Bimalleolar Ankle Fracture

Bimalleolar ankle fracture is a fracture of both the lateral malleolus (distal fibula) and the medial malleolus (distal tibia), or of the lateral malleolus with a deltoid ligament rupture (a bimalleolar equivalent). It is an unstable injury because the talus loses its medial and lateral restraint.

Ankle fractures are among the most common fractures treated surgically, with a bimodal pattern: young men with sports and high energy injuries, and older women with osteoporotic falls. Risk factors are smoking, diabetes, obesity and osteoporosis.

The Lauge-Hansen classification gives the injury mechanism: supination external rotation (about 60%), pronation external rotation, supination adduction and pronation abduction. The Weber classification describes the fibula level relative to the syndesmosis. Weber A is distal to the syndesmosis, B is at the level of the syndesmosis, and C is proximal to it with syndesmosis disruption.

Complications are wound breakdown and infection, malunion, nonunion, post-traumatic arthritis, stiffness, syndesmotic instability, complex regional pain syndrome, venous thromboembolism, and, in diabetes, Charcot arthropathy.

Pathophysiology.

A rotational or abduction force combined with a fixed foot disrupts the stabilising ring formed by the malleoli, the syndesmosis and the deltoid and lateral ligaments. The talus shifts, and displacement of even 1 to 2 mm lateral talar shift reduces the tibiotalar contact area by about 40%, leading to arthritis.

Pain, swelling, bruising and inability to bear weight, with obvious deformity. Tenderness over the medial and lateral malleoli and along the fibula. Check the skin for tension, blisters, tenting or open wounds, and the neurovascular state (dorsalis pedis and posterior tibial pulses, sensation, capillary refill).

Palpate the proximal fibula and knee (Maisonneuve injury) and the base of the fifth metatarsal. Compartment syndrome is uncommon but should be considered with severe pain and swelling.

• Radiographs: anteroposterior, mortise and lateral views of the ankle. Assess:
  • medial clear space (over 4 mm, or over 5 mm in weight bearing, suggests deltoid injury)
  • tibiofibular clear space (over 6 mm)
  • tibiofibular overlap (under 1 mm)
  • talar tilt
  • fibular shortening (the Shenton line of the ankle)
• Full length tibia and fibula radiographs when the proximal fibula is tender.
• External rotation stress or weight bearing views to assess the medial clear space in Weber B fibula fractures with a normal medial clear space.
• CT for comminution, the posterior malleolus and the syndesmosis; MRI when there is a suspected osteochondral talar lesion.
• HbA1c, vitamin D and bone health assessment in fragility fractures.

Differential diagnosis.

• Trimalleolar ankle fracture and Maisonneuve fracture.
• Isolated lateral malleolus fracture and syndesmosis injury.
• Pilon fracture and talar fracture.
• Ankle sprain with avulsion fracture, and fifth metatarsal base fracture.

Initial management. Reduce a displaced fracture with a dislocated ankle at once, without waiting for radiographs when the foot is pale, cool or pulseless. Give analgesia and sedation, apply longitudinal traction, correct the deformity and apply a well padded backslab with the ankle neutral. Elevate the leg and repeat radiographs and a neurovascular check.

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.

Definitive treatment. Bimalleolar fractures are fixed because they are unstable.

• Operate within 24 to 48 hours if the skin is good. Otherwise delay 5 to 10 days until swelling and blisters settle (the wrinkle sign). Use a spanning external fixator for severe swelling or an unstable soft tissue envelope.
• Lateral malleolus: reduction and fixation with a lag screw and a one third tubular or anatomical plate (3.5 mm screws) to restore fibular length and rotation.
• Medial malleolus: two parallel 4.0 mm cancellous lag screws or a tension band wire for the small distal fragment, or a buttress plate for vertical fractures.
• Test the syndesmosis intraoperatively with the hook test or external rotation stress. Fix with a syndesmotic screw (3.5 mm, 3 or 4 cortices) or a suture button device if unstable.
• Fibula nail or percutaneous fixation for older patients with poor skin.
• Postoperative: backslab then a boot or cast. Non-weight bearing for 6 weeks, then progressive weight bearing and physiotherapy. Early movement may begin from 2 weeks with stable fixation. A syndesmotic screw (if used) is not usually removed unless symptomatic.
• Non-operative treatment suits only undisplaced stable injuries or patients unfit for surgery, with a short leg cast for 6 weeks and weekly radiographs for 3 weeks.

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.

Complex regional pain syndrome prevention. Vitamin C (ascorbic acid) 500 mg orally once daily for 50 days from the day of injury (maximum 500 mg daily; the evidence is moderate). Avoid with a history of oxalate kidney stones, and limit with eGFR under 30 mL/min/1.73 m2. No routine monitoring.

Monitoring. Neurovascular status and skin every 4 hours for 24 hours. Radiographs after reduction, at 2 weeks, 6 weeks, 3 months and 12 months. Wound review at 2 weeks. Ankle range and alignment at each visit. Late arthritis and syndesmotic widening on follow up films.

Referral and escalation. Refer every unstable ankle fracture to orthopaedics within 24 hours. Emergency referral for a pulseless or dislocated foot, open fracture, severe skin compromise or compartment syndrome.

Special groups.

• Older adults: osteoporotic bone needs locking plates, long plates or a nail, and early weight bearing is used. Assess bone health and falls.
• Diabetes: higher risk of infection, wound breakdown and Charcot arthropathy; use stronger fixation, longer non-weight bearing (8 to 12 weeks) and tight glucose control.
• Children: physeal injuries (Salter-Harris) need anatomical reduction; growth arrest is possible.
• Kidney impairment: avoid ibuprofen, reduce morphine doses and extend gentamicin intervals.