Knee Joint Laxity and Its Cyclic Variation Influence Tibiofemoral Motion during Weight Acceptance

SHULTZ, S. J., R. J. SCHMITZ, A.-D. NGUYEN, B. LEVINE, H. KIM, M. M. MONTGOMERY, Y. SHIMOKOCHI, B. D. BEYNNON, and D. H. PERRIN. Knee Joint Laxity and Its Cyclic Variation Influence Tibiofemoral Motion during Weight Acceptance. Med. Sci. Sports Exerc., Vol. 43, No. 2, pp. 287-295, 2011. Purpose: To better understand how sex differences in anterior knee laxity (AKL) affect knee joint biomechanics, we examined the consequence of greater absolute baseline (males and females) and cyclic increases in AKL during the menstrual cycle (females) on anterior tibial translation (ATT) as the knee transitioned from non-weight-bearing to weight-bearing conditions, while also controlling for genu recurvatum (GR). Methods: Males and females (71 females and 48 males, aged 18-30 yr) were measured for AKL and GR and underwent measurement of ATT. Women were tested on the days of their cycle when AKL was at its minimum (T-1) and maximum (T-2); males were matched in time to a female with similar AKL. Linear regressions examined relationships between absolute baseline (AKL(T1), GR(T1)) and cyclic changes (Delta = T-2 - T-1; AKL(Delta), GR(Delta)) (females only) in knee laxity with ATT as measured at T-1 and T-2 and Delta (T-2 - T-1) (females only). Results: AKL and GR increased in females, but not in males, from T-1 to T-2. Greater AKL(T1) and GR(T1) predicted greater ATT(T1) and ATT(T2) in males (R-2 = 21.0, P < 0.007). The combination of greater AKL(T1), AK(L Delta), and less GR(Delta) predicted greater ATT(T1) and ATT(T2) in females (R-2 = 12.5-13.1, P < 0.05), with AKL(Delta) being a stronger predictor (coefficient, P value) of ATT(T2) (0.864, P = 0.027) compared with ATT(T1) (0.333, P = 0.370). AKL(Delta) was the sole predictor of ATT(Delta) (R-2 = 0.104 and 0.740, P = 0.042). Conclusions: Greater absolute baseline and cyclic increases in AKL were consistently associated with greater ATT produced by transition of the knee from non-weight-bearing to weight-bearing. Because the anterior cruciate ligament is the primary restraint to ATT, these findings provide insight into the possible mechanisms by which greater AKL may be associated with at-risk knee biomechanics during the weight acceptance phase of dynamic tasks.