Abstract
Aim
To asses the accuracy of total knee replacements performed using CT based patient specific instrumentation by postoperative CT scan.
Method
Approval from the Ethics Committee at The University of New South Wales Sydney Australia was granted prior to commencement of this study. 50 patients who had undergone total knee replacement (Evolis, Medacta International) using CT-based patient specific instrumentation (MY KNEE Medacta International) were assessed postoperatively using a CT scan and a validated measurement technique. The mechanical axis of the limb in the coronal plane, the varus/valgus positioning of the femoral component, the varus/valgus positioning of the tibial component, the flexion/extension of the posterior flange of the femoral component and the posterior slope of the tibial base plate were recorded. These results were then compared to each patient's preoperative planning. The percentage of patients found to be within 3 degrees of planned alignment were calculated. This represents the most comprehensive prospective study to utilize CT assessment of postoperative alignment in patient specific instrumentation. All other studies, to our knowledge have utilized scanograms or scout images and not full CT protocol as performed in this study.
Results
96% of patients were within 3 degrees of planned alignment in the coronal plane reproducing the predicted mechanical axis. Predicted coronal plane orientation of the tibial and femoral component was achieved in 100% and 92% of patients, respectively. The flexion/extension of the posterior flange of the femoral component was within 3 degrees in 92% of patients. The planned posterior tibial slope was achieved in 92% of patients. As a result of difficulty in ascertaining the anatomical landmarks during measurement of the rotation of the femoral component, we are currently repeating the measurements using the original 3D software used for preoperative planning, using the same anatomical landmarks. This data will be available at the time of presentation.
Conclusion
This study constitutes one of the largest series of patients who have undergone CT assessment following patient specific instrumented knee replacement. We have found that total knee replacement using patient specific instrumentation accurately reproduces preoperative planning in at least 5 out of the 6 parameters measured in this study.
