Comparison of Hip Rotation Muscle Strengths between Healthy Women and Anterior Cruciate Ligament Injury Patients: The Internal and External Rotation Muscles' Strength Ratio: —内旋筋と外旋筋の筋力比に着目して—

[Purpose] To clarify the differences in hip internal and external rotation muscle strengths, and their ratio, between subjects with and without a history of anterior cruciate ligament (ACL) injury. [Subjects and Methods] The subjects were 22 healthy females and 9 females with a history of ACL injury. Hip internal and external rotation muscle strengths of the two groups were measured with a hand-held dynamometer, and compared together with their ratio using the Mann-Whitney U-test. [Results] No significant difference was found in the hip external muscle strengths of the two groups; however, in the ACL injury group, the hip internal rotation muscle strength and the internal:external muscle strength ratio were significantly larger. [Conclusion] Subjects in the ACL injury group had imbalance in the strength ratio of the hip internal and external rotation muscles. Therefore, there is a possibility that physical therapy intervention to restore this muscle strength ratio to close to that of healthy individuals would be beneficial for them.