Subtalar Dislocation

Subtalar dislocation is a simultaneous dislocation of the talocalcaneal and talonavicular joints, with the calcaneus and midfoot displaced from the talus while the tibiotalar joint stays intact. It is also called peritalar dislocation. It is rare and accounts for about 1 to 2% of all dislocations.

It follows an inversion or eversion injury of the foot from a fall from height, a basketball landing ("basketball foot"), a road traffic collision or an inversion injury while running.

Direction describes the position of the foot. Medial dislocation (about 80 to 85%) follows forced inversion and places the foot medial to the talus. Lateral dislocation (about 15 to 20%) follows forced eversion and carries more fractures, open injuries and poor outcomes. Anterior and posterior types are rare.

Complications:

• open injury (up to 40% in lateral dislocations)
• associated fractures of the talus, malleoli, calcaneus, navicular and cuboid
• avascular necrosis of the talus (uncommon, 10% or less)
• post-traumatic subtalar arthritis (up to 50%)
• stiffness, instability and neurovascular injury

Pathophysiology.

The talus is held by the interosseous talocalcaneal ligament and the capsule. A force through the foot tears those ligaments and the talonavicular capsule, and the foot slides around the talus. In medial dislocations the talar head is prominent dorsolaterally and may press on the skin.

Irreducible dislocation follows interposed tendons: the tibialis posterior tendon, flexor digitorum longus or flexor hallucis longus. In medial dislocations the head buttonholes through the extensor retinaculum or extensor digitorum brevis. In lateral dislocations the tibialis posterior tendon blocks reduction.

Severe hindfoot pain and deformity. In a medial dislocation the foot is inverted and adducted, with the talar head prominent on the dorsolateral foot and the heel displaced medially. In a lateral dislocation the foot is everted and abducted with the talar head prominent on the medial side.

Skin tenting, which can lead to necrosis, calls for urgent reduction. Check the dorsalis pedis and posterior tibial pulses, capillary refill and sensation (tibial and peroneal nerves). Examine the ankle, midfoot and knee.

• Radiographs: anteroposterior, lateral and oblique views of the foot and ankle. The talar head is displaced from the navicular and the calcaneus lies lateral or medial to the talus, with the tibiotalar joint normal.
• CT after reduction is essential to define associated fractures, intra-articular fragments (talar, calcaneal, navicular), incongruence and entrapped soft tissues.
• MRI later for ligament injury, tendon entrapment and avascular necrosis.
• Doppler or angiography if pulses stay absent after reduction.

Differential diagnosis.

• Total talar dislocation and talar neck fracture.
• Midfoot dislocation (Chopart) and calcaneal fracture.
• Ankle fracture dislocation and tibiotalar dislocation.
• Lisfranc injury and navicular fracture.

Closed reduction as soon as possible, under sedation or general anaesthesia.

• Flex the knee to relax the gastrocnemius, plantar flex the foot, apply longitudinal traction on the heel and forefoot, then exaggerate the deformity and reverse it, with medial or lateral counterpressure on the talar head. Reduction is confirmed by a clunk and by radiographs.
• Irreducible dislocation (about 10% of medial and over 30% of lateral dislocations) needs open reduction to release the trapped tendon, capsule or bone fragment.
• Open dislocations: urgent washout and debridement, reduction, antibiotics and stabilisation.

Reduction under sedation. Ketamine 1 to 2 mg/kg intravenously over 1 to 2 minutes as a single dose (a further 0.5 to 1 mg/kg after 10 minutes if needed; 4 to 5 mg/kg intramuscularly without access). It should be given by a clinician skilled in airway care, with continuous oximetry and capnography, after fasting. Avoid with raised intracranial pressure, psychosis or acute upper airway infection.

After reduction.

• CT to confirm congruent reduction and show fractures.
• Stable simple dislocations: a short leg backslab then a cast for 3 to 4 weeks, followed by early range-of-motion exercises and progressive weight bearing from 4 to 6 weeks. Prolonged immobilisation causes stiffness.
• Unstable dislocation, associated displaced fractures, or incongruent reduction: ORIF with screws or plates, and temporary Kirschner wire fixation of the subtalar and talonavicular joints.
• Late complications: subtalar arthrodesis for symptomatic arthritis or instability; talar avascular necrosis is observed and protected from loading.

Open fracture.

• Intravenous co-amoxiclav 1.2 g every 8 hours (or cefazolin 2 g every 8 hours) within 1 hour of injury.
• Continue until 24 hours after wound closure for types I and II. For type III, continue until 72 hours or 24 hours after soft tissue cover, whichever is earlier.
• Co-amoxiclav: maximum 3.6 g daily; every 12 hours at creatinine clearance 10 to 30 mL/min; check liver tests in courses over 7 days.
• For heavy contamination or soft tissue loss add gentamicin 5 mg/kg intravenously once daily for up to 72 hours. Check creatinine daily and a level before the second dose; avoid or extend the interval at eGFR under 60 mL/min/1.73 m2.
• With severe penicillin allergy use clindamycin 600 mg intravenously every 8 hours (maximum 2.7 g daily) with gentamicin.
• Tetanus booster 0.5 mL intramuscularly if the last dose was over 10 years ago. Add tetanus immunoglobulin 250 units intramuscularly (500 units if over 24 hours since injury or heavily contaminated) when immunisation is incomplete or unknown.
• Debride and stabilise within 24 hours.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose (repeat after 4 hours or blood loss over 1500 mL). With severe penicillin allergy, give vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose, with levels and creatinine checked in prolonged cases.

Thromboprophylaxis. Enoxaparin 40 mg subcutaneously once daily for the period of immobilisation and restricted weight bearing (usually 4 to 6 weeks) in patients with a lower limb cast or non-weight bearing. Start within 24 hours of injury or after surgery. Dose adjustments:

• 20 mg once daily at creatinine clearance under 30 mL/min
• adjust by anti-Xa level in obesity and renal impairment
• check the platelet count on days 5 to 14 for heparin induced thrombocytopenia

Add mechanical prophylaxis as needed.

Analgesia.

• Paracetamol 1 g orally every 6 hours as needed for up to 5 to 7 days (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Ibuprofen 400 mg orally every 8 hours with food for up to 5 days (maximum 1200 mg daily); avoid with eGFR under 30 mL/min/1.73 m2, peptic ulcer, heart failure or anticoagulant use.
• Oral morphine 5 to 10 mg every 4 hours as needed for severe pain for up to 3 days (start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2; avoid exceeding 60 mg in 24 hours without senior review). Monitor sedation and respiration and prescribe a laxative.

Monitoring. Skin, perfusion and sensation before and after reduction and every 4 hours in the first 24 hours. Radiographs at 1 week, 2 weeks, 6 weeks, 3 months and 12 months. MRI at 3 to 6 months if talar avascular necrosis is suspected (the Hawkins sign on radiographs at 6 to 8 weeks suggests an intact blood supply). Subtalar range and arthritis at follow up.

Referral and escalation. Emergency: refer to orthopaedics on diagnosis and arrange reduction within hours. Immediate escalation for skin tenting or necrosis, open injury, vascular compromise, irreducible dislocation or compartment syndrome.

Special groups.

• Children: rare; reduce under sedation and immobilise for 3 weeks.
• Older adults: osteoporotic fractures complicate reduction; assess bone health.
• Diabetes: neuropathy and poor healing increase wound complications.
• Kidney impairment: avoid ibuprofen, reduce morphine doses and extend gentamicin intervals.