by Maria I. Martos
The central nervous system is comprised of the brain and spinal cord. The peripheral nervous system consists of cranial nerves, which branch out of the brain, and spinal nerves, which branch out of the spinal cord. A total of 31 sets of nerves branch out of the spinal cord. The point at which the nerve branches out from the cord is known as the nerve root. Each nerve travels a short distance (about ½ inch) from the cord and then divides into small posterior divisions (dorsal rami) and larger anterior divisions (ventral rami). The dorsal rami innervate the posterior muscles and skin of the trunk; the ventral rami, from, T1 to T12, innervate the anterior and lateral muscles and skin of the trunk. The remaining anterior divisions form networks called plexuses, which then distribute nerves to the body. The nerves from each plexus innervate specific muscles and areas of skin in the body and are numbered according to the location in the spine from which they exit. Following are the four main plexuses:
- cervical plexus, C1 – C4, innervates the diaphragm, shoulder and neck
- brachial plexus, C5 – T1, innervates the upper limbs
- lumbar plexus, T12/L1 – L4, innervates the thigh
- sacral plexus, L4 – S4, innervates the leg and foot.
The latter two plexuses, which innervate the lower limbs, are often considered together as the lumbosacral plexus. This text will focus on the brachial plexus and lumbosacral plexus from level T12/L1 to S1.
Spinal nerves have motor fibers and sensory fibers. The motor fibers innervate certain muscles, while the sensory fibers innervate certain areas of skin. A skin area innervated by the sensory fibers of a single nerve root is known as a dermatome. A group of muscles primarily innervated by the motor fibers of a single nerve root is known as a myotome. Although slight variations do exist, dermatome and myotome patterns of distribution are relatively consistent from person to person.
Nerves are typically injured through compression or tensile forces.
When a nerve root in the brachial or lumbosacral plexus is damaged, certain patterns of motor and sensory deficits occur in the corresponding limbs. Dermatomes and myotomes are used to evaluate these deficits.
To test for nerve root damage, the corresponding dermatomes supplied by that nerve root may be tested for abnormal sensation and the myotomes may be tested for weakness. To test for sensitivity of a dermatome, a pinwheel, cotton ball, paper clip, the pads of the fingers or fingernails may be used. The patient should be asked to provide feedback regarding their response to the various stimuli. Following are possible responses to abnormal sensation:
- Hypoesthesia (decreased sensation).
- Hyperesthesia (excessive sensation).
- Anesthesia (loss of sensation).
- Paresthesia (numbness, tingling, burning sensation).
Dermatome patterns and their corresponding root nerve spinal derivation are illustrated below:
To test for decreased muscle strength, the following standardized grading scale can be used:
|5||Normal||Complete range of motion (ROM) against gravity with full resistance|
|4||Good||Complete ROM against gravity with some resistance|
|3||Fair||Complete ROM against gravity with no resistance; active ROM|
|2||Poor||Complete ROM with some assistance and gravity eliminated|
|1||Trace||Evidence of slight muscular contraction, no joint motion evident|
|0||Zero||No evidence of muscle contraction|
Muscles should be tested on a regular basis in order to determine improvement or deterioration of function. It should be noted that the unaffected side should always be tested as well as the affected side for comparison.
The following section will identify the myotomes within the neurologic levels of the brachial and lumbosacral plexuses, provide detailed illustrations of each level (to include additional illustrations of dermatomal patterns), and site tests which can be performed to check for muscle strength at each level. (Illustrations of reflex testing at each level will also be included, but will not be discussed in this text.)
Brachial Plexus – Neurologic levels C5 – T1
Neurologic Level C5: The muscles found within this myotomal pattern are the deltoid and the biceps brachii. Because the latter is also innervated by C6, the deltoid is the most “pure” C5 muscle. The deltoid’s most powerful motion is abduction. One of the most commonly used tests for shoulder abduction is to instruct the patient to flex the elbow at 90 degrees, then offer gradual resistance to abduction until determining the extent of resistance h/she can overcome. Below are illustrations of neurologic level C5 and of the test for shoulder abduction.
Neurologic Level C6: As mentioned above, the biceps brachii is innervated by C5 and C6. C6 also innervates the most powerful wrist extensors, carpi radialis longus and brevis, which do radial extension. The ulnar extensor, extensor carpi ulnaris, is innervated by C7. To test for wrist extension, stabilize the patient’s forearm with the palm of your hand on the anterior aspect of the wrist. With the patient’s wrist in full extension, place the palm of your free hand over the posterior aspect of the patient’s hand and try to force it out of extension. If no damage is present, the patient will be able to resist movement. If C6 is damaged, ulnar deviation will occur. If C7 is injured, radial deviation will occur. Below are illustrations of neurologic level C6 and of the test for wrist extension
Neurologic Level C7: The muscles found within this myotomal pattern are the triceps, wrist flexors and finger extensors. The triceps muscle primarily does elbow extension. A common test for this action is to ask the patient to fully flex the arm. Stabilize the patient’s arm just above the elbow and ask h/her to slowly extend it. Before the arm reaches a 90 degree angle, begin to offer firm, constant resistance until discerning the maximum resistance h/she can overcome. Below are illustrations of neurologic level C7 and of the test for elbow extension.
Neurologic Level C8: The muscles found within this myotomal pattern are finger flexors—flexor digitorum superficialis, flexor digitorum profundis, and the lumbricals. To test for finger flexion, the patient fully flexes h/her fingers at all joints while you curl your fingers into them. Ask the patient to resist your attempt to pull h/her fingers out of flexion. A normal response is for all joints to remain flexed. Below are illustrations of neurologic level C8 and of the test for finger flexion.
Neurologic level T1: The muscles found within this myotomal pattern are those involved in finger abduction—dorsal interossei and abductor digiti quinti (5th finger)—and adduction—palmar interossei. To test for abduction, instruct the patient to abduct h/her fingers. Then pinch each set of fingers to try to force them together (index to the middle, ring, and little finger, the middle to the ring and little finger, and the ring to the little finger.) Note any significant weaknesses between pairs. Test both hand in order to compare the strength of each, and evaluate them according to the standardized grading scale for muscle strength. To test for finger adduction, ask the patient to extend h/her fingers and hold a piece of paper (or a dollar bill) between two of h/her fingers. Then you pull it out. Test the other hand in the same manner and compare the strength of each. Following are illustrations of neurologic level T1 and of the tests for finger abduction and adduction.
Lumbosacral plexus~Neurologic levels t12 to s1
Neurologic Levels T12 to L3: The muscles found within this myotomal pattern are the iliopsoas (T12-L3—main hip flexor), quadriceps (L2-L4—hip flexion, knee extension), and adductors (L2-L4—hip adduction). Because this myotomal pattern includes multiple muscle groups (and, therefore, does not have individual muscles which can be tested) an injury to this nerve root level can be more easily evaluated by sensory testing of the dermatomal patterns. However, motor testing may be performed if desired. An example of a test for knee extension, for instance, would be to have the patient sit on the treatment table. Place one hand above the knee to stabilize the thigh, and the other hand on the patient’s anterior leg above the ankle. Offer resistance to knee extension, and note the amount of resistance the patient can overcome. Test both limbs in order to compare the strength of each, and evaluate them according to the standardized grading scale for muscle strength. Following is a detailed illustration of the dermatomes of the lower extremities and of the above- mentioned test for knee extension.
Neurologic Level L4: The muscle predominantly innervated at this root nerve level is the tibialis anterior, which does dorsiflexion with inversion. To test this muscle, ask the patient to sit on the treatment table. With one hand, stabilize the patient’s leg by holding it just above the ankle. Instruct the patient to dorsiflex and invert h/her foot. With your free hand, hold the patient’s foot and ask h/her to resist your attempt to move the foot into plantarflexion and eversion. Test both feet in the same manner in order to compare the strength of each, and evaluate them according to the standardized grading scale for muscle strength. Following is an illustration of neurologic level L4 and of the above-mentioned muscle test for dorsiflexion with inversion:
Neurologic Level L5: The muscles found within this myotome are the extensor hallucis longus (big toe extensor), extensor digitorum (heel walk) and the gluteus medius (the most powerful abductor of the hip.) A common test for hip abduction is to ask the patient to lie on h/her side with both legs extended, careful not to flex at the hip. Place one hand on h/her pelvis to stabilize it and ask h/her to fully abduct it. Place your free hand on the lateral knee at the joint and ask the patient to resist your attempt to push the leg into adduction. Test both sides in the same manner in order to compare the strength of each, and evaluate them according to the standardized grading scale for muscle strength. Following is an illustration of neurologic level L5 and of the above-mentioned test for hip abduction:
Neurologic Level S1: The muscles found within this myotome are the peroneus longus (plantarflexion with eversion) peroneus brevis (toe walk) and gluteus maximus (hip extension.) To test for hip extension, ask the patient to lie face down on the treatment table and bend the leg at the knee (this relaxes the hamstrings.) Stabilize the hip by placing your forearm over the iliac crest, and ask the patient to hyperextend h/her hip. Place your other hand on the thigh below the gluts and ask the patient to resist your attempt to push the thigh back down on the table. Test both sides in the same manner in order to compare the strength of each, and evaluate them according to the standardized grading scale for muscle strength. Following is an illustration of neurologic level S1 and of the above-mentioned test for hip extension.
As healthcare professionals, Therapeutic Massage Therapists need to be as educated and knowledgeable about the workings of the human neuromuscular system as possible. Knowledge not only enables us to better educate our clients as to the injury and recovery process, it also helps us facilitate our clients’ recovery process from myofascial pain and dysfunction. Having knowledge of dermatomes and myotomes may help us to differentiate between dysfunction resulting from myofascial trigger points and that resulting from nerve root injury. Myofascial trigger points don’t match dermatomal and myotomal patterns; knowing the patterns of each may help a Massage Therapist to discern between them. However, since numbness and tingling may be due to either myofascial tightness impinging on a nerve or nerve root damage, and since Massage Therapists do not diagnose, it’s important to refer a client to a physician for a definitive diagnosis of symptoms.
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