Muscle tears or strains are common injuries, both in athletes and non-athletes.
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Terminology
Muscle strain is a term that is used variably clinically and in the medical literature. The Munich consensus statement (expert level evidence) states muscle tear is the preferred term denoting "structural injuries of muscle fibres/bundles leading to loss of continuity and contractile properties" 1.
Pathology
Muscle tears are indirect muscle injury that occurs in eccentric contraction during sprinting or stretching 2. Most commonly these injuries occur at the myotendinous junction (MTJ) but can also be peripheral (i.e. myofascial) 3.
Location
Muscles of the lower limbs are most at risk of injury, with the biceps femoris the most commonly injured followed by rectus femoris and gastrocnemius muscles 2,3.
Radiographic features
Ultrasound
Ultrasound examination may be normal or in low-grade injuries demonstrate focal or diffuse regions of increased echogenicity. Fibre disruption is characterised by well-defined hypoechoic/anechoic regions. Disruption at the myofascial junction or myotendinous junction may be present 1.
MRI
MRI features corresponding to clinical grades of injury are 1:
grade 1: T2 high signal with a feathery appearance (usually centred on the MTJ) representing oedema +/- thickening and high signal of the intramuscular tendon but without laxity +/- mild perifascial fluid
grade 2: above features with fibre disruption characterised by high T2 signal and local distortion +/- intramuscular tendon high signal with or without thickening, laxity or partial disruption +/- moderate-severe perifascial fluid
grade 3: complete disruption +/- retraction/laxity with local haematoma
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