Total knee arthroplasty (TKA) is a common procedure with good success rates. The literature shows resection accuracy plays a crucial role in device longevity1. Computer guidance is used by some surgeons to enhance accuracy. This study reports on a continuous series of Optetrak knee prostheses (Exactech Inc., FL, USA) implanted by three senior surgeons between July 2010 and April 2013. 259 TKA were implanted at the Haguenau Hospital, Haguenau, France (Site 1), Joseph Ducuing Hospital, Toulouse, France (Site 2) and Saint Michaels Medical Center, Newark, NJ, USA (Site 3) using Exactech GPS (Blue-Ortho, Grenoble, FR), a new computer-assisted guidance system. Surgeons can use the unique Exactech GPS profiler to define steps to be computer-assisted during surgery. Each centre in this study used different surgical profiles. Planned tibial and femoral cuts were compared to actual cuts digitised using GPS. Operating time and external femoral rotation were analyzed and post-operative leg alignment was compared to pre-operative. The mean error between planned and digitised proximal tibial cuts was 0.26° ± 1.11 of valgus and 0.06° ± 0.99 of posterior slope for Site 1, 0.07° ± 0.89 of varus and 0.53° ± 0.90 of anterior slope for Site 2, and 0.19° ± 0.73 of varus and 0.10° ± 1.17 of posterior slope for Site 3 (see Fig. 1). The mean error between planned and digitised femoral distal cuts was 0.03° ± 0.99 of varus and 0.67° ± 1.36 of extension for Site 1, 0.14° ± 0.85 of varus and 0.49° ± 0.94 of extension for Site 2, and 0.26° ± 0.86 of varus and 0.09° ± 1.22 of flexion for Site 3. Average operating time was 38 minutes for Site 1, 29 minutes for Site 2, and 34 minutes for Site 3. External femoral component rotation ranged from 0° to 18° with an average of 3.7° degrees for Site 1 and from −3° to 8° with an average of 3.0° for Site 2. External rotation was fixed at 3° for Site 3. Post-operative Hip-Knee-Ankle angle (HKA) varied between 177° and 182° with an average of 179° for Site 1, 172° to 184° with an average of 179° for Site 2, and 178° to 185° with an average of 180° for Site 3. Pre-operative HKA ranged from 162 to 191°. Despite different techniques and teams, all surgeons experienced similar results. Cuts were aligned in the frontal plane, while guidance was harder to follow in the sagittal plane, possibly due to saw blade bending during resection. Average surgical time was similar. GPS guidance added an average of 10 minutes to standard surgical times. All surgeons agreed the increased accuracy justified the additional time. Regardless the site, all average femoral rotations were close to the accepted 3° standard. Average post-operative HKA was 179°. HKA scores were within 3° of perfect alignment in all Site 1 cases and 96% of Site 2 and Site 3 cases. According to the literature1, HKA between 177° and 183° is linked with high implant survival. Participating surgeons associated Exactech GPS with satisfactory immediate post-operative results.
