Patient-specific instrumentation in total knee arthroplasty: simpler, faster and more accurate than standard instrumentation-a randomized controlled trial.

PURPOSE: This randomized controlled trial was conducted to compare patient-specific instrumentation (PSI) to standard instrumentation regarding efficacy to achieve a good coronal alignment and differences in surgical time, blood loss and length of stay. METHODS: Ninety-five of 100 randomized patients eligible for total knee arthroplasty were analysed. PSI with magnetic resonance and long-leg radiograph was performed in 47 patients, while 48 patients received standard instrumentation. Primary outcome measure was coronal alignment, evaluated with long-leg radiograph. Deviation >3° varus/valgus was considered an outlier. Surgical time was compared from skin to skin. Length of stay was a post hoc analysis. Blood loss was evaluated comparing the number of blood units spent, fall in haemoglobin and haematocrit levels. RESULTS: Standard instrumentation had a higher number of outliers in the coronal alignment with a relative risk of 3.015, compared to PSI. Surgical time was reduced by 18 min (24.8 %) with the PSI, as well as length of stay, with a half-day reduction. Number of blood units spent was significantly less in the PSI group. Relative risk of transfusion was 7.09 for patients in the standard instrumentation group. Difference in Hg and Htc levels were not significant. No patient had to abandon PSI. Minor changes to preoperative plan occurred in 14.9 % of the patient: cut review in 4.3 % and insert change in 10.6 %. CONCLUSIONS: Patient-specific instrumentation (PSI) is able to provide important advantages over standard instrumentation in total knee arthroplasty: it lowers the risk of outliers and transfusion, is a faster procedure and enables a shorter length of stay with a low rate of intraoperative adjustments. LEVEL OF EVIDENCE: I.