Abstract
Introduction High tibial osteotomies (HTO) are commonly performed for either varus or valgus malalignment of the knee. In the past we have been well aware that HTO corrects the coronal plane of the knee, but we did not consider changes of the tibial slope in the sagittal plane when planning or evaluating osteotomies. Because the tibia is a three-dimensional structure with a triangular shape, osteotomy may result in changes in both the coronal plane and the sagittal plane. Altering the tibial slope has an impact on the in situ forces of the cruciate ligaments and may influence the stability of the knee. The purpose of this study is to investigate any possible alteration of the tibial slope introduced by HTO.
Methods This study was conducted as a retrospective radiographic review of a consecutive series of patients. Between January and September 2001 a total of 80 patients underwent either HTO or the removal of hardware from a prior HTO. The radiographs of 67 of these patients were suitable for review. There were 41 males with an average age of 36.6 years (17 to 67). There were 26 females with an average age of 39.4 years (19 to 62). Routine radiographs of the knee were obtained using standard methods, and these were assessed by comparison to corresponding preoperative studies.
Results The posterior slope on pre-operative radiographs averaged 6.1° (0 to 12). HTO using a closing wedge technique was found to decrease this posterior slope by a mean of 4.9°. The change in the posterior slope was not found to correlate directly with the magnitude of the correction in the coronal plane. HTO of six degrees in the coronal plane decreased the posterior slope by 4.3° degrees, HTO of eight degrees decreased the posterior slope by seven degrees, HTO of 10° altered the slope by 4.8° degrees, and HTO of 12° degrees decreased the posterior slope by 6.5°.
Conclusions HTO by a closing wedge technique for sagittal plane correction often distorts alignment in the coronal plane as well, resulting in a decrease in the normal posterior tibial slope. We found no direct correlation between the degree of correction of the coronal plane and alteration of the tibial slope. Decreasing this slope potentially decreases in situ forces acting on the ACL while simultaneously increasing forces acting on the PCL. This may have advantages when managing combined cases with both malalignment and instability. The closing wedge technique is our preferred method when a combined procedure (HTO and ACL reconstruction) is planned.
In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits.
The abstracts were prepared by Mr Jerzy Sikorski. Correspondence should be addressed to him at the Australian Orthopaedic Association, Ground Floor, William Bland Centre, 229 Macquarie Street, Sydney NSW 2000, Australia.
