Pre-operative radiological measurement of femoral rotation for prosthetic positioning in total knee arthroplasty.

purposeThis study outlines the benefits of the seated view radiograph of the knee in evaluation of the pre-operative individual distal femoral torsion (DFT) and for the follow-up of the post-operative rotational positioning of the femoral component in total knee arthroplasty.

methodsStudy on 20 patients who underwent total knee arthroplasty and the correlation between the DFT measured before surgery with this radiology view, the intra-operative external rotation (ER) necessary for the parallel positioning of the femoral component with the transepicondylar axis (TEA) and the post-operative femoral rotational alignment of the prosthesis on the same view.

resultsIn 90 % of cases the values of internal DFT were between -1(0) and -8(0), while the mean value of the internal rotation (IR) was -4.45(0). The mean value of the ER applied to the posterior bone resection was 4.25(0) (0(0)-7(0)), showing a statistically significant correlation between the pre-operative measurement and the intra-operative one of the posterior condylar angle (PCA) (r = 0.890, p = 0.000). Residual internal femoral malrotation has been identified in four cases, its mean value being 0.4(0). In three patients the pre-operative value of the PCA was higher than the intra-operative one and an internal malrotation of the post-operative femoral component was observed.

conclusionsThe results are encouraging for the further use of this pre-operative view with the premises of increasing the accuracy of prosthetic positioning and reducing the mechanical complications.