Open wedge high tibial osteotomy: cause of patellar descent

High tibial osteotomy (HTO) has been well described as an effective procedure for treatment of medial compartmental osteoarthritis of knee, especially in young and active individuals. It could be done with barrel-vault osteotomy as decribed by Maquet [1], or with closing-wedge osteotomy as suggested by Coventry [2], or with open-wedge osteotomy as described by Hernigou [3]. The last one can be performed on the medial side without any muscle detachment from the anterior tibial compartment. The fibula and proximal tibiofibular joint are left intact, and therefore the risk of peroneal nerve injury is minimal. The correction in both frontal and sagittal planes can be fine-tuned intraoperatively [4]. The resultant tibio-condylar offset is the least [5].Patella baja is a well known complication after HTO. Kaper et al reported that 54% of 46 knees that had undergone lateral closing-wedge HTO had lowering of patellar height of greater than 10% [6]. It also occurred in open-wedge HTO. Actutally, Brouwer et al showed that more patella baja was created after an open-wedge HTO than after a closing-wedge HTO [7].The aim of this study was to discuss the cause of patellar descent after open-wedge HTO. The clinical outcome of the patients and the technical tips to achieve satisfactory result would also be explained.Between July 2006 to August 2008, nine open-wedge HTO in six patients were done. They included four female and two male patients. The mean age was 49 (37-53). Five right knees and four left knees were operated. The inclusion criteria were medial joint line pain and tenderness and minimal lateral compartment and patellofemoral joint symptom. The knee flexion contracture was less than 10° and flexion range was greater than 90°. Radiograph of knee showed varus deformity and predominant narrowing of medial joint space while the lateral and patellofemoral joint spaces were preserved. Exclusion criteria included tricompartmental osteoarthritis, inflammatory arthritis, complete