Comprehensive muscle injury classification: type-specific definitions and clinical presentations
| Type | Classification | Definition | Symptoms | Clinical signs | Location | Ultrasound/MRI |
|---|---|---|---|---|---|---|
| 1A | Fatigue-induced muscle disorder | Circumscribed longitudinal increase of muscle tone (muscle firmness) due to overexertion, change of playing surface or change in training patterns | Aching muscle firmness. Increasing with continued activity. Can provoke pain at rest. During or after activity | Dull, diffuse, tolerable pain in involved muscles, circumscribed increase of tone. Athlete reports of ‘muscle tightness’ | Focal involvement up to entire length of muscle | Negative |
| 1B | Delayed-onset muscle soreness (DOMS) | More generalised muscle pain following unaccustomed, eccentric deceleration movements. | Acute inflammative pain. Pain at rest. Hours after activity | Oedematous swelling, stiff muscles. Limited range of motion of adjacent joints. Pain on isometric contraction. Therapeutic stretching leads to relief | Mostly entire muscle or muscle group | Negative or oedema only |
| 2A | Spine-related neuromuscular muscle disorder | Circumscribed longitudinal increase of muscle tone (muscle firmness) due to functional or structural spinal/lumbopelvical disorder. | Aching muscle firmness. Increasing with continued activity. No pain at rest | Circumscribed longitudinal increase of muscle tone. Discrete oedema between muscle and fascia. Occasional skin sensitivity, defensive reaction on muscle stretching. Pressure pain | Muscle bundle or larger muscle group along entire length of muscle | Negative or oedema only |
| 2B | Muscle-related neuromuscular muscle disorder | Circumscribed (spindle-shaped) area of increased muscle tone (muscle firmness). May result from dysfunctional neuromuscular control such as reciprocal inhibition | Aching, gradually increasing muscle firmness and tension. Cramp-like pain | Circumscribed (spindle-shaped) area of increased muscle tone, oedematous swelling. Therapeutic stretching leads to relief. Pressure pain | Mostly along the entire length of the muscle belly | Negative or oedema only |
| 3A | Minor partial muscle tear | Tear with a maximum diameter of less than muscle fascicle/bundle. | Sharp, needle-like or stabbing pain at time of injury. Athlete often experiences a ‘snap’ followed by a sudden onset of localised pain | Well-defined localised pain. Probably palpable defect in fibre structure within a firm muscle band. Stretch-induced pain aggravation | Primarily muscle–tendon junction | Positive for fibre disruption on high resolution MRI*. Intramuscular haematoma |
| 3B | Moderate partial muscle tear | Tear with a diameter of greater than a fascicle/bundle | Stabbing, sharp pain, often noticeable tearing at time of injury. Athlete often experiences a ‘snap’ followed by a sudden onset of localised pain. Possible fall of athlete | Well-defined localised pain. Palpable defect in muscle structure, often haematoma, fascial injury Stretch-induced pain aggravation | Primarily muscle–tendon junction | Positive for significant fibre disruption, probably including some retraction. With fascial injury and intermuscular haematoma |
| 4 | (Sub)total muscle tear/tendinous avulsion | Tear involving the subtotal/complete muscle diameter/tendinous injury involving the bone–tendon junction | Dull pain at time of injury. Noticeable tearing. Athlete experiences a ‘snap’ followed by a sudden onset of localised pain. Often fall | Large defect in muscle, haematoma, palpable gap, haematoma, muscle retraction, pain with movement, loss of function, haematoma | Primarily muscle–tendon junction or Bone–tendon junction | Subtotal/complete discontinuity of muscle/tendon. Possible wavy tendon morphology and retraction. With fascial injury and intermuscular haematoma |
| Contusion | Direct injury | Direct muscle trauma, caused by blunt external force. Leading to diffuse or circumscribed haematoma within the muscle causing pain and loss of motion | Dull pain at time of injury, possibly increasing due to increasing haematoma. Athlete often reports definite external mechanism | Dull, diffuse pain, haematoma, pain on movement, swelling, decreased range of motion, tenderness to palpation depending on the severity of impact. Athlete may be able to continue sport activity rather than in indirect structural injury | Any muscle, mostly vastus intermedius and rectus femoris | Diffuse or circumscribed haematoma in varying dimensions |
*Recommendations for (high-resolution) MRI: high field strength (minimum 1.5 or 3 T), high spatial resolution (use of surface coils), limited field of view (according to clinical examination/ultrasound), use of skin marker at centre of injury location and multiplanar slice orientation.