OBJECTIVETo compare the changes of nucleus pulposus after in vitro culture of rabbit whole intervertebral disc and spinal motion segment.

METHODSTwenty-one New Zealand white rabbits which were randomly divided into organ group with 8 rabbits and segment group with 13 rabbits. Fifty intervertebral discs and 50 spinal motion segments were harvested respectively under aseptic conditions from two groups. These specimens were maintained in organ culture with hyperosmotic media (410 mOsm/kg), then 10 discs of the two groups were observed respectively by HE staining, immunohistochemistry of collagen type III, proteoglycan content and cells viability of nucleus pulposus before culture and at 3, 7, 14, 21 days after culture.

RESULTSHE staining showed the intervertebral disc tissue structure remained intact after culture of 21 days organ group and 14 days segment group,but there was severely degenerated of 21 days segment group. The intensity value of type II collagen immunohistochemical staining in the nucleus pulposus were not changed significantly between 21 days organ group and 14 days segment group (P > 0.05), but the staining of segment group at 21 days became shallower, there was significant difference compared with before each time points and organ group at 21 days (P < 0.05). PAS/AB staining of proteoglycan of nucleus pulposus showed that there were not decrease of tinting strength of two groups within 7 days, but the strength weakened slightly of two groups at 14 days, and the tinting strength became weaker at 21 days segment group, the change is more obvious than the organ group. The intensity value of fluorescence staining of nucleus pulposus cells was not changed significantly within 7 days of two groups (P > 0.05), the intensity value decreased slightly at 21 days organ group and 14 days segment group, but there were no significant difference compared with before time points (P > 0.05) however at 21 days segment group the intensity decreased as cells viability of nucleus pulposus decreased,and there was a significant difference compared with before each time points and organ group at 21 days (P < 0.05).

CONCLUSIONIt is not obviously degenerated of the discs of organ group cultured within 21 days and segment group cultured within 14 days, but there was significant degeneration of the intervertebral disc of segment group after cultured 21 days, so the rabbit spinal motion segment can be used on research about the biomechanics of intervertebral disc as a vitro experimental model within 14 days.