In severe destructive spinal infections, with neurological deficit, progressive deformity or uncontrolled sepsis, the mainstay of treatment is surgical debridement with anterior and posterior stabilisation. We retrospectively reviewed 14 patients (11 Male 3 female) with a mean age of 63 (range 38 to 85) who underwent anterior only surgery consisting of an expandable vertebral body cage and a ventrolateral locking plate (Synthes). Organisms included Tuberculosis (7), Staphylococcus (5), E-Coli (1) and Pseudomonas (1). Radiological and functional outcomes were assessed upto 18 months post surgery. Cobb angles were used to measure angular deformity.

Good early results in terms of safety, resolution of pain, control of deformity and improvement of neurological deficits was observed. Average blood loss was 633mls (range 300mls to 1500mls) with a mean deformity correction of 23 degrees. Post operative radiological assessment showed the cages to be relatively stable in the under 80 yrs groups (mean loss of correction 15 %). In elderly patients (> 80 yrs) there was significant subsidence leading to a loss of correction (mean 52%) which required stabilisation using vertebral body cement augmentation. In one case, there was implant displacement requiring revision and additional posterior stabilisation. 11 patients showed significant improvement in neurology and 3 patients remained neurologically normal ie Frankel E.

We propose assessing severe spinal infections using the spinal trilogy of neurological deficit, deformity and sepsis. Anterior stabilisation using an expandable cage and locking plate alone or with additional vertebral body cement augmentation in elderly patients provides a satisfactory solution for severe destructive spinal infections. It preserves the posterior column and reduces the need for further posterior surgery.

Introduction: Loads acting on scoliotic spines are thought to be asymmetrical and involved in progression of the scoliotic deformity. Abnormal loading patterns could lead to changes in bone and disc cell and activity and hence to vertebral body and disc wedging. At present however there are no direct measurements of intradiscal stresses or pressures in scoliotic spines.

Methods: Stress profilometry was used to measure horizontal and vertical stresses at 5mm intervals across 25 intervertebral discs of 7 scoliotic patients during anterior reconstructive surgery. Identical horizontal and vertical stresses for at least two consecutive readings defined a region of hydrostatic pressure. Results were compared with similar stress profiles measured during surgery across 10 discs of 4 spines with no lateral curvature and with data from the literature.

Results: Profiles across scoliotic discs were very different from those measured across normal discs of a similar age. Hydrostatic pressure regions were only seen in 16/25 discs, extended only over a short distance and were displaced towards the convexity. Mean pressures were significantly greater (0.24MPa) than those measured in other anaesthetised patients (< 0.06 MPa). A stress peak in the concave annulus was a common feature (13/25) in scoliotic discs. In 21/25 discs, stresses in the concave annulus were greater than in the convex annulus, indicating asymmetric loading in these anaesthetised, recumbent patients.

Conclusions: Intradiscal pressures and stresses in scoliotic discs are abnormal even in the absence of significant applied load. Disc cells respond to changes in pressure, hydration and deformation by altering matrix synthesis and turnover in vivo and in vitro. Hence, whatever the cause of the abnormal pressures and stresses in the scoliotic discs, if present during daily life, these could lead to disc matrix changes and especially if asymmetrical, to disc wedging and progression of the scoliotic deformity.

Work supported by Fondation Cotrel

Introduction: Lateral insufficiency fractures following total hip replacements have been reported with the femoral stems positioned in varus, together with osteopenia of the lateral femoral cortex. Any abnormal alignment of the lower limbs, such as genu valgum, will alter the load distribution across the femoral cortices, and repetitive loading during walking will predispose the bones to stress fractures at any stress riser point, such as the tip of a femoral component. Bilateral femoral stress fractures post total hip replacements have not been previously described

Materials and Methods: We present a 55 yr old lady, diagnosed with juvenile idiopathic arthritis aged 5 years, and had undergone bilateral total hip replacements at the age of 29 and 30 years and bilateral knee replacements aged 37 and 42 years. The right hip required revision of the cup 15 years later. The knees were in valgus and the left knee was extremely stiff flexing to just 5 degrees. She presented to us as an emergency with bilateral thigh pain with plain radiographs confirming bilateral peri-prosthetic fractures of the femur at the tip of well fixed femoral components. There had been no history of injury and her hips were functioning well up to this time.

Results: The patient required revision of both hips to long stem un-cemented components, bypassing the fractures, and revision of both knees to stemed seni-constrained implants, thereby correcting the alignment of both lower limbs.

Both fractures healed and the patient is currently pain free and mobile with walking aids.

Discussion: Surgeons must remain aware that when implants are in situ, abnormal alignments will lead to abnormal forces, and stress fractures are likely to occur at any stress riser around the implant. Avoiding mal-alignment will avoid this complication.

Bilateral peri-prosthetic stress fractures following total hip replacements have not been previously reported.

Purpose: The inflammatory response around herniated tissue in the epidural space is believed to play a major role in the spontaneous regression of herniated lumbar disc. Numerous macrophages invade the herniated tissue along with newly formed blood vessels which influence oxygen gradient. Inflammatory cytokines such as interleukin-1 are produced by macrophages. These chemical mediators could stimulate disc cells to produce proteases such as MMPs which degrade the intervertebral disc matrix and could hence influence regression of the herniation. Here we have examined the influence of IL-1β and oxygen tension on proteoglycan turnover using a three-dimensional disc-cell culture system.

Methods: Cells were isolated from the nucleus pulposus of 18–24 month bovine caudal discs by enzyme digestion. They were initially cultured for 14 days in alginate beads in DMEM containing 6% FBS at 4.10⁶ cells/ml under 21% oxygen to accumulate matrix. They were then cultured for 6 days under 0% or 21% oxygen and with or without IL-1β. Glycosaminoglycan (GAG) accumulation (as a measure of proteoglycan content) was measured using a DMB assay. Lactate and glucose production were measured using a standard enzymatic method. Rates of sulfated GAG synthesis was measured from rates of ³⁵S-sulfate accumulation. MMP activity was measured using coumarin fluorescent assay.

Results: The results showed that IL-1β had a significant effect on GAG accumulation and production and that its effect was dependent on oxygen tension. GAG production and sulfate incorporation rates decreased in the presence of IL-1β at high oxygen but low oxygen inhibited the effects of this cytokine. MMP activity increased with IL-1β under 21% oxygen, but not at low oxygen.

Conclusion: Exogenous IL-1β can activate MMP activity and digest the extracellular matrix of the disc but only at high oxygen tensions. Angiogenesis as well as inflammation is thus required for resorption of herniations.

Scoliosis is a disease characterised by vertebral rotation, lateral curvature and changes in sagittal profile. The role of mechanical forces in producing this deformity is not clear. It is thought that abnormal loading deforms the disc, which becomes permanently wedged. Modelling and in vitro studies suggest that such deformations should increase intradiscal pressure. Intradiscal pressure has been measured previously in a variety of clinical environments. The aim of this study is to measure pressure profiles across scoliotic discs to provide further information on the role of mechanical forces in scoliosis.

Pressure readings were obtained in consented patients with ethical approval using a needle-mounted sterilised pressure transducer (Gaeltec, Dunvegan, Isle of Skye) calibrated as described previously. The transducer needle was introduced into the disc of an anaesthetised patient during routine anterior scoliosis surgery and pressure profiles measured. Signals were collected, amplified and analysed using Power-lab and a laptop computer.

Pressure profiles across 10 human scoliotic discs from 3 patients have been measured to date. Pressures varied from 0.1 to 1.2 MPa.

Annular pressures showed high pressure, non-isotropic regions on the concave but not convex side of these discs.

Nuclear pressures recorded from the discs of these scoliotic patients were higher than those recorded previously in non-scoliotic recumbent individuals.

Glycosaminoglycans (GAGs) govern the osmotic environment of cartilaginous tissues and hence determine their ability to resist the large compressive forces encountered during normal activity. In degeneration GAGs are lost and there is now much interest in biological repair processes where cells from cartilaginous tissues synthesise replacement GAGs and other matrix components in situ. In addition, cells can be grown in tissue engineered constructs. Unfortunately, GAG synthesis is slow.

The aim of this study was to determine whether GAG accumulation could be hastened by increasing cell density in a construct using articular cartilage and intervertebral disc cells cultured in alginate beads.

Bovine chondrocytes and intervertebral disc cells were placed in alginate bead suspension at varying cell densities. GAG synthesis rates, total GAG accumulation and lactate production rates were determined by standard methods. The cell viability profile across intact beads was determined using fluorescent probes.

Increasing cell density causes a reduction in lactate production and sulphate incorporation per million live cells. At greater than 20 million cells per ml, cell death is increased compared with lower densities. GAG produced per bead is not increased in proportion to increasing cell density.

These results show that there is a limit to the rate at which matrix per volume of tissue can be produced and accumulated. At high cell densities cellular activity is limited by toxicity arising from low pH and hypoxia.