INTRODUCTION: In order to know the mechanisms underlying the growth modulation in pinealectomy model, we performed bone histomorphometric analysis with calcein labeling in T7 vertebral bodies before onset of marked scoliosis.
METHODS: The female broiler chickens were divided randomly into nonpinealectomized control group (n=8) and pinealectomy group (n=9). In the pinealectomy group, the operation was performed 3 days after hatching using the method reported by Machida et al in 1993. All chickens were double labeled with calcein at 5 and 7 days and killed 9 days after hatch. Growth modulations were measured under a fluorescent microscope in uncalcified mid‐sagittal sections of T7 vertebral bodies.
RESULTS: Under a fluorescent microscope, the calcein‐labeled area in T7 vertebral body was signifiantly greater in the pinealectomy group than in the control group (3.4% vs. 0.8%, p<0.05). In the calcein‐labeled area, chondrocytes remained in abnormal primary spongiosa occurring following pinealectomy. Average longitudinal growth width (L.G.W.) measured from the thickness of the unstained hypertrophic zone at both upper and lower growth plates was significantly reduced in the pinealectomy group than in the control group (72 microm/day vs. 106 microm/day, p<0.03). Average calcification rate in membranous ossification in ventral and dorsal surfaces, calculated as the interlabel width divided by the time (2) were signifiantly reduced in the pinealectomy group than in the control group (10 microm/day vs. 37 microm/day, p<0.0001). Typical histologies of upper and lower T7 endplates are shown in figure. (cont'd)
DISCUSSION: This study clearly demonstrated that pinealectomy disturbed endochondral and membrabous ossification. Remaining chondrocytes in abnormal primary spongiosa, which is considered to be mechanically fragile, may had crucial role in the pathogenesis of the spinal deformity after pinealectomy.