Influence of medial open wedge high tibial osteotomy on tibial tuberosity–trochlear groove distance.

Purpose: Medial open wedge high tibial osteotomy (MOWHTO) is an effective treatment option for realignment of a varus knee. However, a simple supra-tuberositary osteotomy can lead to patella baja and potentially increases the tibial tuberosity–trochlear groove distance (TTTG). The purpose of this study was to quantify the influence of MOWHTO on TTTG. Methods: Three-dimensional (3D) surface models of five lower extremities with a varus hip–knee–ankle angle (HKA) and a borderline TTTG (≥ 15 mm), five lower extremities with a varus HKA and a normal TTTG (< 15 mm) and a 3D statistical shape model (SSM) of a neutrally aligned healthy knee were analysed by simulating MOWHTO with a stepwise increment of one degree of valgisation from the preoperative coronal deformity (0°–15°) for each patient, resulting in a total of 165 simulations. Postoperative 3D TTTG and tibial torsion (TT) were measured for each simulation. A mathematical formula was developed to calculate the increase of TTTG after MOWHTO. Mean differences between simulated and calculated TTTG were analysed. Results: Mean preoperative HKA was 6.5 ± 3.0° varus (range 0.8°–11.5°). Mean TTTG increased from 14.2 ± 3.2 mm (range 9.6–19.1) preoperatively to 18.8 ± 3.8 mm (range 14.5–25.0) postoperatively (p = 0.001). TTTG increased approximately linear by + 0.5 ± 0.2° (range 0.3–0.8) per 1° of valgisation with a high positive correlation (0.99, p = 0.001) from 0° to 15°. Mean difference between simulated and calculated TTTG was 0.03 ± 0.02 mm (range 0.01–0.07) per 1° of valgisation (p < 0.001). Conclusion: MOWHTO results in an approximately linear increase in TTTG of + 0.5 mm per 1° of valgisation in the range from 0° to 15° and the lateralisation of the tibial tuberosity can be calculated reliably using the described formula. Preoperative analysis of TTTG in patients undergoing MOWHTO may prevent unintentional patellofemoral malalignment. Level of evidence: III. [ABSTRACT FROM AUTHOR]