John Charnley

Radiological Demarcation of Cemented Sockets in Total Hip Replacement

The frequency of radiological demarcation of the cement-bone junction in the acetabulum after total hip replacement has been examined in 141 Charnley low-friction arthroplasties followed for an average of 10.1 years. Sixty-nine per cent showed demarcation of various degrees and 9.2 per cent of the series showed evidence of progressive migration of the socket. The vast majority of cases with demarcation were symptomless. In most cases where demarcation was accompanied by migration the operation notes suggested a technical explanation and in three cases low-grade sepsis was responsible. The fact that nearly 30 per cent of cases showed no demarcation even after 10 years supports the idea that there is no fundamental defect in the principle of employing cement in the acetabulum. Better surgical technique may increase the number of cases showing no demarcation.

Rate of wear in total hip replacement.

The wear of high molecular weight polyethylene sockets was measured on radiographs, over a period of 9 to 10 years, in a group of patients whose ages averaged 73.3 years at the end of the period. The average rate of wear was 0.15 mm/year and 68 per cent of patients followed this pattern. Wear more than 2.5 mm in 10 years occurred in 15 per cent. There was a diminution in the rate of wear with the passage of time; in the second 5 years the rate of wear was approximately 40 per cent less than in the first 5 years. Body weight and physical activity did not appear to have any relationship to the final amount of wear. In a second series of very disabled subjects under 30 years of age (33 patients, 59 hips, followed only for an average of 38.4 months) the wear was rather more than in the previous series. Most remarkable was the performance of 4 patients, below the age of 50, who were considered completely normal for their age (category A); three of these wore less than the average for the main series.

ABDUCTION FORCES IN THE ONE-LEGGED STANCE"

Abstract The forces acting in the abductor muscles and on the head of the femur have been determined experimentally for three subjects in a range of different pelvis attitudes. The position of the centre of gravity of the body was determined by force measurement with simultaneous radiography to relate it to the skeleton. The forces were calculated using muscle positions obtained by dissection and radiography of a specimen. Pelvis angle and the position of the trunk and limbs have a considerable effect on the forces. With the pelvis in the normal walking attitude and the limbs symmetrically disposed, muscle forces range from 1·0 to 1·8 and joint forces from 1·8 to 2·7 times body weight.

Compression arthrodesis of the ankle and shoulder.

Success with arthrodesis of the knee by compression (Charnley 1948) has now prompted the writer to describe his experiences with compression arthrodesis in the ankle and shoulder. The application of compression to arthrodesis of the ankle and shoulder is more difficult than it is in the knee, and the writer does not wish to minimise the fact that the methods to be described perhaps demand a little more mechanical aptitude than is necessary in most orthopaedic procedures ; on this account there may be some who will deplore any tendency to complicate operative procedures, in the belief that all the great operations of surgery are essentially simple. But practically all the classical operations of surgery have now been explored and, unless some revolutionary discovery is made which will put the control of osteogenesis in the surgeon’s power, no great advance is likely to come from modifications of their detail. For the same reason the elaboration of techniques which depend on bone grafting would also seem to have a restricted future, with the exception of a few instances, notably that of the Brittain operation in the hip, where the function of the graft seems to be in harmony with some natural trend in the architecture of the skeleton. Experience with the tibial graft during a quarter of a century, following the pioneer work of Albee in the shaping and fixing of this graft, has shown that the fate of cortical bone is unpredictable ; these grafts sometimes fail to unite, sometimes fracture after union, sometimes fail to heal when fractured, and at all times are slow to become incorporated. In the same way cancellous bone has not shown any phenomenal ability to bridge the moving zone of a joint line either by itself or when its lack of rigidity has been supplemented by metallic internal fixation. Until recently the idea has been prevalent that an autogenous bone-graft was “ osteogenic ‘ ‘ ; but further experience has now made it obvious that the osteogenic powers of a bone graft are almost non-existent and that osteogenesis is a property only of the living bone of the host. In compression arthrodesis direct union is achieved between the living bones forming the joint surfaces without the intervention of an inert graft. One of the effects of compression is to eliminate all shearing strains as well as preventing a gap between the cut hone surfaces. Under these conditions the healing of a compression arthrodesis is more aptly compared to the healing of an accurately coapted skin wound than to the union of a displaced fracture with the production of callus. Technical researches in compression arthrodesis make it inevitable that operative procedures will become more complicated; but with surgeons specially trained to this at an early part of their career, and with the protection now afforded by antibiotics, elaborate techniques will offer no danger in the hands of the orthopaedic surgeon of the future, provided that sufficient attention is paid to the minutiae of the technique. For this reason the technical procedures have been described here in minute detail to emphasize the fact that the time is coming when no surgeon will embark on a new procedure with only a general knowledge of the principle and in the hope of himself improvising the details.

Fracture of femoral prostheses in total hip replacement. A clinical study.

The clinical features are presented of 17 fractured Charnley femoral prostheses occurring over a period of about ten years and arising from some 6,500 operations, with more than a 3 1/2 year follow-up. The patients especially at risk are males weighing over 170 lb (75.5 kg) and from these is an obvious need for a heavier design of prosthesis. Whereas the overall fracture rate is only 0.23 per cent, the rate for males over 196 lb (88 kg) is 6.0 per cent. It is believed that defective surgical technique, in failing to provide adequate support by cement to the concavity of the upper levels of the prosthesis is probably the main cause of fracture and reasonably good cement technique explains why the fracture rate is not higher in the present series. Indications for improving cement technique are outlined.

Ectopic bone formation following low friction arthroplasty of the hip

Ectopic bone formation after low friction arthroplasty (LFA) occurs nearly three times as often in males as in females and, in significant amounts, in 10 per cent of the total number of patients. The more limited the range of motion preoperatively, the more severe the degree of ectopic bone formation. The diagnosis does not closely relate to ectopic bone formation though the incidence is highest in osteoarthritis. The removal of osteophytes does not increase the incidence of ectopic bone formation. Trochanteric osteotomy in the surgical exposure is not an important cause of ectopic bone formation. A patient with ectopic bone after LFA on one side has a 92 per cent chance of developing it in a subsequent LFA on the opposite side. Systemic factors appear to play a dominant role in the production of ectopic bone.

Socket wear in Charnley low friction arthroplasty of the hip.

Five hundred forty-seven Charnley hip arthroplasties were measured for wear radiographically after an average period of 8.3 years. The operations were performed in 1967 and 1968 and the average rate of wear was 0.07 mm per year. This is only half that recorded for the operations in 1963, 1964, and 1965. Clinical radiographic methods of measuring socket wear are valid provided that the socket is inserted with the wear marker not more than 10 degrees from the coronal plane. This can be estimated provided that radiopaque cement is used.

The Lubrication of Animal Joints in Relation to Surgical Reconstruction by Arthroplasty

The accepted theory of joint lubrication is that of MacConaill (1932), who assembled arguments to show that it was an example of hydrodynamic or full-film lubrication. The principal argument in applying the hydrodynamic theory to animal joints was the anatomical fact that in joints the curvatures of articulating surfaces are not completely congruous throughout their whole arc of movement. It was observed by Walmsley (1917, 1928) that the surfaces of the knee and hip are exactly congruous only in the position of full extension, which is the position of the motionless erect stance, but that in the arc employed for walking or running the convex surface has a slightly smaller radius than the concave surface. This presented to MacConaills mind the existence of wedge-shaped spaces, occupied by wedge-shaped films of synovial fluid; it is the essence of the hydrodynamic theory that fluid pressure is generated in a wedge of lubricant as a result of the motion of the surfaces and that this pressure supports the load and keeps the sliding surfaces separated on a cushion of lubricant (Fig. 1). Even before examining the problem experimentally in animal joints, there are theoretical criticisms which make the hydrodynamic theory unlikely. Firstly, the articular cartilage, which is present as layer about I in. thick over the sliding surfaces of the joint, is very resilient, being easily indented by pressure of the thumb-nail. An ankle-joint of an adult male has a projected surface area of less than 2 sq. in., so that a man weighing 12 st. carrying a l-cwt. load on his shoulders will expose an anklejoint to pressures of about 150 lb. per sq. in. There can be little doubt that these resilient surfaces are intimately applied to each other over the whole area especially when carrying loads.

THE REACTION OF BONE TO SELF-CURING ACRYLIC CEMENT

1. A general picture of the histological state of the bone-cement junction, up to seven years after implantation, is presented as a result of the study of twenty-three human specimens. 2. The transmission of load from cement to bone occurs at isolated points through the medium of newly formed fibrocartilage. 3. It is clear that this fibrocartilage has been produced in response to mechanical pressure on fibrous tissue which has undergone compression between cement and underlying bone. 4. Direct contact exists between the surface of the cement and the newly formed fibrocartilage at these sites of load transmission. 5. Load-bearing fibrocartilage frequently shows areas of ossification extending into it from the underlying bone. 6. Where soft tissues in contact with cement are too thick or too delicate for load transmission a thin layer of giant-cell cytoplasm coats the cement surface. 7. No collections of giant cells to form granulomatous or caseating areas have been seen. 8. Fat storage, indicating the absence of chemical irritation, can occur within ten microns of the cement surface.

Surgery of the Hip-joint

In the conditions of the modern world patients with osteoarthritis of the hip are inclined to consider surgical treatment for degrees of discomfort which less than twenty years ago were regarded as inevitable. The orthopaedic surgeon is presented with a problem which has changed completely in two decades. The methods of classical surgery in the past were able to produce gratifying results in osteoarthritis of the hip in patients with pain and fixed deformity, but to-day patients commonly present with hip disorder in such an early form that even the assistance of a stick is not required. A surgeon accepts great responsibility if he recommends surgery before a patient needs a stick, and it takes much soul-searching to decide whether the results obtained in early cases are commensurate with the time and money involved in treatment. The possibility of complications after major surgery in patients affected systemically by degenerative disease needs special consideration. I