INTRODUCTION: High tibial osteotomy (HTO) has been a useful surgical option for medial osteoarthritis (OA). However, open-wedge (OW) HTO have been reported to change the patellar height and tibia length. The authors reported the long term follow-up results of the originally developed inverted V-shaped (iV) HTO (Figure.1). This procedure was classified as neutral (hemi-closing and hemi-opening) wedge osteotomy. This could provide sufficient valgus correction of the knees with severe varus deformity. Mechanically, this iV osteotomy does not change the patellar height, or the length of the lower limb, because the center of tibial alignment correction (hinge point) of iV HTO is located approximately at the center of rotation of angulation (CORA) of the lower limb deformity. The aim of this study was to compare the degree of correct coronal deformity of lower leg and influence on the patella height and leg length between iV and OW HTOs.

METHODS: 140 patients (156 knees) who underwent HTO due to the medial OA were enrolled in this study between 2013 and 2017. There were 50 men and 90 women with a mean age of 59 years (range: 20-73 years) at the time of surgery. All patients were divided into the two groups; OW group (117 knees) and iV group (39 knees). The indication for inverted V HTO is, symptomatic, isolated medial-compartment OA knees with varus deformity, and the valgus correction angle of which is calculated to be 15 degrees or more. The patella height was evaluated by using the Insall-Salvati ratio (IS), Blackburne-peel method (BP), and Caton-Deschanmps (CD) at preoperatively and 2 years after osteotomy (Figure.2). Functional knee (Japan Orthopaedic Association) score, FTA, medial proximal tibial angle (MPTA), the leg length and tibial length were also evaluated. Δ means the difference between pre- and post-operative value. Statistical analysis was performed using t test. The significance level was set at p = 0.05.

RESULTS SECTION: Postoperatively, the functional knee score significantly improved at the final follow-up in both groups. There were no significant differences between the two groups. The pre FTA was significantly larger in iV group (184°) than in OW group (176°) (p=0.0003). The pre MPTA was significantly smaller in iV group (81°) than in OW group (85°) (p=0.003). ΔFTA and ΔMPTA were significantly larger in iV group (12° and 11°) than in OW group (7° and 8°) (p<0.046) (table.1). Patella height was significantly shortened in OW group (BP: 14%, CD:27%) compared to iV group (BP: 7%, CD:27%) (p=0.01 in BP and p=0.02 in CD). ΔIS was not statistically significant. Although there were no significant differences in Δleg length between the two groups, Δtibial length was significantly larger in OW group (7 mm) than in iV group (1 mm) (p= 0.002) (Table.2).

DISCUSSION: This study showed that iVHTO could make a large correction at coronal plane compared with OWHTO, however, iVHTO changed the patella height and tibial length smaller than OWHTO. This was thought to be attributed to the hinge point of iVHTO located just medial side of tibial tuberosity. These data indicated that iVHTO was an osteotomy that was able to correct large coronal deformity and the influence of iVHTO on patellofemoral joint and leg length was smaller than that of OWHTO. This study showed that the 6.5 mm tibial length change in OW group, but not in inverted V group. Because the center of tibial alignment correction is located approximately at the center of rotation of angulation of the lower-limb deformity, no changes occur in the leg length. However, further long-term studies are needed to assess the subjective and objective patient outcomes of inverted V shaped osteotomy in patients with severe varus malalignment.

1744 - Medial Open-Wedge High Tibial Osteotomy Changes the Patellar Height and Tibial Length in Medial Osteoarthritis of the Knee; Comparison with Neural-Wedge High Tibial Osteotomy