Abstract:
"Effects of Implant Design Parameters on Fluid Convection, Potentiating 3rd Body Debris Ingress into the Bearing Surface during THA Impingement/Subluxation"
Aseptic loosening, primarily driven by polyethylene wear debris, remains the leading cause of failure for metal-on-polyethylene total hip implants. A significant contributor to accelerated polyethylene wear is the ingress of third-body debris into the bearing space, which roughens the femoral head. Despite the critical impact, the exact biomechanical mechanisms by which these particles manage to enter the tightly conforming articulating surfaces of the joint are not well understood. This study addresses this knowledge gap by hypothesizing that convective fluid transport during subluxation of the total hip joint plays a key role.
To investigate this biomechanical hypothesis, a three-dimensional computational fluid dynamics (CFD) model was meticulously developed and rigorously validated. This model quantified fluid ingress into the bearing space during a simulated leg-cross subluxation event. The comprehensive study parametrically investigated the effects of various implant design parameters and operating conditions on this fluid convection phenomenon. Key parameters analyzed included femoral head diameter (22, 28, 36 mm), diametral gap width (0.05, 0.1, 0.2 mm), chamfer angle (0, 30, 45, 60 degrees), chamfer thickness (15, 25, 35% of liner thickness), head inset (0, 3.5, 7 mm), and fluid viscosity (0.001, 0.01, 0.1 Pa·s).
The results of the CFD analysis indicated that fluid ingress, and thus the potential for third-body debris transport, was most significantly influenced by increasing the diametral gap width between the femoral head and acetabular liner. Moreover, larger femoral head diameters, greater chamfer angles, and increased chamfer thickness also promoted higher levels of fluid ingress. In contrast, varying the head inset had a minimal impact, while increased fluid viscosity led to a reduction in fluid flow into the bearing space. This biomechanical investigation confirms that fluid convection during subluxation is a viable mechanism for third-body debris ingress and highlights specific implant design parameters that can be optimized to minimize this phenomenon, thereby potentially extending the longevity of total hip arthroplasty implants.
