Evaluation of Arthrometer for Ankle Instability: A Cadaveric Study

Abstract

Background: Stress tests are used to diagnose both acute and chronic lateral ankle instability. Commonly used stress tests require radiography and their reliability and sensitivity is still under debate. We developed a non radiographic ankle arthrometer to objectively assess mechanical ankle stability. This device was validated against stress radiographs in a cadaver investigation. Materials and Methods: Nine cadaver specimens were tested under: 0, 15, and 30 degrees ankle plantarflexion and 50 N, 100 N, 150 N, and 200 N anterior drawer load application. First, intact specimens were tested. Then the anterior talofibular ligament, calcaneofibular ligament and posterior talofibular ligament were sequentially cut. Anterior drawer displacement was analyzed simultaneously by a displacement transducer and by radiographic measurement. Stiffness was calculated as the linear increment of the load deformation curve. Results of a commercially available stress testing device served as a standard. Results: Stable and unstable ankles were differentiated by ankle arthrometer displacement and stiffness analyses (p = 0.012 and 0.003) with the arthrometer adjusted to 0 degrees of plantarflexion and 50 N anterior drawer load application. Standardized stress testing device and ankle arthrometer stress radiographic measurements correlated significantly (p = 0.000 to 0.027). Transducer measured anterior drawer instability was highly sensitive (96.3%), while specificity was 44.4%. Setting a cut off value of 4.5 N/mm, the stiffness analyses discriminated stable and unstable ankles with a sensitivity of 91.7% while the specificity was 62.5%. Conclusion: The ankle arthrometer was able to measure anterior subluxation of the talus in relation to the tibia in a cadaver experiment. The procedure is non-radiographic and highly sensitive in differentiating unstable from stable ankles. Clinical Relevance: Availablity of a nonradiographic device to measure ankle instability could improve diagnostic accuracy and facilitate decision making in patients with chronic ankle instability.