[The effect of open wedge osteotomy on the posterior tibial slope]

Proximal tibial osteotomy improves the alignment and weight distribution of the lower extremity on the coronary plane. However, upper end osteotomy of the tibia may cause changes in the sagittal plane. In this study, we evaluated open wedge osteotomy operations with regard to its effect on the sagittal plane.

The study included 22 knees of 20 female patients (mean age 54.1 years; range 43 to 64 years) who underwent proximal tibial osteotomy for osteoarthritis. Open wedge osteotomy was performed in all the patients with the use of a Puddu plate. Pre- and postoperative posterior tibial slope angles were measured on lateral radiographs. The mean follow-up period was 12.8 months (range 4 to 33 months).

Union of the osteotomy line was obtained in all the patients in a mean of 10.8 weeks (range 8 to 14 weeks). While the tibiofemoral range of motion did not change in 15 knees, it decreased by 5 to 10 degrees in seven knees postoperatively. Complaints of pain or limitation of the patellofemoral joint were observed in three patients. No correction loss or deep infection developed. The mean posterior tibial slope angle showed a significant increase by 3.5 degrees, from preoperative 7.2+/-4.1 degrees to postoperative 10.8+/-4.1 degrees (p<0.005). The more anteriorly the plate was placed in the osteotomy line, the higher increase in the posterior tibial slope angle was noted.

These findings suggest that open wedge osteotomy results in a significant increase in the posterior tibial slope angle, which may be associated with the triangular shape of the upper end of the tibia, the design of the plate, and the site of plate application. The use of a plate with a decreasing height from posterior to anterior may decrease these changes in the posterior tibial slope angle.