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

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. 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: 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%. 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.