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10 MUSCLE AND TENDON INJURY
AND REPAIR
Bradley J Nelson, MD
Dean C Taylor, MDINTRODUCTION
- Muscle and tendon injuries occur frequently in the
athletic population. Most injuries are self-limiting and
a full recovery is to be expected; however, these
injuries can dramatically affect an athlete’s perform-
ance and their ubiquitous nature makes these injuries
an important part of the athlete’s care.- This chapter will review injury and repair of muscle
and tendon tissue. Emphasis will be placed on the
basic science of these injuries.
- This chapter will review injury and repair of muscle
SKELETAL MUSCLE INJURY
AND REPAIR- Muscle injury is the most common musculoskeletal
complaint in the athlete. Common muscle injuries
include muscle strains, delayed muscle soreness, con-
tusions, and cramps. - This section on muscle injury will provide a brief
review of anatomy and physiology, a description of
the reparative process, and then a discussion of the
types of muscle injuries common in athletes.
ANATOMY AND PHYSIOLOGY•Skeletal muscle is composed primarily of contractile
proteins (myosin, actin, tropomyosin, and troponin)
and a connective tissue matrix (Best, 1997).- The muscle fiber is the basic structural element of
skeletal muscle. The fiber is a syncytium of fused
muscle cells with multiple nuclei (Garrett and Best,
2000). Within the fibers are myofibrils which are
composed of repeating units of light and dark bands
called sarcomeres. The bands are made up of thick
(myosin) and thin (actin) filaments. - The muscle fiber originates from bone or tendon, trav-
erses one or more joints, and inserts into a tendon that
connects to bone. Fiber arrangement can be parallel or
oblique (pennate, bipennate, and the like) in orienta-
tion. Fibers can be classified as type I (slow-twitch
oxidative) and type II (fast-twitch). Type II fibers are
further classified into type IIa (fast-twitch oxidative
glycolytic) and IIb (fast-twitch glycolytic). - Satellite cells are separate cells along the periphery of
the muscle fiber that regenerate into muscle cells in
response to injury. - The musculotendinous junction is a specialized region
of highly folded membranes that increase the surface
area for force transmission (Best, 1997). Most muscle
strain injuries occur in this region. - The sarcoplasmic reticulum is a specialized cellular
organelle that is responsible for calcium movement
across the cell membrane and electric transmission
within the cell.
•A motor unit is a single nerve axon and all the muscle
fibers it innervates. The nerve contacts the muscle
fiber at the motor end plate.
•A muscle contraction begins when an electric impulse
travels down a nerve axon to its motor end plates.
The opinions and assertions contained herein are the private views of the
authors and are not to be construed as official nor do they reflect the
views of the U. S. Department of the Army or the U. S. Department of
Defense.