The Ankle syndesmosis: identification of injury.
A joint critical to the stability and function of the ankle, injured in as many as 11% of ankle sprains. The most common mechanisms of injury are in external rotation (or tibial internal rotation vs foot) and hyperdorsiflexion of the foot; both causing a widening of the mortise. A 1mm increase in the width of the mortise reduces the talocrural surface contact by 42%, decreasing stability and increasing the rate of degeneration. Weight bearing though an unstable joint may prevent the joint from adequately tightening as healing progresses by forcing the mortise open during each step.
Anatomy
The syndesmosis is a mortise joint formed by two bones and 4 ligaments. The joint is formed when the lateral tibial ridge bifurcates into an anterior and posterior margin. The triangular concavity between these margins is incisura tibialis. The fibula rests within this concavity and it’s position is maintained by the anterior (ATIFL) and posterior (PTIFL) tibiofibular ligaments, the transverse ligaments and the interosseous ligment. The relative importance for stability: 35% ATIFL, 33% transverse lig, 22% interosseous lig., 9% PTIFL.
Clinical Testing
Very difficult at times due to the low sensitivity of the tests for the syndesmosis injury. Multiple +ve tests can strengthen diagnosis.
Squeeze test: firm pressure applied to approximate the proximal 1/3 of the tibia and fibula. +ve test is indicated by pain over the distal tibiofibular joint (not +ve with pain in the area of the compression).
Dorsiflexion test: Weight bearing dorsiflexion with and without compression of the distal Tibiofibular joint. +ve test indicated by decrease in pain and/or significant increase in ROM with compression.
External rotation test (Kleiger’s): Primarily for testing the deltoid ligament but also used for syndesmosis injury. With the patient sitting on bed with affected leg dangling, grasp plantar foot and apply external rotation force to foot while stabilizing distal leg. +ve test is an application of symptoms at the syndesmosis.
Comparative palpation: A comparison of tenderness between both ATIFL.
Diagnostic Evaluation
Evidence for injury can be obtained by checking the position of the distal fibula in the incisura tibialis, imaging the ligaments or trying to measure change in the size of the joint.
Xrays have been used to determine the fibula’s position relative to the tibia. Views such as the Tibiofibular overlap, Tibiofibular clear space, the ratio between the medial and superior clear space and the dorsiflexion weight bearing stress comparisons are all plagued by inaccuracy.
MRI, CT findings substantially improve the identification of fibular alignment issues and MRI can image the ligament damage but are expensive and inaccessible.
Visualizing the ligaments: ATIFL is very superficial and suspected disruptions can be visualized with diagnostic ultrasound(85% accuracy).
Conclusion
Early clinical identification is critical to avoid missing the proliferative phase of healing. If the joint is braced and protected during early rehabilitation there is a better chance for retightening of many minor injuries. Unfortunately, this part of ankle sprains is commonly missed and only identified when the ankle injury does not resolve.
References:
Hermans J, Beumer A, Jong T, Kleinrensink G. Anatomy of the distal tibiofibular syndesmosis in adults: a pictorial essay with a multimodality approach. Journal of Anatomy: 2010 (217).
Alonso, A. Clinical tests for ankle syndesmosis injury:reliability and prediction of return to function. Journal of orthopedic sports physical therapy: Apr 1998 vol 27 (4)