Identifying multiplanar knee laxity profiles and associated physical characteristics.

CONTEXT A single measure of knee laxity (ie, measurement of laxity in a single plane of motion) is probably inadequate to fully describe how knee joint laxity is associated with anterior cruciate ligament injury. OBJECTIVE To characterize interparticipant differences in the absolute and relative magnitudes of multiplanar knee laxity (ie, sagittal, frontal, and transverse planes) and examine physical characteristics that may contribute to these differences. DESIGN Descriptive laboratory study. SETTING University research laboratory. PATIENTS OR OTHER PARTICIPANTS 140 participants (90 women, 50 men). MAIN OUTCOME MEASURE(S) Using cluster analysis, we grouped participants into distinct multiplanar knee laxity profiles based on the absolute and relative magnitudes of their anterior knee laxity (AKL), genu recurvatum (GR), and varusvalgus (VV) and internal-external rotation (IER) knee laxity. Using multinomial logistic regression, we then examined associations between the different laxity profile clusters and physical characteristics of sex, age, activity level, general joint laxity, body mass index, thigh strength, and 8 measures of lower extremity anatomical alignment. RESULTS Six clusters were identified: low (LOW), moderate (MOD) and high (HIGH) laxity overall and disproportionally higher VV/IER (MOD(VV/IER)), GR (HIGH(GR)), and AKL (HIGH(AKL)) laxity. Once all other physical characteristics were accounted for, the LOW cluster was more likely to be older, with longer femur length. Clusters with greater magnitudes of VV and IER laxity were more likely to be younger and to have lower body mass index, smaller Q-angle, and shorter femur length (MOD, HIGH, MOD(VV/IER)) and less thigh strength (HIGH). The HIGH(GR) cluster was more likely to be female and to have a smaller tibiofemoral angle and longer femur length. The HIGH(AKL) cluster was more likely to have greater hip anteversion and navicular drop. CONCLUSIONS The absolute and relative magnitudes of a person's multiplanar knee laxity are not always uniform across planes of motion and can be influenced by age, body composition, thigh strength, and structural alignment. Except in HIGH(GR), sex was not a significant predictor of cluster membership once other physical characteristics were taken into account.