This study aimed to determine whether the “screw-home mechanism” follows systematic rotation patterns and evaluate differences between OKC and CKC exercises.
A total of thirty-four healthy subjects participated in the study. Each subject performed two tasks: extending their leg three consecutive times (OKC) and standing up straight from a chair three consecutive times (CKC). In vivo three-dimensional data of the tibiofemoral joint were collected using electromagnetic tracking with the Polhemus Liberty system. The data were analysed using machine learning techniques, specifically k-means clustering, to identify patterns in the screw-home mechanism.
Four distinct clusters were identified for each movement. These included: (1) the commonly observed external rotation during the final 20 degrees of knee extension, (2) a gradual external rotation throughout the entire extension, (3) a pattern with no external or internal rotation during the movement, and even (4) a cluster displaying gradual internal rotation either throughout the entire knee extension or during specific parts of the knee extension.
These patterns can be asymmetrical between the left and right knees and may differ or be more pronounced in either CKC or OKC. For instance, the mean and minimum-maximum range of external rotation of the tibia relative to the femur was found to be greater in CKC than in OKC. While the left and right legs may vary and fall into different clusters, no significant differences have been confirmed.
This study provides insights into the kinematics of the screw-home mechanism during open and closed kinetic chain exercises. Distinct rotation patterns were identified, highlighting variability in external and internal rotations across different movements. CKC exercises demonstrated greater external rotation and a wider range of motion compared to OKC exercises, contributing to the ongoing debate regarding their respective impacts on knee biomechanics. The findings suggest that both exercise types influence the screw-home mechanism differently. Further research is needed to investigate how these variations affect long-term knee stability and recovery outcomes.
Insights into the distinct kinematic patterns identified in this study can have practical implications for physiotherapists. By understanding cluster-specific variations in the screw-home mechanism, clinicians may tailor rehabilitation strategies based on individual patient biomechanics. Incorporating biomechanical assessments of screw-home patterns could enhance treatment protocols, helping to optimize recovery outcomes and improve long-term knee stability in for example patients undergoing rehabilitation for ACL injuries.
Screw-Home Mechanism
Kinetic Chain Exercises
