Adequate protection rather than knee flexion prevents popliteal vascular injury during high tibial osteotomy: analysis of three-dimensional knee models in relation to knee flexion and osteotomy techniques

Purpose (1) To analyse popliteal artery (PA) movement in a three-dimensional (3D) coordinate system in relation to knee flexion and high tibial osteotomy (HTO) techniques (lateral closed wedge HTO [LCHTO], uniplane medial open wedge HTO [UP-MOHTO], biplane medial open wedge HTO [BP-MOHTO]) and (2) to identify safe zones of the PA in each osteotomy plane. Methods Sixteen knees of patients who underwent magnetic resonance imaging with extension and 90 degrees flexion were used to develop subject-specific 3D knee flexion models. Displacement of the PA during knee flexion was measured along the X- and Y-axis, as was the distance between the posterior tibial cortex and PA parallel to the Y-axis (d-PCA). Frontal plane safety index (FPSI) and maximal axial safe angles (MASA) of osteotomy, which represented safe zones for the osteotomy from the PA injury, were analysed. All measurements were performed along virtual osteotomy planes. Differences among the three osteotomy methods were analysed for each flexion angle using a linear mixed model. Results The average increments in d-PCA during knee flexion were 1.3 +/- 2.3 mm in LCHTO (n.s.), 1.4 +/- 1.2 mm in UP-MOHTO (P < 0.0001), and 1.7 +/- 2.0 mm in BP-MOHTO (P = 0.015). The mean FPSIs in knee extension were 37.6 +/- 5.9%, 46.4 +/- 5.8%, and 45.1 +/- 8.1% for LCHTO, UP-MOHTO, and BP-MOHTO, respectively. The mean MASA values in knee extension were 45.8 degrees +/- 4.4 degrees, 37.3 degrees +/- 6.1 degrees, and 38.9 degrees +/- 6.5 degrees for LCHTO, UP-MOHTO, and BP-MOHTO, respectively. Conclusion Although the PA moved posteriorly during knee flexion, the small (1.7 mm) increment thereof and inconsistent movements in subjects would not be of clinical relevance to PA safety during HTO.