Imaging Techniques and Applications
- AP, lateral views
- Mortise view – 15-20deg internal oblique
- Views of toes
- Oblique views
- Weight bearing
- Stress views – Varus and valgus force, anterior drawer stress to calcaneus, to test for laxity and instability.
- Proximal fibular shaft for Maisonneuve fracture
- Axial heel
- Harris-Beath/skier’s view – Oblique frontal showing body calcaneus, middle facet and sustentaculum tali.
- Plantodorsal midfoot
- Os tibiale externum
- Skyline sesamoids
MRI of foot & ankle – Footprint (true coronal) are slices along axis of sole, short axis is true axial.
Normal Appearances and Functional Aspects
Anomalous muscles in foot/ankle in ~6%, most commonly accessory soleus and peoneus quartus muscles.
Effusion causes anterior teardrop convexity at ankle joint on lateral. Soft tissue swelling over medial and lateral malleoli, stranding in pre-Achilles triangle fat (usually sharply defined).
Loss of parallel ankle mortise margins implies ligament disruption and instability. Even slight widening of joint space can cause early OA.
Ankle fractures Weber AO classification:
- Weber A – Transverse avulsion lateral malleolus at or distal to joint line ± medial malleolus fracture. Major ligaments usually intact. From supination.
- Weber B – Oblique coronal fracture lateral malleolus beginning at level of joint. From supination-external rotation or pronation. Partial disruption to tibiofibular ligaments ± medial malleolus fracture and deltoid ligament rupture.
- Weber C – Oblique sagittal fracture of fibula proximal to joint line, involving tibiofibular ligaments and tibiofibular syndesmosis. From pronation-external rotation. Maisonneuve fracture – proximal fibular fracture with syndesmosis tear. Usually requires surgery.
Ankle fracture Lauge-Hansen classification based on mechanism of injury.
- Supination (plantarflexion, hindfoot infervion, foot adduction) – Tension of fibula with lateral collateral ligament tear or Weber A fracture (stage 1) ± vertical medial malleolus fracture (stage 2).
- Supination-external rotation (most common) – Stage 1 disruption of anterior distal tibiofibular ligament; stage 2 oblique coronal fracture of distal fibula; stage 3 posterior distal tibiofibular ligament tear or avulsion at posterior malleolus attachment; stage 4 transverse fracture medial malleolus.
- Pronation (dorsiflexion, hindfoot eversion, foor abduction) – Stage 1 avulsion medial malleolus or tear of deltoid ligaments; stage 2 rupture anterior and posterior distal tibiofibular ligaments; stage 3 oblique sagittal fibula fracture.
- Pronation-external rotation (spiral forces onto fibula) – Stage 1 avulsion medial malleolus or tear of deltoid ligament; stage 2 tear of anterior distal tibiofibular ligament and syndesmosis; stage 3 fibula fracture proximal to joint line; stage 4 posterior distal tibiofibular ligament tear or avulsion at posterior malleolus.
- Axial loading (pilon fractures) – Distal tibial comminution with talar dome driving intra-articular fragments apart ± talar fracture. Type 1 nondisplaced; type 2 moderately displaced; type 3 severely displaced and impacted.
Kump’s bump – Fusion of distal tibial epiphyysis at 12-13yo beginning at anteromedial physis, fusing medial->lateral. Prone to lateral SH fractures.
- (Juvenile) Tillaux fracture – SH3 of lateral tibial epiphysis from avulsion of anterior and posterior distal tibiofibular ligaments. Surgery if >2mm displacement or articular incongruence.
- Triplanar fracture – SH4 with coronal-oblique through posterior tibial metaphysis, horizontal through physis and sagittal through lateral tibial epiphysis. If occurs after medial fusion then 2-part fracture; if before then may be 3-fragment with medial epiphysis.
Osteochondral fracture may involve medial or lateral talar dome, esp with ligament laxity, may be part of osteochondritis dissecans.
Calcaneal fracture (lover’s/Don Juan fractures) usually fall from height, associated with spinal fracture. 10% bilateral. Bohler’s angle – superior anterior process to posterior margin of posterior articular facet to posterosuperior calcaneal tuberosity; normal 20-40deg. Rowe classification:
- Type I (21%) – Fracture of calcaneal tuberosity, sustentaculum tali or anterior process.
- Type II (4%) – Horizontal fracture calcaneal tuberosity.
- Type III (20%) – Oblique fracture without extension into subtalar joint.
- Type IV (25%) – Extension into subtalar joint.
- Type V (31%) – Intraarticular fracture with depression of posterior subtalar joint (reduced Bohler’s angle) or substantial comminution. Tx plate fixation along lateral calcaneus.
Avulsion of Achilles insertion esp insufficiency fracture in diabetics.
Avulsion of extensor digitorum brevis origin at anterolateral calcaneus is uncommon.
Talar fractures mostly neck (associated with talar dislocation) and body. Proximal and midpole fracture prone to AVN of proximal pole.
- Avulsion fractures include ankle capsule at anterosuperior neck, snowboarder’s fracture at lateral talus, superomedial talus.
- Osteochondral fracture posteromedial dome or mid-lateral.
- Posterior process (mimics os trigonum).
Navicula avulsion fracture from talonavicular capsule (proximal dorsal fragment), rarely posterior tibialis tendon, tibionavicular ligament of deltoid ligament complex.
- Dance’s/true Jones fracture – Avulsion of tip 5th MT base from peroneus brevis.
- Jones fracture – Fracture 5th MT 15-20mm distal to tuberosity from impaction injury, usually as stress fracture. Prone to delayed union/nonunion.
- March fracture – MT stress fracture, usually nondisplaced, apparent on XR after 7-10/7.
- Stubbed toes commonly fracture distal phalangeal tuft. In skeletally immature may cause SH1/2 as nailbed is attached to periosteum. Prone to osteomyelitis if nail bed is disrupted.
- Plantar/tarsal plate avulsion at MTPJ or PIPJs.
- Turf toe – Variable definition, most are hyperextension injury 1st MTPJ injuring the capsule, esp hard surfaces (eg artificial turf) in sporting.
- Avulsion dorsal chip fracture extensor tendon from proximal dorsal phalanx.
Twisting injury esp with foot stuck in stirrup/strap/pothole or axial loading on plantarflexed foot. May occur with minimal trauma. Common with Charcot joint in diabetes. Rupture or avulsion of lisfranc ligaments (medial cuneiform to 2nd MT base) causing lateral subluxation of 2nd-5th MTs ± dorsal subluxation. Medial border 2nd MT does not line up with medial border 2nd cuneiform. Homolateral/convergent subluxation – all 5 MTs subluxed laterally; divergent is lateral subluxation 2nd-5th MTs and variable medial subluxation of 1st. Usually associated with MT fractures (may be occult). Subluxation may be extremely subtle, requiring weightbearing views or CT/MRI. Common in diabetic neuropathic arthropathy. Poor prognosis with high risk of OA.
Osteochondral Lesion (OCL) of the Talar Dome
(Formerly osteochondritis dessicans OCD). Second most common OCL after the knee. Focal low T1 in subarticular dome. If high T2/T2
- surrounds or within dissecans fragment it is most likely unstable. If displaced becoming loose body may be very difficult to localise.
Avascular Necrosis (AVN)
Esp proximal pole of prox/midpole fracture of talus, lateral fragment of navicular. Sclerosis, subchondral fracture. Diffuse low T1 signal throughout a tarsal bone. High T2 means it may not be reversible.
- Calcaneal stress fracture – Linear sclerotic band posterior calcaneus, perpendicular to major trabeculae. DDx ‘heel spur’ or plantar fasciitis.
- Navicular stress fracture – Joggers, basketball players. Usually sagittal at junction of middle and lateral 1/3s. Usually occult on XR.
- Ankle fatigue fracture – Esp skeletally immature runners. SH1 distal fibula growth plate or linar bands lucency/sclerosis distal tibial metaphysis 30-40mm proximal to plafond or distal fibular 30-70mm from distal tip.
Anterior impingement (dorsiflexion) from anterior tibial osteophytes or traction spurs dorsal talar neck.
- Anterolateral impingement syndrome – Scarring, synovitis and cartilage injury in lateral gutter of ankle (anterolateral tibiotalar joint) with lateral ankle pain, inability to dorsiflex normally ± click. Usually from trauma. Low T2, anterior talofibular ligament commonly torn/fibrosed. Tx arthroscopic resection of scar tissue. Meniscoid syndrome – hyalinisation of anterolateral soft tissues, may undergo ossification.
- Anteromedial impingement
Posterior ankle impingement (plantarflexion) – Posterior tibial osteophytes or os trigonum (V, unfused apophysis attached to inferior posterior talus by synchondrosis or chronic fracture).
- Os trigonum syndrome – Pain, irregular contour, sclerosis, subcortical cysts, marrow oedema. More common in ballet dances and soccer players. May be associated with tenosynovitis of adjacent FHL (DDx joint fluid extending into the tendon sheath).
Commonly calcaneonavicular joint and middle facet talocalcaneal joint. Painful flat-foot. 50% bilatearl. Fibrous or cartilaginous. Joint space irregularity, OA of nearby joints.
Tendons and Ligaments
Tendon injuries usually the flexor tendons (posterior); extensor injury (anteriora) rarely abnormal. Flexor tendonse posteromedial to tibia, arranged (med->lat) ‘Tom Dick and very nervous Harry’ (Tibialis posterior, flexor Digitorum longus, aa, vv, nn, flexor Hallucis longus). Repetitive stress and repair causes mucoid degeneration, hyalinisation, may lead to rupture.
- Tenosynovitis – Fluid in tendon sheath with normal tendon.
- Tendinosis – Increased signal that doesn’t increase on T2 from myxoid degeneration.
- Tendonitis or partial tear – Focal/fusiform tendon swelling with high T2/T2*, thinning/attenuation of tendon if more severe.
- Tendon rupture – Absence of tendon on 1 or more images, best seen on axials except Achilles best on sag. Tx surgery.
Achilles tendon does not have a sheath (hence no tenysynovitis). Normal </=8mm thick with concave/flat anterior margin. Tendonitis/partial tear usually easily diagnosed clinically, blurring on XR. Complete disruption common in athletes, middle-aged men who do sporadic exercise, systemic conditions causing tendon weakening (RA, collagen vascular disease, crystal deposition disease, HPT). Blurring of anterior margin and pre-Achilles fat on XR. Most rupture 20-60mm proximal to calcaneal insertion (relatively avascular). Partial tears may be intrasubstance or marginal, transverse or longitudinal. Peritendinitis causes fluid/oedema from inflamed peritenon (surrounds tendon). Tx surgery (usually if gap is large) or equinus cast (marked plantarflexion) for several months. Intact plantaris tendon may mimic partially intact Achilles tendon, but inserts anteromedially. May be thickened in xanthomas with marked heterogeneous enlargement.
Haglund’s disease – Peritendinous oedema, retrocalcaneal bursitis, heterogeneous thickening of distal Achilles tendon. From ill-fitting shoes compressing the tendon. May be associated with overgrowth of proximal posterior calcaneus.
Tibialis Posterior Tendon
Posterior tibial tendon (PTT) most medial and largest (apart from Achilles) flexor tendon, passes under foot (support for longitudinal arch) onto navicula, 2nd and 3rd cuneiforms and 2nd-4th metatarsals. Problems with longitudinal arch or plantar facia may cause stress on PTT -> tendonitis or rupture. Tendonitis/rupture common in RA.
- Tendinosis – Esp women >50yo with painful worsening flatfoot, microtears with slow stretching; pes planus, lateral subluxation of navicula.
- Tendonitis – High T1 with swelling (>2x area of adjacent FDL apart from where is splays at insertion), increase with T2 but not fluid-bright, tendon sheath fluid; Tx usually nonoperative.
- Tear – Absence of tendon on one or more axial images, usually at or above tibiotalar joint. PTT rupture causes flat foot, stress on spring ligament (just deep to PTT, becomes scarred and thickened) ± tear (visible gap). Next failure is subtalar joint ligaments in sinus tarsi.
PTT may insert solely on an accessory navicular ossicle (os tibiale externum) adjacent to medial navicula, causing traction from navicula, pain. Jagged, oedematous pseudoarticulation between ossicle and navicula.
Flexor Hallucis Longus (FHL) Tendon
Muscle continues to attach to the tendon distally (cf PTT, FDP), passes beneath sustentaculum tali using it as a pulley for plantarflexion. Tendon sheath communicates with ankle joint in 20%. Tenosynovitis in Ballet dances common as it impinges against os trigonum. Rupture is rare.
Peroneus longus and brevis tendons posterior to distal fibula, bound by thin superior retinaculum. Fibula acts as pulley for foot eversion. Tendons pass lateral to calcaneus, separate with brevis inserting to base 5th metatarsal and longus under foot to base 1st metatarsal. Displacement of peroneus tendons from disruption of superior retinaculum (often in skiing accidents) usually with flake fracture (avulsion off fibula); Tx surgery. Entrapment of tendons can occur in fractured calcaneus or fibula.
Split peroneus brevis syndrome (peroneal splits) – Longitudinal split tear, common in inversion/dorsiflexion injury impinged between fibula and peroneus longus. Peroneus longus may be positioned between the split halves in extreme cases. From tight compartment eg accssory muscle, abnormal distal position of muscle bellies, fibula dysplasia, peroneal subluxation (should be adjacent to peroneus longus; increased risk if normal retromalleolar groove of fibula which contains the tendons is convex), hook of posterolateral fibula. Chronic lateral ankle pain, ankle instability if associated with lateral collateral ligamnet disruption (in 80%). Chevron/V/U shape to tendon distal to fibula or division of tendon into two parts. DDx peroneus quartus tendon.
Stenosing tenosynovitis – Tendon sheath contrast study shows beaded appearance.
Much more common than tendon injury, usually in acute trauma (cf tendon repetitive microtrauma), clinical evaluation usually adequate. Deltoid ligament is medial, broad beneath tendons. Lateral ligaments superior group is at or just below tibiotalar joint (anterior and posterior tibiofibular ligaments making up syndesmosis); and inferior group just below tibiotalar joint emanating from mallolar fossa in distal fibula (ant and posterior talofibular and calcaneofibular). Most injuries involve the lateral ligaments esp anterior talofibular then calcaneofibular ligaments. Posterior talofibular ligament tear is rare. Chronic tears of lateral ligaments are associated with chronic lateral ankle instability, sinus tarsi syndrome, anterolateral impingement syndrome.
Syndesmosis strains (high ankle sprains) range from mild distal tibiofibular ligament injury to syndesmotic diastasis. Distance between the distal tibia and fibula at the level of physis should be <5mm. Injury can be confirmed with MRI.
On stress views medial talar tilt should be <10-12deg (more in lateral collateral ligament injury), anterior drawer <10mm (more in anterior talofibular ligament injury.
Normal arthrography may fill the ankle joint, posterior subtalar joint and tendon sheath of FHL. Contrast around the tip of fibula implies anterior talofibular ligament tear. Filling of peroneal tendon sheath implies calcaneofibular ligament tear. Contrast in the tibiofibular syndesmosis above the joint implies anterior distal tibiofibular ligament tear.
Tarsal Tunnel Syndrome
Compression of posterior tibial nerve in the tarsal tunnel; bounded by flexor retinaculum (strong band extending vertically ~50-70mm), talus and calcaneus. Pain, parasthesia in plantar foot. From flexor tendon tenosynovitis, abnormal distal extent of abductor hallucis muscle, thickening of flexor retinaculum, ganglion, tumours (neural, lymphangiomas, haemangiomas), trauma, fibrosis or idiopathic.
Sinus Tarsi Syndrome
Cone-shaped space between talus and anterior process calcaneus. Sinus tarsi syndrome is inflammation or haemorrhage. Lateral ankle pain/tenderness, hindfoot instability. Fat replaced with granulation (high T2) or scar (low T2) tissue, both low T1. May have tear of talocalcaneal ligaments. From inversion injury, RA. DDx acutely sprained ankle with fat replacement by haemorrhage/oedema.
Medial cord is flexor digitorum brevis, lateral cord is abductor digiti minimi, from plantar aspect calcaneal tuberosity. Repetitive trauma may -> tendinopathy, inflammation at plantar aponeurosis origin. Oedema in soft tissues, bone marrow, variable thickening of plantar aponeurosis. May show fatty atrophy of flexor digitorum brevis or abductor digiti minimi. Heel spurs may be from plantar fasciitis or chronic asymptomatic traction, inflammatory enthesitis (Reiter’s, psoriatic arthritis).
Hyperkeratosis of tip of toe (occasionally finger) with progressive bone resorption, may cause ulceration and spontaneous amputation. Middle-aged men of West African descent.
Osteomyelitis usually treated more aggressively including amputation. If marrow normal no osteomyelitis, but if low signal in marrow around joint may be from oedema/hyperaemia or infection. Definitive signs of infection include cortical disruption, bony abscess (uncommon), sinus tract (very uncommon).