The sulcus line of the trochlear groove is more accurate than Whiteside’s Line in determining femoral component rotation

Abstract

Purpose The sulcus line (SL) is a three-dimensional curve produced from multiple points along the trochlear groove. Whiteside’s Line, also known as the anteroposterior axis (APA), is derived from single anterior and posterior points. The purposes of the two studies presented in this paper are to (1) assess the results from the clinical use of the SL in a large clinical series, (2) measure the SL and the APA on three-dimensional CT reconstructions, (3) demonstrate the effect of parallax error on the use of the APA and (4) determine the accuracy of an axis derived by combining the SL and the posterior condylar axis (PCA).MethodsIn the first study, we assessed the SL using a large, single surgeon series of consecutive patients undergoing primary total knee arthroplasties. The post-operative CT scans of patients (n = 200) were examined to determine the final rotational alignment of the femoral component. In the second study, measurements were taken in a series of 3DCT reconstructions of osteoarthritic knees (n = 44).Results The mean position of the femoral component in the clinical series was 0.6° externally rotated to the surgical epicondylar axis, with a standard deviation of 2.9° (ranges from −7.2° to 6.7°). On the 3DCT reconstructions, the APA (88.2° ± 4.2°) had significantly higher variance than the SL (90.3° ± 2.7°) (F = 5.82 and p = 0.017). An axis derived by averaging the SL and the PCA+3° produced a significant decrease in both the number of outliers (p = 0.03 vs. PCA and p = 0.007 vs. SL) and the variance (F = 6.15 and p = 0.015 vs. SL). The coronal alignment of the SL varied widely relative to the mechanical axis (0.4° ± 3.8°) and the distal condylar surface (2.6° ± 4.3°).ConclusionsThe multiple points used to determine the SL confer anatomical and geometrical advantages, and therefore, it should be considered a separate rotational landmark to the APA. These findings may explain the high degree of variability in the measurement of the APA which is documented in the literature. Combining a geometrically correct SL and the PCA is likely to further improve accuracy.

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 sulcus line (SL) uses multiple points along the floor or deepest part of the trochlear groove (Talbot et al, ). The floor of the trochlear groove runs lateral to the center of the intercondylar notch (Iranpour et al, ), therefore, the posterior starting point of the SL is often lateral to the midpoint of the intercondylar notch.…”

“…The sulcus line (SL) landmark, has been shown to more accurately reproduce the SEA with less variability than WL (Talbot et al, ). A previous study in arthritic knees by Talbot () indicated that averaging the SL and the posterior condylar axis + 3° (PC + 3) produced a lower rate of femoral malrotation than using either WL or PC + 3.…”

“…The sulcus line (SL) landmark, has been shown to more accurately reproduce the SEA with less variability than WL (Talbot et al, ). A previous study in arthritic knees by Talbot () indicated that averaging the SL and the posterior condylar axis + 3° (PC + 3) produced a lower rate of femoral malrotation than using either WL or PC + 3. A cadaver study (Talbot et al, ) and clinical trial (Chao et al, ) were performed which used a trochlear alignment guide (STAG, Enztec Ltd, Christchurch, New Zealand http://www.enztec.com) (Fig.…”

“…Prior to the advent of the SL technique, variations in the rotational measurement of the trochlear groove may have been disregarded as measurement error. 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.…”