The relationship between structural changes in paraspinal muscles and intervertebral disc and facet joint degeneration in the lumbar spine of rats.

BACKGROUND: Degenerative spine disease is one of the largest causes of disability worldwide and has a multifactorial aetiology. Determining the leading causes of this multifactorial disease could help create new treatment approaches. PURPOSE: Study the impact of degenerative changes in the paraspinal muscles caused by local (prolonged compression) or systemic (high-fat diet) factors on the structure of the intervertebral discs (IVDs) and facet joints of the lumbar spine in rats. METHODS: The study was conducted using two animal models to create degenerative changes in the paraspinal muscles of 10 white laboratory rats for 90 days and five control rats: 1) high-fat diet model (model 1) involved keeping the rats on a high calorie diet; 2) compression model (model 2) involved binding the paraspinal muscles from L2 to S1 using non-absorbable sutures. Histological analysis for the facet joints and IVDs of rats (at the L1-L4 level) with semi-quantitative analysis of the structure conducted used by degeneration grading system for IVDs and cartilage degeneration score (OARSI) for facet joint. RESULTS: In both models, 90 days after the experiment, the degenerative changes observed in the rats' IVDs were more severe in the annulus fibrosus than in the nucleus pulposus. The height of the IVD in model 1 did not differ from the control group, but in the model 2 was 1.3 times greater (p < 0.001) compared with control. Degenerative changes in the IVD were scored out 5.3 ± 1.7 in model 1 and 5.32 ± 2.1 in model 2 of a possible 16. The height of the articular cartilage of the facet joints was smaller by 1.5 times (p < 0.001) and 1.4 times (p < 0.001) in model 1 and model 2, respectively, compared to the control. Degenerative changes of facet joint were scored out 3.7 ± 0.6 in model 1 and 3.8 ± 0.6 in model 2 of five points according to the cartilage degeneration score. CONCLUSIONS: It was determined that rats who had structural changes in the lumbar paraspinal muscles as a result of being kept on a high-fat diet or subjected to prolonged compression for 90 days, showed degenerative changes in intervertebral discs and osteoarthritis in facet joints of lumbar spine.

Histological evaluation of the incorporation and remodeling of structural allografts in critical size metaphyseal femur defects in rats of different ages.

Insufficient bone regeneration is a common issue for patients with extensive bone damage, therefore the use of allografts is required. With increasing life expectancy, there is a higher risk of bone repair issues after fractures or orthopedic surgical intervention. We studied incorporation and remodeling of structural allografts in critical size metaphyseal femur defects in 52 rats aged 3-month-old and 12-month-old who underwent surgeries creating a bone defect, which was either filled with a structural allograft (3-month-old - 3moAllo; 12-month-old - 12moAllo) or left empty (3-month-old - 3moE; 12-month-old - 12moE). Histological analyses were performed 14, 28 and 90 days after the surgery. The percentage of bone and fibrous tissues, and allograft relative to the defect area was evaluated. The transmission electron microscopy was carried out 14 days after allograft implantation. When the defect was empty, slower bone regeneration was observed in 12moE rats versus 3moE, leading to sufficient irregularities in the anatomic structure of the femur 90 days after the surgery. When a structural allograft was used, the area of the fibrous tissue was larger in the defects of 12moAllo compared with 3moAllo rats 90 days after surgery. No age-related differences were found in the allograft remodeling and structures of the osteocytes, osteoblasts, and osteoclasts over the observation period. Evident issues with bone regeneration were found in critical size defects both of 12moE and 12moAllo rats. However, the allograft use allowed the bone maintaining anatomic structure 90 days after the surgery.

MODELS OF PARASPINAL MUSCLE DEGENERATION IN RATS: HIGH-FAT DIET AND PROLONGED COMPRESSION.

OBJECTIVE: The aim: To study the structural features of the lumbar m. multifidus and the m. psoas after keeping rats on a high-fat diet (obesity) or compressing their lumbar paraspinal muscles by binding the muscles using non-absorbable sutures. PATIENTS AND METHODS: Materials and methods: The study was performed on 2-month-old male rats (n=15) into three groups of 5: control group (normal diet without any surgical interventions), high-fat diet (model I: 40-45% kcal fat), and paraspinal muscles compression (model II: paraspinal muscles were tied from L2 to S1 with non-absorbable sutures Nurolon® 3). The experiment lasted for 90 days, after those fragments of the lumbar m. multifidus and m. psoas removed and histomorphometry analysis performed. RESULTS: Results: 12 weeks from the beginning of the experiment, the high-fat diet rats weighed, on average, 22% (p=0.001) more than the control group rats. Similar degenerative changes such as uneven muscle fibre width and sarcoplasm colouring, 'wavy' and swollen fibres, loss of striation, karyopyknosis were observed in the lumbar paraspinal muscles in both models. In high-fat diet group the fat area (%) in the m. multifidus was 1.8 times larger (р<0.001) and in the m. psoas was greater by 2.2 times (р<0.001) than in the control. Fibrous tissue replaced muscle fibres in m. multifidus in model II and was 12.66%. CONCLUSION: Conclusions: The relevance of the models is proven: after 3 months, it is possible to obtain degenerative changes in the muscle tissue that are extremely similar to those observed in the muscles of patients with degenerative spine diseases.