The ACL of the Ankle Joint: A Cadaveric Evaluation of the Subtalar Intrinsic Ligaments and Optimal Surgical Approach

Abstract

Category: Ankle; Basic Sciences/Biologics; Sports Introduction/Purpose: The biomechanics of ankle sprains involves a multiplanar-supination motion and not the strict inversion as is often described. During supination, calcaneal inversion occurs at the anatomic subtalar joint. The intrinsic subtalar ligaments include a series of broad thick ligaments situated in the tarsal canal that separate the anterior and posterior compartments. The subtalar intrinsic ligaments are damaged in an estimated 25% to 80% of all lateral ankle sprains. We hypothesize that the intrinsic subtalar ligaments have a multiplanar role in ankle joint stabilization similar to that of the anterior cruciate ligament at the knee. The purpose of this study is to evaluate the efficacy of four surgical approaches to the subtalar ligaments through cadaveric dissection. Methods: Four fresh-frozen cadaveric ankle specimens were utilized. Ability to access the extrinsic lateral ankle ligament (anterior talofibular), the extrinsic subtalar ligaments (calcaneofibular, lateral talocalcaneal) and the intrinsic subtalar ligaments (interosseous talocalcaneal, cervical) was evaluated. The first cadaveric specimen was dissected as a baseline to identify the extrinsic and intrinsic subtalar ligaments. The three remaining cadaveric specimens were utilized to evaluate the efficacy of three standard surgical approaches (a curvilinear incision made over the distal anterior border of lateral malleolus, a posterolateral longitudinal incision, and an extensile sinus tarsi approach) to access both the extrinsic ankle and subtalar ligaments as well as the intrinsic subtalar ligaments. Ability to access all ligaments as well as identification of neurovascular structures at risk during the dissection was recorded for each approach. Results: The curvilinear incision made over the distal anterior border of the lateral malleolus provided access to the anterior talofibular, calcaneofibular ligaments. Branches of the superficial peroneal nerve were noted to be at direct risk. The posterior longitudinal incision provided access to the calcaneofibular, lateral talocalcaneal ligaments. Branches of the sural nerve were noted to be at direct risk with this approach. An extensile posterolateral incision improved access to the anterior talofibular ligament. An extensile sinus tarsi approach provided the most direct access to the interosseous talocalcaneal and cervical ligaments. Visualization of the calcaneofibular and lateral talocalcaneal was also provided with this incision. The saphenous and superficial nerve branches and the sinus tarsi artery were noted to be at risk. Conclusion: We hypothesize that the intrinsic subtalar ligaments have a multiplanar role in ankle joint stabilization similar to that of the anterior cruciate ligament at the knee. Accurate identification and optimal surgical approach to these structures has not been well described in the orthopaedic foot and ankle literature. This cadaveric study provides evidence that an extensile sinus tarsi approach can provide access to the extrinsic ankle and subtalar ligaments as well as the intrinsic ligaments of the subtalar joint.