Long-term outcomes of a 3D printed cementless fixed bearing unicompartmental knee arthroplasty

Cementless fixation of medial unicompartmental knee arthroplasty (UKA) is attracting growing interest as a way to improve implant survival. This study aimed to evaluate the near-decade results, survivorship, and revision causes for a fixed-bearing cementless fully 3D printed UKA.

From 2011 to 2014, 168 consecutive cementless UKA implants on 165 patients had been performed in our hospital using a fixed bearing implant with a 3D printed Hydroxyapatite coated ingrowth surface both on the femoral and tibia components. At a mean follow-up of 8.73 years, 132 patients were retrospectively available for long-term assessment. Clinical outcomes and survivorship were analyzed using validated Patient Reported Outcome Measures (PROMs) such as the Oxford Knee Score (OKS), the International Knee Society (IKS) Score and the Numeric Rating Scale (NRS). The Hip-Knee-Ankle (HKA) angle was measured preoperatively and postoperatively at the last follow-up. Kaplan-Meier survival analysis was conducted with revision for any reason as primary endpoint and UKA failure as secondary endpoint.

Significant reductions were observed in terms of mean NRS from 6.90 to 1.49 points (p < 0.0001), OKS from 34.82 to 19.05 points (p < 0.0001), and IKS Score, in particular clinical knee score from 59.13 to 85.61 points (p < 0.0001) and functional knee score from 58.70 to 88.94 points (p < 0.0001). The 10-year survival rate for revision for any reason was 93.6% (95% CI: 89.5-97.8). For revision specifically due to implant mechanical failure, the 10-year survival rate was 94.9% (95% CI: 91.3-98.8). The primary revision cause was aseptic loosening of the tibial component. Factors such as age, BMI, and sex were not significantly associated with an increased risk of revision.

The present study shows good clinical results and long-term implant survivorship, compared to literature data, confirming the effectiveness of cementless UKA.