Summary

The Sulcus Line is a more accurate technique for referencing the rotational alignment of the trochlear groove than Whiteside's Line. By combining it with the posterior condylar axis the risk of femoral component malrotation is reduced. Intraoperative measurements detected a high rate of femoral rotational asymmetry. This deformity is compensated for by combining landmarks.

Abstract

Introduction

Femoral component malrotation is a common cause of patient dissatisfaction after total knee arthroplasty. The Sulcus Line (SL) is formed from multiple points along the floor of the trochlear groove, and has been shown to be more accurate than Whiteside Line. A trochlear alignment guide (TAG) is required to correct for coronal variation of the SL and allow intraoperative comparison of the SL and the posterior condylar axis (PCA). The hypothesis is that averaging these two landmarks will lead to less femoral malrotation.

Methods

Surgery was performed in 91 patients using the TAG. The component was inserted at a position between the SL and PCA. An intraoperative photograph was taken of the distal cut surface of the femur showing the pin-holes representing the SL, the PCA and the final component position. These were compared to the component position achieved relative to the surgical epicondylar axis (SEA) on a postoperative CT scan. Comparison was made between the final component position and the position which would have been achieved using either the SL or PCA individually. The theoretical position which could be achieved by averaging the SL and PCA was also calculated.

Results

The SEA was identified on CT scan in 84 cases. The final component position was 0.6° (SD 1.5°, range -4.2° to +4.0°), the calculated coronally corrected SL position was -0.7° (SD 2.3°, -5.5° to +4.6°), the calculated PCA position was 0.9° (SD 1.9°, -6.1° to +5.0°), the calculated average position between SL and PCA was 0.1° (SD 1.4°, -3.7° to +2.7°). There was a significant decrease in variance between both the component position and the calculated average when each was compared to the SL and PCA individually. The number of outliers greater than 3° from the SEA was also significantly less (p<0.05) for both the component position (2/84) and the calculated average position(2/84) when each was compared to the SL (16/84) and PCA (14/84) individually. In 21/84 (25%) of cases there was more than 4° of divergence between the SL and PCA.

Conclusion

Averaging the SL and the PCA intraoperatively leads to decreased femoral component malrotation compared to the use of either landmark individually. Femora are frequently asymmetrical in the axial plane. Any technique, including kinematic alignment, which only references the posterior condyles to set rotation is likely to cause high rates of patellofemoral malalignment.