A method is described of measuring radiological subsidence of a femoral prosthesis in relation to the femur after total hip arthroplasty. The method depends on measuring the distance from the tip of the femoral prosthesis to a fixed point in the bone. Subsidence after the use of a conventional design of femoral stem is compared with that after the use of a stem with a dorsal flange (Cobra). A significant reduction in the incidence and amount of subsidence was found when using the dorsal flange. There was also a notable absence of transverse fractures involving the cement near the tip of the stem, which occurred in 26 per cent of the cases using a conventional prosthesis.

Forty hips, which had previously been the site of tuberculous or pyogenic arthritis and which had later developed a degenerative arthritis, were treated by low-friction arthroplasty some forty years after the original infection. The results suggest that, when healing of the primary infection has been followed by a long period of quiescence with acceptable function before the onset of degenerative change, the arthroplasty can be confidently expected to result in greatly improved function and that this improvement is long-lasting.

Sixty-six patients are presented who have had a total hip replacement by the Charnley low-friction technique after injuries of the hip, the majority of which were fracture-dislocations. The clinical results of the arthroplasties in this relatively young group of patients are shown to be very good. The selection of young patients for total hip replacement arthroplasty is discussed.

In laboratory tests, the ultra-high molecular weight polyethylene used for the acetabular cups of Charnley hip prostheses has a very low wear rate against steel. In the body radiographic measurements indicate that the polyethylene wears more rapidly. In order to investigate this higher wear rate, the sockets of acetabular cups removed at post-mortem have been examined using optical and electron microscopy. It has been shown that a socket wears predominantly on its superior part and that this is a direct consequence of the orientation of the cup in the body and the direction of loading of the hip. In the worn region the femoral head in effect bores out a new socket for itself, a process which is visible with the naked eye after approximately eight years. Electron microscopy shows that the predominant wear mechanism is adhesion, but after about eight years the appearance of surface cracks suggests that surface fatigue is taking place in addition to this. Laboratory wear tests have shown that pure surface fatigue is not sufficient to account for the high clinical wear rate. Other deformation processes are suggested and discussed with regard to the higher clinical wear rate.

Fifty-four hips converted to low friction arthroplasty between 1965 and 1975 have been reviewed one to eleven years after operation. In many cases malposition had led to degenerative changes in the opposite hip, the lumbar spine or the knee, often with severe loss of function due to pain. It was found that total replacement could give useful relief of pain and improved function, though the range of movement obtained was not as good as in primary replacement. An outstanding feature was the correction of inequality of leg length. In general, the results were much better in cases of ankylosis acquired in adult life than in cases of spontaneous fusion after sepsis in childhood. The most important complication was a single case of sciatic palsy.

The incidence and prognostic significance of fractures of acrylic cement related to the stem of a femoral head prosthesis in total hip replacement are examined. These fractures are demonsfrated when the cement has been rendered radio-opaque by the addition of barium sulphate. One and a half per cent of the radiographs of 6,649 patients showed these fractures, which were sometimes associated with subsidence of the prosthesis. Fracture of the cement was usually evident at the six-month post-operative review, if it occurred at all. This radiological complication was devoid of symptoms in the majority of cases and tended to occur in patients with excellent functional recovery. In a minority of patients pain in the thigh during the first six months seemed likely to be explained by this fracture. Slight subsidence of the prosthesis in the cement bed appeared to result in a new and final position of stability. The prognosis was very good; only when separation of the fracture exceeded about 4 millimetres was the prognosis doubtful, in which case a chronic deep infection might be suspected. Possible mechanical and structural causes of fracture of the cement are discussed.

1. Two hundred and seventeen low-friction arthroplasties performed between November 1962 and April 1969 in 203 patients with failed previous operations have been analysed.

2. The technical details of operation in relation to these conversion problems have been outlined.

3. The quality of the results in relation to pain, mobility and ability to walk has been assessed before operation and one year afterwards, with small numbers at three and five years.

4. Pain was completely relieved or was minimal in 96·3 per cent of the patients, and in no case was the pain worse.

5. The total range of movement was 100 degrees or more in 98·5 per cent. No hip lost movement after conversion.

6. The failures were principally due to infection and to technical difficulties. There were no mechanical failures without a technical or radiological explanation.

7. Low-friction arthroplasty is an excellent salvage procedure, especially for failed cup arthroplasty.

1. The results have been reported of total hip replacement by a low-friction technique using high-density polyethylene for the acetabular component in 379 primary interventions, performed between November 1962 and December 1965 and followed for between four and seven years.

2. Apart from failures due to infection, the rate of which in the era under review was 3·8 per cent, late failures from mechanical causes were unusual after total hip replacement by this technique. When the socket was cemented in position, which is now routine, the late mechanical failure from all causes was only 1·3 per cent in 210 cases.

3. As regards the quality of the results and their maintenance over the years, the results were so good (Table X) that it was unnecessary to distinguish an intermediate class of "improvement" between success and failure.

4. As regards relief of pain and ability to walk, the average final rating, on a scale numbered 1 to 6, was 5·9 for both, indicating 90 per cent of patients in Grade 6 (excellent) and only 10 per cent in Grade 5 (good).

5. The average recovery of movement was not as spectacular and was influenced considerably by the pre-operative range, but in all cases that range was improved on. Even starting with the stiffest of hips about one patient in four regained a right angle of flexion movement. There was no tendency to lose movement with the passage of time.

6. As regards late infection (2·2 per cent out of a total of 3·8 per cent), the various findings tend to exonerate cement as a cause.

7. The mechanical details of the technique became stabilised in the period 1959 to 1962 in the Teflon era, and with the exception of improved methods of reattachment of the greater trochanter, they are identical with our current practice in 1971.

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.

1. Specimens are described in which osteoid was seen in undecalcified bone sections prepared from a number of osteoarthritic femoral heads.

2. It was localised mostly in the pressure segments.

3. The reason for the presence of this osteoid is not well understood and the possibilities of local histochemical changes and/or cellular metaplasia are discussed.

1. A study is reported of 190 femora in 174 patients in whom self-curing acrylic cement had been present in the medullary cavity of the upper end of the femur for the fixation of an endoprosthesis for an average period of four years.

2. The bone remained radiologically normal in 81 per cent of cases.

3. Improvement in the thickness of the cortex from pre-existing atrophy was noted in 2·6 per cent.

4. In 4·7 per cent the bone showed some atrophy after insertion of the cement. This exceeded 10 per cent in only two cases. All were originally osteoporotic from polyarthritis; all were satisfactory as regards the arthroplasty itself, and the atrophy could usually be explained by disuse resulting from the state of the opposite lower extremity, or the knee on the same side.

5. In 9·4 per cent there was fusiform hypertrophy of the femoral cortex, the bony texture remaining normal. This appearance was considered physiological and benign.

6. In 2·2 per cent there were changes for which the most likely explanation is chronic non-suppurative osteitis, though no collateral evidence of infection was found.

7. In 44·8 per cent there was a thin line of condensation in the cancellous bone demarcating the outer limits of the cement. This is considered to be physiological and not to indicate failure of immobilisation.

8. In 37·2 per cent there was slight resorption of the cut surface of the calcar femorale. This is considered to be physiological and to confirm the efficacy of weight transmission by cement lower down in the medullary cavity.

It has been shown by mechanical analysis that by using cement to bond the stem of a femoral head prosthesis to bone two advantages are obtained when the conditions are compared with conventional methods.

1. "Fretting" between the implant and the living bone is eliminated. This source of persistent relative movement is probably the most important starting point for the progressive loosening of weight-bearing implants.

2. When cement is used the bond with the bone is exposed to stresses which are of an order three hundred times less than the shear strength of bone. The conventional prostheses expose the bond to compressive stresses which are near to the failure limits of the compressive strength of bone, especially in elderly patients with atrophic cortical bone in the femoral neck.

1. The customary method of broaching and of knocking the prosthesis down into the neck of the femur produces an indeterminate interference fit.

2. The usual interference fit may suffer progressive breakdown under even small, steady loads. This results in a permanent relative movement between prosthesis and femur as the metal insert "beds " into the bone.

3. Modification of the usual practice by providing a clearance fit between prosthesis and femur and cementing of the metal into the bone provides a system which has been shown to be free of breakdown under steady loads up to about 450 pounds.

4. By cementing the prosthesis shaft into the femur permanent relative movement between the elements has been shown to be reduced from approximately four-hundredths of an inch per 100 pounds load to two ten-thousandths of an inch per 100 pounds load–that is, a reduction of 200 to 1.

1. A series of twenty-three compression arthrodeses of the shoulder are reviewed.

2. The review demonstrates compression arthrodesis to be an excellent method of obtaining bony fusion of the shoulder.

3. The consistent success in achieving arthrodesis, in what is to be considered a difficult joint to fuse, is significant in the theory of compression arthrodesis, because the shoulder offers a more perfect example of compression arthrodesis than the knee in that the element of absolute fixation is less obvious.

1. The use of acrylic cement in bonding femoral head prostheses to bone is described.

2. No sign of deterioration of the bond between the cement and bone has been seen in histological preparations up to three and a quarter years after operation, and no harmful effects have been recognised, or suspected, in 455 patients in whom it has been used.

3. The technique is considered justifiable in elderly patients where the medullary canal is large and the cortex of the femur is thin and brittle.

1 . The results of transplanting the greater trochanter in 225 "low-friction" arthroplasties of the hip have been examined.

2. Non-union occurred in an average of 7 per cent of cases.

3. When non-union occurred the results still showed improvement.

4. Four different methods of fixation were used, of which that using two wires, crossed in the horizontal and coronal planes, never failed to secure union.

5. Transplantation of the greater trochanter to the best position is only possible if the neck of the femur is shortened or if the centre of motion of the arthroplasty is displaced medially by deepening the acetabulum, or by a combination of both.

6. In the best position the transplanted trochanter considerably improved active abduction against gravity.