Instrumented measurement of anteroposterior and inversion-eversion laxity of the normal ankle joint complex

Manual examination is the most common method for the evaluation of ankle an teroposterior (AP) and inversion-eversion (I-E) laxity. Objective assessmen t data of normal ankle laxity must be provided before comparison with an in jured ankle can be made. The purpose of this study was to compare AP transl ation and I-E rotation at three force loads between dominant and nondominan t ankles and to assess the test-retest reliability of a portable arthromete r in obtaining these measurements. The arthrometer consists of a frame that is fixed to the foot, a pad that is attached to the tibia, and a load-meas uring handle that is attached to the foot plate through which the load is a pplied. A six-degrees-of-freedom spatial kinematic linkage system is connec ted between the tibial pad and the foot frame to measure motion. Instrument ed measurement testing of total AP displacement and I-E rotation of both an kles was performed in 41 subjects (21 men and 20 women; mean age, 23.8 +/- 4.4 years). Subjects had no history of ankle injury. Subjects were tested i n the supine position while lying on a table with the knee secured in exten sion and the foot positioned at 0 degrees of flexion, Laxity was measured f rom total AP displacement (millimeters) during loading to 125 N of AP force and from total I-E rotation (degrees of range of motion) during loading to 4000 N-mm, Reliability was evaluated by calculating intraclass correlation coefficients (2,1) at 75 N, 100 N, and 125 N of AP force and at 2000, 3000 , and 4000 N-mm torque loads. Mean differences for displacement and rotatio n between the dominant and nondominant ankles at each of the force and torq ue loads were analyzed by dependent t-tests, For both the dominant and nond ominant ankles, respectively, the reliability coefficients at each of the f orce loads for AP displacement (range, 0.82-0.89) and I-E rotation (range, 0.86-0.97) were high. The t-test analyses showed no significant differences (P greater than or equal to 0.05) for total AP displacement or I-E rotatio n between the dominant and nondominant ankles at any of the force loads. Th e results are clinically useful in providing information about the reliabil ity of measures at different AP and I-E force loads using a portable ankle ligament arthrometer.