Patient specific instrumentation (PSI) for elective knee replacements in arthritic knees with severe deformities and in revision scenarios is becoming increasingly popular due to the advantage of restoring the limb axes, improved theatre efficiency and outcomes. Currently available systems use CT scan or MRI for pre-operative templating for design considerations with varied accuracy for sizing of implants.

We prospectively evaluated 200 knees in 188 patients with arthritic knees with deformities requiring serial clinical assessment, radiographs and CT scans for PSI templating for TruMatch knee system (DepuySynthes, Leeds, UK). The common indications included severe arthritic deformities, previous limb fractures and in obese limbs with difficult clinical assessment. Surgical procedure was performed on standard lines with the customised cutting blocks.

The ‘lead up’ time between the implant request and the operating date was 5 weeks on an average. We compared the pre op CT images and the best fit post-operative x- rays. The sizing accuracy for femur and tibia was 98.93 % and 95.75% respectively. All blocks fitted the femur and tibia. There were no bail outs, no cutting block breakage, 1 patient had residual deformity of 20 degrees, and 1 patient had late infection. The length of hospital stay, economic viability in terms of theatre turnover, less operating time, cost of sterilisation in comparison to conventional knee replacement surgery with other factors being unchanged was also assessed.

The projected savings was substantial along with improved geometrical restoration of the knee anatomy. We recommend the use of PSI based on CT scan templating in difficult arthritic knees.

Introduction

Computed tomography (CT) can be utilized to design patient specific instruments (PSI) for total knee arthroplasty (TKA). The PSI preoperative plans predict bone resection, anterior-posterior implant position, implant rotation and implant size. The purpose of this study was to compare preoperatively predicted implant sizes (tibia and femur) to the actual implanted sizes. Data were compiled from two surgeons, one in the United Kingdom (Surgeon 1, cruciate retaining) and one in the United States (Surgeon 2, posterior stabilizing). Both used the same primary TKA implant systems (Sigma® and Attune®; DePuySynthes®, Warsaw, Indiana). This is the largest comparison of CT-based PSI size accuracy between two implant systems.