1. Hip-socket anthroplasty is a procedure developed from a study of the biomechanechanics of the hip joint, histophysiological observations of joint repair, and clinical experience with a Vitallium socket attached to the pelvis.

2. Special surgical instruments have been designed for implanting the socket through a posterolateral approach. The hip socket is a self-sustained lining for the acetabulum and is stable enough to allow motions immediately after the operation. The socket is opens at the inferior margins to permit regeneration of a structure resembling the ligamentum teres and mucin-forming synovial cells inside the joint. It encloses only half of the head of the femur and thereby permits a wide range of motions.

3. The morphological and chemical structure of a pseudarthrosis and a functioning arthroplasty are identical and the two coditions involve the same connective-tissue-cell processes. The first covering of the articular surface is granulation tissue, fibrinoid, and fibrous tissue. After six months differentiations occurs to form fibrocartilage and after eighteen months new cartilage, resembling hyaline cartilage, appears in the deep layers in contact with cacellous bone. The joint surface formed from an arthroplasty after years of functions resembles articular cartilage. Although it is not true articular cartilage, it becomes increasingly like articular cartilage after a period of years of weight-bearing and after remodeling of the underlying spongiosa to produce a new articular cortex of compact bone.

4. Forty-eight hip-socket arthroplasties have been perfomed in the years between 1953 and the present time. Five arthroplasties with complications were subjected to revision, arthrodesis, or resection operations six to eighteens months after the arthroplasty. Results in the first twelve hip-socket arthroplasties (including two bilateral) examined betweens two and three years after the operation were regarded as fair in one, good in one, and excellent in ten. The patients had less pain than before the operation, had an increase of range of motion, and had a stable joint. Compared with other surgical methods, there was a remarkably free range of rotations combined with flexion. A theoretical explanation is that hip-socket arthroplasty permitted derotations or unscrewing of the head of the femur during the swing phase of the joint motions. Further investigations and long-term end-result studies are in progress and will be reported later.