Effects of intervertebral disc infection on the developing ovine spine.

STUDY DESIGN: A prospective in vivo animal study. OBJECTIVES: To determine whether infection in the juvenile spine influences spinal development. SUMMARY OF BACKGROUND DATA: Discitis is thought to occur in children when blood-borne infection penetrates the highly vascular immature disc. The condition generally resolves without apparent complication, but little is known about the long-term effects on the growing spine. METHODS: Twenty-nine 6-week-old lambs underwent discography at multiple lumbar levels using radiographic contrast deliberately inoculated with Staphylococcus epidermidis. No antibiotics were given. Plain radiographs were taken at intervals up to 52 weeks after inoculation for morphometric analysis of the vertebral bodies and discs, and the lumbar spines were prepared for histology. RESULTS: Sixteen of 44 inoculated discs showed radiological evidence of discitis between 2 and 6 weeks after inoculation. Disc height and disc area were significantly reduced from 2 weeks, and did not recover during the study period. Vertebral body dimensions and overall lumbar spine length were not significantly affected. CONCLUSION: Infection of juvenile ovine discs impedes disc development but has no significant effect on vertebral body growth.

Does intradiscal electrothermal therapy denervate and repair experimentally induced posterolateral annular tears in an animal model?

STUDY DESIGN: The effects of intradiscal electrothermal therapy (IDET) on intervertebral discs in sheep were studied experimentally. OBJECTIVES: Posterolateral annular lesions were experimentally induced and allowed to mature for 12 weeks in the intervertebral discs of sheep. IDET was performed in an attempt to denervate and repair the annular lesion. The histologic and immunohistochemical effects of IDET were studied. SUMMARY OF BACKGROUND DATA: IDET continues to be used as a minimally invasive treatment for chronic discogenic low back pain, with success rates reported in up to 70% of cases. The mechanism of action by which IDET exerts its effect is poorly understood. Proposed mechanisms include the contraction of collagen and the coagulation of annular nociceptors. An ovine model was used firstly to induce a posterolateral annular lesion, secondly to assess the innervation of such a lesion, and thirdly to assess the effect of IDET on this innervation. MATERIALS AND METHODS: Posterolateral annular incisions were made in 40 lumbar discs of 20 sheep. Twelve weeks were allowed for each annular lesion to mature. IDET was then performed in the disc with the posterolateral annular tear and in another control level. IDET was performed using a modified intradiscal catheter (Spine-CATH; Oratec Interventions, Menlo Park, CA). Temperatures were recorded in the nucleus (TN) and the posterior annulus (TPA). The spines were harvested at predetermined intervals up to 18 months. Histologic sections of the discs were graded for disc morphology to assess degeneration and immunohistochemical staining to assess potential denervation. RESULTS: Vascular granulation tissue consistent with a healing response was observed in the posterior annular tear of all incised discs from 12 weeks. Protein gene product 9.5 (PGP 9.5) positive nerve fibers were clearly identified in the adjacent periannular tissue and the outer few lamellae of the posterior annulus. During the IDET procedure, the mean maximum TPA was 63.6C and the mean maximum TN was 67.C.At sacrifice, the number of nerve fibers identified in the posterior annular tear was the same for those specimens that had undergone IDET and those that had not. From 6 weeks after IDET, there was evidence of thermal necrosisin the inner annulus and adjacent nucleus but sparing the periphery of the disc. CONCLUSIONS: Vascular granulation tissue and posterior annular neo-innervation was observed in the experimentally induced posterolateral annular lesion. IDET delivered at 90C in the sheep consistently heated the posterior annulus and the nucleus to a temperature normally associated with coagulation of nociceptors and collagen contraction. IDET did not denervate the posterior annular lesion. Thermal necrosis was observed within the inner annulus and adjacent nucleus from 6 weeks after IDET. The reported benefits from IDET appear to be related to factors other than denervation and repair.

The biologic response to particles from a lumbar disc prosthesis.

STUDY DESIGN: Particles of a proprietary polyolefin rubber compound used in a lumbar disc prosthesis were generated in vitro and tested for biocompatibility in two animal models. OBJECTIVE To characterize any tissue response to polyolefin rubber particles. SUMMARY OF BACKGROUND DATA: Intervertebral disc prostheses are emerging as alternatives to fusion techniques for the treatment of symptomatic disc degeneration. The biocompatibility of all novel components used in the construction of these devices must be verified before they can be considered for general use. METHODS: Laboratory-generated polyolefin rubber particles were either injected into dorsal subcutaneous air pouches of 30 rats or placed directly onto the lumbosacral dura and nerve roots of 9 sheep. Histologic sections of tissues from, and remote from, the site of implantation were examined for evidence of inflammation and wound-healing responses. RESULTS: Polyolefin rubber particle debris induced a tissue response that was consistent with a normal foreign body reaction to large particles. The response was not significantly greater than that seen with similar size particles of ultrahigh molecular weight polyethylene. There was no evidence of particle migration from the site of implantation, and there was no evidence of local or systemic toxic effects. CONCLUSION: Polyolefin rubber particles induce only localized tissue response that is consistent with a normal foreign body reaction to large nontoxic particles.