Evaluation of accuracy of bone cuts and implant positioning in total knee arthroplasty using patient specific instrumentation.

In the last years new surgical techniques are developing to improve prosthesis positioning, increasing clinical and functional results and reducing invasiveness. In this scenario patient-specific instrumentations have been introduced in order to enhance surgical accuracy and ease of implantation. The purpose of this study was to assess the compliance of the pre-operative planning data with bone resections measured intraoperatively and to evaluate prosthesis positioning in patients undergoing total knee arthroplasty (TKA) using an MRI-based pin-guides instrumentation. Thirty consecutive patients (20 women and 10 men) undergoing 30 total knee replacements (20 right- and 10 left-sided knees) were included in this study. The same cemented cruciate ligament sacrificing prosthesis (NexGen LPS, Zimmer, Warsaw, Indiana, USA) was implanted in all patients by a single surgeon using Patient-Specific Instruments (PSI, Zimmer, Warsaw, Indiana, USA). Femoral and tibial bone resections were measured using a manual caliper intra-operatively and compared with the corresponding pre-operative values. Each patient underwent A CT examination following surgery in order to investigate individual component positioning. None of the cases was converted from PSI technique to conventional TKA and adequate femoral and tibial bone cuts were performed without the need for intraoperative adjustments. Two outliers were detected among the intra-operative bone cuts measurements. In all patients the size of femoral and tibial prosthetic components, hypothesized at preoperative planning, was confirmed intra-operatively. Two outliers were detected among post-operative CT measurements as for components positioning. PSI system can assist in obtaining good component positioning with reduction of outliers. Despite the small number of patients, our data demonstrate the validity of this patient-specific pin-guides system in TKA and may support repeatable improvements in surgical accuracy. Level of evidence: IV.