Many knee replacement prostheses, embodying various principles of design, are now available and there is need for a method by which valid comparisons of results can be made. An important criterion of success is durability, so the length of time the prostheses have been in situ must be taken into account. Such a method is proposed here and is applied to the results of 673 knee replacements, of nine different types, implanted at the same hospital between 1970 and 1983. A prosthesis was considered to have failed if it had been removed or persistently caused severe pain. Two types of prosthesis were found to be significantly less successful than the other seven, between which none consistently showed significant superiority. Results for the seven types were similar despite the facts that they had been used for knees with different degrees of damage, some as secondary implants, and that they were of different design and at different stages of technical development. The more recently introduced types of prosthesis, designed to have theoretical advantages, were found in practice to be no more successful than the models they superseded.

We examine the hypothesis that a knee replacement is most likely to survive successfully if it is stable with a coronal tibiofemoral angle close to 7 degrees of valgus, the accepted normal. The records of 428 knee replacements followed up for one to nine years were analysed. The highest success rate was indeed found in those so aligned at operation and such knees were most likely to remain stable. Nevertheless, half of the failures occurred in knees correctly aligned at operation and two-fifths in knees which had remained stable in this alignment; many failures must have been caused by factors other than malalignment. Some knees, well aligned at operation, deteriorated into severely varus or valgus positions; their failure rate was significantly higher than that for knees which remained normally aligned and higher also than for knees severely varus or valgus from operation onwards. Malalignment, in itself, may not be the most important cause of failure, though it probably does compound failure from other causes.

A method of analysing the results of knee replacement operations, which makes it possible to estimate the annual failure rate and the proportion of implants which will survive successfully for 10 years, is applied to the post-operative data for 365 operations, using Freeman, Sheehan and Manchester prostheses, carried out from 1972 to 1980 at Harlow Wood Orthopaedic Hospital. Two criteria of success are defined. On both, and for all prostheses, the annual failure rate is found to be much lower in the first two than in the later years. Thus, account must be taken of the period since operation if the success of different prostheses is to be validly compared. This is not possible using conventional statistical methods. But significant trends in annual failure rates and significant differences between prostheses can only be identified from samples larger than are usually available in individual series. Hence it will be necessary for many centres to co-operate in pooling results if reliable conclusions are to be reached and valid comparisons made.

A prospective study was made of 100 knees which had been operated on for various kinds of internal derangement. An observer, who did not know the clinical condition of the knee, recorded whether or not there were articular lesions of the femoral condyles. Lesions were found to be localised to a triangular area on the medial condyle and to a strip on the lateral condyle. Similar lesions have been described in association with flexion deformities in rheumatoid and osteoarthritic knees. Lesions were found in 49 out of 50 knees which had been locked for more than three days. They were also found in 29 knees in which there appeared to be full extension before operation, but where there was either a torn meniscus with a history of intermittent locking or serious anterolateral instability. In these cases it was considered that the final "screw-home" mechanism of full extension had been lost. Lesions were not present in 10 knees which appeared locked, but in nine of these the interval between injury and operation was less than three days. Lesions were not found in eight knees where there was full extension and no history of locking or instability. In four knees with a plica syndrome similar lesions were present.

An anteroposterior radiograph of the leg to include the hip and ankle, taken with the patient standing, provides an estimate of the line of load-bearing at the knee. Gait analysis may be used to determine the way in which the load in the knee is shared between the medial and lateral compartments during normal walking. A comparison of the results from the two methods, carried out on a group of 47 patients, led to the conclusion that both calculations are required for the successful outcome of a tibial osteotomy or a total arthroplasty.

In a consecutive series of 87 operations for knee replacement prospective observations were made of the pattern of articular destruction in the form of a triangle of erosion or osteophyte formation, which is seen on the medial femoral condyle, sometimes with an associated strip on the lateral femoral condyle. These areas represent the surfaces which are normally in contact with the anterior horns of the menisci when the knee is fully extended. The lesions in question were found only in association with a flexion contracture in 84 out of the 87 cases.

One hundred and seventy feet have been reviewed after operations for hallux valgus; eighty-five had had arthrodesis of the first metatarso-phalangeal joint and eighty-five had had Keller's operation. Footprints were made in order to assess the patterns of weight-bearing on the big toe and on the lesser metatarsal heads. After arthrodesis the big toe bore weight in 80 per cent compared with 40 per cent after Keller's operation. The ability to bear weight on the big toe is related to the presence of metatarsalgia and excessive weight bearing on the lesser metatarsal heads. These complications were seen more commonly after Keller's operation (particularly when more than one-third of the phalanx had been excised) than after arthrodesis.

1. A series of 226 upper tibial osteotomies is reviewed with special reference to the complications occurring in each of the six different operative techniques that have been used.

2 Wedge osteotomy above the tuberosity is the safest operation, but care must be taken to avoid a fracture into the joint.

3. Wedge osteotomy through the lowest part of the tuberosity may be indicated in the presence of large subarticular cysts or collapse of a tibial condyle.

4. The significance of weakness of dorsiflexion of the foot and the dangers of injury to the anterior tibial artery in osteotomies below the tuberosity are discussed.

1. Arthrodesis of the first metatarso-phalangeal joint combined with excision of those lesser metatarsal heads with fixed subluxation and painful callosities is an excellent treatment for painful hallux valgus with metatarsalgia.

2. A series of thirty feet in twenty-five patients is reported in which this combined operation was done.

1. If osteoarthritis of the knee is confined mainly to one tibio-femoral compartment and the range of flexion is 90 degrees or more it can be treated safely and reliably by proximal tibial osteotomy.

2. The operation relieves pain in a large proportion of cases while retaining a useful range of knee flexion.

We are grateful to Miss H. M. Briggs, Research Secretary at Harlow Wood Orthopaedic Hospital, for secretarial assistance.

1. Four cases of congenital lateral dislocation of the patella are described.

2. The significance of the associated flexion contracture is emphasised.

3. Early diagnosis and operative realignment of the extensor mechanism is considered to be important because it should avoid the secondary growth changes which can produce serious disability.