TKR backside wear studies have concluded that, compared to rough trays, polished trays decrease total amount of backside wear by 80% to 87%. However, size and volumetric concentration of sub-micron-sized polyethylene particles are critical factors for macrophage-mediated osteolysis. We assessed the size and morphology of polyethylene wear debris from TKR backside wear simulations comparing polyethylene fretting against polished and blasted metal surfaces. A 3-station fretting wear simulator reproduced loads and motions typical of the backside of fixed-bearing inserts of TKRs. 5-million cyclic experiments combined low (50μm) or high (200μm) linear motion with +3o rotational motion. Load profile was double-peak Paul curve (peak 10MPa). Eight 3-station experiments measured polyethylene wear against blasted or polished metal surfaces of Ti6Al4V or CoCr. Polyethylene particles were isolated from serum following gradient separation and filtration on 0.01μm polycarbonate filters. Using SEM analysis, average 200 particles per sample were characterized with Meta-morph™ image analysis software. Concentration of submicron particles in the debris from rough surfaces was 31–32% under 50μm motion, 28–30% under 200μm. Surprisingly, this concentration from polished surfaces was substantially greater: 69–78% (50μm), and 57–63% (200μm). However, total poly wear against rough surfaces was 0.45–1.63mm3/ Mcycles, and 0–0.35mm3/Mcycles against polished. Taking this into account, the volume of submicron particles from polished surfaces is less than 0.1mm3/ Mcycles and from rough surfaces between 0.1 and 0.45mm3/Mcycles. In conclusion, although polished metal trays produce up to five times less wear than blasted surfaces, they may also lead to an increase in the osteolytic potential of the polyethylene debris.
Aims. Wear of the polyethylene (PE) tibial insert of total knee arthroplasty (TKA) increases the risk of revision surgery with a significant cost burden on the healthcare system. This study quantifies wear performance of tibial inserts in a large and diverse series of retrieved TKAs to evaluate the effect of factors related to the patient, knee design, and bearing material on tibial insert wear performance. Methods. An institutional review board-approved retrieval archive was surveyed for modular PE tibial inserts over a range of in vivo duration (mean 58 months (0 to 290)). Five knee designs, totalling 1,585 devices, were studied. Insert wear was estimated from measured thickness change using a previously published method. Linear regression statistical analyses were used to test association of 12 patient and implant design variables with calculated wear rate. Results. Five patient-specific variables and seven implant-specific variables were evaluated for significant association with lower insert wear rate. Six were significant when controlling for other factors: greater patient age, female sex, shorter duration in vivo, polished tray, highly cross-linked PE (HXLPE), and constrained knee design. Conclusion. This study confirmed that knee wear rate increased with duration in vivo. Older patients and females had significantly lower wear rates.
