[Biomechanical mechanism of acupotomy on cartilage degeneration in KOA rabbits based on three-dimensional finite element model]

To observe the effect of acupotomy on cartilage degeneration in rabbits with knee osteoarthritis (KOA) from the perspectives of force line and knee joint stress distribution, and to explore the biomechanical mechanism of acupotomy for KOA.

A total of 24 male New Zealand rabbits were randomly divided into a normal group, a model group, an electroacupuncture (EA) group and an acupotomy group, 6 rabbits in each group. Except for the normal group, in the other 3 groups, the left hind limbs were immobilized for 6 weeks to establish KOA model using the modified Videman method. In the EA group, EA was applied at left "Neixiyan" (EX-LE4), "Dubi" (ST35), "Zusanli" (ST36) and "Yanglingquan" (GB34), with disperse-dense wave, in frequency of 2 Hz/100 Hz and current of 3 mA, 20 min each time, once every other day. In the acupotomy group, acupotomy intervention was delivered at the insertion site of the vastus medialis tendon, insertion site of the vastus lateralis tendon, etc. of the left knee joint, once a week. The interventions lasted for 3 weeks in the EA group and the acupotomy group. Before and after intervention, the Lequesne MG score was observed. After intervention, the force line angle of knee joint was measured by magnetic resonance imaging (MRI); the stress distribution of the knee joint was observed by the three-dimensional finite element analysis; the morphology of knee joint cartilage was observed by HE staining; the protein expression of type Ⅱ collagen (Col-Ⅱ) and Aggrecan in the knee joint cartilage was detected by Western blot.

Compared with the normal group, the Lequesne MG score was increased (P<0.01), the knee joint force line angle was increased (P<0.05), and the protein expression of Col-Ⅱ and Aggrecan in the knee joint cartilage was decreased (P<0.01) in the model group. Compared with the model group, the Lequesne MG scores were decreased (P<0.05, P<0.01), the knee joint force line angles were decreased (P<0.05), and the protein expression of Col-Ⅱ and Aggrecan in the knee joint cartilage was increased (P<0.05) in the EA group and the acupotomy group. All the above indexes in the acupotomy group were superior to those in the EA group (P<0.05). Severe cartilage damage, disordered arrangement of chondrocytes and unclear tide line could be observed in the model group. Compared with the model group, the damage of knee joint cartilage was alleviated, the arrangement of chondrocytes was more orderly and the tide line was clearer in the EA group and the acupotomy group, and the improvement of knee joint cartilage damage in the acupotomy group was superior to that in the EA group. Compared with the normal group, in the model group, the peak Von Mises stress and peak contact stress, the stress value and the contact stress value in the high-stress areas of the knee joint were increased (P<0.05), the stress was more concentrated. Compared with the model group, in the EA group and the acupotomy group, the above stress-related indexes were decreased (P<0.05), the stress concentration was relieved, and those in the acupotomy group were superior to the EA group (P<0.05). Compared with the normal group, in the model group, the ratios and the contact areas of the medial and lateral condyles of the meniscus, femoral cartilage and tibial cartilage were significantly deviated. Those in the EA group and the acupotomy group tended to be more similar to the normal group, and those in the acupotomy group were superior to the EA group.

Acupotomy can correct the knee joint force line, improve the stress concentration, delay cartilage degeneration of the knee joint, thereby improving the symptoms of KOA.