Intramuscular Nerve Effect On Muscle Injury And Repair

At the present time the therapeutic efficacy of lacerated skeletal muscle is suboptimal in clinic. This poor outcome is ascribed to three factors: the difficulty in suturing muscle tissue that holds sutures poorly, the development at the repair site of a fibrous scar that impedes muscle fiber regeneration, and the denervation of the distal segment that results in muscle atrophy. Previous research studies has mainly focused on the first two factors to decrease fibrosis or improve muscle fiber regeneration. Antifibrotic agents have been used in experimental studies and have shown a reduction in muscle fibrosis at the laceration site. However their role in the distal segment is yet to be studied. Muscle has potential to regenerate itself after injury. The nucleolus of skeletal muscle fiber doesn't synthesize the DNA, nor develop karyokinesis. The only source of skeletal muscle regeneration of the adult advanced vertebrate is muscle satellite cell, but without innervation, the regeneration process cannot develop further and the myotube will be replaced by connective tissue scar and adipose tissue. It is thus evident that the nerve is very important to the regeneration of skeletal muscle. Presently little is known about the role of the intramuscular nerve which may concomitantly be severed in the lacerated skeletal muscle. This study will determine the effect of the lacerated skeletal muscle recovery at the condition of preservation intramuscular nerve or not, to evaluate the role of the intramuscular nerve to the lacerated skeletal muscle recovery, and accordingly offer direction on what needs to be done in the future in these situations where the main intramuscular nerve is concomitantly severed in the lacerated skeletal muscle.Objective: To determine the intramuscular nerve effect on the recovery of lacerated muscle.Method: Twenty (20) healthy New Zealand rabbits were involved in the study and randomly divided into groups A and B. The right musculus rectus femoris of the animal was chosen as the lacerated skeletal muscle model with the contralateral muscle as a sham control. Group A underwent incomplete muscle laceration with the intramuscular nerve preserved intact; group B underwent complete muscle laceration with the intramuscular nerve cut concomitantly. After a postoperative period of ~28 weeks, measured the muscle wet weight, determined the muscle strength of musculus rectus femoris by electrical stimulation test and observed the change of morphology by Hematoxyline/eosin stain,Masson stain, NADH-TR stain and mATPase stain. Compared the difference of two groups through t-test and ANOVA to decide the effects of intramuscular nerve effect on muscle injury and repair. Results: At 28 weeks postoperative,the wet weight of musculus rectus femoris of the model side of group A was 9.96±0.96g , the control side was 10.85±0.94g, t-test:t=2.252,P>0.05;the muscle's isometric contraction force of the model side of group A was 8.22±0.85N, the control side was 8.86±0.61N, t-test:t=2.258,P>0.05;the type I muscle fiber's CSA of model side was 2742.78±146.62μm2,the type IIa CSA was 2793.11±115.00μm2; the type IIb CSA was 4492.44±364.03μm2,the ratio of I:II was 21 :79;the type I muscle fiber's CSA of control side (for A,B group sharing)was 2732.12±158.51μm2,the type IIa CSA was 2901.41±153.08μm2,the type IIb CSA was 5303.53±206.74μm2,the tario of I:II was 19:81;t-test :for the type I, t=1.161,p>0.05,for the type IIa, t=2.210,p>0.05,for the type IIb , t=5.348,p<0.05;showed numerous centronucleated regenerating myofibers. the wet weight of musculus rectus femoris of the model side of group B was 7.29±1.03g , the control side was 10.91±1.11g, t-test:t=25.061,P<0.05;the muscle's isometric contraction force of the model side of group B was 5.98±0.78N N, the control side was 8.98±0.37N, t-test:t=11.658,P<0.05;the type I muscle fiber's CSA of model side was 2406.13±75.67μm2,the type IIa CSA was 2132.88±147.13μm2; the type IIb CSA was 3977.75±115.41μm2,the ratio of I:II was 48 :52;t-test :for the type I, t=7.195,p<0.05,for the type IIa, t=9.405,p<0.05,for the type IIb , t=13.836,p<0.05;the general morphology and the muscle fiber type distribution and size closely represented the contralateral muscle. In contrast Group B showed significant muscle atrophy, adipose infiltration, fibrosis, and few regenerating muscle fibers compared to the contralateral muscle. the ANOVA analysis between two groups was: for the muscle wet weight, F=39.57 , p<0.05,showed statistically significant; for the muscle's isometric contraction force , F=41.61 , p<0.05, showed statistically significant.Conclusion: Intramuscular nerve could promote muscle fiber regeneration of lacerated muscle, lighten muscle atrophy and fibrosis, restore the muscle morphous and construction of muscle fiber type, thus resulting in better functional recovery.