Physiological Knee Motion
The biomechanical rationale for kinematic alignment lies in its ability to restore physiological knee motion, rather than imposing an externally defined alignment target. The native knee is not mechanically neutral; it exhibits patient-specific joint line obliquity, axial rotation, and ligament tension patterns that evolve throughout flexion and extension.
Biomechanical studies suggest that kinematically aligned knees more closely replicate natural femorotibial motion, particularly in mid-flexion and deep flexion activities. By preserving the native joint line orientation, kinematic alignment may reduce abnormal contact forces and facilitate smoother femoral rollback and tibial rotation.
Functionally, these biomechanical differences may translate into improved activities of daily living such as stair climbing, squatting, and rising from a seated position. Patients frequently report that the knee feels more “normal,” a subjective but clinically meaningful outcome that reflects alignment between joint mechanics and neuromuscular control.
Asymmetry
Another important consideration is load distribution. Mechanical alignment aims to equalise medial and lateral compartment loading, whereas kinematic alignment respects the patient’s natural load-sharing pattern. This challenges traditional assumptions but is supported by the observation that many individuals function asymmetrically without developing pathology prior to arthritis.
While long-term biomechanical implications continue to be studied, current evidence indicates that restoring native kinematics does not inherently increase implant stress when alignment remains within acceptable ranges. Instead, it may reduce compensatory movement patterns that contribute to dissatisfaction and functional limitation.
Understanding biomechanics is essential when evaluating alignment philosophies. Kinematic alignment represents a shift toward reconstructing how the knee moves, not just how it appears on radiographs—a distinction that may explain its growing appeal among both surgeons and patients.
Suggested reading
Victor J, Bellemans J. Physiological kinematics of the knee. Knee Surg Sports Traumatol Arthrosc. 2006;14(6):513–521.
Matsumoto T, Muratsu H, Kubo S, et al. Soft tissue balance and kinematics in kinematically aligned TKA. Knee Surg Sports Traumatol Arthrosc. 2014;22(8):1819–1827.
Nishio Y, Matsumoto T, Muratsu H, et al. In vivo kinematics after kinematic alignment TKA. Knee. 2018;25(6):1272–1280.
Rivière C, Iranpour F, Harris S, et al. Differences in kinematics between mechanical and kinematic alignment. Bone Joint J. 2017;99-B(7):862–868.