Muscle Injury

KEY FACTS

Terminology

• Contusion : Direct blunt compressive trauma to muscle without definable tear
• Tear : Discontinuity of muscle fibers typically at myofascial or myotendinous junction
• Hernia : Focal protrusion of part of muscle through epimysium
• DOMS : Overuse → muscle edema without definable tear

Pain peaking 1-3 days after overuse

Imaging

• Muscle contusion

Ill-defined hyperechogenicity of muscle or muscles

No discrete muscle tear (fiber discontinuity)
• Muscle tear

Discontinuity ± retraction of muscle fibers

Tear filled with hematoma or fluid

± mild muscle edema or hemorrhage

Estimate what actual percentage of muscle fibers torn

Grade 1: < 5% muscle fibers torn

Grade 2: 5-99% muscle fibers torn

Grade 3: 100% muscle fibers torn
• Muscle hematoma

Typically associated with grade 2 or 3 tears

Appearance varies with duration of hematoma, severity, and location
• DOMS

Affected muscle may be normal or diffusely hyperechoic due to diffuse muscle edema
• Muscle hernia

Focal protrusion of muscle through epimysium

Accentuated by muscle contraction or exercise

Clinical Issues

• Most muscle injuries improve with conservative treatment

Serial US examination not shown to be useful for guiding speed of rehabilitation
• Functional recovery precedes structural recovery

TERMINOLOGY

Synonyms

• Muscle tear, muscle contusion, muscle hematoma, muscle strain, “pulled muscle,” “tennis leg,” delayed-onset muscle soreness (DOMS), muscle hernia

Definitions

• Tear: Discontinuity of muscle fibers typically at myofascial or myotendinous junction
• Contusion: Direct blunt compressive trauma to muscle without definable tear
• Hernia: Focal protrusion of part of muscle through epimysium
• DOMS: Overuse causing muscle edema without definable tear

Pain peaking 1-3 days after overuse

IMAGING

General Features

• Best diagnostic clue

Muscle tear; hypoechoic area within muscle or at myotendinous junction
• Location

Usually affects lower limb muscles (gastrocnemius > rectus femoris, adductor longus, biceps femoris, semimembranous, semitendinosus, and soleus muscles)

Typically at myofascial junction within muscle or myotendinous junction

– These are weak areas at interface between tissues of different elastic property
• Morphology

Muscle fiber discontinuity with local hemorrhage and edema

MR Findings

• T1WI

Muscle tears

– Low to intermediate signal intensity hemorrhage

– ± hyperintense subacute hemorrhage

– Peripheral hypointense hemosiderin

– Loss of normal muscle striations ± retracted muscle belly

DOMS

– Muscle swelling of intermediate signal intensity

Muscle hernia

– Focal defect in investing fascia ± muscle protrusion
• T2WI

Muscle tear

– Hyperintense edema in affected muscle

– Inhomogeneous signal intensity mass in midsubstance tears due to hemorrhage and edema

– Perimuscular hyperintense fluid

DOMS

– Diffuse homogeneous hyperintensity
• T2* GRE

Susceptibility artifact due to hemorrhage

Ultrasonographic Findings

• Muscle contusion

Direct injury

Ill-defined hyperechogenicity of muscle or muscles due to edema ± hemorrhage

No discrete muscle tear (fiber discontinuity)

Hyperemia during reparative phase
• Muscle tear

Usually indirect injury

– Typically at myofascial or myotendinous junction

Grade 1 injury (Peetrons 2002)

– Muscle injury with either no visible tear or small tear involving few muscle fibers (< 5% muscle fibers torn)

– Muscle either normal, focal, or diffuse hyperechogenicity of muscle

Grade 2 injury

– Partial (5-99%) muscle fibers torn

– Discontinuity (tear) ± retraction of muscle fibers

Tear filled with hematoma or fluid

± mild to moderate muscle edema

Grade 3 injury

– Complete tear of muscle at musculotendinous junction usually with retraction
• Healing muscle tear

Bridging scar tissue or regenerated muscle at site of tear

Clearer definition of injured area

Localized hyperemia, which will disappear when healing is complete
• Muscle hematoma

Typically associated with grade 2 or 3 tears

Appearance varies with duration, severity, and location of hematoma

During first 48 hours, initially hypoechoic then becomes more hyperechoic as hematoma solidifies

– ± acoustic enhancement

After 72 hours, hematoma can start to liquefy

– Liquefaction seen as anechoic areas, starting centrally in hematoma

Marginal hyperemia during reparative phase (reparative fibrovascular granulation tissue)

– Peripheral granulation tissue usually hyperechoic and hyperemic

– Granulation tissue is more hyperechoic than fresh hematoma
• DOMS

Affected muscle may be normal or, if severe, diffusely hyperechoic due to diffuse muscle edema

No discernible muscle tear
• Muscle hernia

Focal protrusion of muscle fibers through epimysial fascial defect

Accentuated by muscle contraction or exercise

Imaging Recommendations

• Best imaging tool

US since most muscle tears are accessible

– MR preferable in pelvitrochanteric muscles, adductor or hamstring insertions as less accessible with US
• Protocol advice

Examine with muscle at rest and compare with contralateral side

Examine all tears in 2 planes

Measure dimensions of tear and try to gauge what percentage of muscle or musculotendinous junction is torn

– US during muscle contraction can help accentuate muscle retraction

Gastrocnemius muscle tear: Look closely at distal end of myotendinous junction medial belly

– ± comparison with opposite side

– Check for integrity of plantaris tendon

Seen medial to Achilles tendon and deep to medial belly gastrocnemius muscle

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Tags: Diagnostic Ultrasound Musculoskeletal

Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

KEY FACTS

Terminology

TERMINOLOGY

Synonyms

IMAGING

General Features

Radiology Key

Fastest Radiology Insight Engine

Muscle Injury

Muscle Injury

Imaging

Clinical Issues

Definitions

MR Findings

Ultrasonographic Findings

Imaging Recommendations

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Muscle Injury

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