week 1 formative MSK

Question 1

what is a rare cause of AVN ?

Answer 1

A rare cause is Caisson’s disease or decompression sickness which causes AVN from nitrogen gas bubbles forming in the circulation after too rapid a depressurization after deep sea diving.

Question 2

label structures A and B

Answer 2

A - Haversian canal

B - Cement line

Question 3

what do the striations in skeletal muscle originate from ?

Answer 3

There is nothing that runs across the fibres, but the fact that components of adjacent myofibrils are held in registry with each other (i.e. dark band adjacent to dark bank, etc.) gives the appearance of a ‘stripe’ running across the cell.

Question 4

What is the name of the layer of connective tissue that surrounds a bundle of muscle fibres, such as shown at ‘A’?

Answer 4

Perimysium

Question 5

What is the name of the layer of thin connective tissue that surrounds individual muscle fibres, such as shown at ‘B’?

Answer 5

endomysium

Note:

Muscle fibres are grouped into bundles called fascicles and a muscle typically contains several fascicles.

The connective tissue that surrounds the muscle as a whole is called the epimysium, the connective tissue around a single fascicle is the perimysium and the connetive tissue around a single muscle fibre is theendomysium.

Question 6

What is The most common form of primary bone tumour, producing abnormal bone. Most cases are seen in younger age groups (adolescence and early adulthood) with 60% involving the bones around the knee.

osteosarcoma, ewings sarcoma, fibrosarcoma

Answer 6

osteosarcoma

Question 7

What is a malignant tumour of endothelial cells in the marrow. Most cases occur between the ages of 10 and 20. It may be associated with fever, raised inflammatory markers and a warm swelling and may be misdiagnosed as osteomyelitis.

osteosarcoma, ewings sarcoma, fibrosarcoma

Answer 7

ewings sarcoma

Question 8

What is a malignant primary bone tumour which tends to occur in abnormal bone (bone infarct, fibrous dysplasia, post irradiation, Paget’s disease), most commonly in adolescents or young adults.

osteosarcoma, ewings sarcoma, fibrosarcoma

Answer 8

fibrosarcoma

Question 9

what are the two types of bone which can be seen in a longitudinal section through a long bone ? and in which area of the bone are they found ?

Answer 9

An outer shell of dense cortical bone makes up the shaft (diaphysis).

Cancellous or trabecular bone occupies the ends of the bone (the epiphyses).

Cancellous bone is a fine meshwork of bone that looks a bit like the inside of an Aero bar. Bone undergoes remodelling throughout life.

Question 10

what does this microscopic pic show?

Answer 10

chondrocytes (chondroblasts when immature)

Question 11

Bone is constantly undergoing remodelling. In this process, a number of _____ will congregate and begin to ‘drill’ into the bone, forming a tunnel. A blood vessel will grow into the tunnel bringing with it X, which line the tunnel and begin laying down new lamellar bone. This process continues until only the space of a Haversian canal remains.

Answer 11

osteoclasts

Question 12

are osteochondromas always benign ?

Answer 12

no - 1% can be malignant

Question 13

diagnose what this is:

Inflammation of the usually present, small fluid filled sac lined by synovium around joints which prevents friction between tendons, bones, muscle and skin. This inflammation commonly occurs after repeatedpressure or trauma and, therefore, may present as a soft tissue swelling.

bursitis, ganglion, abscess

Answer 13

bursitis

Question 14

diagnose what this is:

A cystic swelling which occurs around a synovial joint or tendon sheath, as a result of herniation or out‐pouching of a weak portion of joint capsule or tendon sheath

bursitis, ganglion, abscess

Answer 14

ganglion

Question 15

diagnose what this is:

A collection of pus which can be formed secondary to a penetrating wound

bursitis, ganglion, abscess

Question 16

Malignant soft tissue tumours arising from the connective tissues are known as sarcomas. Sarcomas are relatively uncommon accounting for less than 1% of all malignant tumours.

Sarcomas can arise from and are named according to the tissue type from which they arise. Match the names of these malignant soft tissue tumours to the tissue from which they arise:

muscle, fat, blood vessels to

liposarcoma, angiosarcoma, rhabdomyosarcoma

Answer 16

muscle - rhabdomyosarcoma

fat - liposarcoma

blood vessels - angiosarcoma

Question 17

You are the orthopaedic reigistrar in the out-patient clinic. You are referred an 11 year old boy by his GP because he is concerned about a lump which has appeared on the outside of his thigh, just above his knee. The boy and his father tell you it has grown in size and they’re quite concerned. The lump itself is painless although it sometimes catches on the ilio-tibial band on the lateral aspect of his thigh. The boy is well, he doesn’t complain of any other symptoms and doesn’t have any significant past medical history. There is no family history of similar problems.

On examination, the boy is slim and you can feel a firm, bony lump on the lateral aspect of the distal femoral metaphysis. The skin and soft tissues overlying the lump are healthy. You do an x-ray and it shows a bony spur originating from the distal femoral metaphysis. The cortex is otherwise normal.

What is the diagnosis?

Select one:

Osteochondritis

Osteochondroma

Ewing’s sarcoma

Enchondroma

Fiberous dysplasia

Answer 17

osteochondroma

The commonest benign bone tumour is an osteochondroma which produces a bony outgrowth on the external surface with a cartilaginous cap (which isn’t visible on the x-ray). These do not usually cause any problems but can produce local pain.

There is a very small (1%) risk of malignant transformation and any lesion growing in size or producing pain may require excisional biopsy. Multiple osteochondromata can occur as an autosomal dominant hereditary disorder.

Question 18

You are the orthopaedic registrar in the fracture clinic. An 8 year old girl has been referred from A&E with a fracture to her right clavicle. She dis this when she fell from a swing onto her outstretched hand. She’s comfortable in the broad arm sling she has been given and she’s neurovasularly intact in the right arm. She had no preceding symptoms, such as pain, in the shoulder or collar bone prior to the accident. She is fit and well.

On examination, there is a mild deformity in the middle 1/3 of the clavicle at the site of the fracture but the skin is intact.

So far, there is nothing atypical about this girl’s story or injury. However, when you look at the x-ray, you notice that the bone at the fracture site isn’t completely normal. There is a lucent lesion in the middle 1/3 of the clavicle with a smooth edge where it meets the more normal looking bone. There is mild expansion of the cortex.

What do you suspect has caused this pathological fracture?

Select one:

a. Osteoid osteoma
b. A simple bone cyst
c. Avascular necrosis
d. An aneurysmal bone cyst
e. Osteochondritis

Answer 18

A simple bone cyst (aka unicameral bone cyst) is a single cavity benign fluid filled cyst in a bone. They are probably a growth defect from the physis and are therefore metaphyseal in long bones (usually in the proximal humerus and femur) although they can occur in the talus or calcaneus.

They may be asymptomatic and an incidental finding on xray (usually a child or young adult), however, they can cause weakness leading to pathological fracture. Treatment with curettage and bone grafting with or without stabilization may be required. Pathological fractures caused by a weakness due to a simple bone cyst usually heal with normal treatment for that fracture, so this patient would be treated conservatively as is usual for a clavicle fracture. However, the patient should be seen in clinic until the fracture has definitely healed. After the fracture has healed, the bone will be stronger than before as the bone cyst will have filled with normal bone!

Question 19

A sarcomere is defined as the region from one …. to the next

Answer 19

Viewed under the microscope the fibres have a regular pattern of bands running across the fibre at right angles to the long axis. This is also true for cardiac muscle. This is because the sarcomeres in the myofibrils with their alternating dark and light bands, are held in registry with one another across the fibre. That is, the Z-disks in the sarcomere of one myofibril will be lined up with the Z-disks of the sarcomeres in the surrounding myofibrils. Although nothing is physically running across the fibre, it looks like there is.

Question 21

what are the features suggestive of a benign soft neoplasm ?

Answer 21

smaller size, fluctuation in size, cystic lesions, well‐defined lesions, fluid filled lesions and soft / fatty lesions. (transluminable lesions)

Question 22

what are the features suggestive of a malignant soft tissue neoplasm ?

Answer 22

Larger lesions (>5cm), rapid growth in size, a solid lesion, an ill‐defined lesion, an irregular surface, associated lymphadenopathy and systemic upset (weight loss, loss of appetite, fatigue).

Question 23

The radographic features of which biochemical bone disorder include: bone enlargement, thickened cortices, thickened trabeculae with mixed areas of lysis and sclerosis?

Question 24

The arrows indicate chondrocytes. What is the name given to the space that each of these cells occupies?

Answer 24

Chondrocytes live within a space in the extracellular matrix termed a lacuna.

Question 25

what type of tissue is shown?

Answer 25

Skeletal muscle.

Note the features of striations (visible on the longitudinally sectioned fibres) and the peripheral nuclei (seen on the transversely sectioned fibres).

Question 26

what benign bone tumour is being described?

A tumour extensively involving the proximal femur with cortical thinning and a’Shepherd’s crook’ deformity.

Answer 26

Fibrous dysplasia

Question 27

What benign bone tumour is being described?

Tumour often occuring arround the knee and distal radius with a ‘soap bubble’ appearance

Answer 27

Giant cell tumour

Question 28

What benign bone tumour is being described?

A single lucent lesion, often an incidental finding, found most commonly within metaphyseal regions.

Answer 28

A simple bone cyst

Question 29

What are the primary malignant tumours which commonly metastasise to bone ?

Answer 29

• Breast carcinoma
• Prostate carcinoma
• Lung carcinoma
• Renal cell carcinoma
• Thyroid adenocarcinoma

Question 31

AVN is a cause of secondary osteoarthritis. T/F ?

Answer 31

true

Question 32

Traction osteochondritis occurs at an apophysis (a bony tubercle where a tendon attaches) including the tibial tubercle. What is this known as ?

Answer 32

Osgood Schlatters disease

Question 33

Traction osteochondritis occurs which occurs at the calcaneus is known as ?

Answer 33

Sever’s disease

Question 34

what is Scheuermann’s disease ?

Answer 34

A compression-type osteochondritis

Question 35

What is the benign bone tumour causing a bony spur, originating the in metaphyseal regions of long bones, growing away from the epiphysis.

Answer 35

osteochondroma

Question 36

what is the benign bone tumour causing a lucent, multi-loculated cyst found within the medulla of many different bones, often with associated cortical expansion.

Answer 36

aneurysmal bone cyst

Question 37

What is the benign bone tumour causing a mostly lucent lesion, with a patchy sclerosis, found within the metaphyseal region of long bones.

Answer 37

Enchondroma