Influence of constraint mechanism on kinematics, contact mechanics, and polyethylene wear in dual-axis rotating hinge and ball-and-socket knee prostheses: a finite element study.

Background: Severe metaphyseal bone defects following revision total knee arthroplasty or tumor resection often require highly constrained knee prostheses. Although rotating hinge knee (RHK) designs provide reliable stability, polyethylene wear and aseptic loosening remain important concerns. A novel ball-and-socket knee prosthesis has been developed to improve rotational accommodation and joint kinematics; however, its biomechanical performance relative to conventional rotating hinge designs remains unclear. Methods: Finite element models of a dual-axis rotating hinge knee prosthesis and a ball-and-socket knee prosthesis were developed and subjected to five million gait cycles under ISO 14243-1:2009 loading and motion conditions. Kinematics, contact mechanics, and polyethylene wear were evaluated using a contact-pressure-independent modified Archard wear formulation incorporating cross-shear effects. The reported wear volume for the ball-and-socket prosthesis represents the analyzed bearing side and its associated constraint interfaces. Results: Both prosthetic designs exhibited limited anterior-posterior translation and maintained relatively low contact pressures due to highly conforming articulations. Compared with the dual-axis rotating hinge prosthesis, the ball-and-socket prosthesis demonstrated greater internal-external rotational freedom (21.6° vs. 3.2°) and broader contact migration during gait. Although the ball-and-socket design exhibited larger contact areas and lower contact pressures, its polyethylene wear rate (10.06 mm Conclusion: Prosthetic design influences kinematics, contact mechanics, and wear behavior in highly constrained knee systems. The results indicate that multidirectional motion and cross-shear may play a more important role in polyethylene wear than contact pressure alone. Although the ball-and-socket prosthesis exhibited greater wear than the dual-axis design, it provided increased rotational accommodation and may better accommodate rotational demands during gait. These features support its potential as an alternative design strategy for constrained knee reconstruction after further experimental validation and design optimization. Future optimization should focus on reducing excessive multidirectional sliding and cross-shear while preserving rotational adaptability.