Introduction: The operation method selected for acetabular revisions depends on the type of deþciency; Type 1: contained cavitary; the acetabular rim is preserved and thus supportive. Type 2: non-contained deþciencies; the acetabular rim and the peripheral zones are non- supportive defects. In non-contained, rim non-supportive defects acetabular reinforcement rings are used as a rule. Material and methods: Between July 1988 and December 1997 465 acetabular revisions with 229 Reinforcement Rings and 236 Press- Fit Cups (4 bilaterally) were performed. A 7.5 (5.0–10.8) year clinical and radiological follow-up of the Press-Fit Cup inserted in 130 women and 102 men was effected. Mean age at revisions surgery was 70 in women and 73 in men. 39 patients (17%) died without needing a re-revision, and 17 (7%) could only be interviewed by phone. One patient was lost to follow-up. Of the remaining 175 patients (75%) with 179 hips (76%) were available for complete evaluation. Results: The clinical results (according to Merle dñAubignŽ) was excellent and good in 82% 143 pts), moderate in 17% (30 pts) and poor in 1% (2 pts). 22 (9%) reinterventions were noted during the observation period: 12 for dislocations, 5 for aseptic stem loosening, 1 for septic loosening, 2 for secondary periprosthetic fractures and 2 for removal of heterotopic ossiþcations. Conclusions: No Press-Fit Cup had to be re-revised for aseptic loosening. Reconstruction for contained, rim supportive defects with the Press-Fit Cup provides excellent results, comparable to those of primary arthroplasties.

The longevity of the fixation of implants in a formerly dysplastic hip is compromised by several risk factors:

Young age.

Preoperative planning is mandatory. Procedure, choice of method, and availability of appropriate equipment and endoprosthetic implants must be ensured. Computerised tomography with 3-D reconstruction is recommended for more complex anatomical situations.

We used a rabbit model to investigate the mechanism by which the angulation of fractures is corrected in children. We produced a transverse proximal tibial fracture in one leg of 12 eight-week-old New Zealand white rabbits and measured bone alignment and length and the patterns of bone growth and remodelling.

The angle between the joint surfaces changed rapidly to correct the alignment of the limb as a result of asymmetrical growth of epiphyseal plates. In an adult with closed plates, the angle between the joint surfaces cannot therefore improve. The angle at the fracture itself showed slow improvement because of bone drift and the asymmetrical growth of the epiphyseal plates. Remodelling corrected the shape of the bone in the region of the fracture.

Periosteal division on the convex side increased the growth of the epiphyseal plate on that side, thus slowing the correction. The effect was relatively small, providing an indication that factors other than the periosteum are important in inducing correction.

External torsional deformities developed because of helical growth at the plate. This was probably caused by abnormal posture which induced a torque at the growth plate. Helical growth is the mechanism by which rotational deformities can occur and correct.

We reviewed the results of 545 consecutive total hip replacements using a cementless non-coated high-density polyethylene acetabular component combined with a cemented Muller stem at five to 10 years. In all, 421 patients (445 hips) were available for review, 118 by questionnaire and 303 by examination and radiography. Of these, 86% had a good or excellent result. We found a high rate of radiological loosening of the cup after the sixth year, and a high rate of clinical loosening after the eighth year. Loosening was commoner in women, in younger patients and where a smaller size of acetabulum had been used. Calcar resorption was significantly related to loosening of the acetabulum. Loosening appeared to be mainly due to polyethylene debris produced by micro-movement of the acetabulum against the bone, which had resulted in a giant cell foreign body reaction and subsequent bone erosion. We have abandoned the use of this prosthesis and suggest that direct contact between bone and polyethylene should be prevented by a coating of metal or some other material.

We subjected the proximal tibial growth plates of six-week-old rabbits to either compression or distraction of 1 kg on both legs. On one side the proximal tibial periosteum was divided circumferentially and stripped for 1 cm. After six weeks, growth was measured at both proximal and distal growth plates. Compression inhibited total tibial growth and distraction enhanced it. The compressed growth plate grew less and the distracted growth plate grew more, but there was a reciprocal change at the other end of the bone. Periosteal division enhanced growth at the adjacent growth plate but inhibited it distally; the effect of distraction was enhanced and that of compression reduced. We found reciprocal growth rates at the proximal and distal growth plates. Relatively small amounts of compression or distraction did affect total bone growth. Periosteal division appeared to induce overgrowth at least partly by a mechanical effect; it may be useful as an adjunct to other methods of leg lengthening, though not to epiphyseolysis.