Derotational femoral osteotomy changes patella tilt, patella engagement and tibial tuberosity trochlear groove distance

Abstract

Purpose: The aim was to assess the influence of femoral derotational osteotomy on patella tilt (PT), axial patella engagement (AEI) and tibial tuberosity trochlear groove distance (TTTG). Methods: Derotational femoral osteotomy was performed on ten lower limbs of body donors embalmed with alcohol–glycerine. Femoral torsion, tibial torsion, knee torsion, PT, AEI and TTTG were evaluated on axial CT slices for an absolute femoral torsion of 15°, 20°, 25°, 30°, 35° and 40°. A linear mixed model analysis was used to estimate the effect of femoral torsion on PT, AEI, TTTG and knee torsion adjusted for correlation due to repeated observations. Estimates with 95% confidence intervals were used to represent the mean change in the dependent variables for one unit of change (degree, mm or AEI) in the predictor variable. Results: A significant correlation was observed between femoral torsion and AEI (p < 0.001), PT (p < 0.001) and TTTG distance (p = 0.002). In cases of increased internal femoral torsion, a significant decreased AEI (estimate − 0.003, 95% CI − 0.003 to − 0.002), an increased PT (estimate 0.3, 95% CI 0.2–0.4) and an increased TTTG distance (estimate 0.1, 95% CI 0.1–0.2) were observed. No correlation was seen between change in femoral torsion and knee torsion (n.s.). Conclusions: Derotational femoral osteotomy has a significant impact on patella tilt and axial patella engagement. Moreover, TTTG distance is slightly changed by a derotational femoral osteotomy, which has to be taken into account preoperatively when considering surgical procedures. Level of evidence: Level V.