1. Arthroplasty of the knee joint should be performed only in carefully selected cases. Criteria for the operation are outlined. 2. In our experience, 70 per cent. of properly selected patients secure good or fair results. An additional 12 per cent., whose anatomical or functional results were classified as poor, preferred the movement which had been gained to ankylosis of the joint. 3. The major functional adaptation of the knee joint takes place during the first five years after arthroplasty. Several patients who had a poor range of movement after one or two years developed an excellent range by the end of five years. 4. Instability, when present, usually became apparent within the first five years. 5. Joints which were still stable at the end of five years usually remained so over a long period of time. Four patients have been traced for twenty to twenty-five years, and three have been traced for over twenty-five years. 6. Since the incidence of ankylosis of the knee joint from gonococcal and pyogenic infections has been reduced by the use of antibiotics, fewer patients are suitable subjects for arthroplasty.
