A modification of a previously reported one-stage technique for reduction and stabilisation of severe spondylolisthesis using a posterior route is described. Reduction is obtained by inserting Harrington rods to lift L5 vertically out of the pelvis and two double-threaded screws to pull it backwards. After reduction the rods are taken away and stabilisation achieved by means of screws and a sacral bar. With this modified technique lumbar vertebrae above L5 are never immobilised, compared with the previous method where the retention of the Harrington rods resulted in more lumbar vertebrae being immobilised than was necessary for fusion. Bone is resected from the sacrum and the fifth lumbar vertebra to avoid too much tension on the nerve roots. Bone grafts are not needed and lumbosacral fusion is achieved within six months due to close contact between the raw bone of the vertebral bodies. Three patients have been treated with this modified technique; there was no reslip, neither during the period when the metallic fixation was in situ nor after its removal.

The different methods described in the literature for the reduction of severe spondylolisthesis are reviewed. The case histories of two girls with neurological deficits in their legs due to Grade IV spondylolisthesis are described. Reduction and fusion by the posterior route in a one-stage operation were performed on these patients. For this purpose special instruments have been designed to exert a controlled force on the displaced vertebra in two perpendicular directions. Technical details of the procedure are reported. In both patients intervertebral and posterolateral fusion were carried out. Fusion was successful and redisplacement did not occur. There have been only few descriptions in the literature of a technique that reduces and stabilises spondylolisthesis in one stage. However, only patients with Grade III and IV spondylolisthesis require reduction and in less severe cases fusion without reduction is sufficient.

1. Dislocation and subluxation of the hip has been produced in young rats by application of splints reaching from the hip to the foot, bringing the hip into extension.

2. Progressive acetabular dysplasia and anatomical abnormalities of the head and neck of the femur occurred.

3. Results of the experiments suggest that post-natal extension of the hip is of importance in the pathogenesis of congenital dislocation of the hip in man.