The Lateral Hook Test: What is the Amount of Force that Should Be Applied to Evaluate Syndesmotic Instability Using Arthroscopy?

CATEGORY: Ankle; Arthroscopy; Basic Sciences/Biologics INTRODUCTION/PURPOSE: The lateral hook test is considered the gold standard for the diagnosis of coronal plane syndesmotic instability during arthroscopy. The amount of distal tibiofibular space is directly related to the amount of lateral directed applied force. This study aims to determine the optimal amount of forced needed during a lateral hook test to evaluate syndesmotic instability in the coronal plane. The secondary aim was to determine the amount of displacement variation that occurs when the lateral force is angled anteriorly or posteriorly. METHODS: Ten fresh-frozen above-knee amputated cadaveric specimens underwent arthroscopic evaluation of the distal tibiofibular joint. The assessment was done first with all syndesmotic and ankle ligaments intact and subsequently with transection of the anterior inferior tibiofibular ligament (AITFL) and the interosseous ligament (IOL). In all scenarios, a lateral hook test was performed under increasing force from 0N to 120N of direct force, with increments of 20N. The lateral hook test was performed in: 1) the neutral position (no angulation), 2) anterior inclination of 15 degrees, and 3) posterior inclination of 15 degrees under the aforementioned force. Anterior and posterior coronal plane distal tibiofibular space were arthroscopically measured. Descriptive statistics were employed to determine the force and the most sensitive method to pull during arthroscopic evaluation to detect syndesmotic instability. RESULTS: Among the specimens, after transection of AITFL and IOL, the anterior and posterior coronal plane space increased with increment in force until 60N and then displayed no change in these measurements despite the increase in force. In the intact state, there was an increase in syndesmosis coronal space with increase in force. Of the three methods of force application, the posteriorly directed force has the largest absolute value for the anterior and posterior coronal space, suggesting it is the most sensitive in distinguishing between stable and unstable syndesmotic injury. CONCLUSION: Arthroscopic coronal plane evaluation under 60N of direct force is best suited to distinguish stable from an unstable syndesmosis. Syndesmosis anterior and posterior coronal plane space measurement demonstrate the largest absolute difference when subjected to posteriorly directed force, suggesting that this new method of assessment has the highest potential for diagnosing even subtle syndesmotic instability, along with a lower propensity for error.