Effect of ascending and descending medial open wedge high tibial osteotomy on patella height and functional outcomes—a retrospective study

Background High tibial osteotomy (HTO) is a popular joint-preserving option for medial compartmental osteoarthritis. However, this is associated with alterations in the patellar height (PH) and tibial slope (TS). This study aims to compare the effect of ascending (AMHTO) and descending medial opening wedge HTO (DMHTO) on patella height, posterior tibial slope and functional outcomes.Material and methodsA retrospective study was conducted between February 2018 and July 2021. Patients with medial compartment osteoarthritis, varus alignment, and complete pre- and postoperative lateral and full-length anteroposterior radiographs were included. Pre- and postoperative radiological measurements include the Caton–Deschamps index (CDI), the mechanical axis deviation (MAD), and the posterior tibial slope. The functional outcomes were measured using the Oxford Knee Score (OKS), Lysholm Knee Score (LKS), and Tegner Activity Scale (TAS). The osteotomy union was checked with serial X-rays every 6 weeks till a satisfactory union was achieved.ResultsFifty-eight patients were included in the study. Thirty-four (58%) patients received AMHTO, and 24 (42%) received DMHTO. There was no baseline difference in the demographic variables or functional scores between the two groups. The preoperative mean MAD of − 9.65° ± 3.67° was corrected significantly to + 0.08 ± 2.80° (varus −, valgus + , P = 0.034). A significant difference in preoperative and postoperative CDI of 0.93 ± 0.45 and 0.83 ± 0.27, respectively, was noted (P = 0.023). In the AMHTO group, a statistically significant decrease in PH from preoperative 1.03 ± 0.77 to 0.84 ± 0.12 was noted (P = 0.003). There was a significant improvement in functional outcomes between baseline and 9-month follow-up in both groups. There was no significant difference between the functional outcomes of the two groups at 9-month follow-up.Conclusion The study confirmed our hypothesis that descending HTO caused less alteration in the patella height compared to ascending HTO. There is no significant difference in the functional outcomes between the groups. However, in patients with PFOA, and when attempting higher degree of correction through AMHTO, the possibility of worsening of symptoms due to change in PH must be considered.