Assessing accuracy requirements in high tibial osteotomy: a theoretical, computer-based model using AP radiographs

Purpose High tibial osteotomy (HTO) is a recognised treatment for medial compartment knee arthritis and in recent years has regained popularity. Preoperative planning of wedge opening is based on standing AP radiographs, aiming to deliver the WBL to a desired point. Clinical results can be unpredictable, and this may be due to an inability to deliver the preoperative plan. This study explores the theoretical wedge opening accuracy required to deliver preoperative plans, based on clinical AP radiographs. Methods A theoretical 2-D model of osteotomy was developed to determine the degree of radiological wedge opening accuracy required to deliver the weight-bearing line to a preoperative target of 62–66 % of the width of the tibial plateau. Results This model suggests that, to deliver the weight-bearing line to the preoperative target on plane radiographs, the theoretical medial wedge must be opened to an accuracy of ±0.9 mm. Conclusion Although this study only explores a model of wedge opening based on AP radiographs, with current surgical systems, it is unlikely that the surgeon can achieve this level of accuracy within a real-life surgical setting. Surgical accuracy in HTO is known to be important for both short- and long-term clinical outcomes. This study highlights the need for improved surgical accuracy aids and/or patient stratification to mitigate the effects of surgical errors. Level of evidence II.