Effectiveness of 3D-printed femoral positioning guides in Oxford Unicompartmental Knee Arthroplasty: a randomized controlled trial with femoral mechanical-anatomical angle subgroup analysis

BACKGROUND: Knee osteoarthritis (KOA) is a common degenerative disease impairing elderly mobility. Oxford Unicompartmental Knee Arthroplasty (OUKA) is effective for unicompartmental degenerative osteoarthritis, yet traditional intramedullary alignment methods may cause inaccuracies, compromising outcomes. The purpose of this study was to assess the safety and accuracy of a 3D-printed intramedullary femoral positioning guide in Oxford Unicompartmental Knee Arthroplasty (OUKA), with subgroup analysis by femoral mechanical-anatomical angle (FMA). METHODS: A prospective randomized controlled trial enrolled 120 patients with severe medial knee osteoarthritis undergoing OUKA. Patients were randomly divided into two groups: the experimental group (n = 60) used a 3D-printed intramedullary femoral positioning guide, while the control group (n = 60) employed traditional femoral intramedullary localization. The primary outcome measures were femoral component valgus/varus angle (FCVA) and femoral component posterior slope angle (FCPSA). Secondary outcomes included operative time, tourniquet time, and early postoperative complications. Stratified analyses were performed based on the femoral mechanical-anatomical angle (FMA) using cutoff values of 7°. RESULTS: Among the 119 patients with complete data (one lost to follow-up), no significant differences in FCVA (experimental: -0.63 ° [-2.46 ° to 1.60 °]; control: 2.31 ° [-4.17 ° to 3.12 °], P = 0.438) or FCPSA (9.72 ° [7.24 ° to 11.64 °] vs. 6.93 ° [3.96 ° to 15.70 °], P = 0.401) were observed overall. However, subgroups with FMA 7° showed significant improvements in FCVA (mean difference: -2.42 °, 95% CI: -3.12 ° to -1.72 °) and FCPSA (3.79 °, 95% CI: 2.45 ° to 5.13 °, both P < 0.05). No differences in operative time, complications, or functional scores were noted. Safety outcomes, including rates of deep vein thrombosis, infection, and prosthesis-related complications, were comparable between groups, with no severe adverse events reported. CONCLUSION: 3D-printed guides improve prosthesis alignment in OUKA for patients with FMA 7° but not for FMA 5-7 °. Clinicians should consider patient-specific anatomical variations when deciding whether to use 3D-printed guides in OUKA. LEVEL OF EVIDENCE: I; Randomized controlled trial.