neoangiogenesis, and ultimately damage to both the articular cartilage and subchondral bone 8.

Haemophilic arthropathy is characterised by synovial hyperplasia, chronic inflammation, fibrosis, and haemosiderosis. The synovium mass erodes cartilage and subchondral bone leading to subarticular cyst formation 3.

Location

Haemophilic arthropathy is often monoarticular or oligoarticular. Large joints are most commonly involved in the following order of frequency 2:

knee

elbow

ankle

hip

shoulder

Radiographic features

Plain radiograph

joint effusion is seen in the setting of haemarthrosis

periarticular osteoporosis: from hyperaemia

epiphyseal enlargement with associated gracile diaphysis: from hyperaemia (appearances can be similar to juvenile rheumatoid arthritis and paralysis)

secondary degenerative disease: symmetrical loss of joint cartilage involving all compartments equally with periarticular erosions and subchondral cysts, osteophytes and sclerosis

knee 3

widened intercondylar notch

squared inferior margin of the patella

bulbous femoral condyles

flattened condylar surfaces

changes can be classified through the Arnold-Hilgartner classification 4

elbow 2

enlarged radial head

widened trochlear notch

ankle 1

talar tilt: relative undergrowth of the lateral side of the tibial epiphysis leads to a pronated foot

Question 31

LCL

Answer 31

ant post - ITB, LCL, biceps fem

ITB inserts on gerdys tubercle

Question 33

Question 34

significance of ulnar variance.

Answer 34

Associations

positive ulnar variance is associated with ulnar impaction syndrome.

negative ulnar variance is associated with Kienbock disease and ulnar impingement syndrome

Ulnar variance (also known as Hulten variance) refers to the relative lengths of the distal articular surfaces of the radius and ulna.

Ulnar variance may be:

neutral (both the ulnar and radial articular surfaces at the same level)

positive (ulna projects more distally)

negative (ulna projects more proximally)

Variance is independent of the length of the ulnar styloid process.

Pathology

Aetiology

trauma or mechanical

distal radius/ulnar fractures with shortening (e.g. impaction) and angulation

DRUJ ligamentous injuries (e.g. Galeazzi and Essex-Lopresti-fracture dislocations)

surgical shortening of ulna or radius

growth arrest (e.g. previous Salter-Harris fracture)

congenital

Madelung deformity/reverse Madelung deformity

Radiographic assessment

Ulnar variance changes with wrist position (more positive with maximum forearm pronation and negative with maximum forearm supination) and increases significantly during a firm grip 1.

To determine ulnar variance on radiographs, the generally accepted standard view is a posteroanterior view obtained with the wrist in neutral forearm rotation, the elbow flexed 90° and the shoulder abducted 90°.

Positive variance occurs when the level of the ulna is >2.5 mm beyond the radius margin at the distal radio-ulnar joint. Negative variance is when the ulna is ≤2.5 mm than the radius at the DRUJ 1.

Question 35

what is this?

Answer 35

Rheumatoid arthritis (RA) is a chronic multi-system disease with predominant musculoskeletal manifestations. Being a disease that primarily attacks synovial tissues, RA affects synovial joints, tendons, and bursae.

Refer to the related articles for a general discussion of rheumatoid arthritis and for the particular discussion of its respiratory and/or cardiac manifestations.

Radiographic features

Regarding disease detection, as the early RA manifestations are non-osseous in nature, ultrasound and MRI have shown to be superior to radiographs and CT. Plain radiography, however, remains the mainstay of imaging in the diagnosis and follow-up of RA 2.

Plain radiograph

One large cohort study showed that radiographically demonstrable erosions were present in 30% of patients at diagnosis, and in 70% three years later 4.

The radiographic hallmarks of rheumatoid arthritis are:

erosions; important early finding, in the “bare areas”, frequently in the radial side of the metacarpophalangeal (MCP) joints 7

soft tissue swelling

fusiform and periarticular; it represents a combination of joint effusion, oedema and tenosynovitis 5

this can be an early/only radiographic finding

osteoporosis: initially juxta-articular, and later generalised; compounded by corticosteroid therapy and disuse

joint space narrowing: symmetrical or concentric

Hands and wrists

Diagnosis and follow-up of patients with RA commonly involve imaging of the hands and wrists. The disease tends to affect the proximal joints in a bilaterally symmetrical distribution.

RA is a synovial based process, with a predilection for:

PIP and MCP joints (especially 2nd and 3rd MCP)

ulnar styloid

triquetrum

As a rule, the DIP joints are spared.

Late changes include:

subchondral cyst formation: the destruction of cartilage presses synovial fluid into the bone

subluxation causing:

ulnar deviation of the MCP joints

boutonniere and swan neck deformities

hitchhiker’s thumb deformity

carpal instability: scapholunate dissociation, ulnar translocation

ankylosis

scallop sign: erosion of the ulnar aspect of the distal radius which may be predictive of extensor tendon rupture (Vaughan-Jackson syndrome)

pencil-in-cup deformity: classically psoriatic arthropathy but well-recognised in rheumatoid arthritis

Elbow

joint effusion (elevated fat pads)

joint space narrowing

periarticular erosions

cystic changes

Feet

similar to the hands, there is a predilection for the PIP and MTP joints (especially 4th and 5th MTP)

involvement of subtalar joint

posterior calcaneal tubercle erosion

hammertoe deformity

hallux valgus

Shoulder

erosion of the distal clavicle

marginal erosions of the humeral head: the superolateral aspect is a typical location 2

reduction in the acromiohumeral distance: “high-riding shoulder” due to subacromial-subdeltoid bursitis and high incidence of rotator cuff tear

Hip

concentric loss of joint space, compared with osteoarthritis (OA) where there is a tendency for superior loss of joint space

acetabular protrusion

Knee

joint effusion

typically involves the lateral or non-weight bearing portion of the joint

loss of joint space involving all three compartments

lack of subchondral sclerosis and osteophytes, compared with OA

prepatellar bursitis

Spine

The cervical spine is frequently involved in RA (in approximately 50% of patients), whereas thoracic and lumbar involvement is rare. Findings include:

erosion of the dens

atlantoaxial subluxation

atlantoaxial distance is more than 3 mm on a flexion radiograph

atlantoaxial impaction (cranial settling): cephalad migration of C2

erosion and fusion of uncovertebral (apophyseal joints ) and facet joints

osteoporosis and osteoporotic fractures

erosion of spinous processes

Question 36

Answer 36

Tuberculosis (musculoskeletal manifestations)

Dr Daniel J Bell◉ and Dr Prashant Mudgal et al.

Musculoskeletal tuberculosis is always secondary to a primary lesion in the lung.

Epidemiology

The prevalence of the disease is around 30 million globally and 1-3% of the 30 million have involvement of their bones and/or joints. Mycobacterium tuberculosis is responsible for almost all of the cases of osteoarticular tuberculosis; although atypical mycobacteria have been reported in lesions of the synovial sheath.

The predisposing factors are protein-energy malnutrition, environmental conditions and living standards such as poor sanitation, overcrowded housing and slum dwelling. Trauma as a causative factor is debatable, but has been reported. Acquired immunodeficiency syndrome and other causes of immunocompromised status and repeated pregnancies and lactation in women are also a factor.

Pathology

Osteoarticular tuberculosis can occur in the spine, hip, knee, foot, elbow, wrist, hand, shoulder and as diaphysial foci. It has not been reported to affect the mandible or the temporomandibular joint. The major method of spread is haematogenous. The most common method of spread to the vertebral body is through the Batson prevertebral venous plexus.

Osteoarticular tuberculosis is reported in various sites including:

tuberculosis of the spine

tuberculous arthropathy

tuberculosis of the tendon sheath and bursae

tuberculous osteomyelitis

tuberculous dactylitis

case:

Patient Data

AGE: 11 years old

GENDER: Male

4 case questions available

X-RAY

Oblique

Lateral

X-ray

Oblique

Oblique view of both hand radiograph and lateral view of left elbow show soft tissue swelling and multiple cystic bony destructions involving all long tubular bones and carpal bones. Benign solid periosteal reaction along left humerus is partly visualised.

Case Discussion

The patient was known case of paediatric AIDS and diagnosed disseminated tuberculosis. He re-visited hospital with both wrist and left elbow swelling, multiple skin abscesses at left and, right axilla, and left elbow. The AFB staining from the abscesses were positive1+ at right hand, 3+ at right axilla and 1+ at left elbow. The left epitrochlear nodes are enlarged and positive AFB staining 1+.

The plain radiograph of both hands and left elbow show multiple cystic osteolytic lesions involving all long tubular bones and carpal bones. This case demonstrates “osteitis tuberculosa multiplex cystoides” or “Jungling disease” which is the multifocal musculoskeletal TB and often found in disseminated disease and conjoined with pulmonary infection. The differential diagnoses are categorised in infection (e.g. disseminated pyogenic osteomyelitis) and neoplasms (e.g. eosinophilic granuloma or small round cell tumours).

Oblique view of both hand radiograph and lateral view of left elbow show soft tissue swelling and multiple cystic bony destructions involving all long tubular bones and carpal bones. Benign solid periosteal reaction along left humerus is partly visualised.

Case Discussion

The patient was known case of paediatric AIDS and diagnosed disseminated tuberculosis. He re-visited hospital with both wrist and left elbow swelling, multiple skin abscesses at left and, right axilla, and left elbow. The AFB staining from the abscesses were positive1+ at right hand, 3+ at right axilla and 1+ at left elbow. The left epitrochlear nodes are enlarged and positive AFB staining 1+.

The plain radiograph of both hands and left elbow show multiple cystic osteolytic lesions involving all long tubular bones and carpal bones. This case demonstrates “osteitis tuberculosa multiplex cystoides” or “Jungling disease” which is the multifocal musculoskeletal TB and often found in disseminated disease and conjoined with pulmonary infection. The differential diagnoses are categorised in infection (e.g. disseminated pyogenic osteomyelitis) and neoplasms (e.g. eosinophilic granuloma or small round cell tumours).

Tuberculous spondylitis

Dr Bahman Rasuli◉ and Dr Hani Makky Al Salam et al.

Tuberculous spondylitis, also known as Pott disease, refers to vertebral body osteomyelitis and intervertebral discitis from tuberculosis (TB). The spine is the most frequent location of musculoskeletal tuberculosis, and commonly related symptoms are back pain and lower limb weakness/paraplegia.

Epidemiology

Tuberculous spondylitis is one of the more common infections of spine in countries where TB is prevalent. Unfortunately, the incidence of tuberculous spondylitis, as with other forms of TB, is on the rise, due to new multiple drug resistant strains.

Discitis and/or osteomyelitis comprise approximately 50% of all musculoskeletal tuberculosis, and usually affects the lower thoracic and upper lumbar levels of the spine 2.

Clinical presentation

Patients usually present with back pain, lower limb weakness/paraplegia, and kyphotic deformity. Constitutional symptoms (fever and weight loss) are also common but not as pronounced as with bacterial discitis/osteomyelitis.

Pathology

The spine is involved due to hematogenous spread via the venous plexus of Batson 2. There is usually a slow collapse of one or usually more vertebral bodies, which spreads underneath the longitudinal ligaments. This results in an acute kyphotic or “gibbus” deformity. This angulation, coupled with epidural granulation tissue and bony fragments, can lead to cord compression. Unlike pyogenic infections, the discs can be preserved and it more commonly involves the thoracic spine. In late-stage spinal TB, large paraspinal abscesses without severe pain or frank pus are common, leading to the expression “cold abscess”.

Radiographic features

Plain radiograph

The spread of infection is typically described as ‘sub-ligamentous’: beneath the anterior longitudinal ligament, usually sparing the posterior elements and often involving multiple levels.

Tuberculous spondylitis can be difficult to detect in early stages because of relative preservation of the disc space.

A reduction in vertebral height is often seen with the irregularity of the anterosuperior endplate being relatively early and subtle sign. Due to the subligamentous extension, there may be some irregularity of the anterior vertebral margin. This is a classical appearance with TB spondylitis.

Later, paraspinal collections can develop which can be remarkably large.

Ivory vertebrae can result in re-ossification. Other associated features may include:

gibbus deformity

vertebra plana

As with other extrapulmonary TB, the chest film may be unrevealing (no pulmonary lesions seen in up to 50% of cases), with the source being a primary lung lesion that is clinically silent.

CT and MRI

Cross-sectional imaging is required to assess better the extent of involvement and particularly for the presence of an epidural component and cord compression. MRI is the modality of choice for this, with CT with contrast being a distant second.

Features include irregularity of both the endplate and anterior aspect of the vertebral bodies, with bone marrow oedema and enhancement seen on MRI:

T1: hypointense marrow in adjacent vertebrae

T2: hyperintense marrow, disc, soft tissue infection

T1 C+ (Gd): marrow, subligamentous, discal, dural enhancement

The paraspinal collections are typically well circumscribed, with fluid centres and well-defined enhancing margins 7.

Differential diagnosis

In many parts of the developing world, TB is the most common cause of vertebral body infection, with the majority of cases seen in patients under the age of 20. TB can also affect the meninges of the spine, causing an intense pachymeningitis that enhances dramatically.

brucellosis: can present as granulomatous osteomyelitis of the spine that can be difficult to distinguish from TB. Both are acid-fast bacilli, which may cause caseating granuloma(s)

fungal infection

sarcoidosis

pyogenic infection

compared to pyogenic infection tuberculous spondylitis has relatively preserved disk-space height, forms large paraspinal abscesses with a smooth enhancing wall and there is usually systemic involvement of multiple organs

see: tuberculous spondylitis versus pyogenic spondylitis

metastasis

Robins Mycobacterial Osteomyelitis (p. 1196)

Tuberculous osteomyelitis occurs in 1% to 3% of patients with tuberculosis; organisms are typically bloodborne, although direct extension or lymphatic seeding can occur. The spine is involved in 40% of cases (Pott disease) with frequent invasion into soft tissues and abscess formation. Lesions exhibit typical granulomatous reaction with caseous necrosis.

Question 37

Answer 37

Avascular necrosis of the hip

Dr Yuranga Weerakkody◉ and Assoc Prof Frank Gaillard◉◈ et al.

Avascular necrosis of the hip is more common than other sites, presumably due to a combination of precarious blood supply and high loading when standing.

Clinical presentation

The most common presenting symptom is a pain in the region of affected hip, thigh, groin, and buttock. Although few patients may remain asymptomatic until late stages.

Pathology

Typically it affects the superior articular surface (between 10-2 o’clock) and begins in the most anterior part of the hip.

Aetiology

It can be thought of as traumatic (secondary to the neck of femur fractures) or non-traumatic. In non-traumatic cases, it is bilateral in 40%.

traumatic

chronic corticosteroid therapy

alcoholism

smoking

systemic lupus erythematosus (SLE)

hyperlipidaemias

HIV

haemoglobinopathies

chronic renal failure

diabetes mellitus

pregnancy-related

Radiographic features

Specific staging system (Ficat staging) exists for the hip which includes x-ray, MRI and bone scan appearances, and covers much of the imaging appearances, thus please refer to that article.

Other than describing the general appearance of the affected region, the following are necessary to include in the report as they have a bearing on prognosis and treatment:

position

estimating percentage volume of the head involved (axial) and percentage weight-bearing surface involved (coronal)

coexisting osteoarthritis or secondary degenerative change

joint effusion

presence of a potentially unstable osteochondral fragment: rim sign

subchondral fractures

CT

Often more sensitive than plain film in showing subchondral fractures.

MRI

MRI is the most sensitive modality, with a sensitivity of 71-100% and specificity of 94-100%1. As there is a high rate of bilateral involvement, both hips should be included in the field of view of at least some sequences.

T1: usually the initial specific findings are areas of low signal representing oedema, which can be bordered by a hyperintense line which represents blood products

T2: may show a second hyperintense inner line between normal marrow and ischaemic marrow. This appearance is highly specific for AVN hip and known as “double line sign”.

The Mitchell classification is commonly used to classify AVN based on MR-images.

Differential diagnosis

In some situations consider

subchondral insufficiency fracture of the femoral head - considered by some as a different entity 9

General imaging differential considerations include:

haematopoietic marrow (see bone marrow)

Pitt’s pit

fovea centralis

idiopathic transient osteoporosis of the hip (ITOH)

hyperaemia with diffuse increased uptake of radiotracer by the femoral head, neck, and intertrochanteric region

chondroblastoma

fracture

infection

pain and fever

usually involves both sides of the joint

metastases

Question 38

Cortical lesions

Answer 38

(most commonly benign)

Question 39

causes of AVN

Answer 39

mnemonic: GIVE INFARCTS
Gaucher disease
Idiopathic (Legg-Calve-Perthes, Kohler, Chandler)
Vasculitis (SLE, polyarteritis nodosa, rheumatoid arthritis)
Environmental (frostbite, thermal injury)
Irradiation
Neoplasia (-associated coagulopathy)
Fat (prolonged corticosteroid use increases marrow)
Alcoholism
Renal failure + dialysis
Caisson disease
Trauma (femoral neck fracture, hip dislocation)
Sickle cell disease
Location: femoral head (most common), humeral head,
femoral condyles

Question 40

Bennett’s Fracture

Answer 40

Bennet #:

• Dorsal tradial dislocation
• force from abductor pollicis langus
• a small fragment maintains articulations w trapezium

Rolando #:

• Comminuted BENNETT #
• Fracture line may have “Y”, “V” or “T” configuration

Question 41

Answer 41

• Decompression sickness
• Dr Daniel J Bell◉ and Dr M Venkatesh et al.
• Decompression sickness (DCS), also known as diver’s disease, aerobullosis, the bends or caisson disease, is an uncommon diving-related decompression illness that is an acute neurological emergency typically occurring in deep sea divers.
• Clinical Presentation
• Decompression sickness can be further clinically subdivided into:
• mild symptoms: arthralgia, skin marbling, small patchy haemorrhages, and lymphatic obstruction
• serious and life-threatening symptoms: affecting the brain, spinal cord, inner ear, and/or lung
• Pathology
• Nitrogen gas bubbles can cause neurovascular infarction of the brain and spinal cord leading to neurological deficit. There are various theories to explain this, which hypothesise between arterial occlusion, venous infarction and cellular nitrogen toxicity.
• Location
• The white matter tracts of the spinal cord and brain are predominantly affected due to their high myelin content 3. Cord lesions are more common than brain lesions. In the spinal cord, there is a predilection for the thoracic cord segments to be affected, thought to be secondary to more nitrogen accumulating in the lateral and posterior columns where there is higher fat content and also the relatively low blood flow compared to the cervical and lumbar segments.
• Complications
• bone infarction
• spinal cord infarct
• Radiographic features
• MRI
• Radiological changes are seen in early stages in MRI, but have very low specificity. The affected white matter may show ischaemic lesions or the bubbles themselves. There may also be an accumulation of nitrogen bubbles in marrow fat.
• Normal MRI of the cord does not rule out the diagnosis 3. If there are MRI findings, these tend to normalise after a few weeks.
• Treatment and prognosis
• hyperbaric oxygen on site and during transportation followed by treatment in a recompression chamber
• The quicker treatment begins, the higher the chance of successful recovery.
• History and etymology
• A caisson is a watertight container used in underwater construction work.
• The bends refers to the joint pain associated with the disease

https://www.semanticscholar.org/paper/A-study-of-old-lesions-of-caisson-disease-of-bone-Gregg-Walder/06dd820f98223d54ee36dcdf4c42bc4182fdc9b6

Question 42

Answer 42

Post-traumatic digital ischemia from thrombosis of ulnar artery at Guyon’s canal.

Epidemiologyincidence

rare

demographics

male: female ratio is 9:1

age bracket is 40s-50s

location

unilateral, dominant ring finger +/- small finger

less commonly, index and middle fingers

thumb is spared

risk factors

occupations using vibrating tools such as carpenters, machinists, mechanics

sports such as baseball catchers, mountain biking, golf, volleyball, karate

Pathophysiologymechanism

single or repetitive blunt impact on hypothenar eminence leads to ulnar artery thrombosis or aneurysm

hook of hamate functions as an anvil, causing thrombosis

distal embolisation leads to ulceration, gangrene

Question 43

Pes Ansuerinus Bursitis

Answer 43

Medial knee pain

Say Grace before T

Sartorius, Gracillus, Bicepts tendon

Question 44

Plain Xray Approach to solitary bone lesion

Answer 44

1. Lytic or Sclerotic
2. Age <30 or >30
3. Location in the body
4. Location in the bone
5. Periosteal Reaction
6. Tumour Matrix
7. Bone Destruction
8. Margins
9. Soft tissue component

Question 45

Answer 45

• Pedunculated osteochondroma
• sessile osteochondroma
• enchondromas
  
  • usually just lucent lesions
  • but in other bones have a chondroid matrix
• Chondroblastoma
  
  • epiphysis/growth plate tumour
• UBC
  
  • fallen fragment
• ABC
  
  • diaphyseal
• NOF
  
  • cortically based lesion
  • expansile
  • healing NOF as it heals becomes sclerotic

Question 47

Answer 47

Achilles tendinopathy

Dr Mohamed Saber and Dr Yuranga Weerakkody◉ et al.

Achilles tendinopathy refers to a combination of pathological changes affecting the Achilles tendon usually due to overuse and excessive chronic stress upon the tendon. It can be seen both in athletes and non-athletes. It is hard to differentiate clinically from a paratendinopathy (which is most common). It may or may not be associated with an Achilles tendon tear.

Epidemiology

It can affect a range of people from athletes to recreational exercisers and even inactive people. It affects non-athletes in around one-third of cases.

Pathology

Macroscopically, tendinopathy results in enlargement, disruption of fibrillar pattern and an increase in tendon vascularity. Histopathologically, there is evidence of disorganised proliferation of tenocytes, disrupted organisation of collagen fibres, and an increase in the non-collagenous matrix, and neovascularisation. Usually, there is no evidence of inflammation, but the cause is thought of as a failed healing response 1. Repetitive microtrauma from unusual or excessive mechanical loading is deemed to be a causative factor.

Location

It particularly affects the mid and distal portions of the tendon 2.

Radiographic features

Ultrasound

Often shows thickening and rounding of the affected portion of the tendon. The cutoff value of 1 cm in anteroposterior diameter is usually used for diagnosis. There is also evidence of neovascularisation, which, if present, is usually indicative of a poorer outcome and more severe clinical symptoms. Additional signs include increased Kager fat pad echogenicity and thickening of a hypoechoic paratenon.

MRI

Can show increased intratendinous signal and tendon enlargement, with oedema in Kager fat pad in cases of tendinosis.

Question 48

Answer 48

Juxtacortical (periosteal) Chondroma

Non-contrast MR of the knee shows a 2.5 x 1.8 cm T2 hyperintense, T1 intermediate multilobulated mass at the anterolateral proximal right tibial shaft, which appears to arise from the cortex or periosteum. There is T2 hyperintensity within the tibialis anterior muscle surrounding the mass, consistent with intramuscular oedema. There is no evidence of significant bone marrow oedema of the tibia.

Case Discussion

The small lytic mass associated with the anterolateral cortex of the tibia metaphysis shows evidence of chondroid-type mineralisation by radiography (“rings and arcs” pattern of calcification). The MR images nicely demonstrate the lesion originating from the superficial cortex, without intramedullary invasion. The absence of associated reactive marrow oedema is suggestive of a benign aetiology. The MR signal characteristics (T1 intermediate, T2 hyperintense) are typical of chondral tissue.

The differential diagnosis includes:

periosteal (juxta-cortical) chondroma

chondromyxoid fibroma (intramedullary >> juxta-cortical location, sclerotic rim, and radiographically apparent chondroid matrix is uncommon)

non-epiphyseal chondroblastoma (classically T2 hypointense due to immature chondroid matrix, usually associated with reactive marrow oedema)

The presentation and imaging appearance, including the lobulated and exophytic morphology, are most consistent a benign juxtacortical chondroma.

Histology

Soft, gray mass associated with a piece of bone. The mass measures approximately 2.0 x 2.0 x 1.7 cm. Sections show a cartilaginous neoplasm that has some degree of nuclear atypia and areas of myxoid changes. However, it is known that benign periosteal or juxtacortical chondromas can have atypia. Furthermore, the mass is relatively small, measuring 2.5 cm by imaging, and is well-circumscribed. Immunostains (Ki-67, p53) were indeterminate.

DIAGNOSIS: juxtacortical (periosteal) chondroma.

Juxtacortical chondroma

Dr Sarah Robertson and Dr Yuranga Weerakkody◉ et al.

Juxtacortical chondromas, also known as periosteal chondromas, are rare benign chondral tumours that arise from the periosteum of tubular bones. They are thought to account for ~2% of benign bone tumours.

Epidemiology

They tend to present around the 2nd to 4th decades. There is a recognised male predilection 1.

Location

Typical sites include 3:

proximal humerus and distal femur (70%)

phalanges (25%)

tibia

radius

ulna

Radiographic features

Plain radiograph

may be seen as a saucerisation of the adjacent bony cortex with a sclerotic periosteal reaction

distinct soft tissue mass may be difficult to identify

matrix calcification may be seen in ~50% of cases; as with all chondroid lesions, this tends to be ring and arc

most lesions are <3 cm in size 1

MRI

Typically seen as a soft tissue lesion abutting the cortex and may better demonstrate evidence of pressure erosion of neighbouring bone. Often has a lobulated configuration. Tends to lack associated medullary bone or soft tissue oedema.

Signal characteristics include 8:

T1: typically iso to low signal relative to muscle

T2/T2*: high signal but with low signal areas representing calcification

T1 C+ (Gd): heterogeneous and tends to show peripheral predominant contrast enhancement

Treatment and prognosis

They are benign lesions, however, may be similar in imaging and histopathologic appearance to juxtacortical chondrosarcomas. Local excision is often the treatment of choice. Once resected lesions usually do not recur.

Differential diagnosis

Imaging differential considerations include:

periosteal osteosarcoma: lobulated margins and high T2 chondral nodules of periosteal chondroma are absent

non-epiphyseal chondroblastoma: typically associated with reactive marrow oedema on MR

juxtacortical chondrosarcoma: often larger than 3 cm (mean size 5.5 cm)

bizarre parosteal osteochondromatous proliferation (Nora lesion): for phalangeal lesions

cortical desmoid: for the posteromedial distal femoral lesions

tenosynovial giant cell tumour: for phalangeal lesions

Question 49

Answer 49

Question 50

hyperextension injury

Bone bruise pattern

knee

Answer 50

hyperextension injury

direct force to anterior tibia with foot planted

contusion pattern: “kissing contusions” of anterior tibial plateau and anterior femoral condyle

associated with ACL, PCL, meniscal injuries, and in severe cases knee dislocation

Question 51

CPPD

Answer 51

• chondrocalcinosis
• subchonral cysts with little osteophyes
• can mimic OA, RA , Gout or chots
• any joint
• calc in and around joints: hyaline cartilage, fibor cartilage, syndoivum, capsile, tendons ligaments
• Can resemble OA, but WORSE in the patellofemoral joint
• DDx
  
  • Gout
  • Charcot Earth (CPPD is AKA psuedocharcot)
  • OA
  • RA
  • Septic arthritis

Question 52

What are the three types of Partial thickness tear?

RE SHoulder USS

Answer 52

7.3. Partial-Thickness Tears

Partial-thickness tears are defined as a disruption of tendon fibers that does not allow communication between the glenohumeral joint cavity and the subacromial-subdeltoid bursa. Partial tears may be intrasubstance, or extend to either the bursal or articular surfaces of the tendon (figure 1-39). Articular surface partial-thickness tears most commonly affect the anterior aspect of the critical zone of the supraspinatus and are more prevalent than intrasubstance and bursal surface tears. Theoretical basis for the increased frequency of articular surface tears include peculiar histological and biomechanical properties. The bursal side layers are primarily composed of tendon bundles, which are resistant to rupture and may elongate under tensile load, whereas articular side layers are composed of a complex of tendon fibers, ligaments, and joint capsule, which is more susceptible to tear.176

Question 53

Psoriatic arthritis

Answer 53

• asymmetric
• oligo or poly arthropathy
• DIP (primarily) and PIP
• can mimic OA
• proliferative bone chagnes
• periostitis (radio styloid)
• osteolysis Pencil in cup
• enthesitis dactylitis
• RF neg
  *

Question 54

Intertarsal arthropathy

Answer 54

• Matches the prox zone of the hands
• Has the same ddx (RA and CPPD) as well as a few more
  
  • Neuropathic charcot arthropay
    
    • Disorgansies joints, fragmented and sclerotic bone. Starts with systic change
  • CPPD
    
    • Cystic change, can mimic charcot Earth. Aka pseudocharcot
  • Gout
  • OAL usually secondary (coalition, truam, tibiaasias posterior dysfunction (pes planus)

Question 55

Answer 55

boutonniere’s Syndrome

Boutonnière deformity is the eponymous name of a musculoskeletal manifestation of rheumatoid arthritis presenting in a digit, with the combination of:

flexion contracture of a proximal interphalangeal (PIP) joint

extension of a distal interphalangeal (DIP) joint

Pathology

Boutonnière deformities occur when the central slip of the extensor digitorum tendon is torn or stretched resulting in PIP joint flexion. Increasing PIP joint flexion causes further extensor retinaculum damage resulting in “buttonholing” of the proximal phalanx between the lateral bands of the extensor tendon. Secondary DIP joint extension then occurs 4.

Etiology

inflammatory arthritis 4

central slip of extensor digitorum tendinopathy or rupture 4

History and etymology

“Boutonnière” is French for buttonhole. The appearance apparently reminded (presumably French-speaking) surgeons of a buttonhole.

Question 56

Fibrous Dysplasia

Answer 56

Question 57

Answer 57

Segond fracture

Dr Subhan Iqbal◉ and Assoc Prof Frank Gaillard◉◈ et al.

Segond fracture is an avulsion fracture of the knee that involves the lateral aspect of the tibial plateau and is very frequently (~75% of cases) associated with disruption of the anterior cruciate ligament (ACL). On the frontal knee radiograph, it may be referred to as the lateral capsular sign.

Clinical presentation

Contrary to the more common causes of an ACL tear, which typically involve a valgus stress 3, a Segond fracture usually occurs as a result of internal rotation and varus stress 1,4. Typically these injuries are seen in two settings:

falls

sports: especially soccer, skiing, basketball and baseball 4,10

Pathology

Somewhat surprisingly, the exact cause of a Segond fracture continues to be contentious. The conventional teaching has been that it is the result of avulsion of the middle third of the lateral capsular ligaments 7. Other candidate structures include the iliotibial band and anterior oblique band of the fibular collateral ligament 3.

In 2017, the ALL expert group released a consensus paper 8 recognising the presence of the anterolateral ligament 9, and noted a constant attachment to the lateral meniscus. However, the ALL is inconsistently identified on MRI 7.

Radiographic features

Plain radiograph

The classical appearance of a Segond fracture is that of a curvilinear or elliptic bone fragment projected parallel to the lateral aspect of the tibial plateau. This has been referred to as the lateral capsular sign 1, which is best seen on the anteroposterior view of the knee.

MRI

MRI is essential in all cases of Segond fractures to identify internal derangement. Disruption of the ACL is the most common, however, there are additional frequently encountered injuries. Associated injuries include 1,3:

ACL tear

most common associated injury

75-100% of cases 6

medial or lateral meniscal tear

66-75% of cases 6

posterior horn most common

avulsion of ACL from the tibial attachment: rare

avulsion of fibular attachment of the long head of biceps femoris

avulsion of the fibular collateral ligament

Treatment and prognosis

Although the fracture itself is small, the extensive ligamentous injury associated with it usually requires surgical intervention, to correct anterior rotational instability 4. Healing of the Segond fracture is associated with a particular bone excrescence arising below the lateral tibial plateau.

History and etymology

First described by Paul Ferdinand Segond, French surgeon (1851-1912) based on cadaveric experiments 1,2,4.

Differential diagnosis

Imaging differential considerations include:

arcuate sign: avulsion fracture of the head of the fibula 5

fragment orientated more horizontally

Question 58

Answer 58

Olecranon bursitis refers to inflammation of the olecranon bursa. The olecranon bursa is a subcutaneous sac that overlies the olecranon process and contains a small amount of fluid to prevent against injury of subcutaneous tissue and skin from the uncovered bony olecranon.

Pathology

Aetiology

Bursitis can develop secondary to many causes:

excessive use - e.g. student’s elbow

trauma

acute trauma

repetitive trauma

infection - septic

inflammation - rheumatoid arthritis, gouty arthropathy and CPPD

Radiographic features

Plain film

Lateral radiograph of the elbow reveals soft tissue swelling superficial to the olecranon. Traumatic fracture or calcification in gout or CPPD may be evident.

Ultrasound

May show a fluid collection in the olecranon bursa, features of synovial proliferation and/or hyperaemia. A small proportion of patients may also show presence of an associated loose body or features of associated triceps tendonitis (+/- calcifications) 2.

Question 59

Pivot shift

Answer 59

ACL

MCL

Meniscus

Question 60

Posterior Lateral corner injuries

Structures

Answer 60

• PLC
  
  • LCL
  • BF
  • Pop t
  • arcuate lig
  • popliteofibular lig
  • Common peroneal nerve may be injured

Question 61

Answer 61

Flap tear

Dr Balint Botz ◉ and Dr Yuranga Weerakkody◉ et al.

A flap tear is a type of meniscal tear which usually comprises of a displaced flap fragment.

horizontal tears can give rise to flap tears, which can be classified as superior or inferior when displaced. Superior flaps arise from the superior surface of the meniscus and inferior flaps from the inferior surface.

oblique tears could also give rise to flaps which are mechanical unstable and associated with mechanical symptoms 2

Location

Flap tears occur six to seven times more frequently in the medial meniscus 3.

Question 62

Mnemonic For Monteggia and Galleazii Fractures

Answer 62

• MUGR
• “Mugger”
• Monteggia = Ulna fracture and radial dislocation
• Galleazzi = Radial fracture with Ulnar dilocation
• A in Monteggia = proximal in the alphabet = proximal findings
• Z is distal in the alphabet = distal findings.

Question 64

Answer 64

Question 65

Answer 65

Periosteal Chondromas

A rare type of chondroma (benign chondrogenic lesion) which occur on surface of long bones

Epidemiologydemographics

occur in 10-20 year-olds

locationsurface of long bones (under periosteum) in distal femur, proximal humerus, and proximal femur

59% of lesions in proximal humerus

other locations in the hand (metacarpal or phalanges)

Presentation

Symptoms

many are painful secondary to irritation of tendons

Imaging

Radiographs

well-demarcated, shallow cortical defect

punctate mineralization (calcification) in 1/3.

saucerization of underlying bone

radiographs important to differentiate from chondrosarcoma (histology may be similar)

Studies

Histologysimilar to enchondroma except for increased cellularity and more malignant looking cells (can look like chondrosarcoma)

bland hyaline cartilage

small chondroid cells in lacunar spaces

Treatment

Operativemarginal excision including underlying cortexindications

severe symptoms interferring with function

technique

lesion will recur if cartilage is left behind

bone graft any large defects

Question 66

Answer 66

Question 67

Answer 67

Case courtesy of Dr Andrew Dixon, Radiopaedia.org, rID: 62021

Picture frame vertebral body

Dr Yuranga Weerakkody◉ and Dr Mohammad Taghi Niknejad et al.

Picture frame vertebral body is a radiologic appearance in which the cortex of the vertebral body is thickened. This sign can be seen in patients with Paget disease.

It is a result of disorganised new cortical bone formation after excessive osteoclastic activity causes the resorption of normal bone.

Radiographic features

At radiography, this results in increased opacity of the cortex on all sides of the vertebral body.

Differential diagnosis

rugger jersey spine

the characteristic sclerosis is seen only at the superior and inferior vertebral endplates

Question 68

Answer 68

Question 69

Answer 69

Phocomelia

Dr Karwan T. Khoshnaw and Dr Yuranga Weerakkody◉ et al.

Phocomelia is an extremely rare congenital skeletal disorder that characteristically affects the limbs. It can affect either the upper limbs or lower limbs or both. Phocomelia is also a descriptive term to describe the characteristic limb anomalies occurring with its associated conditions.

Pathology

It characteristically manifests as a deficiency or shortening of the proximal to mid portions of the limbs.

Associations

Phocomelia can occur sporadically. However, recognised associations include:

thalidomide embryopathy: most common cause of historically

Roberts syndrome

TAR syndrome 4

Grebe syndrome

Holt-Oram syndrome

DK phocomelia syndrome/von Voss-Cherstvoy syndrome

Schinzel-phocomelia syndrome 5

Radiographic features

Antenatal ultrasound

Classically with upper limb involvement, the hands are present, but with variable deficiency and or foreshortening of the arm and/or forearm. The hands may be of normal or abnormal morphology.

History and etymology

Derived from the Greek phoco meaning “seal” and melia meaning “limb”.

Differential diagnosis

congenital limb amputation

amelia

Question 70

Answer 70

Findings: A bony overgrowth extending outwards from the surface of the right radial head away from the joint. The appearance is typical for an osteochondroma (exostosis). Cross-sectional imaging, preferably MRI, is advised to measure the cartilage cap, especially if there is a history of pain.

Epidemiology

Osteochondromas develop during childhood (period of most rapid skeletal growth), but once formed remain for the rest of the individual’s life. They can present at any age and are most frequently found incidentally.

They are usually sporadic, but can be part of:

hereditary multiple exostoses (HME): also known as diaphyseal aclasis

Trevor disease: also known as dysplasia epiphysealis hemimelica

Malignant transformation occurs in the cartilage cap, and is uncommon in sporadic solitary osteochondromas (~1%), whereas in the setting of hereditary multiple exostoses the rate is much higher (5-25%) 5.

Clinical presentation

Symptomatic presentation is either due to mechanical effects of the lesion, fracture, or malignant transformation.

Mechanical symptoms include:

impingement upon nearby structures:

nerve compression

vascular compression

reactive myositis

palpable lump

bursal formation and bursitis

Fractures occur typically through the neck of pedunculated lesions.

Ongoing growth and or pain after skeletal maturity has been reached is suspicious for malignant degeneration.

Pathology

Osteochondromas are considered a chondroid neoplasm and are primarily a part of the growth plate which separates and continues growing independently, without an associated epiphysis, usually away from the nearby joint. The medullary cavity is continuous with the parent bone, and hyaline cartilage caps them. Osteochondromas can be congenital or occur as a result of previous trauma to the growth plate, including previous irradiation 3,4.

Location

They most commonly arise from the appendicular skeleton, especially around the knee 3:

lower limb: 50% of all cases 3

femur (especially distal): most common: 30%

tibia (especially proximal): 15-20%

less common locations: feet, pelvis

upper limb

humerus: 10-20%

less common locations: hands, scapula

spine: the posterior elements of the spine are an uncommon but not rare site for these tumours

Radiographic features

Plain radiograph

An osteochondroma can be either sessile or pedunculated and is seen in the metaphyseal region typically projecting away from the epiphysis. There is often associated broadening of the metaphysis from which it arises. The cartilage cap is variable in appearance. It may be thin and difficult to identify, or thick with rings and arcs calcification and irregular subchondral bone.

New cortical irregularity or continued growth after skeletal maturity has been reached, as well as frankly aggressive features (e.g. bony destruction, large soft tissue component, metastases) are all worrying for malignant transformation.

Question 71

Answer 71

Findings: A displaced and overlapped fracture of the ulnar shaft is present. Additionally, the radial head is dislocated anteriorly.

Case credit: Frank Gaillard, rID: 8012

Key Points

these are typically seen in children and warrant close investigation of both the elbow and the wrist

there is a chance the patient could have an associated distal radius injury as is the case in some studies (24%)

monteggia fracture-dislocations are not easy to image and require highly modified techniques such as horizontal beam lateral

Question 72

Answer 72

Osteochondral injury staging

Dr Mostafa El-Feky◉ and Assoc Prof Frank Gaillard◉◈ et al.

Osteochondral injury staging system for MRI attempts to grade the stability and severity of osteochondral injury and is used to plan management.

stage I

injury limited to articular cartilage

MRI findings: subchondral oedema

x-ray findings: none

stage II

cartilage injury with associated subchondral fracture but without detachment

thin sclerotic margin

x-ray findings: usually none; may see fracture as sclerotic or osteopenic area

two subtypes 2,3

type A: cystic on CT and/or oedema on MRI

type B: non-displaced and incompletely undercut by fluid (MR) or lucency (CT), with an open connection to the articular cartilage (essentially 2a without oedema on MRI)

stage III

detached, non-displaced fragment

MRI findings: high signal around osteochondral fracture (rim sign) but not displaced

x-ray findings: slight lucency between osteochondral fragment and remainder of the bone

stage IV

osteochondral fragment displaced

usually joint effusion present, surrounding fragment and filling donor site

x-ray findings: increased lucency between osteochondral fragment and remainder of the bone, or loose body with donor site irregularity

stage V

subchondral cyst formation

secondary degenerative change

x-ray findings: secondary osteoarthritis

Question 73

increased sig in meniscus

Answer 73

• can be normal in kids and young adults. normal gascularity flow of suynovial lfludi
• Signs of OA
  
  • myxoid degn
• Evidence of trauma
  
  • contusion
• Meniscal cyst
  
  • meniscal tear
• Contacts an articular surface on more than 1 slice
  
  • meniscal tear
• if see in only 1 slice
  
  • around 50% chance of a tear
    *

Question 74

Answer 74

Question 75

Answer 75

• Hydroxyapatite deposition disease (HADD)
• globular foci of calcification in the expected location of the supraspinatus (white) infraspinatus (black arrow) and pect major (arrowheads tendon).
• HADD
  
  • no know cause.
  • 2/3 assymptomatic
  • can be the cause of acute pain and a/w fever, increased ESR and CRP.
  • AKA calcific tendonitis, hydroxyapatite rheumatism, calcific periarthritits and pertendinitis calcarea.
  • calc appears clowud like and amorphous and can involve the tendon, ligament, bursa or. joint capusle.
  • intraarticuilar deposition can destroy the point space, resulting in a condition referred to as Milwaukee shoulder.
  • The shoulder is most commonly involved.
  • On CT accompanying erosion of the underlying bone canbe seen.
  • Electron microscopy needed to dx.
  • Can appear aggressive erosive esp when involveing the pect major origin which can be mis interpreted as malignancy.
• Pope Jr, T., 2015. Aunt Minnie’s Atlas And Imaging-Specific Diagnosis. Philadelphia: Wolters Kluwer.

Question 76

Grystal induces arthoropaties

Answer 76

• Gout mono sodium
• Pseudogeout: CPPD intra articular
• HADD

Question 77

Answer 77

Question 78

Answer 78

Question 79

Answer 79

Complex regional pain syndrome

Dr Balint Botz ◉ and Assoc Prof Frank Gaillard◉◈ et al.

Complex regional pain syndrome (CRPS), also known as Sudeck atrophy, is a condition which can affect the extremities in a wide clinical spectrum. CRPS is principally a clinical diagnosis seen more commonly in females than males with a mean age of presentation of 50 to 70 years 12. No one imaging study is sensitive or specific to rule in or rule out the syndrome.

Terminology

Two types of CRPS have been described 8:

type 1: no underlying single nerve lesion (formerly known as reflex sympathetic dystrophy)

type 2: underlying nerve lesion identified (formerly known as causalgia)

Clinical presentation

Patients present after an initiating event (see causes below) with symptoms of more than 6 months duration such as oedema, changes in skin blood flow, abnormal motor activity, allodynia or hyperalgesia 11. Symptoms are often out of proportion to the initiating event and not limited to a single peripheral nerve 8.

Pathology

Aetiology

trauma: often minor

surgery 11

idiopathic: immobilisation

unknown in many cases

CNS disorders

myocardial infarction

Location

Occurs in hands and feet distal to the injury.

Radiographic features

Plain radiograph

severe patchy osteopenia, particularly in the periarticular region

soft tissue swelling, with eventual soft tissue atrophy

subperiosteal bone resorption

preservation of joint space

It is important to differentiate this from disuse osteopenia since the clinician could initiate aggressive physical therapy for the latter.

MRI

patchy bone marrow oedema signal (particularly subcortical), although bone marrow signal may be normal in some cases

soft tissue oedema and enhancement

skin thickening

joint effusion

synovial hypertrophy

muscle atrophy in later stages

Nuclear medicine

increased uptake on all three phases

diffusely increased juxta-articular activity around all joints of a hand or foot on delayed images is the most sensitive indicator

Treatment and prognosis

In most cases, a multidisciplinary approach is required whereby a combination of various treatments may be employed, such as physical therapy, systemic or regional medications, sympathectomy or spinal cord stimulation, and psychotherapy. Interventional radiology can offer pain relief by peripheral nerve block procedures.

References

Question 81

Answer 81

Question 82

Answer 82

Case courtesy of Dr Angela Byrne, Radiopaedia.org, rID: 8112

Chondroblastoma

https://radiopaedia.org/cases/chondroblastoma-distal-femur-2?lang=us

Question 83

Answer 83

LCH

Question 84

Answer 84

5. Gouty arthritis
   • monosodium urate crystals in synovial fluid
   • asymptomatic periods from months to years
   Target areas: commonly CCMC +all hand joints
   ‘./ development of chronic tophaceous gout
   =lobulated soft-tissue masses
   ‘./ well-defined eccentric erosions with overhanging edge
   (often periarticular) + sclerotic margins
   ‘./ preservation of joint spaces
   ‘./ absence of osteoporosis
   ‘./ most extensive changes in common carpometacarpal
   compartment:
   ‘./ scalloped erosions of bases of ulnar metacarpals

Question 85

Answer 85

• Patella dislocation relocation (PDR)
• kissing contusions to the medial patella facet and the lateral femoral condyle
• large lipohaemarthrosis
• sprain/tear of the medial patella retinaculum.
• hoffas fat pad injury
• redislocation occurs in up to 63% of patients
• A/W ACL tears

Pope Jr, T., 2015. Aunt Minnie’s Atlas And Imaging-Specific Diagnosis. Philadelphia: Wolters Kluwer.

Question 86

Answer 86

Parrot beak meniscal tear

Dr Magdalena Chmiel-Nowak◉ and Dr Yuranga Weerakkody◉ et al.

Parrot beak meniscal tear is a type of radial meniscal tear with a more oblique course, which on axial images gives the characteristic appearance of a curved V, similar to a parrot’s beak. As it is obliquely orientated in relation to the coronal and sagittal plane, it results in a marching cleft sign on sagittal images. This type of tear is usually symptomatic, as the partially torn meniscal flap in unstable.

Practical points

Some authors advise that the term should be reserved for arthroscopy reports, and not used in MRI reports as a meniscal tear pattern descriptor 1.

Question 87

Pearls re enchondrona & malignant transformation

Answer 87

• In the absence of a fracture, a painful encondrona is considered malignant until proven otherwise.
• Malignant transformation occurs but is rare.
• Malignant transformation is more common in central lesions

Question 88

Answer 88

haemochromatosis.

Overhanging (hooked) osteophytes of the metacarpal heads of the right index.

Case Discussion

The overhanging osteophytes (a.k.a. hooked or beak-like osteophytes) at the heads of the metacarpals of index and long fingers are typical for haemochromatosis. Chondrocalcinosis is not prominent in this case. The main differential diagnosis of haemochromatosis is CPPD.

References

Question 89

causes of increased bone denisty

Answer 89

Generalised increased bone density (mnemonic)

Dr Sachintha Hapugoda◉ and Dr Maunil Ajay Bhuta et al.

A handy mnemonic for causes of generalised increased bone density / osteosclerosis:

Regular Sex Makes Occasional Perversions Much More Fun, Happening and Lovely

Mnemonic

R: renal osteodystrophy (case 1 and 2)

S: sickle cell disease, salt and pepper skull (case 2)

M: metastasis (osteoblastic/sclerotic)

O: osteopetrosis

P: pyknodysostosis; Paget disease

M: myelofibrosis

M: mastocytosis

F: fluorosis

H: hyperparathyroidism; hypervitaminosis A and D

L: lymphoma

Case 1:

Plain X-ray hands of a young patient with CRF shows signs of secondary hyperparathyroidism:

irregular, frayed and ill-defined cortical outline, pronounced at radial aspect of middle phalanges –> subperiosteal bone resorption

multiple lytic expansile lesions –> brown tumours (arrows)

osteosclerosis

accentuated trabecular pattern non-essential trabeculae are resorbed; those that remain appear prominent)

Case Discussion

Renal osteodystrophy is a constellation of musculoskeletal abnormalities that occur in patients with chronic renal failure.

Manifestations include:

osteomalacia (adults) / rickets (children)

secondary hyperparathyroidism: bone resorption, osteosclerosis, soft tissue & vascular calcifications and brown tumours

aluminium intoxication if the patient is on dialysis

Comment:
Subperiosteal bone resorption is the hallmark of HPTH and is first identified in hands.

Question 90

Answer 90

Ivory vertebra (ewing sarcoma 1st case, BrCa second case)

Dr Mostafa El-Feky and Radswiki◉ et al.

The ivory vertebra (also known as ivory vertebra sign) sign refers to the diffuse and homogeneous increase in opacity of a vertebral body that otherwise retains its size and contours, and with no change in the opacity and size of adjacent intervertebral discs.

Pathology

Etiology

The cause for an ivory vertebra depends on the age of the patient 1.

Pediatric

lymphoma: commonest cause, usually Hodgkin lymphoma

osteosarcoma

osteoblastoma

blastic metastatic disease

neuroblastoma

medulloblastoma

Ewing sarcoma (rare)

Adult

osteoblastic metastases

prostate cancer

breast cancer

lymphoma (usually Hodgkin lymphoma)

tuberculous spondylitis

hemangioma

chordoma

Paget disease of bone

vertebral body expansion (unlike hemangioma)

coarsened trabeculae

SAPHO syndrome 3

Rarely, the ivory vertebra can also be seen in 4:

primary bone sarcoma

sarcoidosis

systemic mastocytosis

Radiographic features

Plain radiograph and CT

Plain radiographs and CT will demonstrate diffuse sclerosis of the vertebral body with variable involvement of the posterior vertebral elements.

MRI

MRI demonstrates hypointense signals within the corresponding vertebra which is directly proportional to the degree of sclerosis of the vertebral body.

Question 91

lateral patellar dislocation

Answer 91

lateral patellar dislocation

twisting injury to flexed knee

anterolateral lateral femoral condyle and inferomedial patella

associated with medial patellar retinaculum +/- medial patellofemoral ligament injury +/- medial patellotibial ligament injuries

References

Question 92

Answer 92

Question 93

Answer 93

Question 94

posterior accessory ligs

which can look like tear

Answer 94

Wrist berg behind PCL

Humpry Anterior

One or the other present in 75% of cases

Question 95

Answer 95

Question 96

Answer 96

poly ostotic

osseous expansion

ground glass appearance

this is Fibrous dysplasia

Question 97

Types of primary osseous osteosarcoma - 5

Answer 97

95% of OSA = Primary Osseous

• Conventional OSA
• Low grade OSA
• telangiectatic OSA
• Small Cell OSA
• multicentric OSA

Question 98

Answer 98

Parosteal osteosarcoma

Dr Matt A. Morgan◉ and Assoc Prof Frank Gaillard◉◈ et al.

Parosteal osteosarcoma is a subtype of osteosarcoma and arises from the outer layer of the periosteum.

Epidemiology

It is the most common type of juxtacortical or surface osteosarcoma and accounts for ~5% of all osteosarcomas. It typically presents in early adulthood and middle age with a peak incidence in the third decade. It affects females slightly more than males 9.

Clinical presentation

Patients usually present with a painless, slowly enlarging mass 9.

Pathology

They are usually located at the metaphysis (80-90%), most commonly at the posterior aspect of the distal femur (60%), followed by either end of the tibia, and then the proximal humerus.

They are composed of a dense osteoid component attached to the outer cortex over a narrow zone. Parosteal osteosarcoma originates from the outer fibrous layer of periosteum. It exhibits extensive bone matrix and minimal fibroblastic cellular atypia, and as such is considered to be a low-grade tumour.

Radiographic features

large lobulated exophytic, ‘cauliflower-like’ mass with central dense ossification adjacent to the bone

string sign: thin radiolucent line separating the tumour from the cortex, seen in 30% of cases

tumour stalk: grows within the tumour in late stages and obliterates the radiolucent cleavage plane

+/- soft tissue mass

cortical thickening without aggressive periosteal reaction is often seen

tumour extension into the medullary cavity is frequently seen

MRI

It exhibits predominantly low signal intensity both on T1 and T2 weighted imaging. High signal intensity on T2 is suggestive of a high-grade tumour.

Treatment and prognosis

Parosteal osteosarcomas are usually low-grade lesions are usually treated with surgical resection and no neoadjuvant chemotherapy or radiation. As they are frequently metaphyseal in location, large parosteal osteosarcomas or those with deep medullary invasion may require limb salvage, including joint replacement.

Parosteal osteosarcomas have an excellent prognosis (80-95% long-term survival).

Differential diagnosis

On imaging consider

cortical desmoid: avulsive injury of the posterior femoral cortex

myositis ossificans: the ossification pattern of parosteal OS is the radiographic inverse of that seen in myositis ossificans, with the densest ossification in the centre of the lesion and the least radiopaque bone at the periphery (eggshell pattern); there is also often a history of trauma, progressive decrease in size or constant size and significant oedema in early stages on MRI.

sessile osteochondroma: parosteal OS lacks corticomedullary continuity between the tumour and the underlying medullary canal.

juxtacortical chondrosarcoma

high-grade surface osteosarcoma

parosteal lipoma: radiolucent mass adjacent to the cortical surface on plain film and on cross-sectional imaging will usually show a definite fat component 2

Question 99

Answer 99

• GCT
  
  • subarticular
• Geode
  
  • synovial fluid escaping into juxtartiular surface
• OM
  
  • any age
  • aggressive
  • lytic
• Pagets
  
  • thickened cortex
  • osseos expansion
  • coarsend trabecular
• Flame sign of lytic phase pagets disease

Question 100

what is the difference between a wide and narrow zone of transition?

Answer 100