Patient-Specific Instrumentation Versus Standard of Care in Total Knee Arthroplasty in an Obese Population: Minimum 5-year Follow-Up.

Abstract

Patient-specific instrumentation (PSI) has been introduced in total knee arthroplasty (TKA) with the goal of increased accuracy by creating custom cutting guides to match the patient's anatomy. Obese patients present increased technical challenges associated with exposure and implant alignment. Techniques to improve accuracy in this cohort could have a particular benefit. The aim of the study was to compare PSI to standard of care (SOC) with conventional instrumentation in obese patients undergoing primary TKA. Patients who had a body mass index (BMI) greater than 30 and who had osteoarthritis and were undergoing primary TKA were randomized to SOC or PSI. Patients were followed for five years postoperatively. Patient-reported outcome measures (PROM), surgical information, postoperative lower extremity alignment, complications, and revision rates were recorded. There were 158 patients included (80 PSI and 78 SOC). The primary radiographic outcome, medial proximal tibial angle, showed a statistically significant, but not clinically meaningful, difference between groups (PSI = 88.2 ± 2.2, SOC = 88.7 ± 1.8, P = 0.02). No significant differences were observed in the anatomic femoral-tibial angle (P = 0.075) or lateral distal femoral angle (P = 0.53). Patient-reported outcomes at five years, including Western Ontario and McMaster Universities Arthritis Index (WOMAC) (PSI: 82.5 ± 18.7, SOC: 83.2 ± 15.9, P = 0.83), 12-Item Short Form Survey (SF-12) physical and mental composite scores (P = 0.35 and P = 0.40), and Knee Society Score (KSS) total scores (PSI: 177.3 ± 24.3, SOC: 168.2 ± 31.2, P = 0.08), were similar between groups. A higher rate of deviation from the preoperative surgical plan was observed in the PSI group (30.2%) compared to SOC (5.1%). Complication and revision rates were comparable between groups. Use of PSI in primary TKA did not result in clinically relevant improvements in radiographic alignment compared to SOC. Despite increased preoperative planning, intraoperative deviations from the PSI surgical plan were common. There were no differences in PROMs, complications, or revision rates observed at five years.