Syndesmosis Instability

Abstract

The syndesmosis is one of important stabilizer of the ankle joint and consists of a complex ligamentous structure: the anterior inferior tibiofibular ligament; the interosseous ligament; the posterior inferior tibiofibular and the transverse ligaments. The posterior syndesmosis plays the most important role providing 40–45% of the resistance to diastasis, while the AITFL provides around 35%. Major injuries of two of the syndesmosis components represent a loss of more than 50% of resistance to diastasis and may result in instability. Syndesmosis injury or a high ankle sprain, is a frequent athletic trauma accounting for 1% to 18% of all ankle sprains, 17 to 84% of all sport injuries, and 10% of all ankle fractures. Most of the mechanism injury is external rotation injury. A radiographic study suggested that about 20.3% of ankle sprains were combined with a syndesmosis injury. Without proper treatment, the chronic syndesmosis injury remains symptomatic for more than 6 months after the initial trauma, with persistent pain, functional disability, and early-stage ankle arthritis. Normally, syndesmosis widens 1 mm during normal gait. Widening of syndesmosis more than 1 mm can reduce tibiotalar contact surface about 42%. The degenerative changes can occur if the lateral talar shift more than 2 mm. Clinical tests for syndesmosis injuries are external rotation stress test, Cotton test, dorsiflexion-compression test, squeeze test, crossed-leg test, fibular translation and AITFL palpation. Standard radiographs are part of ankle trauma evaluation, especially for fracture exclusion, applying the Ottawa criteria. Computerized tomography (CT) scan is a useful tool to assess tibiofibular diastasis, fibular rotation and joint asymmetry, but shows low sensitivity. MRI is showing very high sensitivity and specificity in identification of syndesmotic injuries. For stable lesion can be treated with conservative means, including non weight bearing or protected weight bearing with a cast or walking boot and a rehabilitation protocol. An unstable lesion requires a surgical procedure to avoid long-term disability and chronic instability. Ankle arthroscopy remains essential for diagnosis and treatment. With accessory tools that measure the syndesmosis gap (e.g. 3.5 mm shaver canula or a metallic tools). Passage of a 3 mm spherical probe during external rotation indicates very high likelihood of rupture of both the AITFL and the IOL. Also, concomitant intra-articular pathologies (osteochondral lesions, other ligamentous rupture or loose bodies) can be presented, with 19% needs to be addressed, reinforcing the role of arthroscopy not only for diagnosis but also for treatment. It is also an excellent tool to evaluate anatomic reduction and residual diastasis.