Joint line elevation and tibial slope are associated with increased polyethylene wear in cruciate-retaining total knee replacement.

The purpose of this retrieval study was to determine the effect of implant positioning on wear, taking patient-related factors into account. Therefore, the volumetric material loss of 59 retrieved tibial liners was quantitatively determined using a coordinate measuring-machine. All retrievals were made of the same polyethylene and design by a single manufacturer. Using time in-situ and linear regression, a wear rate for each liner was determined and corrected for bedding-in. Backside damage was qualitatively scored. The following implant positioning parameters were obtained from radiographs: anatomical lateral-distal femoral angle, anatomical medial-proximal tibial angle, femoral tilt angle, and posterior tibial slope. The patella position was assessed by the Blackburne-Peel index and the Insall-Salvati ratio. Unlike the Insall-Salvati ratio, the Blackburne-Peel index is known to detect surgical joint line elevation. Using general linear modeling the most impactful factors on wear rate and backside damage was determined, thereby taking patient demographic factors into account. The mean volumetric wear rate was 11.6 mm /y. Wear decreased with older age (P = .021) and female sex (P = .001). The wear rate increased with joint line elevation as indicated from a decreased Blackburne-Peel index (P = .019), and increased with increased posterior tibial slope (P = .026). The backside damage score also increased with joint line elevation (P = .036). A Blackburne-Peel index decrease of 0.1, signifying joint line elevation, was found to increase the wear rate by 1.8 mm /y and increase back-sided wear. A high tibial slope (>7°) led to a 9.3 mm /y increase in wear rate compared with a low tibial slope (<3°). The results of this study demonstrate that tibial liner positioning has a significant impact on polyethylene wear with potential implications on osteolysis over time.