Effect of repeated sciatic nerve crush on the conditioning lesion response: Generating an experimental animal model to prolong the denervation period while maintaining peripheral nerve continuity.

Peripheral nerves exhibit long-term residual motor dysfunction following injury. The length of the denervation period before nerve and muscle reconnection is an important factor in motor function recovery. We aimed to investigate whether repeated nerve crush injuries to the same site every 7 days would preserve the conditioning lesion (CL) response and to determine the number of nerve crush injuries required to create an experimental animal model that would prolong the denervation period while maintaining peripheral nerve continuity. Rats were grouped according to the number of sciatic nerve crushes. A significant decrease in the soleus muscle fiber cross-sectional area was observed with increased crushes. After a single crush, macrophage accumulation and macrophage chemotaxis factor CCL2 expression in dorsal root ganglia were markedly increased, which aligned with the gene expression of Ccl2 and its receptor Ccr2. Macrophage numbers, histological CCL2 expression, and Ccl2 and Ccr2 gene expression levels decreased, depending on the number of repeated crushes. Histological analysis and gene expression analysis in the group with four repeated crushes did not differ significantly when compared with uninjured animals. Our findings indicated that repeated nerve crushes at the same site every 7 days sustained innervation loss and caused a loss of the CL response. The experimental model did not require nerve stump suturing and is useful for exploring factors causing prolonged denervation-induced motor dysfunction. SIGNIFICANCE STATEMENT: This study elucidates the effects of repeated nerve crush injury to the same site on innervation and conditioning lesion responses and demonstrates the utility of an experimental animal model that recapitulates the persistent residual motor deficits owing to prolonged denervation without requiring nerve transection and transection suturing.

Chronic Ankle Joint Instability Induces Ankle Sensorimotor Dysfunction: A Controlled Laboratory Study.

BACKGROUND: Chronic ankle instability (CAI) is a clinical sequela that causes the recurrence of ankle sprain by inducing ankle sensorimotor dysfunction. Animal models of CAI have recently shown that ankle ligament injuries mimicking an ankle sprain result in chronic loss of ankle sensorimotor function. However, the underlying mechanisms determining the pathogenesis of CAI remain unclear. HYPOTHESIS: Ankle instability after an ankle sprain leads to the degeneration of the mechanoreceptors, resulting in ankle sensorimotor dysfunction and the development of CAI. STUDY DESIGN: Controlled laboratory study. METHODS: Four-week-old male Wistar rats (N = 30) were divided into 2 groups: (1) the ankle joint instability (AJI) group with ankle instability induced by transecting the calcaneofibular ligament (n = 15) and (2) the sham group (n = 15). Ankle instability was assessed using the anterior drawer test and the talar tilt test at 4, 6, and 8 weeks after the operation (n = 5, for each group at each time point), and ankle sensorimotor function was assessed using behavioral tests, including ladder walking and balance beam tests, every 2 weeks during the postoperative period. Morphology and number of mechanoreceptors in the intact anterior talofibular ligament (ATFL) were histologically analyzed by immunofluorescence staining targeting the neurofilament medium chain and S100 proteins at 4, 6, and 8 weeks postoperatively (n = 5 per group). Sensory neurons that form mechanoreceptors were histologically analyzed using immunofluorescence staining targeting the mechanosensitive ion channel PIEZO2 at 8 weeks postoperatively (n = 5). RESULTS: Ankle sensorimotor function decreased over time in the AJI group, exhibiting decreased ankle instability compared with the sham group (P = .045). The number of mechanoreceptors in the ATFL was reduced (P < .001) and PIEZO2 expression in the sensory neurons decreased (P = .008) at 8 weeks postoperatively. The number of mechanoreceptors was negatively correlated with ankle sensorimotor dysfunction (P < .001). CONCLUSION: The AJI model demonstrated degeneration of the mechanoreceptors in the ATFL and decreased mechanosensitivity of the sensory neurons, which may contribute to CAI. CLINICAL RELEVANCE: Ankle instability causes degeneration of mechanoreceptors and decreases the mechanosensitivity of sensory neurons involved in the development of CAI. This finding emphasizes the importance of controlling ankle instability after ankle sprains to prevent recurrence and the onset of CAI.

The infrapatellar fat pad contributes to spontaneous healing after complete anterior cruciate ligament injury.

Anterior cruciate ligament (ACL) injuries have a very low healing capacity but have recently been shown to heal spontaneously with conservative treatment. This study examined the mechanism of spontaneous ACL healing by focusing on the intra-articular tissues of the knee joint. Skeletally mature Wistar rats (n = 70) were randomly assigned to two groups: the controlled abnormal movement (CAM) and anterior cruciate ligament transection (ACLT) groups. The ACL was completely transected at the mid-portion in both groups. Only the CAM group underwent extra-articular braking to control for abnormal tibial translation. The animals were allowed full cage activity until sacrifice for histological, and molecular biology analyses. The results showed that the behavior of the stump after ACL injury differed between models 12 h after injury. The femoral stump in the ACLT group retreated posteriorly and upwardly. Macrophage polarity analysis revealed that the stump immune response in the CAM group was more activated than that in the ACLT group 6 h after injury. Microarray analysis of the ACL parenchyma and infrapatellar fat pads suggested the involvement of nuclear factor kappa B (NF-κB) signaling. Real-time polymerase chain reaction (PCR) analysis showed that NF-κB gene expression in the infrapatellar fat pad was significantly increased in the CAM group than in the ACLT group. However, there was no difference in the gene expression levels in the ACL parenchyma between models. In conclusion, the healing response of the ACL was activated within 12 h of injury, resulting in differences in the healing response between the models. It has been suggested that infrapatellar fat pads are involved in the healing process and that angiogenesis and antiapoptotic effects through NF-κB signaling may contribute to this mechanism.