High Early Failure Rate of a Novel Cementless Unicompartmental Knee Arthroplasty

Unicompartmental knee arthroplasty (UKA) is an accepted treatment for antero-medial osteoarthritis with low overall failure rates. In the United States, cementation remains the gold standard of implant fixation; however, multiple studies have shown potential benefits of increased survivorship with cementless fixation. The aim of this study was to evaluate clinical and radiographic outcomes of a novel cementless medial UKA implant. We hypothesized that cementless UKA would perform as well as or better than cemented UKA.

Clinical outcomes, including patient-reported outcome measures, were prospectively collected for 111 patients (127 knees) implanted with a novel cementless UKA from February 2021 to December 2022. Radiographic lucency zones surrounding the femoral and tibial components were evaluated from postoperative radiographs. Data were collected preoperatively and at standard postoperative intervals until final follow-up or implant revision. Revisions were necessary in 15 of 127 UKAs (11.8%) at a mean of 0.9 years (range, zero to two).

The most common revision reason was aseptic loosening (12). Kaplan-Meier survival was 84.0% (95% CI [confidence interval] ± 3.98%) at 2.4 years. The Knee injury and Osteoarthritis Outcome Score for Joint Replacement 12-month scores differed significantly between revision and nonrevision groups (61.9, 95% CI ± 13.4 versus 75.1, 95% CI ± 16.9; P = 0.01). In patients revised for aseptic loosening, 11 of 12 tibial implants had progressive radiolucent lines on prerevision imaging. Revision operative records noted minimal to no bone ingrowth on the tibial implant undersurface.

This novel cementless medial UKA implant demonstrated a high rate of early revision, mostly for tibial-sided complications. Compared to nonrevised implants, revised implants had higher rates of tibial and femoral radiolucencies on postoperative radiographs as well as lower Knee injury and Osteoarthritis Outcome Score for Joint Replacement 12-month scores prerevision. When recorded in the operative record, no significant bone ingrowth was seen on the porous implant surfaces.

IV.