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Objectives and questions: Patient-specific instrumentation (PSI) has been introduced in total knee arthroplasty (TKA) to enhance surgical accuracy and efficiency by creating preoperative, patient-specific cutting guides. While PSI has been shown to improve intraoperative efficiency, its impact on long-term clinical outcomes remains uncertain. Obese patients (BMI >30 kg/m²) present technical challenges in achieving optimal implant alignment due to altered limb morphology, soft tissue bulk, and increased mechanical stresses. This study compares PSI to standard of care (SOC) using conventional instrumentation in obese patients undergoing primary TKA, evaluating functional outcomes, radiographic alignment, and revision rates at five-year follow-up.

Material and methods: This prospective, randomized trial included 158 patients undergoing primary TKA, with 80 receiving PSI (TRUMATCH^® Personalized Solutions) and 78 treated with SOC. All procedures were performed using the same implant design by experienced arthroplasty surgeons. Functional outcomes were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Knee Society Score (KSS), and SF-12. Radiographic parameters, including femoral-tibial angle (FTA), lateral distal femoral angle (LDFA), and medial proximal tibial angle (MPTA), were measured postoperatively. The frequency of surgical deviations from the preoperative plan, intraoperative complications, and revision rates were recorded. Statistical analysis included t-tests and linear regression models, with significance set at p<0.05.

Results: At five years, 158 patients completed follow-up. There was no significant difference in mean WOMAC scores (PSI: 82.53 ± 18.68 vs. SOC: 83.15 ± 15.92; p=0.83), SF-12 mental and physical scores (p=0.35, p=0.40, respectively), or KSS total scores (p=0.08). Radiographic alignment outcomes showed no clinically meaningful differences, except for a minor but statistically significant variation in MPTA (PSI: 88.17 ± 2.2, SOC: 88.65 ± 1.8; p=0.02). The PSI group exhibited a significantly higher rate of surgical deviation from the preoperative plan (34.6% vs. 5.1%). Revision rates were similar (PSI: 6.3%, SOC: 2.6%; p=0.44), and no significant differences in complication rates were observed.

Discussion and conclusion: At five years, PSI did not confer superior clinical benefits over SOC in obese patients undergoing primary TKA. Patient-reported outcomes, revision rates, and radiographic alignment were comparable between groups, while PSI demonstrated a higher rate of intraoperative plan deviations. These findings suggest that despite the theoretical advantages of PSI, it does not provide a significant long-term benefit in this population. Further research is needed to refine patient selection criteria for PSI to optimize its clinical utility.