Chapter 115 Surgery of Skeletal Muscle and Tendon
Injuries to skeletal muscle and tendon are frequently seen in small animal practice. Injuries to skeletal muscle can either occur secondary to strain from high-impact activity, or result from lacerations, either externally from sharp objects or internally from fracture ends. Injuries to tendons most commonly occur secondary to sharp trauma.
ANATOMY
Skeletal Muscle
• Skeletal muscle is composed of many muscle fibers, which are very long and cylindrical muscle cells. Each fiber has many peripherally located nuclei. Muscle fibers are grouped into bundles, or fascicles. Each muscle fiber is composed of myofibrils, which are the basic subunit of skeletal muscle.
• The whole muscle is encased in a thick connective tissue called the epimysium. The perimysium binds myofibers into groups to form fasciculi and carries blood vessels and nerves. The endomysium is a sparse, reticulated connective tissue between the muscle fibers and carries blood capillaries and nerve fibers.
Tendon
• Tendons are composed of long bands of collagen fibers arranged in parallel rows and are embedded in ground substance and extracellular fluids. The fibroblast (or tenocyte) is the cellular component of tendon fibers.
• Collagen fibers are surrounded by a woven mesh of loose areolar connective tissue called the endotenon. The endotenon allows longitudinal movement of the collagen bundles and carries all of the blood vessels, lymphatics, and nerves. The epitenon covers the entire tendon, and is continuous on its undersurface with the endotenon.
• Free gliding is provided by the outer sheath of the tendon called the paratenon. The paratenon covers and separates tendons from each other. The paratenon forms a synovial membrane in areas of local pressure.
• Blood supply to tendons enters at three locations. Blood vessels entering at the musculo-tendinous junction supply the proximal one-third of the tendon. Blood vessels penetrating longitudinally in the paratenon or synovial sheath supply the middle one-third of the tendon, while the distal one-third of the tendon is supplied by vessels at the bone-tendon insertion.
Healing of Muscle
• Muscle can be injured by contusion, ischemia, denervation, sprains, and ruptures. The type and severity of the injury determines whether the muscle will heal with functional myofibers or scar tissue.
• The following classification system for muscle injury is based on the severity of the injury and resulting muscle damage:
• Grade III: Tearing of a large amount of muscle. Muscle fascia is torn, so hemorrhage can be diffuse.
• Factors that cause an increase in the amount of scar tissue are a poor source of healing myoblasts, poor vascularization or innervation, and excessive stress across the healing wound. Vascular supply is a very important factor for healing. The rate of vascular ingrowth is approximately 0.5 to 1 mm per day. Therefore, large areas that cannot revascularize quickly heal with scar tissue.
• Dense fibrous tissue prevents regeneration of muscle fibers across the wound. Factors causing excessive scar tissue formation include a large gap across the wound and inappropriate stress or motion across the wound during the healing period. Therefore, there is a delicate balance between early return to function versus immobilization. Early motion across the wound promotes desirable parallel orientation of regenerating muscle fibers, but it may also promote excessive granulation tissue formation. This would cause poor penetration of regenerating muscle fibers through the connective tissue scar.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
