The results of morphological studies of auxiliary elements (patella, meniscus, cruciate ligament, synovial bags) of 60 knee joints of adult corpses, 30 of which were intact (without signs of deforming arthrosis) and 30 with signs of deforming arthrosis of stages III-IV are presented. It is established that the auxiliary apparatus undergoes significant changes in the progression of deforming arthrosis. In a greater degree degenerative changes prone articular cartilage of the patella and medial condyles of the knee joint. The affected areas were characterized by thinning of the articular cartilage or its complete absence, as well as the presence of osteophytes along the edges of the articular surfaces. The measurements of the relative length, width, and thickness of the meniscus also confirmed the fact of their substantial deformation and degeneration, mainly of the medial meniscus. The posterior part of the body and the horn of the medial meniscus were most susceptible to the destruction of the cartilaginous tissue and were accompanied by the erasure and disintegration of the inner margin. Synovial membranes with deforming arthrosis were thickened, compacted and locally hyperemic, had papillary growths, which indicates the presence of synovitis and fluid accumulation not only in the joint cavity but also in synovial bags, the sizes of which were significantly increased. Intra-articular ligaments are hyperemic, and fragments are noted. Pterygoid folds are enlarged, locally hyperemic, with a vascular pattern, elongated processes are visualized along the edges. Identified morphological changes in the progression of deforming arthrosis lead to trophic and metabolic disturbances of all structures of the knee joint. The results of the study of the auxiliary elements of the knee joint can be used as a control in the diagnosis of deforming arthrosis.