Aims/background

Current treatment recommendations advocate various exercise modalities for people with chronic Low Back Pain (cLBP)1. Walking appears to represent an inexpensive and readily accessible activity for a range of individuals, including those who were previously sedentary. However, the effectiveness of such interventions are uncertain in cLBP.

The purpose of this study: is to test the hypothesis that there is little or no stress shielding afforded by a carbon composite femoral hip prosthesis when implanted in the human subject, and to investigate the possibility that a hydroxyapatite coating would prevent loosening.

The need for this development: is that loosening remains a problem for young patients who need a long term, reliable fixation of hip replacements, and it appears that if a solution exists to this problem then it probably lies away from the traditional cemented metal varieties.

One of the causes of loosening is stress shielding caused by rigid metal implants and a carbon composite femoral stem has been developed to overcome this. Paradoxically, flexible stems result in increased micro-motion at the prosthetic-bone interface and as a result they tend to loosen more frequently than metal ones. To overcome this, the carbon stem has been coated on its proximal third with hydroxyapatite, in order to get a secure fixation to the upper femur, but left bare distally to minimise weight transfer within the lower shaft.

The Study: 50 patients have entered the trial to date, and the detailed results of the first 35, which have been followed up for an average of 4 years will be presented. Stress shielding by the prosthesis was assessed, clinically, radiologically, and by dexa-scanning (usinga Hologic scanner with metal exclusion software). Two dexa-scan studies were carried out on each patient, at 1 and 2 years post operatively, and the bone mineral density of the implanted bone was compared with that of the normal contralateral side, using the Gruen zones as the basis of comparison. These results were compared with published figures for metal stems, and also with a small series of our own metal stems.

Results: 13 males and 22 females entered the trial, with an average age of 61.

Bone density around the carbon composite hip was found to increase by an average of 2% between the measurements carried out at 1 and 2 years post-op.

Conclusion: it appears that this prosthesis is fulfilling the predictions made for it, and although there is a spread of responses to it, the average patient is showing a steady increase in periprosthetic bone mineral density and is

Clinically asymptomatic. Progress to a wider trial can now be recommended.

We evaluated the effects of a serum protein coating on prosthetic infection in 29 adult male rabbits divided into three groups: control, albumin-coated and uncoated. We used 34 grit-blasted, commercially pure titanium implants. Eleven were coated with cross-linked albumin. All the implants were exposed to a suspension of Staphylococcus epidermidis before implantation.

Our findings showed that albumin-coated implants had a much lower infection rate (27%) than the uncoated implants (62%). This may be a useful method of reducing the infection of prostheses.

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.

We report the arthroscopic drilling of classical lesions of osteochondritis dissecans in 11 knees in 10 children with at least six months history and no sign of clinical or radiological improvement. There were eight boys and two girls and the average age at operation was 12 years 11 months. Relief of pain was noticed within days of operation; radiological healing occurred within 12 months in nine of the 11 knees.

We reviewed lesions of the femoral condyles seen in 5,000 knee arthroscopies, recording the findings and the age and sex of the patients. We were able to distinguish the characteristics of developing and late osteochondritis dissecans, acute and old osteochondral fractures, chondral separations, chondral flaps and idiopathic osteonecrosis, and suggest that these are separate distinct conditions. Haemarthrosis was associated only with acute osteochondral fractures. The characteristic feature of osteochondritis dissecans was an expanding concentric lesion at the 'classical' site on the medial femoral condyle which appeared during the second decade of life and progressed to a concave steep-sided defect in the mature skeleton. Caffey's (1958) classification of epiphyseal dysplasias could not be applied to osteochondritis dissecans, which appeared to have a gradual onset without acute trauma. Much of the controversy about the cause of osteochondritis dissecans is the result of imprecise nomenclature.

We have studied the kinematics of the knee in the sagittal plane, using a four-bar linkage as model, and assuming that a "neutral fibre" in each ligament remains isometric throughout flexion. We devised a computer program to calculate the distance separating any pair of points, one on each bone, for various cruciate attachments at various angles of flexion. The parameters for the linkage in four cadaveric knees were obtained by marking the centre of attachment of the cruciate ligaments with tacks and taking lateral radiographs. The movements of the bones were then calculated, in the computer model, for various attachments of "replacement" ligament fibres, the distance between the attachment sites being plotted against the angle of flexion. It was then possible to define zones around the isometric attachment points within which changes in length would be predictable. Our results show that the position of the femoral sites of attachment of both anterior and posterior cruciate replacement was more critical than that of the tibial attachments.

After a unicompartmental Oxford knee replacement, a clear lateral radiographic view of the components may be obtained without the shadow of prosthetic components in the other compartment. Radiographs of 20 knees were studied; with the patient supine and the muscles relaxed, views with the knee at full extension and 90 degrees of flexion were obtained and the movement of the meniscal bearings over this range of flexion was measured. The bearings were found to move backwards on the tibia through an average distance of 4.4 mm (range 0.0 to 13.5 mm) in the medial compartment and 6.0 mm (range 1.6 to 13.0 mm) in the lateral compartment. These movements were in the same direction as that observed in cadaver specimens but smaller in magnitude. At 90 degrees of flexion, radiographs were obtained with the tibia twisted manually to the limits of medial and lateral rotation. The average movement of the bearings between these extremes was found to be 6.6 mm in the medial compartment and 5.1 mm in the lateral; their movements on the tibia were in opposite directions in the two compartments. Bearing movement was still present in knees examined five years after operation.

Two-hundred and fifteen children with 288 unstable hips have been treated by splintage during the first nine months of life. A simple treatment protocol was followed and the aim was to test the safety and reliability of this protocol as well as of the Von Rosen splint and the Pavlik harness. A vascular necrosis occurred in 3.8% of the splinted hips. Despite splintage, a proportion of children needed operation at a later date.

Test results on carbon-fibre-reinforced plastic plates are presented, all of which had been used as semi-rigid fixation in a series of fractures of the middle third of the human tibia. Symptoms of pain experienced by the patients were found to be related to the stiffness of the plates and it is suggested that a stiffness of 2.0 newton-metres per degree is most suitable for this type of fixation of the tibia.