BACKGROUND:Needle-knife release of the ligamentum flavum can effectively improve symptoms in patients with lumbar degeneration,and ultrasound guidance can increase the precision of needle-knife release;however,the specific effects of needle-knife release of the ligamentum flavum on the degenerated intervertebral discs and the possible mechanisms remain to be clarified. OBJECTIVE:To investigate the effect of ultrasound-guided needle-knife release of the ligamentum flavum. METHODS:Twenty-four New Zealand rabbits were randomized into control(n=6)and model(n=18)groups.A rabbit model of lumbar disc degeneration model was established in the model group by cutting the supraspinous and interspinous ligaments of the L5/6 and L6/7 segments to maintain a standing posture and apply axial load to the lumbar spine.After successful modeling,the model rabbits were subdivided into a control group,a model group,an ultrasonic needle-knife group,and a sham needle-knife group according to a random number table method,with six animals in each group.The ultrasonic needle-knife group underwent ultrasound-guided needle-knife release of the right yellow ligament of L7/S1,once every week,for a total of four times.The needle-knife approach in the sham needle-knife group was the same as that in the ultrasound needle-knife group,but the ligamentum flavum was not released.At 30 days after the intervention,MRI was used to observe the changes in the signal intensity of the nucleus pulposus within the L7/S1 segment.Hematoxylin-eosin staining was used to observe the morphological changes of the L7/S1 segment.Immunohistochemical staining was used to detect the expression of type I and II collagen in the nucleus pulposus of the L7/S1 segment.RT-PCR and western blot were used to detect the expression of integrin α5 and β1,p38,and nuclear factor κB in the L7/S1 segment. RESULTS AND CONCLUSION:MRI findings indicated that the nucleus pulposus of the intervertebral disc of rabbits in the model group was gray-black in color,and the gray value of the nucleus pulposus was significantly lower than that of the control group(P<0.01).The brightness of the nucleus pulposus of the intervertebral disc of the rabbits in the ultrasonic needle-knife group was elevated compared with that of the model group,and the gray value of the nucleus pulposus was higher than that of the model group(P<0.01).Results from hematoxylin-eosin staining showed that in the model group,the shape of the nucleus pulposus was irregular,the number of nucleus pulposus cells was reduced,the extracellular matrix was compressed,the fibrous ring was ruptured,the structure and boundary of the end plate were unclear,and the chondrocytes were arranged disorderly.Compared with the model group,the ultrasonic needle-knife group showed an increase in the number of the nucleus pulposus,an improvement in the rupture of the fibrous ring,and more regular arrangement of cartilage endplate cells.Results from immunohistochemical staining showed an increase in positive expression of type I collagen(P<0.01)and a decrease in positive expression of type II collagen in the nucleus pulposus of the model group compared with the control group as well as a decrease in positive expression of type I collagen and an increase in positive expression of type II collagen in the nucleus pulposus of the ultrasonic needle-knife group compared with the model group(P<0.01).RT-PCR and western blot assays showed that the mRNA and protein expression of integrin α5,integrin β1,p38,and nuclear factor κB in the intervertebral discs of rabbits in the model group were increased compared with that in the control group(P<0.01);the mRNA and protein expression of integrin α5,integrin β1,p38,and nuclear factor κB in the intervertebral discs of rabbits in the ultrasonic needle-knife group was decreased compared with that in the model group(P<0.01).To conclude,ultrasound-guided needle-knife release of the ligamentum flavum can improve the degree of lumbar disc degeneration in rabbits,which may be related to the inhibition of p38 and nuclear factor-κB expression by modulating integrin α5 and β1 expression.