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The Kortelainen Study | The Nitta Study | Lower Extremity Dermatome Maps

Dermatome Research:

Did you know that most of the dermatome charts that are floating around the internet and on the walls of doctors' offices were based on investigations made over 35 years ago at best (31), and over 90 years ago at worst(30). Heck, some investigation date back to the 1800s (32)! Although in 1948 Keegan et al. had the right idea for developing dermatome charts (33), in that he studies and mapped the effects of disc herniations on the skin in the extremities, his results still couldn't confirm any of the prior work!

Kortelainen et al: In 1985, Kortelainen et al. (1) conducted an investigation into the 'pain referral patterns' (dermatomes) and neurological findings prospectively in 403 patients who were about to have a discectomy. CT results and surgical results (confirming compressive disc herniation) were compared with those patients pain referral zones. They discovered that spinal nerve root irritation (via disc herniation) did NOT always correlate with the anticipated pain referral zones as classically described. This was especially true of the S1 dermatome. Here is a table of what they found:

Level of disc rupture

Number of patients

L4 Dermatome

L5 Dermatome

S1 Dermatome

No specific dermatome

L2 Disc

3 (0.7%)

(0%)

1 (0.6%)

2 (1%)

L3 Disc

7 (1.7%)

1 (9%)

3 (1.8%)

3 (1.5%)

L4 Disc

229 (57%)

7 (64%)

136 (80%)

66 (34%)

20 (74%)

L5 Disc

164 (41%)

3 (27%)

31 (18%)

123 (63%)

7 (26%)

Total

403

11 (3%)

171 (42%)

194 (48%)

27 (7%)

In summary, the pain projection into the L5 dermatome was caused by L5 nerve root compression in 79% of the cases, and by L4 nerve root compression in 21% of the cases; pain project in into the S1 dermatome was caused by S1 nerve root compression in only 56% of the cases, and by L5 nerve root compression in 44% of the cases! As you can see by these results, S1 dermatomal pain (pain in the side of the foot and little toe) is not very accurate at predicting the level of nerve root compression/irritation. (1) In closing they noted the the high disc herniations (L3/4) were not predictive of any expected neurological pattern. (I would note that the Kortelainen study was not as 'scientific' as the up-coming Nitta study, and we can only assume that the disc herniations all caused compression of the traversing spinal nerve root and NOT the exiting spinal nerve root. (There was no mention of this very important factor in the paper!)

Nitta et al: Finally, Nitta et al. published the first investigation that was of high scientific design (2)! In 1992, this group of investigators successfully mapped the sensory-dermatomal distribution of the L4, L5, and S1 nerve roots. They gathered 71 patients, who were suffering disc herniation-associated radicular pain, and 'blocked' (anesthetized) their problematic nerve root with Xylocain; this was done under fluoroscopy to ensure the correct nerve roots were blocked. Next they carefully marked (aka: mapped) the areas on the patients skin that were numbed by the Xylocain nerve blocks. The results were tabulated and are shown below; however, the bottom line is this: "The L4 nerve root innervates (connects, gives-life-to) the medial side (inside) of the lower leg in 88% of the patients tested. The L5 nerve root innervates the side of the first digit (big toe) on the dorsum (top) of the foot in 82% of the patients. The S1 nerve root innervates the side of the fifth digit of the foot in 83% of the individuals." (2)

Although the majority of patients seem to share the same 'nerve root dermatomal distributions' (wiring), this investigation has clearly demonstrated that the neural anatomy of the lumbar spine does have some degree of variation, i.e., some 20% of the patients did NOT have the typical 'nerve root dermatomal distributions'. For example, in some patients, a L5 nerve root block would result in numbness of the S1 dermatome and not the anticipated L5 dermatome (2).

I've based my recommended Dermatome Maps (as has Volvo Award Winner Dr. Nikolai Bogduk) on Nitta's work simply because today, this is the most accurate information we have on nerve root sensory distribution.

DERMATOME MAPS:

S1 RADICULAR PAIN:

If the L5 disc herniates into the 'lateral recess' (which is where it usually does) and compresses / irritates the descending S1 nerve root, the patient may suffer an S1 radicular pain (aka: S1 root-pain, or S1 Sciatica). Fig.# 4 shows the regions in the lower limb where the patient will most likely suffer the symptoms of S1 sciatica (2). As you can see, the majority of patients (75%) suffer the burning, stinging, and numbing pain of sciatica in the lateral foot, posterolateral leg, thigh, and butt, as well as, the bottom, outer 1/2 of the foot. These pains are the result of damage and irritation to the 'sensory portion' (portion of the nerve root which connects to skin) of the nerve root.

If the 'motor portion' (portion of the nerve root which connects to muscle) of the S1 nerve root is damaged or irritated by the disc herniation, the patient my suffer weakness and/or atrophy in the Gastrocnemius muscle (the calf), the peroneal muscles (foot evertors), and/or the muscles which flex or curl the 'big toe'. The Achilles' Reflex and Plantar Reflex may also be diminished or absent. If severe, the patient will be unable to do 'calf raises' with the effected foot. Calf raising is the 'gold standard' muscle test for S1.

L5 RADICULAR PAIN:

If the L4 disc herniates into the 'lateral recess' (which is where it usually does) and compresses / irritates the descending L5 nerve root, the patient may suffer an L5 radicular pain (aka: L5 root-pain, or L5 Sciatica). Fig. # 5 shows the regions in the lower limb where the patient will most likely suffer the symptoms of L5 sciatica (2). As you can see, the majority of patients (75%) suffer the burning, stinging, and numbing pain of sciatica in the top and inner surface (dorsum) of the foot, the outer-front of the leg, and the bottom of the big toe. These pains are the result of damage and irritation to the 'sensory portion' (portion of the nerve root which connects to skin) of the nerve root.

If the 'motor portion' (portion of the nerve root which connects to muscle) of the L5 nerve root is damaged or irritated by the disc herniation, the patient my suffer weakness in the Extensor Hallusis Longus muscle (muscle that lifts the big toe - classic finding) or the muscles that dorsi-flex the foot (lift the foot up) upward. If severe, the patient will be unable to 'walk on their heals' with their toes and ball-of-the-foot off the ground. There is no reliable reflex test for this nerve root.

L4 RADICULAR PAIN:

If the L3 disc herniates into the 'lateral recess' (which is where it usually does) and compresses / irritates the descending L4 nerve root, the patient may suffer an L4 radicular pain (aka: L4 root-pain, or L4 Sciatica). Fig. # 6 shows the regions in the lower limb where the patient will most likely suffer the symptoms of L4 sciatica (2). As you can see, the majority of patients (75%) suffer the burning, stinging, and numbing pain of sciatica in the top and inner surface (dorsum) of the foot, the outer-front of the leg, and the bottom of the big toe. These pains are the result of damage and irritation to the 'sensory portion' (portion of the nerve root which connects to skin) of the nerve root.

If the 'motor portion' (portion of the nerve root which connects to muscle) of the L4 nerve root is damaged or irritated by the disc herniation, the patient my suffer weakness in the quadriceps muscle (muscle that extend the knee). If severe, the patient will be unable to perform a squat or get out of a chair because. If the problem is severe, the patient will often have a diminished or absent Patellar Reflex (aka: knee jerk).

 

REFERENCES:

1) Kortelainen P, et al. “Symptoms and signs of sciatic and their relation to the location of the lumbar disc herniation.” Spine – 1985; 10:88-92

2) Nitta H, et al. "Study on dermatomes by means of selective lumbar spinal nerve root block." Spine 1993;18:1782-6

31) Uihlein A, et al. "neurologic changes, surgical treatment, and post operation evaluation. Symposium: Low back and sciatic pain." J Bone Joint Surg 50A:1, 1968

32) Bolk L. "Die Segmentaldifferenzigrung des menschlichen Rumpfes und seiner Extremitaten." morphol Jahrb 1898 - 1899; 25:465-543; 26:91-211; 27:630-711; 28:105-46

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