Abstract
Introduction
An appropriate positioning of a total knee replacement (TKR) is a prerequisite for a good functional outcome and a prolonged survival. Navigation systems may facilitate this proper positioning. Patient specific templates have been developed to achieve at least the same accuracy than conventional instruments at a lower cost. We hypothesised that there was no learning curve at our academic department when using patient specific templates for TKR instead of the routinely used navigation system.
Material
The first 20 patients operated on for TKR at our academic department using a patient specific template entered the study. All patients had a pre-operative CT-scan planning with a dedicated software.
The patient specific templates were positioned on the bone according to the best fit technique. The position of the templates was controlled at each step of the procedure by the navigation system, and eventually corrected to achieve the expected goal. The discrepancy between the initial and the final positioning was recorded. The paired difference between each set of measurement was analysed with appropriate statistical tests at a 0.05 level of significance.
Results
The mean difference between the initial positioning of the tibia template in the coronal plane was 3° ± 4° (p<0.01); 5/10 cases were off the expected range. The mean difference between the initial positioning of the tibia template in the sagittal plane was 4° ± 3° (p<0.001); 6/10 cases were off the expected range. The mean difference between the initial positioning of the femur template in the coronal plane was 2° ± 2° (p<0.01); 3/10 cases were off the expected range. The mean difference between the initial positioning of the tibia template in the sagittal plane was 3° ± 3° (p<0.01); 4/10 cases were off the expected range. After correction of the position according to the navigation system, all templates were placed in the expected range in all directions. There was a trend to improve the initial positioning of the templates at the end of the study, especially for the femoral template.
Discussion
The global accuracy of the system tested was less than the navigated reference. The current system should not be used without extensive intra-operative control of the positioning of the templates. However, when the positioning of the templates was adequate, the orientation of the resection was correct. We conclude that the planning and manufacturing process may be adequate, but the question of the intra-operative positioning should be addressed. As the results about positioning improved during the time of the study, one might argue that one of the relevant question is the learning curve of the surgeon when using such templates.
