**19. The three post-lesion weeks**

leukotrienes and thromboxanes. This enzyme is located in the sarcolemma, in the mitochon‐ drial membrane, in the cytosolic compartment and in the lysosomes (Van der Vusse et al., 1989). In particular we suppose that the PLA2 present in the mitochondrial membrane may be implied in the mechanisms that induce the loss of the homeostasis of Ca++ (Cheah and Cheah, 1985). Likewise an increase of the concentrate of intracellular Ca++ would involve an activation of PLA2(Vane and Botting, 1987) The arachidonic acid and the lysophospholipids produced by the activation of PLA2, would cause a destabilization of the membrane structure assuming, in such a way, an important role in the field of autogenic processes following the harmful event (Jackson and Edwards, 1986; Chang et al., 1987). In addition the PLA2 would contribute to the loss of intramuscular enzymes observable in a muscular injury (Jackson et al., 1987). It is interesting to know that the PLA2 is one of the most important active principals of snake and bee poison. In fact the injection of poison of the coral snake (*Micrurus fulvius*) in the muscle of a mouse, provokes similar damage to that of an eccentric contraction (Arroyo et al., 1987) even if we need to underline the fact that the muscular necrosis induced by the snake's poison is much faster and larger than that seen in eccentric exercise. It is enough to think that an injection of only two micrograms of poison of the Australian tiger snake (*Notechis scutatus*) on rat muscle, leads to the total destruction of fiber in only 24 hours (Harris, 1989). It is also interesting to know that PLA possesses a protective role regarding oxidative stress (Van Kuijk et al., 1987)

The distinctive element which differentiates a muscular lesion and a lesion at bone level, is represented by the fact that the skeletal muscle heals through a phenomena of "repair", whereas the bone damage heals thanks to a process of "regeneration"- The main part of biological body tissue, at the moment in which it is damaged, heals through a process which hesitates in the formation of a scar area, which represents a biologically different tissue in comparison to the pre-existing one. On the contrary, when a bone segment becomes injured the regenerated tissue results identical in comparison to the pre-existent tissue. The process of repair of an injured skeletal muscle inescapably follows a constant pattern, independently of the cause which provoked the injury itself, whatever the injury may be contusion, elongation or tear (Hurme et al., 1991; Kalimo et al., 1997). In this type of process we may essentially

**1.** The destruction phase, which is characterized by the breakage and by the consequent necrosis of the muscular fibers, by the formation of a hematoma between the stumps of

**2.** The repair phase, which consists in the phagocytosis of the necrotic tissue, in the repair of fibers and the contextually production of healing connective tissue, contextual to the

**3.** The remodeling phase, a period during which the maturation of the repaired fibers, the contraction, or the reduction and the re-organization of the scar tissue and lastly, the

the injured fibers and by the inflammatory cellular reaction.

recovery of the functional capacities of the muscle come about.

capillary growth in the injured area.

**18. The pathobiology of muscular lesion**

identify three phases:

28 Muscle Injuries in Sport Medicine

The processes of muscular repair are completed in a period of about three weeks during which follow precise and expiring biological stages which we can schematically illustrate in six fundamental phases as follows:

**Second post-lesion day**: the necrotic parts of muscular fibers have been removed by the macrophages whereas, con‐ textually, the formation, on behalf of the fibers-blasts, of the healing connective tissue inside the central zone (CZ) has started.

**Third day**: the satellite cells have already started their activation which takes place inside the cylinders of the basal lamina in the zone of repair (RZ).

**Fifth day**: the myoblasts collect inside the myotubes of the RZ and the connective tissue of the CZ starts to become more dense.

**Twenty-first day**: the twining of the myo-fibres is virtually complete with the interposition of a small quantity of scar tissue. The quantity of scar tissue is linked to the quality of the repair processes themselves. The remodeling phase of the injured area may lengthen for a period of up to 60 days, depending on the anatomic and functional entity of dam‐ age. It is interesting to note that some authors have shown that, in the case which when the muscular lesion extends to more than 50% of the anatomic surface, the complete tissue repair comes about in a period not inferior to five

Etiology, Biology and Treatment of Muscular Lesions

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

31

At the moment in which the skeletal muscle is injured, we can generally observe a mechanical force which extends through the whole transversal section of each single fiber and causes the breakage of the sarcolemma inside the stumps of already injured fibers; leaving the latter am‐ ply open. From the moment that the myofibrillars (and consequently the muscular fibers)are, from a structural point of view, cells of notable length and of a lengthened and tapered form, there exists a real risk that the process of necrosis, begun in the location of the injury, extends along the whole length of the fiber itself. However, there exists a special anatomic structure named "contraction band" made up of a particularly dense cytoskeletal material, which be‐ haves as a true "fire door" (Hurme et al., 1991). Some hours following the traumatic event, the propagation of the necrotic process is blocked by a local phenomena represented by a sort of seal carried out by the contraction band on a level of modified areas of the cellular membrane. In such a way, a sort of protective barrier is created inside which starts the repair processes re‐ garding the laceration of the cellular membrane (Hurme et al., 1991). Recent studies have also shown that the lysosomal vesicles found inside the site of destruction of the cellular membrane, cover the role of a temporary membrane and carry out a central task in the healing process of

Contextually into the muscular fiber injury, in the traumatic event, also the blood vessels of the injured muscle tissue are lacerated. In such a way the inflammatory cells, transported by the blood flow, have direct access to the injured site. The inflammatory reaction is "amplified"

weeks (Pomeranz and Heidt, 1993).

**20. The necrosis of the muscular fibre**

the cellular membrane (Miyake et al., 2001; McNeil, 2002).

**21. The inflammatory phase**

**Seventh day**: the repair processes of the muscular cells extend outside the old cylinders of the basal lamina up to the CZ area and start to penetrate through the scar area.

**Fourteenth day:** the healing area in the CZ area is further condensed and reduced in dimension and the repaired myo-fibres fill the remaining gap of the CZ area itself.

**Twenty-first day**: the twining of the myo-fibres is virtually complete with the interposition of a small quantity of scar tissue. The quantity of scar tissue is linked to the quality of the repair processes themselves. The remodeling phase of the injured area may lengthen for a period of up to 60 days, depending on the anatomic and functional entity of dam‐ age. It is interesting to note that some authors have shown that, in the case which when the muscular lesion extends to more than 50% of the anatomic surface, the complete tissue repair comes about in a period not inferior to five weeks (Pomeranz and Heidt, 1993).
