Jump to content

Myotomes

Original Editor - Lucinda hampton Top Contributors - Lucinda hampton, Kim Jackson, Nikhil Benhur Abburi, Candace Goh, Rachael Lowe, Joao Costa, Rucha Gadgil, Oyemi Sillo, Naomi O'Reilly, Shaimaa Eldib and Tony Lowe


Myotome

A myotome (Greek: myo=muscle, tome = a cut, slice) is defined as a group of muscles which is innervated by single spinal nerve root. Myotome testing is an essential part of neurological examination when suspecting radiculopathy. Myotomes are much more complex to test than dermatomes, since each skeletal muscle is innervated by nerves derived from more than one spinal cord level.[1]

Myotomes are clinically significant as they help clinicians localise neurological lesions and diagnose radiculopathies, which affect approximately 3-5% of the population.[2] Understanding myotome distribution is essential for differentiating between nerve root compression and peripheral nerve injuries, guiding both diagnosis and treatment planning.[3]

Myotomes are a part of the somatic nervous system and the somatic nervous system is a part of peripheral nervous system.

Figure 1: Differentiation of somites into dermatome, sclerotome and myotome showing embryological development of myotomes
Figure 1: Differentiation of somites into dermatome, sclerotome and myotome showing embryological development of myotomes

Spinal Nerves

Figure 2: Spinal cord cross-section showing nerve root emergence and myotome innervation patterns

There are 31 pairs of spinal nerves. The nerves are categorised by their exit point from the vertebral column. There are 8 cervical nerves (C1-C8), 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve. Note that while there are only 7 cervical vertebrae, there are 8 cervical nerves because C8 exits between the C7 and T1 vertebrae.[4] Sixteen of these 31 nerve pairs have specific myotomes that control voluntary muscle movement.[5][6]

Myotome Distribution

It is important to distinguish between myotomes (muscles innervated by a single nerve root) and peripheral nerve innervation patterns.[7] While a myotome represents all muscles innervated by one spinal nerve root, these muscles may be supplied by different peripheral nerves. For example, the C5 nerve root contributes to both the axillary nerve (deltoid) and musculocutaneous nerve (biceps), explaining why both shoulder abduction and elbow flexion can be affected by C5 radiculopathy.

Most muscles in the limbs receive innervation from more than one spinal nerve root, and are hence comprised of multiple myotomes. Eg Biceps Brachii muscle flexes the elbow. It is innervated by the musculocutaneous nerve, which is innervated by C5, C6 and C7 nerve roots. All three of these spinal nerve roots can be said to be associated with elbow flexion.

The list below details which movement(s) has the strongest association with each myotome[8]:

Myotome Testing - ISNCSCI Standard[9]
Spinal Nerve Root Key Muscle Action (Clinical Test)
C5 Elbow flexion (biceps, brachialis)
C6 Wrist extension (extensor carpi radialis longus/brevis)
C7 Elbow extension (triceps)
C8 Finger flexion (flexor digitorum profundus to middle finger)
T1 Finger abduction (dorsal interossei)
L2 Hip flexion (iliopsoas)
L3 Knee extension (quadriceps)
L4 Ankle dorsiflexion (tibialis anterior)
L5 Great toe extension (extensor hallucis longus)
S1 Ankle plantarflexion (gastrocnemius, soleus)
Additional Myotomes (Traditional Anatomical Testing)[10]
Spinal Nerve Root Key Muscle Action
C1-C2 Neck flexion and extension
C3 Neck lateral flexion
C4 Shoulder elevation (trapezius, levator scapulae)
S2 Knee flexion (hamstrings)
S3-S5 Anal sphincter contraction

Purpose

Testing of myotomes, in the form of isometric resisted muscle testing, gives information about the level in the spine where a lesion may be present. During myotome testing, you are looking for muscle weakness of a particular group of muscles. Results may indicate lesion to the spinal cord nerve root, or intervertebral disc herniation pressing on the spinal nerve roots. The muscle strength grading scale, which assigns a rating to the degree of muscle weakness, is often used.

Medical Research Council (MRC) Muscle Strength Grading Scale

[11]

  • Grade 0: No contraction
  • Grade 1: Flicker or trace of contraction
  • Grade 2: Active movement with gravity eliminated
  • Grade 3: Active movement against gravity
  • Grade 4: Active movement against gravity and resistance
  • Grade 5: Normal power

Technique

Begin by instructing the client to perform a movement as per instructions and hold an isometric contraction against therapist resistance for a count of 5.

C5- Elbow flexion (ISNCSCI standard).[12] Instruct the patient to flex their elbow while the examiner provides resistance at the wrist. Test with the forearm in supination. This primarily tests the biceps and brachialis muscles. Note: Some clinicians also test shoulder abduction (deltoid) as an additional C5 assessment.

C6- Elbow flexion & wrist extension. Test the strength of forearm flexion by holding the patient's wrist from above and instructing them to "flex their hand up to their shoulder". Provide resistance at the wrist. Repeat and compare to the opposite arm. This tests the biceps muscle. Test the strength of wrist extension by instructing the patient to extend their wrist while the examiner resists the movement. This tests the forearm extensors. Repeat with the other arm.

C7- Elbow extension & wrist flexion. Instruct the patient to extend their forearm against the examiner's resistance. Begin their extension from a fully flexed position because this part of the movement is most sensitive to a loss in strength. This tests the triceps. Note any asymmetry in the other arm.

C8- Finger Flexion.[13] Examine the patient's hands. Look for intrinsic hand, thenar and hypothenar muscle wasting. Test the patient's grip by having the patient hold the examiner's fingers in their fist tightly and instructing them not to let go while the examiner attempts to remove them. Normally the examiner cannot remove their fingers. This tests the forearm flexors, specifically the flexor digitorum profundus to the middle finger. Compare the hands for strength asymmetry.

T1- Finger abduction. Test the intrinsic hand muscles by having the patient abduct or "fan out" all of their fingers. Instruct the patient to not allow the examiner to compress them back in. Normally, one can resist the examiner from replacing the fingers. Finger abduction or "fanning" is innervated by the T1 nerve root via the ulnar nerve.

C8 & T1- Thumb Opposition. To complete the motor examination of the upper extremities, test the strength of the thumb opposition by instructing the patient to touch the tip of their thumb to the tip of their pinky finger. Apply resistance to the thumb with your index finger. Repeat with the other thumb and compare. Thumb opposition is innervated by the C8 and T1 nerve roots via the median nerve.

L1 & L2 : Hip Flexion. Proceeding to the lower extremities, first test the flexion of the hip by instructing the patient to lie down and raise each leg separately while the examiner resists. Repeat and compare with the other leg. This tests the iliopsoas muscles.

L3: Knee Extension. Test extension at the knee by placing one hand under the knee and the other on top of the lower leg to provide resistance. Instruct the patient to "kick out" or extend the lower leg at the knee. Repeat and compare to the other leg. This tests the quadriceps muscle.

L4: Ankle Dorsiflexion. Test dorsiflexion of the ankle by holding the top of the ankle and have the patient pull their foot up towards their face as hard as possible. Repeat with the other foot. This tests the muscles in the anterior compartment of the lower leg.

L5: Great toe extension. Instruct the patient to move the large toe against the examiner's resistance "up towards the patient's face". This tests the extensor hallucis longus muscle.

S1: Ankle plantarflexion and eversion/knee flexion. Holding the bottom of the foot, instruct the patient to press down as hard as possible. Or in standing rise up onto the ball of their foot. Repeat with the other foot and compare. This tests the gastrocnemius and soleus muscles in the posterior compartment of the lower leg.

S2: Knee flexion. Test flexion at the knee by holding the knee from the side and applying resistance under the ankle and instructing the patient to pull the lower leg towards their buttock as hard as possible. Repeat with the other leg. This tests the hamstrings.[14]

S3-S5: Anal sphincter contraction.[15] With the patient's consent and a gloved finger, assess voluntary anal contraction. Instruct the patient to contract the anal sphincter as if trying to hold in a bowel movement. This tests the pudendal nerve and is crucial for assessing cauda equina function.

Clinical relevance

Myotomes are mainly useful for clinical evaluation of patients in understanding the pattern of neurological deficit after a complex nerve injury. Injury to one or more spinal myotomes can help localise lesions to a specific spinal nerve or nerve trunk.[16]

Reliability and Diagnostic Accuracy

Myotome testing demonstrates moderate to good inter-rater reliability (κ = 0.54-0.72) when performed by trained examiners.[17] The diagnostic accuracy improves when myotome testing is combined with other neurological tests such as reflex and sensory testing. Individual myotome tests have sensitivity ranging from 12-50% but specificity of 85-95% for detecting radiculopathy.[18]

Differential Diagnosis Considerations

When assessing muscle weakness, clinicians must differentiate between myotomal (nerve root) and peripheral nerve patterns:[19]

  • Myotomal weakness affects all muscles innervated by that root, regardless of peripheral nerve
  • Peripheral nerve lesions affect only muscles supplied by that specific nerve
  • Example: C8 radiculopathy causes weakness in all C8-innervated muscles (finger flexors and intrinsics), while ulnar nerve compression spares median nerve-innervated C8 muscles

References

  1. ↑ Earths lab Myotomes Available:https://www.earthslab.com/anatomy/myotomes/ (accessed 25.5.2022)
  2. ↑ Childress MA, Becker BA. Nonoperative Management of Cervical Radiculopathy. Am Fam Physician. 2016;93(9):746-754. Available from: https://www.aafp.org/pubs/afp/issues/2016/0501/p93-p9.html
  3. ↑ Wainner RS, Fritz JM, Irrgang JJ, et al. Reliability and diagnostic accuracy of the clinical examination and patient self-report measures for cervical radiculopathy. Spine. 2003;28(1):52-62. Available from: https://journals.lww.com/spinejournal/abstract/2003/01010/reliability_and_diagnostic_accuracy_of_the.10.aspx
  4. ↑ Waxenbaum JA, Reddy V, Futterman B. Anatomy, Back, Cervical Vertebrae. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459209/
  5. ↑ Study.com. What are myotomes. Available from: https://study.com/academy/lesson/what-are-myotomes-definition-testing.html (last accessed 22.4.2019)
  6. ↑ Waxenbaum JA, Reddy V, Futterman B. Anatomy, Back, Cervical Vertebrae. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459209/
  7. ↑ Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020.
  8. ↑ Kirshblum S, Burns SP, Biering-Sørensen F, et al. International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), 2011. J Spinal Cord Med. 2011;34(6):535–546. doi:10.1179/204577211X13207446293695
  9. ↑ Kirshblum S, Burns SP, Biering-Sørensen F, et al. International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), 2011. J Spinal Cord Med. 2011;34(6):535–546.
  10. ↑ Magee DJ. Orthopedic Physical Assessment. 8th ed. St. Louis: Elsevier; 2021. ISBN 978-0-323-73625-3.
  11. ↑ Compston A. Aids to the Investigation of Peripheral Nerve Injuries. Medical Research Council: Nerve Injuries Research Committee. His Majesty's Stationery Office: 1942; pp. 48–74. Brain. 2010;133(10):2838-2844. Available from: https://academic.oup.com/brain/article/133/10/2838/321042
  12. ↑ Kirshblum S, Burns SP, Biering-Sørensen F, et al. International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), 2011. J Spinal Cord Med. 2011;34(6):535–546.
  13. ↑ Preston DC, Shapiro BE. Electromyography and Neuromuscular Disorders: Clinical-Electrophysiologic-Ultrasound Correlations. 4th ed. Philadelphia: Elsevier; 2020.
  14. ↑ Slide share. Dermatomes and myotomes. Available from: https://www.slideshare.net/TafzzSailo/special-test-for-dermatomes-and-myotomes (last accessed 22.4.2019)
  15. ↑ Kirshblum S, Waring W 3rd. Updates for the International Standards for Neurological Classification of Spinal Cord Injury. Phys Med Rehabil Clin N Am. 2014;25(3):505-517. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4119635/
  16. ↑ Duff SV, DeMatteo C. Clinical assessment of the infant and child following perinatal brachial plexus injury. J Hand Ther. 2015 Apr-Jun;28(2):126-33; quiz 134. doi: 10.1016/j.jht.2015.01.001. Epub 2015 Jan 16. PMID: 25840493; PMCID: PMC4425986.
  17. ↑ Wainner RS, Fritz JM, Irrgang JJ, et al. Reliability and diagnostic accuracy of the clinical examination and patient self-report measures for cervical radiculopathy. Spine. 2003;28(1):52-62. Available from: https://journals.lww.com/spinejournal/abstract/2003/01010/reliability_and_diagnostic_accuracy_of_the.10.aspx
  18. ↑ Tawa N, Rhoda A, Diener I. Accuracy of clinical neurological examination in diagnosing lumbo-sacral radiculopathy: a systematic literature review. BMC Musculoskelet Disord. 2017;18(1):93. Available from: https://bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/s12891-016-1383-2
  19. ↑ Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic Medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002.
Retrieved from "https://www.physio-pedia.com/w/index.php?title=Myotomes&oldid=371716"