Patellar height modification after high tibial osteotomy by either medial opening-wedge or lateral closing-wedge osteotomies

High valgus tibial osteotomy is used to treat medial femoro-tibial osteoarthritis. Changes in patellar height due to high valgus tibial osteotomy can cause technical difficulties during subsequent knee arthroplasty. The primary objective of this study was to assess the hypothesis that patellar height decreases after opening-wedge osteotomy and increases after closing-wedge osteotomy. The secondary objective was to assess whether frontal axis correction and tibial slope modification correlated with patellar height changes. A multicentre, prospective, comparative, observational, non-randomised study was conducted in consecutive patients undergoing isolated high valgus tibial osteotomy according to standard practice in each of the ten study centres. Patellar height was assessed based on the Caton-Deschamps index. Of 321 included patients, 224 underwent opening-wedge and 97 closing-wedge osteotomy. Patellar height did not change significantly after closing-wedge osteotomy (1.07 +/- A 0.2 pre-operatively and 1.0 +/- A 0.19 postoperatively). Patellar height decreased significantly after opening-wedge osteotomy (from 0.98 +/- A 0.19 to 0.88 +/- A 0.21, p < 0.0001, mean decrease 9 +/- A 22 %). Patellar height decreased by more than 20 % in 49 (28 %) patients after opening-wedge osteotomy. The patellar height decrease after opening-wedge osteotomy correlated significantly with axis correction magnitude and tibial slope change. Our results support routine baseline measurement of patellar height before high valgus tibial osteotomy and posterior positioning of the opening wedge to limit the tibial slope change in patients requiring major axis correction by opening-wedge osteotomy. Prospective cohort study, Level II.