Study design: Pinealectomy was used to induce scoliosis in Broiler chickens, and a histologic investigation of the pinealectomized chickens was performed.
Objectives: To investigate the incidence of scoliosis in pinealectomized Broiler chickens and to determine histologic changes in vertebrae in the pinealectomized chickens before the occurrence of a secondary vertebral wedging deformity due to scoliosis.
Summary of background data: White Leghorn chickens have previously been used as an experimental model of scoliosis, but the occurrence of scoliosis in these chickens following pinealectomy has varied in different reports and is not always high. It is accepted that the development of scoliosis has a close association with growth, but the etiology and mechanism of the disease remain unknown. Histologic findings in vertebrae after the occurrence of scoliosis include those caused by secondary changes due to mechanical compression, and no histologic data for the period before the occurrence of scoliosis are available.
Methods: Study 1. A total of 100 female "Broiler" chickens were pinealectomized, and the frequency with which scoliosis occurred was investigated. Study 2. 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 death: 3 days after the operation (Group 3-C, 3-S, 3-P, n = 10), and 6 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. Histologic examinations of the growth plate, trabecular structure, and osteoclast number were performed.
Results: The incidence of scoliosis in the pinealectomized Broiler chickens was 93.6%. Nine of the 10 chickens in Group 6-P showed scoliosis deformity, while the presence of scoliosis was unclear in chickens in Group 3-P. The osteoclast number increased significantly in Group 3-P, compared with 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.
Conclusions: The results show that the incidence of scoliosis using pinealectomized Broiler chickens is sufficient to study histologic changes of the vertebral body before onset of scoliosis. We found that the osteoclast number and trabecular thickness increased in pinealectomized chickens after 3 days after surgery, just before scoliosis began to develop, and that no change in the growth plate occurred. This suggests that there is no association between changes in the growth plate and the development of scoliosis. However, the change in osteoclast number may have an association with the development of scoliosis, through changes in bone modeling.