Summary

Conventional assumptions about the axes' relationships may need to be reassessed.

Abstract

Background

Evaluating the landmarks for rotation of the distal femur and proximal tibia components has been challenging for orthopaedic surgeons. Optimal rotational alignment is critical for the longevity and functional outcome of total knee arthroplasty(TKA). Multiple anatomical landmarks on femur have been described, such as transepicondylar axis (TEA), the Whiteside’s line (WSL) and the posterior condylar line (PCL). Traditionally it has been assumed that the WSL is perpendicular to the TEA while the PCL is 3 degrees internally rotated compared to the TEA. Two types of TEA have been described; (i) clinical transepicondylar axis (cTEA) (ii) surgical transepicondylar axis (sTEA) among which sTEA is considered the gold standard to determine the optimum rotation of the femoral component. However, no consensus exists on the most reliable landmarks or axes for tibial rotational alignment. The purpose of this study was to ascertain relationships among the axes’ guiding distal femur rotational alignment and the relationship between sTEA to proximal tibial reference axes’ in preoperative CT scans in our patients who were candidates for TKA.

Materials And Methods

A single-centre CT-based cross-sectional study was conducted on 73 patients (59 women and 14 men) with mean age of 63.51 years and mean varus deformity of 10.81 +/- 4.12 degrees who underwent knee arthroplasty accounting for 110 knees with primary osteoarthritis were utilised. Lower limb scanogram and preoperative CT scans were performed in supine position and the following were deduced using a uniform standardised method by two independent observers: On the femoral side; the relationship of sTEA with (i)WSL (ii) PCL (iii) cTEA. On the tibial side; the relationship of projected sTEA with (i)posterior tibial margin (PTM)(ii) anterior condylar axis (ACA) (iii)Akagi’s line and (iv) a line from geometric centre (GC) of tibial plateau to 1/3rd tibial tuberosity(TT).

Results

On the femoral side; the mean angle between the sTEA and (i)WSL (ii) PCL (iii) cTEA were 95.64 +/- 2.85, 1.77 +/- 1.88, 4.19 ± 0.99 degrees respectively. On the tibial side; the relationship of projected sTEA with (i)PTM (ii) ACA (iii) Akagi’s line (iv) a line from geometric centre of tibial plateau to 1/3rd tibial tuberosity; were 1.10 +/- 4.69, 11.98 +/- 4.51, 92.43 +/- 4.35, 106.04 ± 5.93 degrees respectively.

Conclusion

Conventional assumptions about the axis relationships may need to be reassessed, and a preoperative computed tomography scan was a valuable, simple, and relatively reasonable means to identify relevant anatomical landmarks. However, we do not recommend its routine use; the surgeons should be aware of the multiple axes used in TKA to optimise the rotational alignment of the components & the range of deviation from sTEA in our group of patients.