Reduced Acetabular Backside Wear, Particle Migration and Osteolysis

Purpose: We hypothesized that design improvements in 3rd-generation acetabular components would result in reduced backside wear and less osteolysis compared with earlier designs.

Methods: Fourteen 3rd-generation acetabular implants were harvested postmortem 1 to 12 yrs after insertion for OA. Histomorphologic and tribological data were compared to duration-matched data for 1st (n=17) and 2nd (n=16) generation cups. The extent of particle-induced granuloma at the bone-implant interface was quantified. The area and severity of backside damage were graded. Data were analyzed using the Mann-Whitney test and Spearman correlations.

Results: Particle-induced granuloma in the porous coating was markedly reduced (p=0.003) in 3rd generation components compared to 1st or 2nd generation devices. In several 1st and 2nd generation and in none of the 3rd generation cups, granulomas containing abundant intracellular PE and metallic particles increased with time, occupying 15 to 40% of the porous coating after 6 or more years. The granulomas extended from screw holes, in some cases ballooning into large lesions into pelvic bone. In 3rd generation cups, only scant particles were detected at screw holes and within the porous coating. Liner backside damage was minimal in 3rd generation components and greater for 1st generation (p=0.003) and 2nd generation (p=0.061) devices. Backside damage was correlated with the extent of granuloma at the implant-bone interface for the 1st (r=0.572, p=0.021) and 2nd-generation (r=0.717, p=0.002) cups, but not for the 3rd-generation components.

Conclusions: Damage to the backside of the PE liner and particle-induced granuloma in the periprosthetic bone and porous coating of 3rd generation components were remarkably reduced relative to 1st and 2nd generation components up to 12 years following insertion. This suggests that the improved locking mechanism and stability between the liner and metal shell were effective in limiting the backside generation of PE debris and migration of particles from the joint.