Preoperative planning of surgical treatment is an important stage of preparation for surgical treatment in traumatology and orthopaedics, which makes it possible to emphasise the peculiarities of the clinical case, prevent possible problems during surgery and reduce the risks of postoperative complications. The leading method of diagnostics for further planning of surgical treatment nowadays is radiological studies, primarily radiography and computed tomography. The results of radiological studies allow a sufficiently qualitative assessment of the zone of interest, planning of the required degree of correction and placement of fixing metal structures and endoprostheses. At the same time, when planning, the doctor relies mostly on the knowledge of the norms of anatomical relations and structures. And in the case of a multitude of possible treatment options, the doctor relies on his or her own medical experience to make a choice. This article presents a developed generalising methodology of preoperative planning in traumatology-orthopaedics, which includes biomechanical analysis and methods of accumulation and processing of quantitative data of clinical cases along with the usual methods of preoperative planning for doctors. The methodology brings together into a single system the criteria for evaluating the success of treatment by applying three classes of criteria: geometric (anatomical), biomechanical and clinical. The methodology allows the physician to perform biomechanical modelling of the proposed treatment options and quantitatively evaluate them on the basis of comparison of stress-strain states arising in the «bone-implant» system as a result of each of the planned options. The methodology allows to determine successful treatment options and to predict changes in the patient's quality of life after treatment. The presented methodology includes a mechanism for accumulation of quantitative data on clinical cases and quality control of the used biomechanical models.