Clinical and instrumented measurements of hip laxity and their associations with knee laxity and general joint laxity.

Abstract

Hip-joint laxity may be a relevant anterior cruciate ligament injury risk factor. With no devices currently available to measure hip laxity, it is important to determine if clinical measurements sufficiently capture passive displacement of the hip. To examine agreement between hip internal-external-rotation range of motion measured clinically (HIER(ROM)) versus internal-external-rotation laxity measured at a fixed load (HIER(LAX)) and to determine their relationships with knee laxity (anterior-posterior [KAP(LAX)], varus-valgus [KVV(LAX)], and internal-external rotation [KIER(LAX)]) and general joint laxity (GJL). Design : Cross-sectional study. Controlled research laboratory. Thirty-two healthy adults (16 women, 16 men; age = 25.56 ± 4.08 years, height = 170.94 ± 10.62 cm, weight = 68.86 ± 14.89 kg). Participants were measured for HIER(ROM), HIER(LAX) at 0° and 30° hip flexion (-10 Nm, 7 Nm), KAP(LAX) (-90 N to 133 N), KVV(LAX) (±10 Nm), KIER(LAX) (±5 Nm), and GJL. We calculated Pearson correlations and 95% limits of agreement between HIER(ROM) and HIER(LAX)_0° and HIER(LAX)_30°. Correlation analyses examined the strength of associations between hip laxity, knee laxity, and GJL. The HIER(ROM) and HIER(LAX) had similar measurement precision and were strongly correlated (r > 0.78). However, HIER(ROM) was systematically smaller in magnitude than HIER(LAX) at 0° (95% limits of agreement = 29.0° ± 22.3°) and 30° (21.4° ± 19.3°). The HIER(ROM) (r = 0.51-0.66), HIER(LAX)_0° (r = 0.52-0.69) and HIER(LAX)_30° (r = 0.53-0.76) were similarly correlated with knee laxity measures and GJL. The combinations of KVV(LAX) and either HIER(ROM), HIER(LAX)_0°, or HIER(LAX)_30° (R2 range, 0.42-0.44) were the strongest predictors of GJL. Although HIER(ROM) and HIER(LAX) differed in magnitude, they were measured with similar consistency and precision and were similarly correlated with knee laxity and GJL measures. Individuals with greater GJL also had greater hip laxity. These findings are relevant to clinicians and investigators conducting prospective risk factor studies, given the need for accessible, efficient, and low-cost alternatives for characterizing an individual's laxity profile.