Effects of implant design parameters on fluid convection, potentiating third-body debris ingress into the bearing surface during THA impingement/subluxation

Abstract

Aseptic loosening from polyethylene wear debris is the leading cause of failure for metal-on-polyethylene total hip implants. Third-body debris ingress to the bearing space results in femoral head roughening and acceleration of polyethylene wear. How third-body particles manage to enter the bearing space between the closely conforming articulating surfaces of the joint is not well understood. We hypothesize that one such mechanism is from convective fluid transport during subluxation of the total hip joint. To test this hypothesis, a three-dimensional (3D) computational fluid dynamics (CFD) model was developed and validated, to quantify fluid ingress into the bearing space during a leg-cross subluxation event. The results indicated that extra-articular joint fluid could be drawn nearly to the pole of the cup with even very small separations of the femoral head (<0.60mm). Debris suspended near the equator of the cup at the site of maximum fluid velocity just before the subluxation began could be transported to within 11 degrees from the cup pole. Larger head diameters resulted in increased fluid velocity at all sites around the entrance to the gap compared to smaller head sizes, with fluid velocity being greatest along the anterosuperolateral cup edge, for all head sizes. Fluid pathlines indicated that suspended debris would reach similar angular positions in the bearing space regardless of head size. Increased inset of the femoral head into the acetabular cup resulted both in higher fluid velocity and in transport of third-body debris further into the bearing space.

Effects of episodic subluxation events on third body ingress and embedment in the THA bearing surface

“…The present hip simulator experiment convincingly demonstrated that subluxation facilitates third body particle entry into the bearing space, and it provides physical confirmation of the results of related computational fluid dynamics (Lundberg et al, 2007b) and retrieval (Lundberg et al, 2007a) studies. Debris embedded in the acetabular liner at wear-critical locations subsequently scratches the femoral head, which can lead to increased wear of the acetabular liner.…”

“…Subluxation is presumably a commonplace occurrence in THA, as retrieval studies have documented a high prevalence of damage (up to 66% of specimens) on the rim of acetabular liners, indicative of femoral neck impingement (Hall et al, 1998;Isaac et al, 1992;Jasty et al, 1997;Murray, 1992;Shon et al, 2005;Wroblewski, 1985;Yamaguchi et al, 2000;Yamaguchi et al, 1999). A recent computational fluid dynamics model has provided theoretical evidence that, during THA subluxation, joint fluid is actively drawn into the space that opens between the head and liner (Lundberg et al, 2007b), providing access to wear-critical regions of the bearing surface near the pole of the liner. Third body particles suspended in this fluid would presumably be convected into the articulating surfaces by this mechanism.…”

Constrained Cups Appear Incapable of Meeting the Demands of Revision THA

“…However, wear rates of components retrieved at revision THA tend to be higher than those derived from primary cases, with average values of 94 and 99 mm 3 /year reported in previous series [20,48]. This increase may be the result of the occurrence of repetitive microseparation with rim impingement and the presence of third-body particles, either within the joint fluid or embedded within the articular surface [36,41].…”

2009 Nicolas Andry Award: Clinical Biomechanics of Third Body Acceleration of Total Hip Wear

“…The data showed the patients who had cable-implantation have fared dramatically worse by virtually all measures associated with wear/osteolysis/loosening. The prevalence of proximal femoral osteolysis was 1.66 times as high (47.4% versus 28.6%; chi square p \ 0.0001), the prevalence of acetabular osteolysis was 2.25 times as high (21.4% versus 9.5%; chi square p \ 0.0003), the mean linear radiographic wear rate was 23 implant survivorship for the patients with third-bodychallenge was worse (p \ 0.026) and becoming increasingly more so (Fig. 14).…”

“…To test this hypothesis [23], a three-dimensional computational fluid dynamics (CFD) model was developed and physically validated to quantify fluid ingress into the bearing space during subluxation events. The physical validation (error \ 15%) was performed using particle image velocimetry (PIV), a technique by which motions of reflective, neutrally buoyant micromarkers dispersed in the fluid are tracked and their velocities measured.…”