Tibial tubercle osteotomy: effect of different osteotomy planes on contact surface area and tubercle anteriorization.

In 1983, Fulkerson introduced a technique of tibial tubercle osteotomy performed according to an inclined plane with respect to frontal plane. Due to obliquity of the osteotomy plane, this procedure allows both anterior and medial transfer of the tibial tubercle. The purpose of the study was to investigate the influence of the different degrees of the oblique plane of osteotomy on anterior displacement and the contact surface area of tibial tubercle. Synthetic bones were used for the study. An osteotomy of the tibial tubercle (TT) was performed in each specimen. Specifically, 3 different degrees of osteotomy planes relative to the reference frontal plane were examined: 20°, 30° and 40°. On each sample, tibial tubercle medial transposition of 5 mm, 10 mm and 15 mm was performed. Anterior displacement was measured with a caliper. Further, the bone contact surface was calculated for each sample and each transposition. Finally, the measured data were statistically compared with a geometric model. At 5 mm of medial TT transposition, the anterior displacement (AD) was 0.1 mm when the osteotomy was performed at 20°. It increased of 1.5 mm and 2.7 mm, respectively at 30° and 40°. At 15 mm of TT transposition, the AD was 3.4 mm at 20°, 7.6 mm at 30° and 10.0 mm at 40°. Concerning the amount of medialization, it was observed a decrease in the overall contact surface passing from 5 to 15 mm of TT transposition. In addition, regarding the oblique plane of the osteotomy, it was observed an increase in the contact surface area passing from 20° to 40°. The main result of the present study is that the amount of anteriorization and medialization of the tibial tubercle could be predicted by the degrees of oblique plane of osteotomy. An increase in medialization significantly reduces the contact surface area at low degrees of osteotomy plane, potentially increasing the risk of non-union.