The effects of osteoporosis and disc degeneration on vertebral cartilage endplate lesions in rats

Evidence has shown that osteoporosis or intervertebral disc degeneration (IDD) led to cartilage endplate lesions (CEL), but their combined effects on the lesion remain unknown. This study developed an innovative rat model combined ovariectomy (OVX) and cervical muscle section (CMS), and aimed to evaluate the combined effects of osteoporosis and IDD on cartilage endplate lesions of cervical spine. Fifty-two Sprague-Dawley female rats were assigned randomly into four groups as follows: the sham group (n = 10) underwent sham surgery; the OVX group (n = 14) was subjected to bilateral ovariectomy; the CMS group (n = 14) had posterior paraspinal muscles cut from C2 to C7; the CMS-OVX group (n = 14) underwent the OVX and CMS surgeries consecutively. Samples of C6-C7 segments were harvested at 12, 18 and 24 weeks post-surgery. Micro-CT analysis was performed to evaluate the CEL, intervertebral disc height (IDH) and structural indices. Histological analysis with Safranine O/fast green stain and histological score were used to observe the characteristics of the degenerative discs. Ovariectomy surgery resulted in significant changes of most structural indices of the C6 body, such as decrease of percent bone volume and number of bone trabecula at 12 weeks, and greater changes at 18 and 24 weeks. The CEL following CMS surgery was seen on the ventral, while the CEL in the OVX and sham groups on the peripheral. The CEL was greatest in the CMS-OVX group and significantly greater than that in the CMS and OVX groups at 12 and 18 weeks (P < 0.05). The CMS surgery resulted in significant IDH decrease at 12, 18 and 24 weeks (P < 0.05), while the OVX surgery resulted in mild IDH decrease when compared with the sham group. The IDH in the CMS-OVX group was significantly lower than that in the CMS group at 24 weeks (P < 0.05). Histological evaluation suggested cartilage endplate abrasion at 12 weeks, and in situ calcification at 18 and 24 weeks in the CMS and CMS-OVX groups. Disc degenerative scores were higher following CMS or OVX surgery, and correlated with the CEL and IDH (P < 0.01), respectively. The present study suggested that a combination of OVX and CMS led to more lesion of cartilage endplate than any one thereof, as well as more decrease of IDH. The lesion and IDH decrease were associated with the disc degeneration levels. The cartilage endplate was worn out at the early stage and calcified in situ later. The results indicate that osteoporosis may deteriorate the disc degeneration at specific time.