Skeletal Muscle Injury: Overview and Organization

Skeletal Muscle Injury General Information

• Skeletal muscle, also called striated muscle, is made of muscle fibers varying in length (up to 50cm) and diameter (10-100 micrometers).
• Muscle fibers contain nuclei along their periphery.
• Muscle fibers are composed of myofibrils with alternating actin and myosin.
• Type I (slow-twitch, red fibers) use oxygen, are resistant to fatigue, and are dominant in postural muscles.
• Type II (fast-twitch, white fibers) rely on anaerobic metabolism, are prevalent in muscles used for quick movement, and are further divided into Ila and IIb based on oxidative capacity.

Muscle Organization

• Skeletal muscle is organized into three layers of connective tissue:
  • Epimysium: Encases the entire muscle.
  • Perimysium: Surrounds groups of muscle fibers (fascicles).
  • Endomysium: Encircles individual muscle fibers.
• Endomysium contains blood vessels, lymphatics, and nerve endings.
• Satellite cells (vestigial embryonic cells with differentiation potential) reside in the basement membrane, crucial for muscle repair.
• Myotendinous junction is where muscle transitions to tendon, transferring forces to bone, and is prone to injury.
• The junction has invaginations that enhance contact surface and load distribution.

Muscle Injury Repair Process

• Muscle injury repair is a continuous process, not sequential.
• Different phases overlap:
  • Injury Day: Fibre tear, inflammation, hematoma.
  • 1st-2nd Week: Maximum degeneration process (chemical factors, interleukins, cytokines, growth factors).

  • 2nd Week: Maximum muscle repair process (Satellite cell activation, growth factor activity).

• Muscles and tendons heal differently from bones.
• Muscle repair involves destruction, repair, and remodelling phases.
  • Tissue breakdown, clot formation via platelets and growth factors.
  • Fibroblasts clean debris, cytokines call for immune response cells.
  • New blood vessels are created by growth factors to support muscle regeneration.
  • Satellite cells differentiate into myoblasts (muscle-building cells), myocytes, new muscle fibers, and innervation/fascia perfection.
  • Tissue can reach 80% strength within 1-2 months. -Full strength restoration possible a year later.

Muscle Pathology & Classification

• Muscle injuries can be caused by fatigue, dehydration, lack of key nutrients.
• Prevention methods include hydration, oral hygiene, and proper warm-up and stretching.
• Muscle injuries can be classified by mechanism and severity (Minor muscle problems, distensions, strains, cramps, Structural abnormalities).
• Symptoms vary based on type and severity.
• Proper classification is important for determining treatment and prognosis.
• Different muscle injuries have varying timelines for resolution.

Specific Muscle Tear Descriptions

• Minor Partial Muscle Tear (3A): Tear < muscle fascicle, sharp pain, palpable defect, stretch-induced pain.
• Moderate Partial Muscle Tear (3B): Tear > fascicle, stabbing pain, noticeable tearing, palpable defect, stretch-induced pain.
• Total Muscle Tear (4): Tear involves complete muscle diameter, dull pain, palpable gap, loss of function.
• Contusion (Direct Injury): Blunt external force, diffuse hematoma, pain, loss of motion, swelling.