The arthrodesis of the ankle joint, in spite of the promising results of the ankle arthroplasty, is still an established procedure for the treatment of advanced ankle osteoarthritis. A number of authors postulate an insufficient rigidity and primary stability of screw arthrodesis in ankle with reduced bone quality, osteoporosis and distinct deformity. This comparative biomechanical study analyses the biomechanical properties of the three-screw arthrodesis and posterolateral plate arthrodesis of the ankle. Particular attention was paid in the detection of differences in the mechanical stability of the bone-implant composite. Another question referred to the influence of the bone quality to each construct. The computertomographic examination of human specimens allowed the analysis of the implant position. Finally, the clinical results of the posterolateral plate arthrodesis were evaluated. In summary, the biomechanical and clinical examinations showed outstanding results. The posterolateral plate arthrodesis has -compared to the three-screw arthrodesis - a significantly higher rigidity in osteoporotic bone. Osteoporosis, neurogenic deformities and polyneuropathy did not increased the complication rate in the clinical analysis.