Evaluation of arthrometer for ankle instability: a cadaveric study.
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.


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%.


CONCLUSIONS
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.


CONCLUSIONS
Availablity of a nonradiographic device to measure ankle instability could improve diagnostic accuracy and facilitate decision making in patients with chronic ankle instability.
Nauck
Tanja
T
Institute of Sports Medicine Frankfurt, Main, Germany. nauck@smi-frankfut.de
Lohrer
Heinz
H
Gollhofer
Albert
A
D000368:Aged; D000369:Aged, 80 and over; D000843:Ankle Joint; D053587:Arthrometry, Articular / Q000295:instrumentation*; D002102:Cadaver; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D011237:Predictive Value of Tests; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D016474:Weight-Bearing