The supramalleolar osteotomy is a surgery, which aims to correct ankle osteoarthritis. Surgeons specializing in osteotomies regularly need to make accurate and precise cuts to a patient's bone with tools like an oscillating bone saw. In order to acquire the knowledge and skills to perform the real ankle surgery, they need to watch tutorials and practice on physical test models beforehand. In this work, we create a training system for the supramalleolar osteotomy in virtual reality. This includes the implementation of a bone cutting simulation and a post-analysis tool to evaluate the performance. A simple cut for this type of surgery requires the knowledge of its starting point, orientation, and current coverage. Furthermore, we design different concepts for visualizations, which aim to provide guidance, assistance, and feedback to the trainee surgeon during the operation. A preliminary study with a medical expert investigates the performance regarding the cut accuracy of each design. The study showed that the overall usage of those designed guidance visualizations improved the user's confidence during the operation. One key observation was that visualization directly positioned onto the cutting region performed better than the ones which were further away.