Photoelastic techniques were used to study the stresses in models which represented the central frontal plane of a normal hip joint. The pelvis and the femur were inclined and the direction of the resultant thrust on the joint was estimated. Inward tilting of the pelvis causes a force which tends to push the head of the femur out of joint. The load distribution on the joint is not significantly changed if the line of action of the load is moved relative to the joint. The directions of the lines of principal stress in both bones are shown

1. A specially designed loading apparatus and dyeing technique have been used to demonstrate the weight-bearing areas in fifty-one normal adult hip joints. 2. Under loads and positions typical of the stance phase of walking the entire articular surface of the acetabulum is involved in weight-bearing. This contact area is reproduced on the femoral head, and its position determined by the attitude of the femur to the acetabulum. 3. With loads typical of the swing phase, the dome of the acetabulum and corresponding areas on the femoral head are not involved in weight-bearing. 4. The results are compared with the conclusions of previous investigators and their possible significance with regard to joint degeneration is discussed

This is the first time that the principle of the mould—the principle of guiding the repair of nature for the purpose of recreating a destroyed or damaged structure, has been applied to surgery. The evolution of the method to its present encouraging stage is the result of the co-operative, professional family spirit of the Massachusetts General Hospital. We all share in it. We share it with the general surgeon because of his contributions to surgical technique. We share it with the "medical man" because of his pre-operative and post-operative care of the patient; because of his guidance as to when, and when not, to operate; and because of the many friendly arguments which are productive of so much good. We share it with the anaesthetist because of his clinical judgment of the patient, his selection of anaesthetic agent, and his continuous, conscientious administration of the anaesthetic throughout the operation. I am going to change from "we" to "I." I owe so much to my assistants, from the first to the last: Bill Rogers, Eddie Cave, George Van Gorder, Paul Norton, Milton Thompson, Otto Aufranc, and Carroll Larson. I want to thank them all for helping to carry the load, for remembering the things that I forgot, and for making helpful suggestions which often led to improvement in surgical technique or to the construction of a useful instrument. I want to pay tribute to the staff of the Orthopaedic Service of the Massachusetts General Hospital and to thank its members for kindly scepticism, constructive criticism, and neverfailing loyal support. The subject of this lecture, "Evolution of Mould Arthroplasty of the Hip Joint," is appropriate for a Moynihan lecture. It is not the work of one man alone. It is the work of one man, supported by a co-operative, helpful, and friendly hospital staff. This is what Lord Moynihan strove so hard to bring about at a time when surgeons viewed one another as rivals. To quote Dr William Mayo: "It is to Lord Moynihan's everlasting credit that, largely as a result of his unceasing efforts, surgeons came to consider themselves as fellow-workers in a cause."

1. The early signs of Paget's disease of the acetabulum and femur are described. 2. The pattern of arthritis is presented in 199 hips in which Paget's disease of bone occurred in either the femur, the acetabulum or both bones. Distinct patterns of disease occur with different bone involvement. 3. Selective narrowing of the medial segment of the joint is common and is particularly associated with pelvic disease. Why the narrowing occurs here preferentially is unexplained. 4. Protrusio acetabuli occurred in only 25 per cent of hips and usually when both the femur and the acetabulum were involved. This may be due to the presence simultaneously of weakened bone and coxa vara, the latter leading to an alteration in the direction of the resultant force across the hip joint. 5. Degenerative arthritis was present with Paget's disease in 14 per cent of hips but it may be a chance relationship in half of these hips

1. Congenital dislocation of the hip can be diagnosed clinically immediately after birth and the diagnosis confirmed radiologically by a special technique. 2. If the affected joint is reduced during the first two or three days after birth and held reduced for a period not exceeding three months, the joint will remain stable. 3. This treatment probably leads to normal development of the hip joint. 4. The cause of congenital dislocation of the hip may be laxity of the soft tissues of the joint and not a primary dysplasia of the acetabulum

1. The operation of "dynamic" osteotomy is designed to secure a stable and freely mobile pseudarthrosis in cases of quiescent tuberculosis of the hip joint. 2. The principles and technique of the operation are described and illustrated. 3. The results of 224 operations are presented

1. A lateral intermuscular approach to the hip joint is described for replacement of the head of the femur by a prosthesis. 2. Advantages claimed for it are that it is attended by little or no shock, because the operation is rapid and relatively bloodless; that adequate exposure can be gained without dividing muscle or tendon; and that muscle function is unimpaired and so walking can be allowed early. The exposure is easily extended if unexpected difficulty is encountered. 3. Prosthetic replacement of the femoral head through this incision is advocated as a primary measure for elderly or unfit patients with fractured femoral neck

Arthrodesis of the hip joint performed between the ages of twelve and fifteen years, is the most satisfactory treatment for cases of pathological dislocation after acute suppurative arthritis in infants

1. Dissection of forty-four developing human hip joints has shown that while the embryonic acetabulum is a deeply set cavity which almost totally encloses the head it gradually becomes more shallow as birth approaches. During the same period the femoral head becomes less globular and at the end of foetal life is almost hemispherical. The cover afforded to the femoral head by the acetabulum also becomes decreased. 2. After birth these trends reverse: the acetabulum becomes deeper again and the femoral head more globular. This process continues throughout childhood. 3. The findings provide a possible explanation for the increased liability to dislocation of the infantile hip

Aims

Femoroacetabular impingement (FAI) has been highlighted and well documented primarily in Western countries and there are few large studies focused on FAI-related morphological assessment in Asian patients. We chose to investigate this subject.

1. A thousand arthritic hips have been replaced by an uncemented metal-on-metal prosthesis, and 942 followed by annual review. The mortality of the operation has been 1·1 per cent, the rate of deep-seated infection 0·7 per cent and the incidence of dislocation 0·3 per cent.

2. Of 169 hips replaced by an earlier type of the prosthesis and followed for five to eight years, 45 per cent have remained excellent and 29 per cent good, but 14 per cent have required revision, mainly for loosening of the femoral component.

3. The current types of prosthesis, now used for five years, have given excellent results in 69 per cent and good results in 21 per cent of 535 patients followed for one to five years. Revision for loosening has been necessary in 2 per cent.

4. The improvement in results has been obtained by the introduction of a tapered screw thread on the pelvic component, and by a range of femoral components that ensures a good cortical fit.

A casting method for measuring the intra-articular space in the loaded hip is described. The results of tests on 22 hips from 22 cadavers show that the joint space is variable both in location and size and can disappear under light loads. It seems likely that the size and shape of the space influence how much access synovial fluid has for lubrication and nutrition.

1. Transient synovitis is an acute, and at times exudative, condition of the synovial membrane.

2. There is no particular association with injury or with upper respiratory infection.

3. The course is short and benign with complete resolution. The occasional hip with chronic or recurrent symptoms can be distinguished from Legg-Perthes' disease by the shorter history, normal radiographs and the complete resolution.

4. There is no evidence that transient synovitis leads to avascular changes in the femoral head.