No change in patellar height following open wedge high tibial osteotomy using a novel femur-referenced measurement method

Abstract Background Open wedge high tibial osteotomy (HTO) can influence the tibial slope and thereby the landmarks of currently used patellar height indices. The purpose of this retrospective study was to compare and validate a new femur-referenced patella height measurement method to currently used patellar height indices in a cohort of HTO patients. Methods Patellar height (Caton–Deschamps, Blackburne–Peel and Insall–Salvati Indices and our newly developed Femoral Patellar Height Index) as well as tibial slope were analysed. Full-weight-bearing long-leg anteroposterior radiographs as well as anteroposterior and lateral radiographs of the knee in 0° of extension were used. Radiographs were performed preoperatively, and at 6 weeks, 3, 6, 12 and 18 months postoperatively. Measurements were recorded twice by two observers. The second observation was performed after a delay of 3 months. Results A total of 99 patients with a mean age of 46.2 ± 8 years were included. A statistically significant pre- to postoperative increase in tibial slope was found in all methods. Patellar height decreased according to Caton–Deschamps and Blackburne–Peel Indices. The Insall–Salvati Index as well as the novel Femoral Patellar Height Index remained unchanged. Intra-rater (interclass correlation coefficient (ICC) 0.914–0.998) and inter-rater (ICC 0.955–0.989) reliability were highest in the new index. Conclusion Detected changes of patellar height following open wedge HTO depend on the method used. Tibial slope increases following surgery. Our new index with a femoral reference for measuring patellar height was validated and good to excellent intra- and inter-rater reliability were demonstrated. Following HTO, the Femoral Patellar Height Index can be recommended as a standardized method to measure patellar height.