Innervation of anulus tears: an experimental animal study.

STUDY DESIGN: A prospective immunohistological study in an animal model. OBJECTIVE: To identify and describe the phenotype of neoinnervation in experimental anular tears. SUMMARY OF BACKGROUND DATA: Controversy surrounds neoinnervation of degenerate discs which has been proposed as the anatomic basis for discogenic pain. Ablation of neoinnervation has been postulated as the theoretical basis for the claimed successes of procedures such as intradiscal electrotherapy. The animal model of disc degeneration previously developed in our research center provides an opportunity to investigate the innervation of anular tears in an extensively characterized lesion. METHODS: A surgical anular tear was created in 5 lumbar discs in 11 sheep which were killed at 1, 2, 3, and 12 months. Each spine was x-rayed and divided into motion segments for histologic analysis. Serial sections through the tear were immunostained for protein gene product 9.5, tyrosine hydroxylase, and calcitonin gene receptor protein. RESULTS: Neoinnervation of the periphery of the anular tear was observed. Ingrowing nerves penetrated marginally deeper than the normal anular innervation but no nerves were identified in the inner anulus or nucleus. A minority of the new axons were calcitonin gene receptor protein or tyrosine hydroxylase positive. CONCLUSION: The anulus tears in this model are innervated only peripherally to a depth only marginally greater than that of the normal anulus.

Pinealectomy in the chicken: a good model of scoliosis?

The phenomenon of spinal deformity in the pinealectomized chicken has led researchers to postulate a disturbance of melatonin activity as a potential cause of adolescent idiopathic scoliosis (AIS). More recently, structural differences between curves seen in this model and those seen in scoliosis have been highlighted suggesting the deformities observed are not as similar as first thought. We examined melatonin levels, and the radiological and histological characteristics of scoliosis after pinealectomy in chickens. They underwent pinealectomy (P) at 2 days of age, sham surgery (S) or served as controls (C). Mean melatonin levels were 32.9 pmol/L (P), 175 pmol/L (S) and 227.3 pmol/L (C). Scoliosis developed in 75% of chickens after pinealectomy and 38% after a sham procedure. Nineteen percent of unoperated controls also developed scoliosis. A lower melatonin level was associated with the development of scoliosis (p < or = 0.001), but exceptions were seen with levels up to 265 pmol/L observed in one case. Most of the curves occurring spontaneously and after sham surgery and almost half after pinealectomy were short angular curves: distinct from those resembling idiopathic scoliosis. These occur over one or two segments and are characterized by marked apical wedging, frequently associated with subluxation or dislocation. The intervertebral joint in the chicken is more like a synovial joint histologically than an intervertebral disc. This study highlights important differences between the chicken and the human, and between their respective spinal deformities. Caution is advised when drawing conclusions regarding the pathogenesis of AIS from this model.

The jigsaw sign. A reliable indicator of congenital aetiology in os odontoideum.

There is evidence in the literature for both a congenital and a post-traumatic aetiology for os odontoideum. In no series published to date has CT been used to aid in the diagnosis. This is a prospective study of the history of trauma and presence of diagnostic features on CT of 18 consecutive cases with os odontoideum. Our objective was to derive clinically useful radiological features enabling accurate differentiation between congenital and post-traumatic aetiologies. A mid-sagittal CT reconstruction of the atlanto-dens joint was obtained. Hypertrophy of the anterior arch of the atlas was quantified by measurement of the arch-peg-area ratio. The presence of dysplastic features (a positive "jigsaw" sign) of the atlanto-axial joint were noted. These included narrowing of the cartilage space and interdigitation of the two joint surfaces. A history of a potential traumatic aetiology was only obtained in one of the 18 (6%) in our series. A significant elevation of the arch-peg ratio was found when comparing this series to 85 controls. And a positive jigsaw sign was observed in 75% of cases. These features were not seen in paediatric cases of atlanto-axial instability, including odontoid non-union. In conclusion, an elevated arch-peg ratio and the presence of a jigsaw sign are sensitive and specific diagnostic criteria for os odontoideum. This series supports a congenital aetiology for this condition.