The Lateral Drawer Test: A Novel Clinical Test to Assess Mortise Instability in Weber B Fibula Fractures

Abstract

Category: Trauma; Ankle Introduction/Purpose: Assessment of mortise stability is paramount in determining appropriate management of ankle fractures. While instability is readily apparent in bimalleolar or trimalleolar ankle fractures, determination of instability in the apparent isolated Weber B fibula fracture often requires further investigations such as stress radiography. While several authors have previously demonstrated poor predictive value of physical examination findings such as tenderness, ecchymosis and swelling with instability, no previous investigation has examined the ability of a translational test to determine deltoid ligament injury. The goal of this study is to test the validity of a novel clinical test, the lateral drawer test, in determining mortise instability in a cohort of patients with Weber B fibula fractures. Methods: Patients presenting with isolated fibula fractures were prospectively identified by an orthopaedic nurse practitioner or resident. Three views of the ankle as well as gravity stress views (GSV) were obtained. Prior to examining radiographs, two foot & ankle fellowship-trained orthopaedic surgeons (JYK, CPM) performed and graded the lateral drawer test. (Grade 0: no instability/symmetric to contralateral ankle, Grade I: translation = 5mm) While the surgeons were made aware of the presence of a Weber B fibula fracture, radiographs were not visualized prior to conducting the drawer test. Medial clear space (MCS) was measured. VAS pain scores were obtained before and after testing. The results of the lateral drawer test results were compared with radiographic measurements of MCS. Results: The study enrolled 57 consecutive patients with Weber B ankle fractures. Twenty-nine (51%) patients demonstrated radiographic instability with widening of the medial clear space >= 5 mm on GSV. When correlated with MCS measurement, the lateral drawer test demonstrated a sensitivity of 83.3%, specificity of 96%, positive predictive value (PPV) of 96% and negative predictive value (NPV) of 84% for determining instability. There was a strong correlation between the lateral drawer test grade and amount of MCS widening (⍴=0.82, p<0.001). Patients tolerated the lateral drawer test well with an average increase of 0.8 points on the VAS pain scale after testing. Conclusion: The lateral drawer test demonstrates high sensitivity, specificity, PPV and NPV for detecting instability in patients presenting with Weber B fibula fractures. While further validation is required in a larger cohort of patients, the lateral drawer test may offer an adjunct tool via physical examination to predict mortise stability.