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