Imaging of the Ankle and Foot Flashcards
1
Q
Common pathology of the ankle/foot
A
- Traumatic: sprain = inversion; fractures
- Non-traumatic: osteomyelitis, vascular insufficiency & complications from diabetic foot
- Congenital: Club foot
2
Q
What are the different ankle/foot fractures
A
- Unimalleolar, bimalleolar, trimalleolar
- Hindfoot: calcaneus
- Midfoot: fracture + dislocation = Lisfranc injury
- Forefoot: metatarsal fractures, stress fractures
3
Q
Imaging of the ankle/foot
A
- Radiographs: acute injuries (Ottawa Rules) such as fracture or dislocation
- CT/MRI: complex fractures in the hind foot
- MRI/US: soft tissue injuries such as osteochondral injury, instability, impingement, Lisfrac injury, osteomyelitis, tendon injuries
- MRI/Bone scan: stress fractures
- AP, lateral, & oblique (mortise) views are most common views
4
Q
Describe the diabetic foot ulcer pathway
A
- X-ray compatible with osteomyelitis: yes or no
- Yes: consider bone biopsy; No: bone visualized or positive probe to bone
- Bone biopsy: treat as osteomyelitis; Probe to bone: Yes or No
- Yes: presumed osteomyelitis; No: high clinical suspicion osteomyelitis
- Presumed step: consider bone biopsy; High suspicion: Yes or No
- Yes: MRI or radionuclide scan; No: Repeat x-ray in 2 wks
- MRI: suggestive of osteo
- Suggestive of osteo: Yes or No
- Yes: consider bone biopsy; No: Repeat x-ray in 2 wks
5
Q
Describe suspected peripheral vascular disease pathway
A
- Noninvasive hemodynamic studies: Disease likely or disease unlikely
- Likely: Doppler US or CTA or MRA; Unlikely: consider other Dx including neurogenic claudication
- Doppler US/CTA/MRA: Surgical tx, Angiography, or Conservative tx
- Angiography: endovascular tx
6
Q
Describe a routine x-ray eval of the ankle
A
- AP view demos distal tibia & fibula & dome of talus
- AP oblique (Mortise) view demos entire joint space of ankle mortise w/o superimposition of tibia over fibula (15º IR)
- Later view demos ant. & post. aspects of tibia, tibiotalar joint, & subtler joint
7
Q
Describe an AP stress view
A
- Inversion & eversion: collateral ligaments
- Anterior drawer stress test
8
Q
Radiographic signs of ankle instability
A
- AP view: abnormal position of talus & increased width of ankle mortise joint space, and positive anterior drawer test
9
Q
Describe common stresses/injuries to the ankle
A
- Most sprained joint in the body
- Many injuries are precipitated by an inversion force
- Damage may range in severity from minor sprains to ligamentous rupture, bony avulsion, & joint instability
10
Q
Normal values of talar tilt during inversion & eversion at the ankle
A
- <5-15º during forced inversion
- Up to 10º during forced eversion
11
Q
Values related to talus in an anterior drawer test
A
- Normal separation = 5mm
- 10mm may or may not be normal, requires comparison to contralateral side
- > 10mm indicates disruption of anterior talofibular ligament
12
Q
What is the ankle anterior drawer test
A
- An orthopedic test used to assess the integrity of the lateral collateral ligaments of the ankle
- Anterior talofibular lig, Calcaneofibular lig, and Posterior talofibular lig
13
Q
Indications for CT of the ankle
A
- Complex fractures, loss bodies
- Osetochondral lesion
- Tarsal coalition
- Pre-operative planning
- Any MRI study when MRI is not available
14
Q
Indicates for MRI of the ankle
A
- Tendon, ligament tears
- Impingement, osteochondral abnormalities, loose bodies
- Plantar fasciitis, rupture
- Neoplasm, marrow abnormalities
- Congenital conditions
15
Q
Describe Ottawa Ankle Rule
A
- Recommends x-ray examination as the initial study for all acute injuries meeting the Ottawa criteria & for assessment of all chronic ankle/foot pain
16
Q
What is the Ottawa Ankle Rule Criteria
A
- Any pain in the malleolar zone AND any one of the following
(1) Bone tenderness along distal 6cm of posterior edge of tibia or tip of medial malleolus OR
(2) Bone tenderness along distal 6cm of posterior edge of fibula or tip of lateral malleolus OR
(3) An inability to bear weight both immediately & in the emergency department for 4 steps
17
Q
Describe the Weber classification system
A
A) fracture below ankle joint (usually stable, may require ORIF if medial malleolus fx)
B) fracture at the level of the joint with tibiofibular ligaments intact (variable stability)
C) fracture above joint level which tears the syndesmotic ligaments (unstable, requires ORIF)
18
Q
List low risk fractures of the ankle/foot
A
- Posteromedial tibia
- 2nd/3rd metatarsals
- Calcaneus
- Distal fibula
- Cuboid
- Cuniforms
19
Q
List high risk fractures of the ankle/foot
A
- Anterior tibial cortex
- Medial malleolus
- Navicular
- Talus
- Base of 5th metatarsal
- Base of 2nd metatarsal
- Hallux sesamoids
20
Q
What does bruising on the bottom of the mid foot that is painful indicate
A
- Think Lisfranc fracture
- Typically will say someone stepped on my foot
21
Q
Describe tendon pathology in the ankle/foot
A
- Paratenonitis is inflammation of the paratenon layers
- Tendinitis refers to inflammation within the tendon
- Tendinosis is the term for tendon degeneration & is difficult to distinguish from a chronic partial tear
- Tendon rupture is a complete tear & often leads to surgical repair
- Achilles tendon is commonly torn in athletics
- Medial posterior tibial tendon is often ruptured in pts with RA & results in a flat foot
- Lateral peroneal tendons are often injured during inversion sprains
22
Q
Describe tarsal coalition
A
- Congenital bony or fibrocartilaginous union between 2 or more tarsal bones
- Sx: painful ambulation & limited foot ROM become pronounced after the bones have ossified in late childhood or early adolescence
- Imaging: x-rays identify the condition, MRI or CT determines whether it is fibrous or bony coalition
23
Q
Describe a fracture of the talar neck
A
- 3/5 of the talus is covered with articular cartilage so most fx are intra-articular, the talus is predisposed to developing AVN after fracture
- MOI: hyper DF forces talus against the anterior tibia, landing from a height or slamming on brakes in a MVA
- Imaging: X-rays, CT, or MRI as other subluxations & fractures typically coexist with this injury
24
Q
Describe osteomyelitis in the foot in the patient with diabetes
A
- Infection of the bone or bone marrow is almost always a result of contiguous spread from a skin ulcer
- Sx: ulcers tend to be a WBing areas (toes, metatarsal heads, calcaneus), cellulitis * draining sinus tracts may be present, pain is variable
- Imaging: MRI is essential as primary modality in assessment of the diabetic foot
25
Describe a routine x-ray eval of the foot
- AP view demos all bones of the forefoot & mid foot & their associated articulations, 1st inter tarsal angle is measured in this view
- Lateral view (@45º) demos bones of the hind foot & mid foot & their associated articulations, Boehler's angle & calcanea inclination are measured on this view
- Oblique view demos subtler, talonavicular, calcaneocuboid, & tarsometatarsal articulations
26
What is the normative angle for the Boehler's angle
- Normal = 20-40º
- >20-40º = will be seen with some calcanea fractures
27
Describe the Boehler's angle
- AKA Tuberosity or Salient angle
- Often used to evaluate the angular relationship of the talus & calcaneus in the presence if trauma
- Angle is determined by the intersection of lines drawn from the posterior aspect of the subtler joint to the anterior process of the calcaneus & across the posterior superior margin of the calcaneus
28
Describe the Ottawa Ankle Rule criteria for the foot imaging
- Any pain in the mid foot zone and any one of the following
(1) Bone tenderness at the base of the 5th metatarsal OR
(2) Bone tenderness at the navicular bone OR
(3) An inability to bear weight both immediately & in the emergency department for 4 steps
29
Describe hind foot fractures
- Calcaneus is most commonly fractured bone, often associated with a vertebral compression fracture in the thoracolumbar spine
- Most fractures of the talus are considered to be intra-articular
- Complications of talar fx include post traumatic arthritis of the ankle & subtler joints as well as AVN
30
Describe Midfoot fractures
- Fx are usually seen in combination with sprains & dislocations at the transverse tarsal & tarsometatarsal joints
- Exception is stress fractures of the navicular
31
Describe forefoot fractures
- Fx of the metatarsals & phalanges are usually caused by direct trauma or "stubbing" injuries
- Stress fx are also common injuries in the forefoot usually appearing at distal shafts of 2nd-4th metatarsals & proximal shaft of the 5th metatarsal
32
Describe 5th metatarsal fractures by zones
- Zone 1: tuberosity avulsion fractures, typically heal well w/o surgery; styloid area
- Zone 2: fractures of metaphyseal/diaphyseal junction (Jones Fx), may require surgery & can have delayed healing and risk of complications
- Zone 3: proximal diaphyseal stress fractures (> 1.5cm from tuberosity), have increased risk of impaired healing due to poor blood supply, considered high risk
33
Describe a Lisfranc fracture
- Fracture + dislocation of midfoot
- Dislocation of the 2nd metatarsal
- Space between metatarsal bones widen
- Torn Lisfranc ligament
- Look for medial plantar bruising (hallmark sign of a Lisfranc injury)
- Most common type of dislocation involving the foot
- Cast or boat for 6 wks and NWB during this time
34
How are deformities of the foot described & evaluated
- Evaluated radiologically by the measurements of lines & angles drawn on the anteroposterior & lateral radiographs
35
Describe Hallux valgus
- Deformity of the forefoot in which the 1st metatarsal is deviated medially & the great toe is deviated laterally
36
Describe Pes cavus
- Abnormally high medial longitudinal arch of the foot with calcanea inclination greater than 30º as measured on the lateral view
37
Describe Pes planus
- Abnormally low medial longitudinal arch of the foot
- Result of a developmental deformity, tarsal coalition, soft tissue injury, or dysfunction, & neuromuscular conditions
38
Describe Talipes equinovarus or clubfoot
- Most common congenital deformity of the lower extremity
- Forefoot is in adduction relative to the hind foot
- Equinus/PF position of the heel
- Inversion of the subtler joint with varus hindfoot
39
What are the normal and abnormal angle measurements related to hallux valgus angle (HVA) and inter metatarsal angel (IMA)
- Normal: <15º (HVA) and 9º (IMA)
- Mild: 15-30º (HVA) and 9-13º (IMA)
- Moderate: 30-40º (HVA) and 13-20º (IMA)
- Severe: >40º (HVA) and >20º (IMA)
40
Describe Charcot foot
- Characterized by 4 different disease stages resembling active & inactive disease phases: inflammation, fragmentation, coalescence, & consolidation
- Normally limited to a single run thorough of disease phases
- Active phase: red, hot, & swollen foot often w/o pain due to polyneuropathy, bone gets fragile
- Inactive phase: not red any more but some soft tissue & bone marrow edema may last, prominent osteophytes & palpable loose bodies as consequence of substantial joint & bone destruction
- End stage: rocker-bottom deformity
41
Ossifications of the foot in children
- At birth: only the calcaneus and talus are ossified
- 1-4 yrs: ossifications centers of remaining tarsals, metatarsal, & phalangeal heads and bases and distal fibula appear
- 18-20 yrs: foot and ankle is fully ossified
