Valgus high tibial osteotomy (HTO) results in changes in the frontal as well as sagittal planes. Our hypothesis suggests that patellar height increases and posterior tibial inclination decreases after closed wedge (cw) HTO, whereas patellar height decreases and tibial slope increases after open wedge (ow) HTO.

Lateral radiographs of 100 knees were assessed for patellar height (PH) using Insall-Salvati (ISI), Caton-De Champ (CDI) and Blackburne-Peel indices (BPI) as well as posterior tibial slope. Measurements were done before HTO (50 cw and 50 ow), direct postoperatively and before hardware removal.

In the cw-group all three PH indices increased direct postoperatively and at removal of the hardware with changes in CDI and BPI being significant (P < 0.05). In the ow-group all three indices showed a significant patellar height decrease direct postoperatively and at hardware removal. There were no significant changes between the two follow-up measurements (P > 0.05). Posterior tibial slope showed a significant decrease of 3.1 ± 3.4° after closed wedge HTO and a significant increase of 2.1 ± 3.6° after ow HTO direct postoperatively. In cw-HTO the correlations between frontal plane correction and PH changes were moderate (CDI: r = 0.57; BPI: r = 0.64). In ow-HTO these correlations were weak (CDI: r = 0.44; BPI: r = 0.46). According to ISI there was no correlation (cw: r = 0.11; ow: r =0.16). There was no correlation between PH changes according to CDI and slope changes.

The incidence of patella infera increases after open wedge HTO, whereas the incidence of patella alta increases after closed wedge HTO. We recommend considering the PH and tibial slope before planning for HTO or TKR after HTO, also performing cw-HTO or ow-HTO with the tuberosity left at the proximal tibia in cases of patellofemoral complaint or patella infera.

Radiographs of 110 patients who had undergone 120 high tibial osteotomies (60 closed-wedge, 60 open-wedge) were assessed for posterior tibial slope before and after operation, and before removal of the hardware. In the closed-wedge group the mean slope was 5.7° (sd 3.8) before and 2.4° (sd 3.9) immediately after operation, and 2.4° (sd 3.4) before removal of the hardware. In the open-wedge group, these values were 5.0° (sd 3.7), 7.7° (sd 4.3) and 8.1° (sd 3.9) respectively, when stabilised with a non-locking plate, and 7.7° (sd 3.5), 9.4° (sd 4.1) and 9.1° (sd 3.8), when stabilised with a locking plate. The reduction in slope (−2.7° (sd 4.1)) in the closed-wedge group and the increase (+2.5° (sd 3.4), in the open-wedge group was significantly different before and after operation (p = 0.002, p = 0.003). In no group were the changes in slope directly after operation and before removal of the hardware significant (p > 0.05). There was no correlation between the amount of correction in the frontal plane and the post-operative change in slope.

Posterior tibial slope decreases after closed-wedge high tibial osteotomy and increases after an open-wedge procedure because of the geometry of the proximal tibia. The changes in the slope are stable over time, emphasising the influence of the operative procedure rather than of the implant.