Skip to content
mskultrasound.net banner

Muscle: Normal And Pathology

Table of Contents show

Author

Kate Ford Daniels, MD

Summary

  • Ultrasound is an excellent bedside tool for direct visualization of muscles and their associated injuries
  • Understanding the basic structure of muscles and surrounding tissues will allow the examiner to identify pathology
  • The examiner must know basic anatomy including attachments and surrounding muscle groups and other soft tissue structures, muscle type, and function of the muscle in question
  • Accurately identifying injuries will facilitate management, disposition decisions, allow for prognostication, and assist with return to play decisions.

Skeletal Muscle Anatomy

  • Muscle Anatomy
    • Parallel muscle fibers are bound into groups called fascicles, which are tethered to one another by the endomysium.
    • The fascicles are then organized longitudinally to act in synchrony and held by the perimysium.
    • Finally, the entire muscle is enclosed by the epimysium.[1]Lee JC, Mitchell AWM, Healy JC. Imaging of muscle injury in the elite athlete. Br J Radiol. 2012;85(1016):1173-1185. doi:10.1259/bjr/84622172
Skeletal Muscle Anatomy Illustration
Illustration of skeletal muscle anatomy.[2]Image courtesy of open.oregonstate.education, “Skeletal Muscle”
  • Muscle fibers themselves are relatively hypoechoic and because of their parallel orientation and being surrounded by more echoic perimysuim and fibroadipose septa they are seen as either a speckled or linear appearance based on the transducer orientation relative to the long axis of the fibers.
    • Short axis orientation will show a speckled appearance, while long axis shows linear.[3]Jacobson JA. Fundamentals of Musculoskeletal Ultrasound. Elsevier; 2018.
  • The more echoic structures, like the perimysium due to its collagen concentration, can be seen internally in pennate muscles, giving a feathered appearance.[4]Pillen S. Skeletal muscle ultrasound. Eur J Transl Myol. 2010;20(4):145-156. doi:10.4081/ejtm.2010.1812
    [5]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267
  • The epimysium is also echogenic and can be noted at the periphery.
Normal muscle ultrasound long axis.
Normal muscle ultrasound short axis.
Muscle Ultrasound Normal Biceps Brachii
Healthy biceps brachii and brachialis muscle in a transverse (A) and longitudinal (B) view. In the longitudinal view the fascicular structure becomes visible, allowing evaluation of the pennation angle (a). Double arrow, subcutaneous tissue; arrow, brachial artery flanked by the median nerve; B, biceps brachii muscle; Br, brachialis muscle; H, humerus.[6]Pillen S. Skeletal muscle ultrasound. Eur J Transl Myol. 2010;20(4):145-156. doi:10.4081/ejtm.2010.1812

Approach to Ultrasound Evaluation

  • Transducer
    • Most muscles can be properly examined using the high frequency 12-15 MHz linear transducer 4,5,6 in conventional grey scale B mode.[7]Whittaker JL, Stokes M. Ultrasound imaging and muscle function. J Orthop Sports Phys Ther. 2011;41(8):572-580. doi:10.2519/jospt.2011.3682[8]Chiang YP, Wang TG, Hsieh SF. Application of ultrasound in sports injury. J Med Ultrasound. 2013;21(1):1-8. doi:10.1016/j.jmu.2013.01.008[9]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267
    • For patients that may have more muscle, adipose, or other soft tissues, a 8-10 MHz curvilinear transducer may be needed to visualize deeper sections.[10]Draghi F, Zacchino M, Canepari M, Nucci P, Alessandrino F. Muscle injuries: ultrasound evaluation in the acute phase. J Ultrasound. 2013;16(4):209-214. doi:10.1007/s40477-013-0019-8
    • Beware of the depth of the muscle in question, as more superficial structures (adipose, other muscles, tendons, etc) may change the resolution of your ultrasound beam.
    • Make sure to scan fully through the area of interest in all directions, with a sweeping or toggling motion.[11]Jacobson JA. Fundamentals of Musculoskeletal Ultrasound. Elsevier; 2018
  • Positioning
    • The patient should be in a comfortable position with the entire muscle of interest exposed in such a way that it can be examined in both the long and short axis.
    • The pt can contract and relax the muscle as needed to examine the injury dynamically.
    • The examiner can also perform passive range of motion.
    • If on an extremity, you can compare to the contralateral limb as a baseline.
  • Findings
    • Make sure to note any surrounding structures to look for other non-musculoskeletal injuries, including other muscle injuries or any neurovascular injuries.
    • If a collection of fluid is seen, or any other fluid filled structure is noted, you can employ power and color doppler modes to assess for flow or fluid movement
    • However, even if no flow is seen, you cannot definitively rule out bleeding from an intramuscular tumor
Example of probe position in long axis.
Example of probe position in short axis.

Pathology

  • Muscle atrophy
    • Ultrasound can be used to determine and quantify muscle atrophy by measuring thickness and may appear as increased echogenicity[12]Jacobson JA. Fundamentals of Musculoskeletal Ultrasound. Elsevier; 2018.[13]Pillen S. Skeletal muscle ultrasound. Eur J Transl Myol. 2010;20(4):145-156. doi:10.4081/ejtm.2010.1812
    • Volume loss and fatty infiltration are common.
    • In isolated or unilateral injuries, imaging contralateral structures can act as controls.
Shoulder US Infraspinatus muscle atrophy
Ultrasound of infraspinatus muscle in an asymptomatic (right) and symptomatic (left) shoulder. Note the left side with increased fatty infiltration and volume loss.[[Case courtesy of Dr Maulik S Patel, Radiopaedia.org, rID: 12493]]
  • Neuromuscular disorders
    • Because of the standard composition of muscle, any change from normal can be easily detected by appreciating the change in echogenicity.
    • For example, neuromuscular disorders that cause infiltration of normal muscle with fat and fibrous tissue will have a brighter, more hyperechoic appearance.
Shoulder US Neuromuscular disorder
Short axis (A) and long axis (B) ultrasound of a normal biceps muscle. Short axis ultrasound of myopathic biceps muscle (C) showing homogenous, hyperechoic tissue in acid maltase deficiency (Pompe’s disease).[14]Image courtesy of practicalneurology.com, “Ultrasound in Neuromuscular Medicine”
  • Contusions[15]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267[16]Draghi F, Zacchino M, Canepari M, Nucci P, Alessandrino F. Muscle injuries: ultrasound evaluation in the acute phase. J Ultrasound. 2013;16(4):209-214. doi:10.1007/s40477-013-0019-8[17]Lee JC, Healy J. Sonography of lower limb muscle injury. AJR Am J Roentgenol. 2004;182(2):341-351. doi:10.2214/ajr.182.2.1820341[18]McMahon CJ, Wu JS, Eisenberg RL. Muscle edema. AJR Am J Roentgenol. 2010;194(4):W284-92. doi:10.2214/AJR.10.4247
    • Defined as direct impact causing blunt trauma injury to a particular muscle or groups of muscles
    • Ultrasound can identify the specific muscles injured, grade the injury, rule out other injuries, and be used to estimate return to play
    • Generally classified into three groups: mild, moderate, and severe.
      • Note, there is no widely accepted sonographic classification
    • Mild: ROM decreased by ⅓
      • US: localized isoechoic swelling in the muscle surrounded by normal muscle tissue, hyperechoic but intact muscle
      • Return to play: average 6 days
    • Moderate: ROM decreased by ⅓ to ⅔
      • US: Muscle appears frayed, but less than 50% of injured in short axis
      • Return to play: variable between 1-8 weeks
    • Severe: ROM decreased by greater than ⅔
      • US: Large hematoma may be seen
      • Return to play: average 56 days
Thigh US Moderate contusion in rectus femoris
Short axis view of normal thigh (left) and contused thigh (right). There is moderate diffuse hyperechoic signal within the left rectus femoris muscle (>50 % of muscle surface area). RF rectus femoris, VI vastus intermedius, fe femur.[19]Image courtesy of musculoskeletalkey.com, “Muscle Contusions: Extrinsic Muscle Lesions”
Thigh US Moderate contusion in long axis rectus femoris
Long axis view of the rectus femoris shows focal loss of normal muscle echo pattern with a central fluid clept and hypervascularity.[20]Case courtesy of Dr Maulik S Patel, Radiopaedia.org, rID: 42686
Leg US Large Calf Hematoma
Ultrasound of calf muscles with large, hypoechoic hematoma seen in short axis.
Thigh US Chronic thigh hematoma
Long axis view of thigh demonstrates chronic hyperechoic, organized fibrotic tissue (arrows) between the rectus femoris and vastus intermedius muscles aponeurosis from chronic hematoma. RF rectus femoris, VI vastus intermedius.[21]Image courtesy of musculoskeletalkey.com, “Muscle Contusions: Extrinsic Muscle Lesions”
    • Frequently, changes in contused muscles will be seen deeper than may be expected, e.g. adjacent to bone
    • Contusions can also cross fascial boundaries 
    • Acute treatment includes compression, ice application, muscle should be placed in an elongated but pain free position with the goal to stop further injury and bleeding. Avoid massage, heat.
    • Subacutely, focus on protecting the injured site while increasing strengthening and stretching.
  • Localized Rhabdomyolysis
    • Ultrasound will show increased echogenicity of the affected muscle, along with change in normal perimysial structure.
    • Consider concomitant laboratory evaluation, including creatinine kinase (CK), based on clinical suspicion.[22]Chiang YP, Wang TG, Hsieh SF. Application of ultrasound in sports injury. J Med Ultrasound. 2013;21(1):1-8. doi:10.1016/j.jmu.2013.01.008[23]McMahon CJ, Wu JS, Eisenberg RL. Muscle edema. AJR Am J Roentgenol. 2010;194(4):W284-92. doi:10.2214/AJR.10.4247
Thigh US localized rhabdomyolysis
Short axis view of the left rectus femoris muscle in showing abundant anechoic areas, compatible with edema (arrows), and increased diameter of the muscle fascia (*).[24] Carrillo-Esper R, Galván-Talamantes Y, Meza-Ayala CM, Cruz-Santana JA, Bonilla-Reséndiz LI. Ultrasound findings in rhabdomyolysis. Cir Cir. 2016;84(6):518-522. doi:10.1016/j.circir.2015.06.036
  • Lacerations[25]Jacobson JA. Fundamentals of Musculoskeletal Ultrasound. Elsevier; 2018.[26]McMahon CJ, Wu JS, Eisenberg RL. Muscle edema. AJR Am J Roentgenol. 2010;194(4):W284-92. doi:10.2214/AJR.10.4247[27]Draghi F, Zacchino M, Canepari M, Nucci P, Alessandrino F. Muscle injuries: ultrasound evaluation in the acute phase. J Ultrasound. 2013;16(4):209-214. doi:10.1007/s40477-013-0019-8
    • Usually seen with penetrating injury and imaging is typically not needed, but will see disruption of the muscle fibers, along with subcutaneous edema, gas, and hematoma2,5,9.
    • Injury introduced gas and air can make complete imaging more difficult.
  • Hematomas[28]Jacobson JA. Fundamentals of Musculoskeletal Ultrasound. Elsevier; 2018.[29]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267[30]Chiang YP, Wang TG, Hsieh SF. Application of ultrasound in sports injury. J Med Ultrasound. 2013;21(1):1-8. doi:10.1016/j.jmu.2013.01.008[31]Lee JC, Healy J. Sonography of lower limb muscle injury. AJR Am J Roentgenol. 2004;182(2):341-351. doi:10.2214/ajr.182.2.1820341[32]Liu W, Wang D, Ouyang H, et al. Ultrasound assessment of muscle injury associated with closed limb fracture. Biomed Res Int. 2019;2019:9365291. doi:10.1155/2019/9365291
    • See Chapter: Hematoma And Morel-Lavallée Lesion
    • Hematomas may be seen interrupting normal muscle anatomy from a variety of injuries
    • They do not follow a strict timeline but, generally, will appear as an ill defined hypoechoic or anechoic fluid collection interrupting the muscle with increased reflectivity in the first 24-48 hours. In the 48-72 hour window, the fluid’s margins become more defined and have a more echogenic outline. Eventually the entire structure become echogenic, usually from an outside in path
    • Because of their evolving state, serial ultrasounds by a consistent provider are useful
    • A honeycomb pattern can be seen if there are multiple small hematomas within neighboring fibers
    • The size of the hematoma cannot always predict loss of function
    • Morel-Lavallee lesion can be seen as a hematoma between subcutaneous fat and muscles, and is classified as an internal degloving injury
Thigh US Large Intramuscular Hematoma
Short axis ultrasound of quad muscles with a large, hypoechoic hematoma and a second smaller one more superficially. Note the layering of blood seen in the larger hematoma.
Thigh US Morel Lavallee Lesion
Ultrasound of lateral thigh with large MLL. Note the fat globules floating in the hypoechoic fluid. Also note that this lesion is between two tissue planes and not intramuscular like a hematoma.[33]Simpson, Grant, and Brandon Allen. “Morel-Lavallée Lesion.” Journal of Education and Teaching in Emergency Medicine 1.2 (2016).
  • Intrinsic muscle injuries[34]Lee JC, Mitchell AWM, Healy JC. Imaging of muscle injury in the elite athlete. Br J Radiol. 2012;85(1016):1173-1185. doi:10.1259/bjr/84622172[35]Jacobson JA. Fundamentals of Musculoskeletal Ultrasound. Elsevier; 2018.[36]Pillen S. Skeletal muscle ultrasound. Eur J Transl Myol. 2010;20(4):145-156. doi:10.4081/ejtm.2010.1812[37]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267[38]Draghi F, Zacchino M, Canepari M, Nucci P, Alessandrino F. Muscle injuries: ultrasound evaluation in the acute phase. J Ultrasound. 2013;16(4):209-214. doi:10.1007/s40477-013-0019-8[39]Chiang YP, Wang TG, Hsieh SF. Application of ultrasound in sports injury. J Med Ultrasound. 2013;21(1):1-8. doi:10.1016/j.jmu.2013.01.008[40]Lee JC, Healy J. Sonography of lower limb muscle injury. AJR Am J Roentgenol. 2004;182(2):341-351. doi:10.2214/ajr.182.2.1820341[41]McMahon CJ, Wu JS, Eisenberg RL. Muscle edema. AJR Am J Roentgenol. 2010;194(4):W284-92. doi:10.2214/AJR.10.4247[42]Liu W, Wang D, Ouyang H, et al. Ultrasound assessment of muscle injury associated with closed limb fracture. Biomed Res Int. 2019;2019:9365291. doi:10.1155/2019/9365291
    • Most commonly involve the myotendinous junction, are injured by eccentric contraction, where the muscle is actively contracting while elongating, and are typically non-contact.
    • The location can vary based on the type of muscle involved- unipennate vs bipennate, etc
    • Classically they are graded by degree of impairment (from grade 1 to grade 3), but are also broken into three grades based on US findings
    • Grade 1: usually only a few fibers involved in a bundle, see less than 5% damage, seen as mostly normal tissue or small areas of hypoechoic or anechoic
      • May see damage of the muscle fibers (seen as loss of striations or pennate pattern), or no specific findings
      • Return to play: typically in 1-2 weeks
    • Grade 2: lesion that is greater than 5%, can involve up to ¾ of the injured muscle (but less than 100%), with perifascial fluid, myotendinous or myofascial junction changes, or muscle fiber injury.
      • Commonly referred to as a “partial tear”
      • Will see hypo or anechoic areas of injury
      • May see a hematoma
      • Function of the injured muscle will be affected, and widening of the fibers may be more apparent with active muscular testing
      • Return to play: Varies.
    • Grade 3: total rupture of muscle, may have a palpable defect on exam
      • Likely accompanied by a hematoma
      • Ultrasound will be able to identify the ends of the torn muscle as well as location
      • Passive ROM by the examiner may be helpful to expose the torn fibers
      • Surgical referral may be needed with avulsion injuries causing defect greater than 2-3 cm
      • Return to play: minimum 5-8 weeks
Grade 1 injury of the biceps femoris in short axis shows normal muscle (*) with a small area of echogenic edematous muscle (arrows) containing a tiny area of hypoechoic disruption (arrowheads)[43]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267
Thigh US grade 2 muscle injury semitendinosis
Short axis view of semitendinosus with grade 2 injury showing hypoechoic muscle disruption (arrows) with hematoma (arrowheads) also present extending along the disrupted perimysium and abutting the sciatic nerve (*).[44]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267
Thigh US grade 2 muscle injury semitendinosis, long axis part 2
Long axis view of semitendinosus with grade 2 injury showing hypoechoic muscle disruption (arrows) with hematoma (arrowheads) also present extending along the disrupted perimysium and abutting the sciatic nerve (*).[45]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267
Grade 3 injury of the medial head gastrocnemius (MHG) in long axis showing edematous muscle (medial head gastrocnemius) with complete tear causing retraction (arrowheads) and extensive hematoma (*).[46]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267
    • Acute treatment focuses on supportive treatment with ice, compression, ROM exercises without pain, gentle massage (not directly over the affected area).
    • Subacute treatment focuses on regaining neuromuscular adaptations, increasing intensity, and using eccentric strengthening
  • Delayed Onset Muscle soreness (DOMS)[47]Longo V, Jacobson JA, Fessell DP, Mautner K. Ultrasound findings of delayed-onset muscle soreness. J Ultrasound Med. 2016;35(11):2517-2521. doi:10.7863/ultra.15.12066[48]Lee JC, Healy J. Sonography of lower limb muscle injury. AJR Am J Roentgenol. 2004;182(2):341-351. doi:10.2214/ajr.182.2.1820341
    • Classified as a type 1 muscular strain
    • Diffuse hyperechoic area of the affected muscles. Generally it is well defined and associated with increase in muscle size.
    • The affected muscles will likely involve multiple compartments
    • History and physical exam help differentiate DOMS from grade 1 strain and localized rhabdomyolysis
Shoulder US Biceps delayed onset muscle soreness DOMS
Short axis ultrasound of right brachial biceps and brachialis muscle (right image) increased in echogenicity and volume compared to the contralateral arm (left image) with alteration of the normal ehcotexture.[49]Case courtesy of Daniel Martin, Radiopaedia.org, rID: 69292
  • Intramuscular Scar
    • [50]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267[51]Lee JC, Mitchell AWM, Healy JC. Imaging of muscle injury in the elite athlete. Br J Radiol. 2012;85(1016):1173-1185. doi:10.1259/bjr/84622172[52]Lee JC, Healy J. Sonography of lower limb muscle injury. AJR Am J Roentgenol. 2004;182(2):341-351. doi:10.2214/ajr.182.2.1820341
    • Abnormal imaging that can have a variety of different appearances: hyperechoic, heterogenous hypoechoic, and may be linear or stellate.
    • Can be seen in the muscle body or near the myotendinous junction.
    • Can be confused for acute injury
    • It will not change appearance when the muscle contracts
    • Can increase future risk of tears
Thigh US intramuscular scar
Long axis ultrasound of a soccer player’s anterior thigh with a large hypoechoic scar seen centrally in the rectus femoris muscle.[53]Lee JC, Mitchell AWM, Healy JC. Imaging of muscle injury in the elite athlete. Br J Radiol. 2012;85(1016):1173-1185. doi:10.1259/bjr/84622172
  • Muscle Hernia[54]Nguyen JT, Nguyen JL, Wheatley MJ, Nguyen TA. Muscle hernias of the leg: A case report and comprehensive review of the literature. Can J Plast Surg. 2013;21(4):243-247. doi:10.1177/229255031302100408
    • Trauma to one muscle causes it to herniate through a surrounding fascial defect. US can identify the injury, but dynamic imaging may be needed if the hernia only occurs with activity
    • Mild symptoms can be treated supportively. Surgical referral can be provided for moderate to severe symptoms
Long axis ultrasound of anterior compartment of leg. Muscle hernia is seen through defect. With compression, hernia regresses.[55]Case courtesy of Dr Maulik S Patel, Radiopaedia.org, rID: 27123
  • Myositis ossificans[56]Jacobson JA. Fundamentals of Musculoskeletal Ultrasound. Elsevier; 2018.[57]Guermazi A, Roemer FW, Robinson P, Tol JL, Regatte RR, Crema MD. Imaging of muscle injuries in sports medicine: Sports imaging series. Radiology. 2017;282(3):646-663. doi:10.1148/radiol.2017160267[58]Machotka ; Brukner P. Chapter 33: Anterior thigh pain. Clinical Sports Medicine. 2017;33:670-671.
    • Abnormal growth of cartilage and bone in pathologic muscle at the location of a previous injury. Doppler US may see increased vascularity and other associated calcifications.
    • Note, Xray can lag behind US detection by two weeks as US can detect a hypoechoic area surrounded by echogenic material before calcific deposits are formed
    • Typically self limiting. Treatment options include ROM exercises, NSAIDs, extracorporeal shock wave therapy, and RICE treatment. Surgical consult can be obtained if the MO persists chronically and affects movement
Thigh US myositis ossificans
Long and short axis view of myositis ossificans. Note the hypoechoic calcifications (white arrow) and posterior acoustic shadowing (clear arrow).[59]Chew K, Stevens KJ, Wang TG, Fredericson M, Lew HL. Introduction to diagnostic musculoskeletal ultrasound: part 2: examination of the lower limb. Am J Phys Med Rehabil. 2008;87(3):238-248. … Continue reading

Pearls & Pitfalls

  • The parallel configuration of muscle septae can easily cause anisotropy , making misdiagnosis easy if care isn’t taken with transducer placement and fanning through the entire area
  • Fluid collections may appear benign and motionless, but can have venous flow and should always have color doppler applied. This will also check for the location of arteries and corresponding veins.
  • Always check the contralateral limb if there is any uncertainty about what is being seen sonographically

References

References[+]