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Clinical management of muscle strains and tears: guidelines for proper diagnosis, treatment, and prevention.

Article Excerpt
Skeletal muscle injuries are found frequently in all types of athletes, young and old, recreational and professional. This category of injury may include strains, tears, delayed onset muscle soreness, and contusions. Here we focus on strains and tears.

A muscle strain is a common injury to a muscle or tendon that occurs when a muscle is stretched excessively. The most common type of strain injuries is hamstring strains, followed by gastrocnemius and soleus strains, quadriceps strains, lumbar strains, and thigh adductor strains. Complete muscle tears are seen less frequently.

Most athletes can return to their sports activities after appropriate diagnosis and treatment of muscle strain injuries. Prevention of reinjury is the major goal after treatment because reinjury is common; hamstring reinjury rates range from 12% to 31%. (1) In this article, we discuss the anatomy and pathophysiology of strain injury, the biology of the muscle healing process, the clinical diagnosis of strains and tears, and various treatment and prevention strategies.

Anatomy and pathophysiology

Muscle groups are composed of tendon-muscle-tendon units that span one or more joints. Contractions of muscle groups induce and control joint motions. For example, the hamstring muscles (semimembranosus, semitendinosus, and biceps femoris) run from the pelvis and femur to the back and side of the knee; with their attached bones, they make up contractile units that stabilize the knee and hip and allow their motion (Figure 1). Injury occurs at the weakest part of the unit.

At the microscopic level, skeletal muscle is composed of contractile and connective tissue elements. Actin and myosin myofilaments constitute the sarcomeric units of muscle fibers, which are surrounded by endomysium and arranged in bundles. Satellite cells surround the muscle fibers; these stem cells are important for tissue regeneration after injury. Muscle bundles are surrounded by perimysium and then by epimysium. Greater degrees of muscle injury tend to involve larger amounts of connective-tissue disruption.

Muscle stretch is resisted by interaction between the contractile units and the surrounding connective tissues. As stretch moves beyond the physiological range, resistance shifts progressively from the contractile elements to the connective tissues.

The most common site of strain injury is the myotendinous junction, a region of highly folded basement membranes between the end of the muscle fiber and the tendon. These involutions maximize surface area for force transmission. However, the transition from compliant muscle fibers to relatively noncompliant tendon probably accounts for the unique vulnerability of the myotendinous junction.

[FIGURE 1 OMITTED]

Of note, the myotendinous junction usually spans a large surface area of the muscle belly (as opposed to the sharp demarcation often depicted in schematic diagrams). For example, the proximal and distal myotendinous junctions of the hamstrings actually overlap on the posterior and anterior surfaces of the muscle. This anatomical detail explains why, on clinical evaluation, strain...

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