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It is accepted that the development of scoliosis has a close relationship with physical growth, but the aetiology and mechanism of the disease remain unknown. Few studies have assessed the bone microarchitecture and histomorphological findings in vertebrae. After the occurrence of scoliosis, those include secondary changes caused by mechanical compression. It is important to investigate those data in the period prior to the occurrence of scoliosis.

Methods: Study One: One hundred female Broiler chickens were divided into 3 groups: the control group (n=20), the sham operation group (n=20), and the pine-alectomy group (n=60). Then the pinealectomy group was divided into three groups according to the time of sacrificing: one week after the operation (Group P-1w, n=20), two weeks and three weeks after the operation respectively (Group P-2w and 3w, n=20 respectively). Using microCT, the bone volume (BV/TV), trabecular thickness (Tb.Th), the number of trabecular (Tb.N), and trabecular separation (Tb.Sp) of the concave and convex sides of the apex vertebrae in the scoliotic chickens were determined.

Study Two: Sixty female Broiler chickens were divided into three groups: the control group (group C, n=20), the sham operation group (group S, n=20), and the pinealectomy group (group P, n=20). Each group was then subdivided into two groups according to the time of sacrificing: 3 days after the operation (group 3-C, 3-S, 3-P, n=10), and six days after the operation (group 6-C, 6-S, 6-P, n=10). Decalcified thin sagittal sections were made using a tartrate-resistant acid phosphatase (TRAP) stain. Histological examinations of the growth plate, trabecular structure and osteoclast number were performed.

Results: Study One: The incidences of scoliosis in the pine-alectomised Broiler chickens was 84.2% (Group P-1w), 88.9% (Group P-2w) and 89.5% (Group P-3w) respectively, and Cobb angles were averaged 11.6, 14.6 and 21.2 degrees respectively. There was no obvious wedging deformity of vertebrae in the groups. Only in Group 3w, the BV/ TV, Tb.Th and Tb.N of the concave side were significantly greater than those of the convex side.

Study Two: Nine out of ten chickens in group 6-P showed scoliosis deformity, while the presence of scoliosis was unclear in any of chickens in group 3-P. The osteoclast number increased significantly in group 3-P, compared to groups 3-C and 3-S, and the trabecular thickness was greater in group 3-P than in groups 3-C and 3-S. There was no significant change in the growth plate or in other aspects of the trabecular structure, except for trabecular thickness, in any of the groups.

The results of study one showed that the change of microarchitecture might be caused by Wolff’s law and was the secondary response to the scoliotic deformity. Therefore, it was difficult to clarify the cause of scoliosis using micro CT. In study 2 we found that the number of osteoclast increased in pinealectomised chickens after 3 days postoperatively, just before scoliosis began to develop. We also found there was no change in the growth plate. These outcomes suggest that there are no relationships between changes in the growth plate and the development of scoliosis. However, the change in osteoclast number may have a relationship with the development of scoliosis through changes in bone modelling.

Correspondence should be addressed to Jeremy C T Fairbank at The Nuffield Orthopaedic Centre, Windmill Road, Headington, Oxford OX7 7LD, UK