L2 l3 dermatome: Dermatomes: Definition, chart, and diagram

23.03.202121.07.2023 by alexxlab

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Dermatomes: Definition, chart, and diagram

Dermatomes are areas of skin that send signals to the brain through the spinal nerves. The dermatome system covers the entire body from the hands and fingers to the feet and toes.

The part of a nerve that exits the spinal cord is called the nerve root. Damage to a nerve root can trigger symptoms in the nerve’s corresponding dermatome.

Below, we show the locations of the dermatomes throughout the body. We also describe health conditions that can damage the spinal nerves and affect their dermatomes.

Share on PinterestVarious health problems damage the spinal nerves and affect the surrounding skin.

A dermatome is an area of skin that sends information to the brain via a single spinal nerve.

Spinal nerves exit the spine in pairs. There are 31 pairs in total, and 30 of these have corresponding dermatomes.

The exception is the C1 spinal nerve, which does not have a corresponding dermatome.

The spinal nerves are classified into five groups, according to the region of the spine from which they exit.

The five groups and their points of exit from the spine are:

Cervical nerves: These exit the neck region and are labeled C1–C8.
Thoracic nerves: These exit the torso region and are labeled T1–T12.
Lumbar nerves: These exit the lower back region and are labeled L1–L5.
Sacral nerves: These exit the base of the spine and are labeled S1–S5.
A coccygeal nerve pair: These exit the tailbone, or coccyx.

Each dermatome shares the label of its corresponding spinal nerve.

Some dermatomes overlap to a certain extent, and the precise layout of the dermatomes can vary slightly from one person to the next.

Below, we list the locations of the dermatomes that correspond to the spinal nerves in each group.

Cervical nerves and their dermatomes

C2: the base of the skull, behind the ear
C3: the back of the head and the upper neck
C4: the lower neck and upper shoulders
C5: the upper shoulders and the two collarbones
C6: the upper forearms and the thumbs and index fingers
C7: the upper back, backs of the arms, and middle fingers
C8: the upper back, inner arms, and ring and pinky fingers

Thoracic nerves and their dermatomes

T1: the upper chest and back and upper forearm
T2, T3, and T4: the upper chest and back
T5, T6, and T7: the mid-chest and back
T8 and T9: the upper abdomen and mid-back
T10: the midline of the abdomen and the mid-back
T11 and T12: the lower abdomen and mid-back

Lumbar nerves and their dermatomes

L1: the groin, upper hips, and lower back
L2: the lower back, hips, and tops of the inner thighs
L3: the lower back, inner thighs, and inner legs just below the knees
L4: the backs of the knees, inner sections of the lower legs, and the heels
L5: the tops of the feet and the fronts of the lower legs

Sacral nerves and their dermatomes

S1: the lower back, buttocks, backs of the legs, and outer toes
S2: the buttocks, genitals, backs of the legs, and heels
S3: the buttocks and genitals
S4 and S5: the buttocks

The coccygeal nerves and their dermatome

The dermatome corresponding with the coccygeal nerves is located on the buttocks, in the area directly around the tailbone, or coccyx.

Symptoms that occur within a dermatome sometimes indicate damage or disruption to the dermatome’s corresponding nerve. The location of these symptoms can, therefore, help doctors diagnose certain underlying medical conditions.

Some conditions that can affect the nerves and their corresponding dermatomes are:

Shingles

Shingles, or herpes zoster, is a viral infection caused by the reactivation of the varicella-zoster virus. This is the same virus that causes chickenpox.

After the body recovers from chickenpox, the virus can lie dormant and eventually reactivate as shingles.

In adults, shingles typically causes a rash to form on the trunk, along one of the thoracic dermatomes. The rash may be preceded by pain, itching, or tingling in the area.

Some other symptoms of shingles can include:

a headache
sensitivity to bright light
a general feeling of being unwell

A person with a weakened immune system may develop a more widespread shingles rash that covers three or more dermatomes. Doctors refer to this as disseminated zoster.

Pinched nerves

A pinched nerve occurs when a nerve root has become compressed by a bone, disc, tendon, or ligament. This compression can occur anywhere along the spine, but it usually occurs in the lower, or lumbar, region.

A pinched nerve can cause pain, tingling, or numbness in its corresponding dermatome. As such, the location of the symptoms can help a doctor identify the affected nerve.

The doctor then diagnoses and treats the underlying cause of the pinched nerve and recommends ways to relieve the symptoms.

Traumatic injury

A traumatic injury to the nerves may result from an accident or surgery.

The severity of symptoms can help doctors determine the extent of the nerve injury.

Dermatomes are areas of skin, each of which is connected to a single spinal nerve. Together, these areas create a surface map of the body.

Dysfunction or damage to a spinal nerve can trigger symptoms in the corresponding dermatome. Nerves damage or dysfunction may result from infection, compression, or traumatic injury.

Doctors can sometimes use the severity of symptoms in a dermatome to determine the extent and location of nerve damage. They then work to diagnose and treat the underlying cause of the damage.

All About the L3-L4 Spinal Segment

The L3-L4 spinal motion segment, positioned in the middle of the lumbar spine, plays an important role in supporting the weight of the torso and protecting the cauda equina (nerves that descend from the spinal cord). While the L3-L4 motion segment is less likely to be injured compared to its lower counterparts, it may be subject to degeneration, trauma, and disc-related problems.

Learn how the lumbar spinal discs function and how lower back conditions can cause back pain and/or radiating pain. Watch Now

This article highlights the anatomy of the L3-L4 motion segment, the potential problems that may occur in this region, and the treatment options.

Anatomy of the L3-L4 Spinal Motion Segment

The L3-L4 motion segment includes the following structures:

The L3-L4 motion segment provides a bony enclosure to protect the cauda equina and other delicate structures.

See Lumbar Spine Anatomy and Pain

Potential Problems at L3-L4

Potential problems that may occur at the L3-L4 motion segment are:

Osteoarthritis. The L3-L4 facets are typically subject to recurrent rotational strain, which may cause osteoarthritis to develop in these joints, resulting in facet joint pain.
¹
Cramer GD. The Lumbar Region. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:246-311. doi:10.1016/b978-0-323-07954-9.00007-4
See Facet Joint Disorders and Back Pain
Degenerative spondylolisthesis. Age-related changes in the facet joints may result in the forward slippage of the L3 vertebra over L4.
¹
Cramer GD. The Lumbar Region. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:246-311. doi:10.1016/b978-0-323-07954-9.00007-4
See Degenerative Spondylolisthesis
Disc problems. The L3-L4 disc may degenerate or herniate due to age-related changes or from trauma.
See Lumbar Herniated Disc: What You Should Know

When subject to acute trauma, the L3-L4 motion segment may rarely undergo facet joint dislocation, fracture, and/or damage to the cauda equina. Rarely, tumors and infections may affect the L3-L4 motion segment.

The L3-L4 motion segment may cause muscle pain, discogenic pain, radicular (nerve root) pain, and/or radiculopathy (neurologic deficit) that typically affects the lower back and/or the legs.

When the L3 spinal nerve is involved, the following symptoms may occur:

Sharp pain, typically felt as a shooting and/or burning feeling that may occur in the thigh and/or inner part of the leg.
³
Dulebohn SC, Ngnitewe Massa R, Mesfin FB. Disc Herniation. [Updated 2019 Aug 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441822/
Numbness in the thigh and/or inner part of the leg.
³
Dulebohn SC, Ngnitewe Massa R, Mesfin FB. Disc Herniation. [Updated 2019 Aug 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441822/
Weakness while moving the thigh and/or knee in different directions.
³
Dulebohn SC, Ngnitewe Massa R, Mesfin FB. Disc Herniation. [Updated 2019 Aug 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441822/
Abnormal sensations, such as a feeling of pins-and-needles and/or tingling.

These symptoms are typically experienced in one leg. Rarely, both legs may be affected together.

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Dermatomes – e-Anatomy – IMAIOS

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Classification of the level and severity of spinal cord injury

Medical rehabilitation

Until the early 1990s, there was no single generally accepted classification of the level and severity of spinal cord injury. Doctors often used different definitions of the level of injury, complete and incomplete injuries. This article provides a classification developed by the American Spinal Injury Association (ASIA).

The spinal cord is located inside the spinal canal. Segmental levels of the spinal cord are determined by the anterior and posterior spinal roots, which connect to the spinal nerves near the intervertebral foramina. There are 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-3 coccygeal segments of the spinal cord (Figure 1) . The upper cervical segments are located at the level of the bodies of the cervical vertebrae corresponding to their serial number. The lower cervical and upper thoracic segments are one vertebra higher than the corresponding vertebral bodies. In the middle thoracic region, this difference is equal to two vertebrae, in the lower thoracic region, to three vertebrae. The lumbar segments are located at the level of the bodies of the tenth and eleventh thoracic vertebrae, the sacral and coccygeal segments correspond to the levels of the twelfth thoracic and first lumbar vertebrae. The lower border of the spinal cord tapering in the form of a cone is located at the level of the second lumbar vertebra. Below this level is the terminal filament, which is the remnant of the final section of the embryonic spinal cord and is surrounded by the roots of the spinal nerves and the membranes of the spinal cord. The roots of the spinal nerves at this level form the so-called cauda equina.

Figure 1. Spine and segmentation of the spinal cord

Sensory and motor levels

A dermatome is a skin area innervated by a certain segment of the spinal cord. Figures 2 and 3 show dermatomes and key points for their definition, as well as muscle groups recommended for testing by the American Spinal Injury Association. After injury, dermatomes may expand or contract due to spinal cord plasticity. The complete form that ASIA recommends filling out when examining a patient with a spinal cord injury is available in English in pdf format (Adobe Acrobat Reader required to view).

Figure 2. Areas of sensitive innervation

C2-C4. C2-dermatome includes the skin of the occiput and upper neck. C3 – lower neck and collarbone. C4 – subclavian region.
C5-T1. These dermatomes are located on the arms. C5 – outer surface of the arm at and above the elbow. C6 – radial (from the side of the thumb) part of the forearm and hand. C7 – middle finger, C8 – lateral part of the hand, T1 – inner side of the forearm.
T2-T12. Thoracic dermatomes are located in the axillary and thoracic region. T3-T12 cover chest and back to hips. The nipples are located in the middle of T4. T10 is located near the navel. T12 ends just above the thigh.
L1-L5. Dermatomes located in the area of the hip joints and groin are innervated by the L1 segment of the spinal cord. L2 and L3 cover the front of the thighs and knees. L4 and L5 – medial (inner) and lateral (outer) parts of the legs.
S1-S5. S1 is located on the heel and calf. S2 – back of the thighs and popliteal fossa. S3 – medial buttocks and S4-S5 – perineum. S5 – anal area.

Figure 3. Key muscle groups

Ten muscle groups reflect the motor innervation of the cervical and lumbosacral sections of the spinal cord. The ASIA system does not test the abdominal muscles (i.e., T2-11), since at the thoracic level it is much easier to locate the affected segment of the spinal cord along the corresponding dermatome. Some other muscles (such as the popliteal) are also excluded, since the segments that innervate them are already represented by other muscles.
Muscles of the hand. C5 innervates the flexors of the forearm (biceps), C6 the extensors of the wrist, C7 the extensors of the forearm (triceps), C8 the flexors of the fingers, and T1 the abductor (adductor) of the little finger.
Leg muscles. Innervated by the lumbar segments of the spinal cord. L2 innervates the hip flexors (m. psoas), L3 – knee extensors (m. quadriceps), L4 – dorsal foot flexors (m. tibialis anterior), L5 – thumb extensors (m. extensor hallucis longus), S1 – plantar flexors of the foot (m. gastrocnemius).
The anal sphincter is innervated by S4-S5. It is very important in the neurological examination of patients with spinal cord injury. If voluntary contraction of the anal sphincter is possible, the spinal cord injury is considered incomplete, regardless of any other evidence. It is important to note that testing certain muscle groups according to the ASIA classification simplifies the real situation, since almost every muscle receives innervation from two or more segments of the spinal cord.

Levels of spinal cord injury

Doctors use two different definitions of the level of spinal cord injury. Based on the same neurological examination, neuropathologists and rehabilitation specialists can determine a different level of injury. Neuropathologists usually determine the level of damage by the first segment of the spinal cord in which dysfunction is detected. At the same time, physical therapy and rehabilitation doctors determine the level of damage in the lowest segment with preserved function. Thus, if a patient has normal sensitivity at the C3 level and none with C4, the rehabilitator will say that the sensory level is C3, and the neuropathologist or neurosurgeon will call the damage level C4. Most traumatologists and orthopedists determine the level of damage by the level of damage to the spine.
ASIA recommends determining the level of damage by the lowest segment with preserved function.

Complete or partial damage

In the clinic, spinal cord injury is usually described as complete or incomplete. A complete injury is one in which there is no motor or sensory function below the site of injury. However, this definition is not always applicable. The following three examples illustrate the shortcomings and ambiguities of the traditional definition. The ASIA committee considered these issues when developing the spinal cord injury classification in 1992 year.

Partially protected areas. Often, some segments of the spinal cord below the injury site retain a partial function, although in the other underlying segments, both motor and sensory function are absent. This is a fairly common occurrence. Many patients have areas of partial preservation. What kind of damage in this case – complete or incomplete, and at what level?
Lateral preservation. A function can be partially saved on one side, but not on the other, or be there on another level. For example, if a patient has no sensitivity with C4 on the right and with T1 on the left, is this damage complete or incomplete, and at what level?
Restore function. An initially missing function below the fault can then be restored. Does this mean that the spinal cord injury was complete and became incomplete? This is not a trivial matter, because if, for example, a clinical trial is being conducted in which only patients with complete spinal cord injury participate, it is necessary to stipulate the timing of the assessment of the status.

Most clinicians consider damage complete if there is a level of the spinal cord below which no function is detected. The Committee of the American Spinal Injury Association decided to take this criterion to its logical limit: the injury is considered complete if there is no motor and sensory function in the anal and perineal regions, which are innervated by the sacral (S4-S5) spinal cord.
The decision to make the absence of function at the S4-S5 level the criterion for complete damage not only removed the issue of zones of partial and lateral function preservation, but also solved the problem of restoration of function. As it turned out, only in a small number of patients in whom neurological functions at the level of S4-S5 were absent, they are restored spontaneously. The ASIA classification separately indicates the motor and sensory levels on each side and the zones of partial preservation, as this simplifies the criterion for assessing the completeness of the damage.
Finally, the question itself: complete damage or incomplete, can be debatable. The absence of motor and sensory function below the injury site does not necessarily mean the absence of axons that cross the injury site. Animal studies and clinical data indicate that the function that is absent below the site of injury can be restored to some extent by restoring the blood supply to the spinal cord (in the case of arteriovenous malformation caused by ischemia), decompression (if there is chronic compression – compression of the spinal cord) or drug therapy, for example, 4-aminopyridine. Assessing spinal cord injury as complete, one should not deprive a person of hope for recovery.

Classification of severity of spinal cord injury

Physicians have long used the clinical neurological deficit score, developed at Stokes Manville before World War II and introduced by Frankel in the 1970s. On this scale, patients were divided into five categories: no function (A), only sensory function (B), some sensory and motor function preserved (C), useful motor function (D), and normal (E).

ASIA Injury Severity Scale

A=Complete: No motor or sensory function in the sacral segments S4-S5
B=Incomplete: Sensation preserved but no motor function in segments below the neurological level, including S4-S5.
C=Incomplete: Motor function below the neurological level is preserved, but more than half of the key muscles are below
neurological level have a strength of less than 3 points.
D=Incomplete: Below neurological level of motor function is preserved, and at least half of the key muscles below the neurological level have a strength of 3 or more.
E=Normal: motor and sensory functions are normal.

Clinical syndromes

Central
Brown-Sekara
Front pillars
Brain cone
Pony tail

The ASIA Spinal Cord Injury Severity Scale is based on the Frankel scale, but differs from it in a number of important ways.
First, the absence of any function below the level of damage was replaced in category A with the absence of motor and sensory function in the sacral segments S4-S5. This definition is clear and unambiguous.
Category B ASIA is essentially identical to Frankel B, but adds a requirement for retained sensory function in S4-S5. It should be noted that the defining moment in categories A and B on the ASIA scale is the preservation of motor and sensory function in S4-S5.
ASIA also added a quantitative measure for categories C and D. The Frankel scale required clinicians to rate the functional fitness of the lower extremities. This not only introduced a subjective element into the classification, but also ignored the assessment of hand function in patients with cervical spinal cord injury. To circumvent this problem, ASIA specifies that category C includes patients with more than half of the key (recommended for testing) muscles retaining strength less than 3 points. Otherwise, the patient is assigned to category D.
Category E is interesting in that it includes patients with spinal cord injury without any neurological deficit, at least detectable on neurological examination. The ASIA Motor and Sensory Scale does not take into account the presence of spasticity, pain, muscle weakness, and some forms of dysesthesia that may result from spinal cord injury. Such patients should be assigned to category E.
ASIA has also classified incomplete spinal cord injury into five types.
Central syndrome (with greater damage to the gray matter of the spinal cord – hemorrhages, necrosis): unequal severity of motor disorders in the upper and lower extremities, a varied degree of sensitivity impairment.
Brown-Sequard syndrome – damage to one half of the spinal cord: impaired motor functions and proprioceptive sensitivity on the side of the lesion and loss of pain and temperature sensitivity on the other side.
Syndrome of the anterior pillars: impaired motor functions of both pain and temperature sensitivity while maintaining proprioceptive sensitivity (damage affects the lateral corticospinal and corticothalamic tracts, the posterior columns remain intact).
Syndromes of the conus medullary and cauda equina are observed when there is damage in the region of the cone of the spinal cord and cauda equina. In this case, the spinal nerves are injured, which is manifested by flaccid paralysis of the lower extremities, anesthesia of the sciatic zone, impaired bowel and bladder functions.

Conclusion

There is no unity in terminology related to the level and severity of spinal cord injury. The American Spinal Injury Association has attempted to standardize the terms used to describe spinal cord injury.