Ankle Syndesmosis Injury

The syndesmosis is the fibrous joint between the distal tibia and fibula, held by the anterior inferior tibiofibular ligament, the posterior inferior tibiofibular ligament, the transverse ligament and the interosseous ligament and membrane. It keeps the talus seated in the mortise. Isolated injury (the "high ankle sprain") accounts for 1 to 18% of ankle sprains, and is more frequent in contact sports. Syndesmosis disruption accompanies up to 20% of ankle fractures.

Mechanism: external rotation of the foot, often with dorsiflexion and abduction, or a direct forced external rotation of the leg on a planted foot. Grades:

• Grade I: sprain without widening
• Grade II: partial tears, subtle instability on stress
• Grade III: complete rupture with diastasis, with or without fibular and deltoid injury
• Proximal fibular fracture with syndesmotic and deltoid injury: a high energy variant in which pain may be at the knee

Recovery is slower than for a lateral sprain, usually 6 to 8 weeks or more for stable injury and 3 to 6 months after surgery. Complications are chronic instability, heterotopic ossification, post-traumatic arthritis and persistent pain.

• Anterolateral ankle pain above the joint line, pain on push off and with stairs, and inability to hop
• Swelling, often less than in a lateral sprain, and tenderness over the anterior tibiofibular ligament that extends proximally between the tibia and fibula
• Squeeze test (compressing the mid-calf provokes distal pain), external rotation stress test, dorsiflexion compression test, and a lateral translation (cotton) test
• Deltoid tenderness and bruising
• Red flags: inability to bear weight, proximal fibular or knee tenderness, neurovascular compromise, and fracture dislocation

• Weight bearing radiographs of both ankles (anteroposterior, mortise and lateral), and a full length tibia and fibula view when proximal tenderness exists.
• Radiographic measurements: tibiofibular clear space over 6 mm at 1 cm above the plafond, tibiofibular overlap under 6 mm on the anteroposterior view (under 1 mm on mortise), and medial clear space over 4 mm.
• Weight bearing bilateral CT: side-to-side diastasis difference over 2 mm, and rotational or sagittal malalignment.
• MRI to show ligament injury, deltoid involvement and osteochondral lesion.
• Stress radiographs or arthroscopy when instability is uncertain.

Differentials: lateral ankle sprain, fibular fracture, talar osteochondral lesion, peroneal tendon injury, deltoid ligament injury, fifth metatarsal base fracture, lateral process talus fracture.

Stable injury (no diastasis):

• Walking boot with crutches for 2 to 3 weeks, then lace up brace.
• Rest, ice, compression and elevation. Ibuprofen 400 mg orally every 8 hours with food for up to 7 days, and paracetamol 1 g every 6 hours.
• Physiotherapy: range of motion, peroneal and calf strength, proprioception. Return to sport in 4 to 8 weeks.

Unstable injury or diastasis over 2 mm:

• Surgery as soon as soft tissues allow (within 1 to 2 weeks).
• Open or arthroscopic reduction with a clamp, checking the fibula in the incisura on the axial plane, and fixation with 1 or 2 suture button devices, or one or two 3.5 mm cortical screws through 3 to 4 cortices placed 1.5 to 2 cm above the joint, with the ankle held in neutral or slight dorsiflexion.
• Fix the fibular fracture, a posterior malleolar fragment over 25% of the plafond (or smaller if unstable), and repair or address the deltoid when the medial clear space remains wide after fixation.
• Cefazolin 2 g IV before incision (3 g if over 120 kg). Enoxaparin 40 mg SC daily while non-weight-bearing.
• Postoperative: non-weight-bearing for 6 weeks, then a boot with progressive loading. Screws may be removed at 12 to 16 weeks if symptomatic or broken (not required routinely).

Chronic instability: syndesmosis reconstruction with hamstring autograft, or arthrodesis of the distal tibiofibular joint.

Complications: malreduction (up to 25 to 50% on CT), infection, hardware failure or prominence, heterotopic ossification, recurrent diastasis and post-traumatic arthritis.

Follow up at 2 weeks, 6 weeks, 3 months and 6 months with weight bearing radiographs. Counsel on sports return at 3 to 6 months after surgery.