Diagnostic evaluation of mechanical ankle instability by comparing injured and uninjured contralateral ankles using arthrometry.

CONTEXT: Individuals with mechanical ankle instability (MAI) have obvious lateral ligament laxity and excessive ankle joint motion beyond the physiologic range. Arthrometry has been introduced to quantitatively measure the laxity of ankle joint. However, the diagnostic accuracy of arthrometers in diagnosing MAI is still debatable.

OBJECTIVES: To (1) evaluate the difference in laxity between bilateral ankles in patients with and without MAI and (2) calculate the diagnostic accuracy of ankle arthrometry using bilateral comparisons.

DESIGN: Cross-sectional study.

SETTING: Research laboratory.

PATIENTS OR OTHER PARTICIPANTS: A total of 38 individuals with unilateral MAI and another 38 healthy controls.

MAIN OUTCOME MEASURE(S): Bilateral ankle laxity in each individual was quantitatively measured by performing arthrometric anterior drawer test of ankles. Continuous data of loading force and joint displacement were recorded. Data of both ankles were compared in the following two aspects: ankle joint displacement when the loading force of the arthrometer was maintained at 75 N (D75) and load-displacement ratio when the loading force was increased from 10 N to 40 N (LDR 10-40).

RESULTS: The D75 between injured and uninjured ankles in patients with MAI was significantly different (p < 0.001). The mean LDR 10-40 in injured ankles was significantly higher than that in uninjured ankles (p < 0.001). In the control group, no significant differences were found between left and right ankles. The MAI group had significantly larger bilateral differences than the control group (p < 0.001). When LDR 10-40 was used for the diagnosis of MAI, the arthrometer showed a sensitivity and specificity of 0.900 and 0.933 with the cut-off value of 0.0351mm/N, respectively.

CONCLUSION: The ankle arthrometer could quantitatively measure the difference in bilateral ankle laxity in patients with MAI. Arthrometer-measured LDR 10-40 could be used to diagnose patients with MAI with high diagnostic accuracy.