Annually, these injuries account for 4.1 million presentations to GPs across Australia, of which, 40 % are sprains and / or muscle strains. 2, 3 However, despite this high prevalence, many doctors frequently report a lack of training and confidence in the management of musculoskeletal presentations. 4

Pathophysiology‘ Soft tissue injury’ is an umbrella term, incorporating sprains, strains, contusions and haematomas that all have related and well-understood pathology. The musculotendinous unit is responsible for the generation of external force required for functional movement. Muscles contract in three ways: concentrically, isometrically and eccentrically( figure 1). 5

A muscle strain is a disruption

of the musculotendinous unit, usually occurring during an eccentric contraction, or deceleration, in which sufficient tensile forces develop to overload the myofibres and cause irreversible changes in the muscle structure. 6-9

The most common classification system grades the injury by the extent of tissue damage and associated loss of function.

A grade 1 injury has partial or no separation of fibres with mild pain, swelling, and minimal loss of function. Grade 2 injuries have partial disruption of the tissue with moderate pain, swelling, and some loss of function.

A grade 3 injury is one in which there is a complete disruption or tear, with severe pain, swelling and loss of function. 6, 10 If a grade 3 injury is suspected or found on imaging, surgical specialist consultation should be sought immediately.

Once a muscle is torn, the tissue progresses through three main phases of repair that correspond directly to the management of muscular soft tissue injuries( see box‘ Stages of muscle repair’). 11

Figure 1.

Muscle contracts( concentric contraction

Muscle elongates( eccentric contraction)

Muscle contracts( isometric contraction)

History and examination As with all consultations, a thorough patient interview is always important in order to improve diagnostic accuracy.

Movement

Movement

No movement

Strains most commonly occur in the musculotendinous junction of muscles that principally comprise fasttwitch fibres spanning two

Stages of muscle repair

Inflammatory phase( 0-72 hours)

Myofibres and microvasculature of the muscle are torn, and resulting haematoma and myonecrosis induces an inflammatory cascade. 1 Local and systemic responses, including altered vascular permeability and capillary dilation, result in transmission of fluid and plasma proteins into the extravascular space, and a concentration of inflammatory mediators. 11

Reparative phase( 72 hours to three weeks)

Resident macrophages and fibroblasts remove necrotic debris, and produce proteins to restore connective tissue and release growth factors and cytokines, which stimulate precursor cells to proliferate and regenerate myofibres, as well as neovascularisation to support growth. 1

Maturation / Remodelling phase( three weeks to two years)

Myofibres begin to mature and reorganise, and type 3 collagen is slowly remodelled into type 1 collagen causing reorganisation and contraction of scar tissue. Damaged ends of myofibres are not reunited, but form new junctions with the scar tissue. 1 During this time, force must be applied to reorganise tissue along lines of stress.

or more joints, such as the hamstrings, quadriceps and gastrocnemius muscles. 6

Important predisposing

factors include muscle weakness and deconditioning, anatomical abnormalities, previous injury to the same site, activity-specific

and environmental factors. Important outcome-related

factors include the mechanism of injury, blunt trauma and haematoma formation, area of pain, neurovascular compromise, and the ability to weight-bear after injury.

Physical examination should focus on observation and palpation of obvious deformities in the muscle cont’ d next page