SELF-ALIGNMENT TECHNIQUE OF EXTRAMEDULLARY TIBIAL GUIDE MAY IMPROVE THE ACCURACY OF BONE CUT IN TOTAL KNEE ARTHROPLASTY

Introduction Several investigations have shown that a proper implant alignment may reduce the risk of aseptic loosening and improve the longevity of the implant in total knee arthroplasty (TKA). However, implant misalignment [3° were found in 2–40 % of patients when standard TKA are performed. In the present investigation we assessed the accuracy in tibial cut alignment using a new surgical technique for the orientation of extramedullary guide. Materials and methods Eighty patients undergoing standard TKA were analysed prospectively. In 40 patients (group A) the orientation of extramedullary guide was aligned proximally on the medial 1/3 of the tibial tuberosity and distally on a point located 5–10 mm medially to centre of intermalleolar distance. In the remaining 40 patients (group B), the extramedullary guide was aligned, proximally, as in group A and distally using a self-alignment technique. This included that the extra- medullary guide was left in the middle of the perimalleolar clamp without align it to any definite anatomical landmark of the ankle joint. The coronal alignment of the tibial cut was assessed intra-operatively using naviga- tion and postoperatively on standing radiographs. ResultsIntra-operativeevaluationshowedavarus-valguscut[3°in 11 cases (27.5 %) in group A and in 3 cases (7.5 %) in group B (p = 0.03). Of the patients showing misalignment, a bone cut in varus was found in 10 subjects in group A and in 1 of those in group. A misalignment[4° was found in 2 patients (5 %) in group A and in no patient in group B. Percentage of outliers on post-operative radio- graphs were similar to intra-operative evaluation, being 12 and 2 cases in group A and B, respectively. Discussion Previous studies showed that tibial torsion may play a role in reducing the accuracy of extramedullary instrumentations either because tibial torsion was found to affect the distal alignment of extramedullary guide and because tibial torsion showed a wide var- iability among patients, which is difficult to recognize during surgery. This potential source of error in the alignment of extramedullary guide could be reduced by using a surgical technique which is not affected by tibial torsion, as the self-alignment technique used in this study. Conclusions Using standard instrumentation for TKA, the percentage of outliers in tibial cut orientation may be reduced using a surgical technique in which the extramedullary instrumentation is aligned to the proximal tibia only.