Background-Gender differences in passive frontal plane knee stiffness may contribute to the increased anterior cruciate ligament injury rate in females. Gender-based stiffness differences have been attributed to anthropometric variations, but little data exist describing this relationship. Furthermore, sex hormone levels appear to influence joint stiffness, but the differential effects of instantaneous and prior hormonal concentrations remain unknown. This study sought to explore the effect of gender, prior hormonal status, and anthropometry on passive frontal plane knee joint stiffness.

Though the knee experiences three-dimensional loading during everyday tasks, assessment of proprioceptive acuity has typically been limited to the primary direction of movement, knee flexion and extension. While loading in the constrained directions (varus/valgus and internal/external rotation) may contribute to injury and joint disease, little information is available regarding proprioceptive acuity in these planes of movement. The primary aim of this study was to characterize proprioceptive acuity in the frontal plane (varus/valgus) and to compare it with sagittal plane (flexion/extension) proprioceptive acuity in healthy subjects. Proprioception was assessed in 17 young, healthy subjects (11 females, 6 males, ages 21–33 years) using the threshold to detection of passive movement (TDPM). TDPM was found to be significantly (P < 0.001) lower in the frontal plane [valgus: mean (SD) 0.60 (0.20)° and varus: 0.58 (0.23)°] compared with the sagittal plane [extension: 0.78 (0.34)°, flexion: 0.82 (0.48)°]; however, no significant differences were noted within the same plane of movement. Results from this preliminary study may suggest more accurate proprioceptive acuity in the frontal plane compared with the sagittal plane. While further examination is necessary to confirm this relationship, more accurate frontal plane acuity may reflect a protective neural mechanism which enables more precise neuromuscular control of the joint in this constrained plane of movement.

Objective Impaired proprioception may alter joint loading and contribute to the progression of knee osteoarthritis (OA). Though frontal plane loading at the knee contributes to OA, proprioception and its modulation with OA in this direction have not been examined. The aim of this study was to assess knee proprioceptive acuity in the frontal and sagittal planes in knee OA and healthy participants. We hypothesized that proprioceptive acuity will be decreased in the OA population in both planes of movement. Methods Thirteen persons with knee OA and fourteen healthy age-matched subjects participated. Proprioceptive acuity was assessed in varus, valgus, flexion, and extension using the threshold to detection of passive movement (TDPM). Repeated measures analysis of variance was used to assess differences in TDPM between subject groups and across movement directions. Linear regression analyses were performed to assess the correlation of TDPM between and within planes of movement. Results TDPM was found to be significantly higher (P<0.05), in the knee OA group compared to the control group for all directions tested, indicating reduced proprioceptive acuity. Differences in TDPM between groups were consistent across all movement directions, with mean difference (95% CI) for valgus: 0.94° (0.20°, 1.65°), varus: 0.92° (0.18°, 1.68°), extension: 0.93° (0.19°, 1.66°), and flexion: 1.11° (0.38°, 1.85°). TDPM measures across planes of movement were only weakly correlated, especially in the OA group. Conclusions Consistent differences in TDPM between the OA and control groups across all movement directions suggest a global, not direction-specific, reduction in sensation in knee OA patients.