Evaluation of the accuracy of a patient-specific instrumentation by navigation

The aim of this study is to evaluate the accuracy of a patient-specific instrumentation (PSI) as assessed by the intraoperative use of knee navigation software during the surgical procedure. Fifteen patients with primary gonarthrosis were selected for unilateral total knee arthroplasty. The first three patients were excluded from this study, as they were considered to be a warm up to set-up the procedure. All patients were operated on with a cemented posterior-stabilised prosthesis cruciate ligament-sacrificing by the same surgeon using the patient matched cutting jigs. The size of the implant, level of resection, and alignment in the coronal and sagittal planes were evaluated. An unsatisfactory result was considered an error a parts per thousand yen2A degrees in both planes for each component as a possible error of 4A degrees could result in aggravation. On the coronal plane the mean deviation of the tibial guide from the ideal alignment was 1.2 +/- A 1.5 (range 0-5A degrees) and in the sagittal plane was 3.8 +/- A 2.4 (range 0-7.5A degrees). On the coronal plane the mean deviation of the femoral guide from the ideal alignment was 1.2 +/- A 0.6 and in the sagittal was 3.7 +/- A 2. On the basis of this preliminary experience the PSI system based only on data acquisition with A-P radiograms and RMN cannot be defined as accurate. In cases of the use of the custom made cutting jigs it is recommended to perform an accurate control of the alignment before making the cuts, for any step of the procedure. II.