Abstract:
This study investigates a hypothesized mechanism for the ingress of third body debris into the bearing space of total hip arthroplasty (THA) implants, which is a leading cause of aseptic loosening. The hypothesis posits that convective fluid transport during subluxation events is responsible for drawing extra-articular debris into the bearing space. To test this, a three-dimensional computational fluid dynamics (CFD) model of a leg-cross subluxation event was developed and validated. The model simulated the movement of a femoral head separating from the acetabular cup and quantified the resulting fluid velocities and pathlines. The results indicated that even small separations (<0.60 mm) could generate high fluid ingress velocities, capable of transporting debris from the entrance of the gap to near the pole of the cup. The study parametrically explored the effects of various implant design parameters. It was found that larger femoral head diameters and increased head inset led to higher fluid velocities, potentially drawing debris further into the bearing space. In contrast, increasing the initial gap width between the head and cup decreased fluid velocity. The chamfer angle and width of the cup had no appreciable effect on fluid velocity. Fluid viscosity also influenced the velocity, with higher viscosities leading to increased fluid path lengths. The authors concluded that impingement-induced subluxation is a plausible mechanism for third body debris ingress and that implant designs which reduce the propensity for subluxation would be beneficial in reducing the third body burden on the implant.
