Overview of muscle strain
Muscle strain (often referred to as a tear) is an acute injury to muscle caused by excessive tension. Pain occurs immediately and tenderness is focal. It is both aetiologically and mechanistically different from delayed-onset muscle soreness.
Delayed-onset muscle soreness occurs diffusely in muscle that has been subjected to unaccustomed activity. Soreness develops slowly and diffuse tenderness may be felt a day or 2 after the inciting activity. It resolves without treatment over about 7 days.
There are many classification systems for muscle strain. Muscle strain is a clinical diagnosis and investigation may not be required.
A grade 1 muscle strain involves damage to only a small number of muscle fibres, resulting in minor, well localised pain and tenderness. There is little or no reduction in range of movement or muscle strength.
A grade 2 muscle strain involves damage to a significantly larger number of muscle fibres than grade 1 injury, without complete rupture of the muscle. People with these injuries are more likely to present to a general practitioner or an emergency department with:
- acute, moderately severe, poorly localised pain
- significant muscle tenderness
- limp (if lower limb injury) or inability to continue activity
- associated bruising
- contraction and lengthening of the muscle inhibited by pain.
A grade 3 muscle strain involves complete disruption of the muscle. Pain is acute and initially severe and muscle function is lost. Considerable bruising may be present.
Some muscle strains occur at the musculotendinous junction (eg medial head of gastrocnemius). Management for these injuries is the same as for injuries to the muscle belly.
Muscle strain is a clinical diagnosis and in cases of grade 1 and 2 injury, investigation is usually not required. If investigation is indicated, ultrasound is the investigation of choice. In grade 3 injury, a magnetic resonance imaging (MRI) scan may be more appropriate if an ultrasound scan does not supply adequate information.
People with grade 1 muscle strains usually do not present for medical attention and the strain resolves spontaneously within a few days. They do not require any rehabilitation. People with grade 2 muscle strains often present to their general practitioner for initial management. People with grade 3 muscle strains often present to an emergency department for initial management.
Rehabilitation programs for grade 2 and 3 injuries are complex and surgical repair may be considered in cases of grade 3 injury.