Acute Sports Injuries - MUSCLE STRAIN/TEAR

Muscle injuries are among the most common injuries in sports, accounting for up to half of all sport-related injuries at the elite level. They result from either intrinsic or extrinsic causes, with the former contributing to strains/tears and the latter resulting in contusion. In this post we will take a closer look at muscle strains/tears, and further posts will explore contusions, myositis ossificans, acute compartment syndrome and cramp.

A muscle is strained or torn when excessive tensile and/or sheer forces within the muscle cause muscle fibres and their surrounding connective tissue to fail. During muscle contraction, actin and myosin form cross-bridges to generate force, transmitted either via the surrounding connective tissue or directly to an attached tendon and subsequently the skeleton, to produce motion. Excessive tensile force results in ruptures of the cell membrane and basal membrane to which the membrane attaches, damages the surrounding connective tissue sheaths and tears blood vessels within them. Depending on the severity of the injury, the net result can be pain on active contraction and passive stretch of the muscle, a reduction in strength due to pain-inhibition, decreased range of motion due to muscle spasm and loss of function. Muscle strains most commonly occur within the hamstrings, quadriceps and gastrocnemius muscles.

To guide prognosis, muscle strains have been historically graded using a 3-tier system, with increasing grade suggesting a greater severity of injury requiring longer recovery. A grade I strain is characterised by localised pain but no/minimal loss of strength, suggesting the involvement of a small number of muscle fibres. A grade II strain is characterised by greater pain, swelling and loss of strength, involving a greater number of muscle fibres. A grade III strain involves a complete tear of the muscle fibres. In addition to these 3 grades, a grade 0 injury has been described where an athlete presents with a clinical syndrome of muscle abnormality, but without imaging evidence of pathology.

There has been growing interest in the variable recovery times for individuals with similarly graded injuries. Advances in magnetic resonance imaging and ultrasonography have shown that strains involving tendinous components of the muscle have a worse prognosis. Muscle strains often occur at or near the musculotendinous junction, which appears as an area of relative weakness in skeletally mature individuals. The traditional view of the muscle-tendon unit involved a relatively distinct separation between the muscle belly and the free tendon at the end via which active contractile forces are transmitted to the bone. However, advanced imaging and anatomical dissection studies have clearly shown that tendinous structures extend deeply into the muscle belly and that some muscles also have isolated central tendinous structures within the muscle belly itself.

The goal of management of an acute muscle strain is to return the athlete to activity at the prior level of performance and with minimal risk of re-injury. This requires the underlying pathology and the changes it introduces (e.g. pain, swelling, weakness, reduced range of motion) to be addressed. A previous muscle injury is the largest risk factor for a future strain. Acute management of muscle strains focuses on minimisation of pain and oedema, restoration of neuromuscular control at slow speeds and prevention of excessive scar formation whilst protecting the healing fibres from excessive lengthening. Recommended early techniques include: 1) ice and compression; 2) mobilisation and motion (within pain limits and avoiding aggressive stretching techniques; 3) gentle massage of the affected muscle peripheral to the lesion. Subsequent management allows for increased exercise intensity, neuromuscular training at faster speeds and larger amplitudes and the initiation of eccentric resistance training. The final stage of recovery progresses to high-speed neuromuscular training and eccentric resistance training in a lengthened position in preparation for return to sport.

REFERENCES

Brukner, P., 2012. Brukner & Khan's clinical sports medicine. North Ryde: McGraw-Hill.