The Screw-Home Mechanism in Healthy Female Walkers and Runners: 652

Females are highly susceptible to non-contact knee injuries, particularly rupture of the anterior cruciate ligament. There is evidence that the function of the screw-home mechanism to control kinematic knee coupling may play a role in this injury mechanism. Therefore, it is important to understand how the screw-home mechanism is affected by different tasks (walking vs. running) and during different phases of these tasks (stance vs. swing). PURPOSE: To compare the magnitude of kinematic knee coupling between the stance phase and swing phase of walking and running. It was hypothesized that stance phase and the task of walking would demonstrate a greater degree of coupling than swing phase and the task of running. METHODS: Nine female walkers (31yrs±7; 1.6m±0.1; 58kg±3) and nine female runners (31yrs±7; 1.6m±0.1; 54kg±5) were included in this study. Three-dimensional kinematic data was acquired using a 12-camera configuration. The walking and running tasks were each divided into portions of the stance and swing phase, defined as heel strike to first wave peak knee flexion, and peak knee flexion to heel strike respectively. Vector coding was used to calculate the kinematic coupling of the knee joint as an angle, where a value of 45° indicates perfect coupling and values less than 45° suggest more sagittal than transverse plane motion. A two-way mixed-effect ANOVA was used to compare the magnitudes of the coupling angles between tasks and phases. P ≤ 0.05 was considered significant. RESULTS: The mean coupling angle for walkers was 22.7°±12.7 and 7.3°±5.7 for stance and swing phase respectively. The mean coupling angle for runners was 17.2°±6.4 and 0.1°±4.1 for stance and swing phase respectively. There was no significant interaction between task and phase. However, there was a significant difference in the magnitude of coupling between walkers and runners (p = 0.05), as well as between stance and swing phases (p < 0.01). CONCLUSIONS: For both walkers and runners, the magnitude of coupling was closer to 45° (perfect coupling) during stance phase than swing phase. Similarly, during both stance and swing phase, the walkers were closer to 45° than the runners. This suggests that the sagittal and transverse plane motions are more closely coupled during activities that occur more slowly and with lower joint loads.