No improvement in reducing outliers in coronal axis alignment with patient-specific instrumentation

Purpose and hypothesis Patient-specific instrumentation (PSI) uses 3D preoperative imaging to produce individualized cutting blocks specific to patients' anatomy and according to the preoperative plan with the aim to reduce the number of mechanical leg alignment (MLA) outliers, to improve implant positioning and to decrease surgery time. The primary purpose of this study was to investigate the efficacy of a specific PSI in comparison with standard instrumentation (SI) in reducing the number of MLA outliers. It was hypothesized that the number of MLA outliers would be significantly lower in the PSI group. Methods A multicenter randomized controlled trial was implemented. There were 59 patients in the PSI group and 66 in the SI group. The absolute number of outliers outside the +/- 3 degrees target neutral MLA was compared between the groups with a Chi-square test. As secondary outcomes, the Knee Society Score (KSS) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) were compared between the groups preoperatively and at 90-day follow-up. Results There were 15 (26.3%) MLA outliers in the PSI group and 8 (12.3%) in the SI group. The number of outliers was not independent from the group ((2)(X) (1) = 3.8, p = 0.04; Relative risk = 1.5). Preoperatively, there were no significant differences between the groups when comparing their KSS and KOOS sub-scores. At 90 days postoperatively, the patients in the SI group showed better KOOS-Quality of Life (KOSS-QOL) in comparison with the PSI group (p < 0.0001). Conclusion The use of PSI did not significantly reduce the number of MLA outliers in comparison with SI. There were no differences when comparing the achieved mean MLA of both groups.