CT-based patient-specific instrumentation for total knee arthroplasty in over 700 cases: single-use instruments are as accurate as standard instruments

Purpose Efforts in total knee arthroplasty are made to improve accuracy for a correct leg axis and reduce component malpositioning using patient-specific instruments. It was hypothesized that use of patient-specific instruments (vs. computer-navigated and conventional techniques) will reduce the number of outliers. Our second hypothesis was that single-use instrumentation will lead to the same accuracy compared to patient-specific instruments made of metal. Methods 708 primary total knee arthroplasties between 2014 and 2018 using computer tomography (CT)-based patient-specific cutting block technique and a preoperative planning protocol were retrospectively reviewed. Preoperative data [hip-knee-angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), tibial slope, femoral component flexion] was compared to postoperative performed standard radiological follow-up X-rays. Differences of > 3 degrees between measurements were defined as outliers. Results Overall 500 prostheses using standard instrumentation and 208 prostheses using single-use instruments were implanted. Preoperative HKA axes (- 1.2 degrees;p < 0.001), femoral component flexion (Delta 0.8 degrees,p < 0.001), LDFA (Delta - 1.5 degrees,p < 0.001), MPTA (Delta - 0.5 degrees,p < 0.001) and tibial posterior slopes (Delta 0.5 degrees,p < 0.001), respectively, were different from postoperative axes. More outliers occurred using standard (vs. single-use) instruments (p < 0.001) regarding postoperative HKA (ranges of standard- vs. single-use: instruments: HKA 178.0 degrees-180.5 degrees vs. 178.0 degrees-180.5 degrees, femoral component flexion 0.0 degrees-6.0 degrees vs. 0.0 degrees-4.5 degrees, LDFA 90.0 degrees-91.0 degrees vs. 90.0 degrees-90.0 degrees, MPTA 90.0 degrees-90.0 degrees vs. 90.0 degrees-90.0 degrees, tibial posterior slope - 10 degrees to 10 degrees vs. - 1 degrees to 10 degrees). No differences were seen for other angles measured. Comparing both systems, total number of outliers was higher using standard (8%) vs. single-use instruments (4.3%). Conclusion This study shows a high accuracy of CT-based patient-specific instrumentation concerning postoperative achieved knee angles and mechanical leg axes. Single-use instruments showed a similar accuracy.