Effect Of Osteoporosis On The Normal Knee Articular Cartilage In Rats

Objective As our country has entered the aging society, the elderly-related diseases was increasing. Of these, osteoporosis and osteoarthritis are most common musculoskeletal diseases. In recent years, there were a lot of clinical investigations and animal experiments on the relationship between OA and OP. However, all the results reported are not consistent. The medical professions at home and abroad on the relationship between OA and OP have not yet formed a unified view. Animal model experiment is an effective method to study the relationship between OA and OP, Operation is a common means to establish the OA animal models, but the joint cartilage erosion after operation and post-menopause induced OA are not exactly the same. Ovariectomized rat is the most commonly used animal model to simulate post-menopausal OP. Recent researchs suggest that mature ovariectomized rats (over5months) can be used to make non-traumatic post-menopausal OA model. Although we already know that estrogen has a dual protective effects both on bone and cartilage, it is unclear if OP secondary to OA is due to estrogen deficiency. We try to investigate the the pathological changes of articular cartilage in ovariectomized SD rats and to explore the relationship between osteoporosis and degeneration of articular cartilage.Methods Twenty-four Sprague-Dawley female rats (6months old) were randomly divided into two groups. One is sham operation group (SHAM), the other is ovariectomized group (OVX). The rats in group OVX accepted bilateral ovariectomy operation through ventral operation approach after with5%chloral hydrate (7ml/kg) intraperitoneal injection of anesthesia. While the rats in group SHAM accepted resection the same amount of fat around bilateral ovarian by the same operation approach. Three months later, the models of osteoporosis were established. four rats were sacrificed in each group respectively after4、8、12post-operation and eliminated ligaments、meniscus and soft tissues.we acquired the distal femoral articular cartilage of rats, after gross observation of articular cartilage, we remove the lateral femoral condyle and reserve the medial femoral condyle. Each bone specimen was fixed in4%formalin solution for24hours and then decalcified for6weeks in an ethylenediaminetetraacetic acid (EDTA) solution. The decalcified knee joints were cleaved in a sagittal plane along the central portion of the articular surface of each medial femoral condyle corresponding to the weight bearing area, and following embedded in paraffin wax. Cartilage sections (5mm) were stained with hematoxylin and eosin to assess cellularity and structural abnormalities, and with safranin O to evaluate matrix abnormalities. Each specimen was histopathologically assessed using the Mankin’s grading system by an experienced cartilage pathologist. The observer was blinded for the treatment received by the rabbit group source and macroscopic description of the samples, which were presented in random order. The number of cartilage cells and subchondral trabecula and the thickness of total articular cartilage were measured under the microscope. Finially, we compare the differences between the the Mankin scores, the thickness of articular cartilage, the number of cartilage cells and the degree of sparse with subchondral trabecular bone in both groups.Results1. At12week, we measured the bone mineral density (BMD) of each rats respectively in two groups using dual energy X-ray absorptiometry(DEXA). The results showed that the BMD in femoral and tibial of group OVX are0.126±0.018g/cm2、0.115±0.012g/cm2, while the group SHAM are0.187±0.011g/cm2、0.146±0.011g/cm2. Compared with SHAM group, the BMD in group OVX was lower, there was statistically significant difference,(P＜0.05).2. At12week, the body mass of rats in the group OVX increased significantly than that in1week,(P<0.01). While the SHAM group showed no changes in body mass over time.3. Gross pathology: At4or8week, no abnormalities could be found on gross inspection both in the sham-operated controls and OVX group. There was no difference on the cartilage surface between the two groups. At12week, Rats in SHAM group shows the articular cartilage surface smooth, shiny, no erosion, while the OVX group shows that cartilage surface was discoloration, lost its brightness, thinned its thickness and exposed the colour of subchondral. In the weight-bearing area, fibrous tissue proliferation could be observed. Rats also revealed some areas of pitting and presented a small initial osteophyte at the medial rim of the femoral condyle.4. Histology: At4week, there was no significant difference on the cartilage and subchondral between the two groups. At8week, compared to group SHAM, rats in group OVX show the cartilage surface partial erosion,no smooth, tidemark line not integrity, cartilage cells decreased, subchondral trabecular sparse and the thickness of artiular cartilage thinning. The Mankin scores were significantly increased. At12week, in group OVX, the cartilage tidemark line disappeared, the cartilage cells significantly decreased, the subchondral trabecular became more sparse and the thickness of cartilage thinner. There were more significant differences on the Mankin scores between the two groups.Conclusions1. The femoral and tibial bone density decreased as the level of estrogen decreasing in ovariectomized rats, suggesting succeeded in duplicating the postmenopausal osteoporosis model.2. There was a gradual destruction of cartilage at the site of the weight-bearing of the femoral medial condyle in ovariectomized rats, showing that osteoporosis can cause normal cartilage degeneration and probably promote the occurrence of of osteoarthritis.3. The articular cartilage and subchondral bone appeared changes at the same time, and with a parallel relationship to each other, which shows cartilage and subchondral bone were both involved in the occurrence of OA, and there may be a certain interactive relationship between them.