OBJECTIVE

To show the relationship between direct measurements of tibial-calcaneal bone motion and instrumented measurements of ankle-subtalar-joint-complex laxity using a portable ankle arthrometer; to assess within and between-tester measurement reliability; and to determine if the ankle arthrometer can detect increased mechanical laxity of the ankle-subtalar-joint-complex after simulated injury of the lateral ankle ligaments. DESIGN AND SETTING: We used linear regression analysis to examine the relationship between direct measurements of tibial-calcaneal bone motion and instrumented measurements of ankle-subtalar-joint-complex laxity. An intraclass correlation coefficient (2,1) was calculated to determine intratester and intertester reliability for instrumented measurements of ankle-subtalar-joint-complex laxity. In addition, 2 separate, one-way, repeated-measures analyses of variance were used to compare instrumented measures of anteroposterior displacement and inversion-eversion rotation among the intact ankles after sectioning the anterior talofibular ligament and both the anterior talofibular and calcaneofibular ligaments. Data were collected in a biomechanics laboratory setting. SUBJECTS: Six fresh-frozen human-cadaver ankle specimens were studied. MEASUREMENTS: Testing involved the concurrent measurement of tibial-calcaneal bone motion and ankle-subtalar-joint-complex motion during the application of external loads. An instrumented ankle arthrometer was used to load the ankle in a controlled manner. Two spatial kinematic linkages measured the 3-dimensional motion of the calcaneus relative to the tibia and the motion of the arthrometer's footplate relative to the tibia. RESULTS: The correlation between tibial-calcaneal bone motion and instrumented measurement for anterior-posterior displacement was.878 (P =.0001). Its linear relationship with bone motion accounted for approximately 77% of the variance of the instrumented measurement. The correlation between tibial-calcaneal bone motion and instrumented measurement for inversion-eversion rotation was.858 (P =.0001), with approximately 74% of the variance of the instrumented measurement accounted for by its linear relationship with bone motion. High intratester and intertester reliability coefficients (ICC [2,1] =.80 to.97) were observed for instrumented measurements of ankle-subtalar-joint-complex laxity. In addition, ligamentous sectioning resulted in significantly increased ankle-subtalar-joint-complex laxity. When compared with the intact condition, sectioning both the anterior talofibular and calcaneofibular ligaments produced significant increases in anterior-posterior displacement (P =.0001) and inversion-eversion rotation (P =.002). CONCLUSIONS: We found a strong relationship between tibial-calcaneal bone motion and arthrometric measurements of ankle-subtalar-joint-complex laxity. The instrumented ankle arthrometer may be suitable as a diagnostic tool for the evaluation of lateral ankle-ligament laxity.