[The causes of failures in unicondylar knee arthroplasties].

Our study of failures of unicompartmental prostheses deals with 38 revisions. A failure is most often the result of several factors; they will be grouped into four chapters.1°)Selection of operated on patients: The diffusion of lesions beyond the prosthetized compartment is frequently responsible for he failure: rhumatoid polyarthritis (0 case), injury of the opposite compartment side (3 cases) and deterioration of the patella (0 case). The non-correction of an important deviation overburdens the prosthesis which deteriorates (3 cases) all the more so that there is a laxity of the concavity (3 cases).2°Errors in the operative technique: They are divided up into ill positioning of the femoral component (6 conflicts between the frontal patin and the mass of the épines), source of oblique space and of 3 frontal subluxations. The errors in the femoro-tibial alignment are responsible for 5 hypercorrectings with degradating of the opposed compartment and of 3 hypocorrectings overloading the prosthesis.3°Bad conception of the prosthesis: Either at the femoral component level (defect in the condylar curvature and incorrect osseous support) or at the tibial plate level (weakness of the polyethylene, 4 cases and bad osseous support, 1 fracture). The degree of conformity of the prosthesis is also responsible for failures: 2 by constraint prosthesis.4°Longevity of the prosthesis: Time realizes with wear and unsealing a real trilogy very often responsible for failures: 8 femoral unsealing and 21 tibial unsealings. Let us not forget the responsibility in these wears and unsealings of the ligamentous unbalance and of the knee morphotype (constitutional varum). The analysis of the causes of failures of unicompartmental prostheses should enable to better encircle the indications of this type of prostheses and to place only prostheses respecting the concept of resurfacing. The unicompartmental prosthesis must be a wedge of substitution of an osteo-cartilagenous substance loss. Thus, it should be ale to give results that can be compared in a distance to those of tricompartmental prostheses.