**26. The regeneration of intramuscular nerves**

Similarly to what happens in the course of the process of re-vascularization, the healing of the skeletal muscle may be blocked by a failure in the regeneration of intramuscular nerves (Hurme et al., 1991; Rantenen et al., 1995; Vaittinen et al., 1999; Vaittinen et al., 2001). The regeneration of the myofiber continues from the phase of myotubes formation also in absence of innervations; but if innervations were not completed correctly, a process of atrophy would inevitably occur (Rantanen et al., 1995). In the case of neurogenic denervation, or the breakage of the axon, the re-innervation process requires the growth of a new axon, distally with respect to the breakage area. However, since the moment the axons usually undergo go thorug a breakage inside or around the muscle, the nerve-muscle contact is, generally, rapidly raidly restabilized.

aside. The final part of the myofibers in repair which attempt to pass through the scar tissue, maintains a visible growth cone for a relatively long period during the repair process (Hurme et al., 1991; Hurme and Kalimo, 1992), this represents a period of time during which the final part of the myofibers cannot adhere firmly to the scar tissue. However, the myofibers in the course of repair strengthen their adherence to the ECM in both parts of their lateral profile, both in their intact part and in the part of re-growth (Kääriänen et al., 2000; Sorokin et al., 2000; Allikian et al., 2004) (Figure 9), This strengthening of the lateral adherence reduces both the movement of the stumps and the push on the still fragile scar, reducing in such a way the risk of re-breakage and allowing, at the same time, some use of the injured muscle before the healing process is complete (Kääriänen et al., 2001; 2002). It appears very interesting the fact of how mechanical stress is a pre-requisite for the process of lateral adherence, as recently some studies have suggested that they show how the phenomena does not come about in absence of the latter (Kääriänen et al., 2001). In a more advanced phase of the repair process a strong terminal adherence at the end of each stump is stabilized, which consists in the same type of molecule associated with integrin and distrofin that we can observe in a normal MJT (Song et al.., 1992; Kääriänen et al., 2000a; 2000b; 2001; 2002) (Figure9). Contextually, the original (prelesion) unit "tendon-myofiber-tendon, is replaced by two consecutive units of "tendon-

innervation when the repair process in zone RZ is completed.

**Figure 8.** Schematic representation of a breakage trauma of the skeletal muscle. The injured muscle fiber contract and the gap between the stumps, or the central zone CZ; initially begins to fill with the hematoma. The muscular fibers are necrotic inside their basal lamina, of a distance which is usually between 1 and 2 millimeters. Inside this segment gen‐ erally, with time, complete repair occurs (repair zone RZ; we prefer, in this case, the term "repair zone" to the term "regeneration zone" used by anglo-saxon autors. The reason of this choice derives from the different biological con‐ cept between the term "repair" and "regeneration", already illustrated at the beginning of the chapter), whereas in the part of the muscle which is not injured by trauma, we may observe only changes of reactive type (survival zone SZ). Each muscular fiber is innerved, in a single and precise site,by a neuromuscular junction (NMJs, full point in the dia‐ gram). Since the muscular fibbers generally break from one or the other side with respect to the line of NMJs of the same fiber, the accessory stumps of fibre 1 and of the fibres that go from 3 to 5, of the "ad" side (right), remain in‐ nerved, whereas their accessory stumps on side"ab" (left), remain denerved. At the same time the accessory stump of fibre 2 has remained denerved, because its NMJ is found in the RZ zone. The re-innervation of the accessory stump will come about through the penetration of a new axon sprout through the scar zone in formation (CZ) and so thanks to the formation of a new NMJ (represented by the white point in the diagram ). Fibre 2 will go back to its normal re-

Etiology, Biology and Treatment of Muscular Lesions

http://dx.doi.org/10.5772/56602

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