Averaging rotational landmarks during total knee arthroplasty reduces component malrotation caused by femoral asymmetry

Abstract

BackgroundFemoral component malrotation is a common cause of patient dissatisfaction after total knee arthroplasty. The sulcus line (SL) is more accurate than Whiteside’s line as it corrects for variation in the coronal orientation of the groove. The hypothesis is that averaging the SL and posterior condylar axis (PCA) will reduce femoral malrotation.MethodsThe component was inserted at a position between the SL and PCA in 91 patients. An intraoperative photograph was taken showing the landmarks. These were compared to the component position achieved relative to the surgical epicondylar axis (SEA) on a postoperative CT scan. The component position was compared to the position achieved using the individual landmarks.ResultsRelative to the SEA, the final component position was 0.6° (SD 1.4°, range −3.8° to +4.0°), the coronally corrected SL position was −0.7° (SD 2.3°, −5.5° to +4.6°), the PCA position was 0.9° (SD 1.9°, −6.1° to +5.0°). Averaging the landmarks significantly decreased the variance of the component position compared to using the SL and PCA individually. The number of outliers (>3° from SEA) was also significantly less (p < 0.05) for the 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.ConclusionsAveraging the SL and the PCA decreases femoral component malrotation. Femora are frequently asymmetrical in the axial plane. Referencing posterior condyles alone to set rotation is likely to cause high rates of patellofemoral malalignment.

Femoral rotational asymmetry is a common anatomical variant

“…Correcting for variation in the coronal direction in which the trochlear groove runs improves the accuracy of the trochlear groove as a landmark for femoral rotation. The improvement in variability is similar to the previous CT study in arthritic knees (WL SD = 4.2° vs. SL SD = 2.7°) and the clinical trial (WL SD = 5.7°, SL SD 2.3°) (Chao et al, ; Talbot et al, ), meaning that the variation is unlikely to be due to arthritic distortion.…”

“…The SL technique has been shown to be reproducible in several studies both on 3 D CT reconstruction and intraoperatively using the sulcus line of the Trochlear Alignment guide (Chao et al, 2017). The average interobserver error in this study was 0.98.…”

“…This would indicate that the PC is more likely to be affected by osteoarthritis than the SL. Interestingly, the direction of the variation in outliers which occurred when referencing the PC was not predicted by the location of the osteoarthritis (Chao et al, ). This makes it very difficult to correct for the error intraoperatively.…”

“…Therefore, the variation between the PC and SL cannot be explained by measurement error. This asymmetry was noted in the previous clinical trial (Chao et al, ).…”

“…The identification of this variation has led to discussion about combining landmarks to compensate for asymmetry (Cinotti et al, , Paternostre et al, , Talbot et al, ). The previous CT study (Talbot et al, ) and the subsequent clinical trial (Chao et al, ) confirmed the clinical relevance of the SL and described its use during surgery. Both of these studies, however, measured angles in patients with osteoarthritis, which does not prove anatomical variation on account of distorted anatomy.…”