Medial femoro-tibal arthritis in cases of genu varum is almost always associated with metaphyseal varus. Correcting this deformation should ideally be done at the place at which it is situated, that is, in the internal tibial metaphyseal region, with an open internal tibial osteotomy. OSTEO + restores the anatomy of the tibial metaphysis, making it easier to implant a prosthesis if necessary, unlike the external closed osteotomy which induces metaphyseal malunion.