Replacement arthroplasty of the knee joint: trends and treatment after failure

Knee joint replacement has progressed considerably in the past 15 years, although the difficulties are greater than those of hip replacement. At first, only the constrained hinge joint and a limited variety of unconstrained joints were available. Severe deformities of diseased knees and ligamentous insufficiency forced great changes to be made in unconstrained prostheses to ensure greater stability and motion and less wear and loosening. Further changes have also been made in constrained hinge joints; this has resulted in a great proliferation of prostheses of all types. Fully constrained prostheses now have restricted indications. Poor results are greatest with the fully constrained hinge group (36%) and lowest with the semiconstrained group (13%). The unconstrained prosthesis gives results intermediate between the others. Infection rate is highest in constrained and lowest in unconstrained prostheses. The loosening rate is lowest in the semiconstrained and unconstrained types.