What is a Myotome?
Myotome is a group of muscles innervated by one spinal nerve root. Myotome comes from two words in Greek, namely "myo" which means muscle, and "tome" which means a "piece" or "thin segment".
Myotome examination is very helpful in clinical practice. Myotome can be used as a basis for diagnosing patients who experience weakness or atrophy. Myotome can also help in the treatment process, because based on the results of the myotome examination, it will provide identification of problematic or disturbed nerve roots at the spinal level. Based on knowledge of the myotome and dermatome, it will provide clues to the surgeon regarding the roots or vertebrae that will be explored.
Myotome Distributione
A. Upper Limbs
| Nerve Roots | Upper Limb Movement |
| C5 | Shoulder abduction |
| C6 | Elbow flexion |
| Wrist extension | |
| C7 | Elbow extension |
| C8 | Thumb extension |
| Ulnar deviation | |
| T1 | Finger abduction |
B. Lower limbs
| Nerve Roots | Upper Limb Movement |
| L2 | Hip flexion |
| L3 | Knee extension |
| L4 | Ankle dorsiflexion |
| L5 | Big toe extension |
| S1 | Ankle plantarflexion |
| S2 | Knee flexion |
Myotome Examinatione
Myotome examination is carried out to assess whether there is a disturbance in the distribution of motor nerves in the nerve roots. A myotome examination is performed by asking the patient to perform several different movements related to the spinal cord. The examination is carried out by carrying out tests such as isometric and concentric contractions. In isometric contractions, muscle contractions must be held for a minimum of 5 seconds. The results of this test will be used as evaluation material for whether the spinal cord is affected by lesions, disease or injury if the patient is unable to fully move.
A. Cervical and thoracic
The cervical and thoracic myotomes (C1-T12) were tested with the patient in a sitting position. The myotome will be tested for movement of the neck and upper extremities through the shoulders, elbows, wrists, metacarpophalangeal, and interphalangeal.
Movement to examine the cervical and thoracic areas
| C1-C2 | Neck flexion |
| C3 dan CN XI | Lateral flexion of the neck |
| C4 dan CN XI | Shoulder elevation |
| C5 | Abduction, external rotation, and shoulder flexion |
| C5 – C6 | Shoulder flexion |
| C6 | Shoulder supination |
| C6 – C7 | Extension of the arm from the elbow Flexion and extension of the hand |
| C6 – C8 | Internal rotation, adduction and extension of the shoulder |
| C7 – C8 | Pronation of the shoulder joint Flexion and extension of the knuckles of the hand |
| C8 | Thumb extension Ulnar deviation |
| T1 | Abduction of fingers 2, 3, 4 |
| T2-T12 | Generally not tested. This nerve innervates the chest and abdominal muscles |
If the patient is unconscious, the myotome can be tested by tendon reflexes:
- C6 – tendon of the biceps brachii muscle in the cubital fossa
- C7 – tendon of the triceps brachii muscle behind the elbow
B. Lumbar and sacral
Lumbar and sacral myotomes (L1-S3) were tested with the patient lying supine. Can be tested by hip, knee, ankle, intertarsal, and metatarsophalangeal joint movements.
| L1-L3 | Flexion and internal rotation of the hip and thigh |
| L1-L4 | Hip and thigh adduction |
| L1, L5 | External rotation of hips and thighs |
| L3-L4 | Knee extension |
| L4-L5 | Thigh extension Leg inversion |
| L4-S1 | Dorsiflexion of the foot and ankle |
| L5-S1 | Thigh abduction. Eversion of the leg |
| L5-S2 | Knee flexion |
| L5 | Toe extension |
| S1-S2 | Ankle plantarflexion |
| S2-S3 | Adduction of the big toe |
| S3-S4 | Anal reflex contraction of the external anal sphincter |
| S4-S5 | Rectal and/or bladder dysfunction |
Lumbar and sacral myotomes can be tested with tendon reflexes if the patient is unconscious:
- L3-L4 – tap the patellar ligament (tendon).
- S1-S2 – calcaneal tendon tap
Also read: Cedera Saraf Dan Sistem Klasifikasinya
Reference :
- Physiopedia. Myotomes. diakses pada tanggal 30 Oktober 2023 melalui https://www.physio-pedia.com/Myotomes
- Kenhub. Myotomes. diakses pada tanggal 30 Oktober 2023 melalui https://www.kenhub.com/en/library/anatomy/myotomes
- Sonoo MRecent advances in neuroanatomy: the myotome updateJournal of Neurology, Neurosurgery & Psychiatry 2023;94:643-648.
