Open wedge tibial osteotomies influence on axial rotation and tibial slope

Inaccurate coronal plane and inadvertent sagittal plane realignment is a common problem after high tibial osteotomies (HTO). While the effects of an HTO on the coronal have been studied extensively, the influence on axial rotation has not been described in detail. The current study examines the effect of HTO on tibial rotation in the axial plane as determined by computed tomography. We hypothesized that high tibial osteotomies have an effect on tibial rotation in the axial plane and that depending on the predefined osteosynthetic implant used, a corresponding change in the tibial slope would occur. HTOs with a tapered 12.5 mm Puddu plate were performed on 13 limbs under computer-navigated control. All limbs were CT scanned before and after the HTO. Using specific software, the CT data was converted into 3D computer models and the following parameters compared: (a) varus-valgus leg alignment; (b) tibial axial rotation; (c) tibial slope (including determination of lateral and medial tibial slope, (d) leg length including determination of the tibial length. Results revealed: (a) a varus-valgus alignment increase of 11 +/- 4.7 degrees (P < 0.005); (b) an axial tibial rotation of 2.7 +/- 6.3 degrees (P < 0.075) occurred with external rotation in 10 out of 13 limbs (12 degrees max external; 9.5 degrees max internal); (c) tibial slope revealed differences of 4.2 +/- 5.9 degrees (P < 0.025); (d) the tibial length increased after HTO by 7.1 +/- 3.7 mm (P < 0.005), while there was no significant change in overall leg length. In summary, tibial rotation does occur in high tibial osteotomies with though the degree of external rotation in this study tended not to be statiscally significant. Tapered implants do not guarantee maintenance of a steady tibial slope, while tibial length changes significantly when HTOs are performed. The combined use of CT and 3D software measurement techniques is reproducible and can be used without any further invasive fixation devices.