Abstract. The presented article is an original contribution which implies the design of a specialized modular device used at the different surgical procedures applied at the human knee. The increasing of the precision and quality of the surgical procedures using specialized devices is an important goal both for the engineers and for the doctors. In the paper are presented some diseases which affect the human knee and also the possibilities of surgical treatment of those. The main knee pathology which was researched, regards the axial deviations of the human lower member and correction using HIGH TIBIAL OSTEOTOMY (HTO) in all possibilities: with opening wedge or closing wedge, medial or lateral, uniplanar or biplanar. The complexity of these surgical procedures from geometrical point of view opens up the possibility to increase the quality of the medical act through using specialized devices. In this regard, in the present article it is approached the design and the modelling of the modular device destined for the knee surgery using HTO techniques. The main objectives are: establishing the needs and requirements that the device should accomplish, the identification of the primary functions, the development of the implementation solutions, the synthesis of these solutions and finally the 3D design of the device using Catia V5R20.