WEAR IN RETRIEVED CONDYLAR KNEE ARTHROPLASTIES - A COMPARISON OF WEARIN DIFFERENT DESIGNS OF 280 RETRIEVED CONDYLAR KNEE PROSTHESES

The plastic components of 280 retrieved unicondylar and total knee art hroplasties were studied. Wear was visually scored using a relative ra nked data method. Although wear on the components was highly variable, several conclusions could be drawn regarding the nature and causes. W ear was associated more with the medial than the lateral condyle. Dela mination was the most severe type of wear and occurred in short (< 5 y ears)-, medium (5-10 years)-, and long (> 10 years)-term retrievals. I n the short term, delamination wear was associated with hot pressing o f the tibial plastic or with fracture of the tibial baseplate. For a s ingle design, a significant difference in the amount of delamination o n hot-pressed and non-hot-pressed tibial components was observed. In m edium- and long-term retrieved specimens of the designs with moderatel y high conformity, delamination wear was associated with restriction o f rotational movement of the femoral component or with abrupt changes in the radius of the tibial component. In flatter, less conforming des igns, wear was associated with laxity, such that the polyethylene dela minated toward the edges of the tibial component. Wear attributed to c ement abrasion or entrapment occurred on the more conforming designs. Delamination was associated with the presence of fusion defects in the polyethylene but could also occur in the absence of such defects. Tha t delamination was the principal wear type and that this is caused by a fatigue mechanism mean that the incidence of failure could accelerat e considerably over follow-up periods beyond IO years. Designs of mode rate conformity without abrupt changes in radii may prolong the durati on of plastic tibial components before serious delamination occurs.