The results of fifty-one Manchester knee arthroplasties in forty-one patients are reviewed and discussed. Excellent and good results were obtained in 85.4 per cent of arthroplasties. Varus and valgus deformity can be corrected and stability preserved or restored. Complications occurred in only twelve patients but resolved in all except one.

This is a preliminary report of the results of knee joint replacements using the Liverpool Mark II knee joint system which consists of a bicondylar prosthesis and a set of stereotactic instruments. The prosthesis has been developed from Gunston's concept, and the special instruments ensure its accurate insertion through meniscectomy-type incisions placed on either side of the patella. Particular features of the prosthesis are near-normal articulation, and the simplicity of the operation. Sixty-two knee replacements were implanted in forty-two patients between the spring of 1974 and January 1977. After the operation fifty-six knees were painless and four others produced only slight pain. Full extension was obtained in fifty-eight knees, and none showed a valgus or varus deformity. Collateral laxity was absent in all knees. There were two failures. These early results are most encouraging.

The stabilised gliding knee prosthesis is a compromise between hinged joints and condylar prostheses. It is a two-piece implant designed to allow normal gliding movements of flexion and extension and which, stabilised by a connecting rod between the femoral and tibial components, allows a designed laxity of rotation and lateral movements. A modification of the original femoral component is described. Two hundred and forty-five knee replacement operations have been done between January 1973 and September 1977 and the results are reported. The results using this prosthesis are at least equal to those using hinged or condylar prostheses. So far there has been no case of spontaneous loosening of the components and the implant can be used in patients who, because of severe deformities and instability, are unsuitable for condylar prostheses.

The Stanmore hinged total knee replacement was introduced in 1969 for severe destructive arthropathy of the knee, and the results of one hundred consecutive operations are presented after an average interval of two and a half years. Insertion of the prosthesis relieved pain in 94 per cent, improved the range of movement in 67 per cent, invariably restored stability and corrected valgus or varus deformity. Gross flexion contractures were improved but not always fully corrected. Serious complications were few, though of three cases of deep infection two came to amputation and one to fibrous ankylosis. There were no mechanical failures of components of the prosthesis.

Arthrodesis of the knee is a simple and safe operation that ensures stability and freedom from pain. But it is achieved at the expense of movement and occasionally of social acceptability. If arthroplasty is to be recommended, the advantages of arthrodesis must be retained, with the added bonus of a functional arc of movement.

The essentially satisfactory results from the ICLH implant as used until 1975 were marred by examples of loosening and sinking of the tibial implant, by patellar pain of varying severity, by wear of the tibial implant caused by fragments of cement and by failure consistently to control the alignment of the leg. This report describes the methods now being used to overcome these complications and gives an account of the success so far achieved.

Static force transmission at the knee is analysed using measurements from radiographs showing the position of the line of body weight and also the bones of the knee in their correct orientation during function. With this technique it is possible to suggest values for a variety of forces acting at the knee. During function the degree of knee flexion is not as important as the angle that the thigh makes with the vertical. The tension in the extensor mechanism is not the same above and below the patella. Failure to recognise these two features results in fundamental errors. The patella, the effects of patellectomy and of forward displacement of the attachment of the patellar ligament are discussed. The importance of the transmission of force in the coronal plane is emphasised with particular reference to total knee replacement. It is suggested that small errors of geometry, as seen in the anteroposterior radiograph, can produce large changes of load.

Eighty-one patients treated by patellectomy for osteoarthritis have been reviewed. Eighty-seven knees were examined with a mean follow-up period of six and a half years. Clinical and radiological assessment was carried out and the results have been analysed. A good result was achieved in 53 per cent, a fair result in 26 per cent and a poor result in 21 per cent. The overall result did not deteriorate significantly with time and the radiological appearance of the tibiofemoral joint deteriorated minimally. Pain before operation, radiological changes at the patellofemoral and tibiofemoral joints and the duration of immobilisation after operation were analysed against the end-result. The only factor before operation that indicated a good prognosis was a minimal radiological change at the tibiofemoral joint. Immobilisation for at least three weeks after operation appeared to be beneficial.

The mechanisms controlling and limiting movement and serving to transmit load between the femur and the tibia are discussed. Having accounted for the transmission of all components of force and couple across the joint and noted the load-bearing role of the menisci, some principles which might guide the design of knee prostheses are deduced. It is shown that current designs transgress some of these principles. An experimental prosthesis is then described, which incorporates analogues of the natural menisci. The possible practical application of this novel principle has been studied in cadaveric human joints and in living patients.

The radiation crosslinking of high-density polyethylene prostheses was investigated over a wide range of doses in the presence and absence of gaseous crosslinking agents. It was found that in the bulk polymer the crosslinking pattern is completely different from the homogeneous crosslinking that occurs in polymer films. The presence of crosslinking agents causes highly crosslinked polymer to be formed on the surface while the bulk of the polymer is largely unaffected--which is explained in terms of diffusion phenomena. This surface crosslinking has a profound effect on the mechanical properties of the prostheses and restricts cold flow and deformation of the polymer without sacrificing the excellent abrasion-resistance properties of the polyethylene when subjected to high pressures. Based on this research a number of high-density polyethylene knee prostheses have been radiation-crosslinked and the results in vitro appear to be very promising.

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.

The management of an anterior supracondylar fracture by closed reduction, traction, percutaneous pinning or open reduction is seldom satisfactory, especially for adults and the aged with a lesser ability to remodel and a slower functional recovery. A new, safe, and simple technique is described in which the condylar mass is pushed posteriorly along the axis of the forearm and the hand is rotated to full supination while the elbow is held in flexion to correct deformities. Fixation is divided into two parts: the circular cast around the upper arm provides a firm buttress onto which the lower fragment is reduced and then the arm is immobilised in a plaster which includes the wrist. Four cases of delayed, comminuted, compound fractures have been fully evaluated clinically and radiologically and the results assessed as good or excellent.

Sixteen severely haemophilic patients have undergone arthrodesis of one joint of the lower limb in the period 1966 to 1976. There have been nine arthrodeses of the knee and seven of the ankle. The follow-up period was from nine months to eight years. The arthrodeses were secured by internal fixation. The method was not without complications, but a satisfactory bony union resulted in all cases without further surgical intervention.

Intertrochanteric osteotomy gives compensatory correction for the severely slipped upper femoral epiphysis without endangering its blood supply. The results of thirty-five such osteotomies carried out over an eighteen-year period are reviewed. The indication for operation was a chronic slip of a third or more of the growth plate in the lateral radiograph. The mean age at operation was fourteen years and the mean follow-up period seven and a half years. The results showed that even a moderate correction of deformity as shown by the radiograph could produce a hip with a functionally satisfactory range of movement. Chondrolysis was the most serious complication and occurred in four hips. The radiological results are discussed in relation to details of operative technique and also to long-term prognosis.

The stages in adolescent slipping of the upper femoral epiphysis are classified in relation to treatment. The operation of open replacement of the displaced femoral head is described, and the results of a personal series of seventy-three such operations are presented. Open replacement is excellent treatment for severe chronic slipping so long as the growth plate is still open. The greater incidence of avascular necrosis in acute-on-chronic cases is probably due to damage to the blood supply of the head at the time of the acute slip or kinking of the vessels before replacement. Prolonged traction before operation may increase the risk of chondrolysis. Late onset of osteoarthritis when neither avascular necrosis nor chondrolysis has occurred may be due to misfitting of the articular cartilage because of inaccurate reduction.

In a series of over 250 patients, four suffered peritoneal penetration by one of the pelvic pins while being put into a halo-pelvic apparatus. In each case a point on the iliac crest two to three centimetres posterior to the anterior superior iliac crest had been used as the anterior landmark for the positioning of the pelvic pin guide. To avoid this complication we advise that the anterior landmark for the guide should be the "tubercle of the crest", five centimetres or more posterior to the anterior superior iliac spine.

Aneurysmal bone cysts are uncommon lesions, especially in the spine. Seventy-eight cases have been previously documented in the English literature and an additional fourteen cases are now reported. There is a definite predilection for the lumbar region and the neural arch is the part of the vertebra most commonly affected. It is recommended that treatment should consist of total excision or when this is not possible, curettage. Radiotherapy should be reserved for those few cases where operation is inadvisable.

Congenital spinal extradural cysts are rare and may be the cause of acute paraplegia. In their clinical features they closely resemble acute transverse myelitis. Immediate decompression of the spinal cord and removal of the cyst may lead to restoration of normal function. Myelography differentiates these two conditions by showing a cyst in communication with the spinal canal. This investigation must be mandatory.

Three members of a family with a symmetrical distribution of multiple metaphysial lesions presented during childhood with pathological fractures and showed a tendency to spontaneous resolution after maturity. The histological and radiological features suggested multiple non-osteogenic fibromata of bone.

The histodynamic response to long-term "non-traumatic" immobilisation was studied in young adult Beagle dogs by means of radiomorphometry and histomorphometry, the right forelimb being encased in plaster and the left forelimb serving as a control. The dogs were killed at two, four, six, eight, twelve, sixteen, twenty, twenty-four, thirty-two and forty weeks and the third metacarpal, radius, ulna and humerus removed for analysis of the contributions of the periosteal, haversian and endosteal envelopes to the bone loss at the mid-diaphysis. The bone mass responded to long-term immobilisation in three stages. First there was a rapid initial loss of bone, reaching its maximum (some 16 per cent of original mass) at six weeks, to which all three bone envelopes, to some extent, contributed. A rapid reversal followed, the bone mass approaching the control values between eight and twelve weeks after immobilisation. A second stage of slower but longer lasting bone loss ended twenty-four to thirty-two weeks after immobilisation; the periosteal envelope was the main contributor (80 to 90 per cent of the total loss). The third stage was characterised by maintenance of the bone mass which had been reduced by some 30 to 50 per cent of original values. This pattern was qualitatively similar in all four bones but the distal bones lost more bone than the proximal bones. The extent of resorption surface and the total histologically "active" periosteal envelope increased parallel to the phases of bone loss. The linear mineralisation rate did not differ significantly between the experimental and control sides.

We have observed congenital hypophosphataemic rickets in two sons of a marriage between first cousins, their mother being clinically and biochemically normal. Both patients are now approaching middle age. In addition to severe childhood rickets and lifelong hypophosphataemia, their disease is characterised by gross osteosclerosis with extraskeletal ossification, clinically persistent osteomalacia in one and spinal cord compression in the other. The genetics of this disease can be satisfactorily explained only on the basis of autosomal recessive inheritance, a mode which has only once before been reported in the literature. The severity of certain features, which would be expected in a homozygous state, may help our understanding of the more usual X-linked form.