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Hi this is Dr. John Shim and today I want to talk about some basic nerve patterns. You've all heard the term radiculopathy. Radiculopathy is a description of a certain pattern of nerve irritation it can cause weakness numbness pain and also manifest in some changes of your reflexes well. As a orthopedic surgeon and as a doctor I understand nerves have certain patterns associated with it. The best analogy I can use is similar to using a switch at the door. That switch turns on the light in the far end of the office. Well that individual wire that goes from the switch to the far end of the office is similar to a nerve. Nerves that go from your brain also travel down to very specific areas of your body and nerves have certain patterns in the neck. The nerves that were mostly interested in our C5, C6 and C7. The C5 nerve pattern is such that the C5 nerve gives you the ability to use your deltoid. You can bring your arm out to the side. It is also associated with sensation typically to patchy areas along your shoulder and also it's associated with some reflex findings along your biceps. The biceps reflex. As opposed to the C5 nerve pattern there's also the C6 nerve pattern. The c6 nerve pattern is associated with use of the hand. Specifically extension of your wrist. There's also an associated reflex of what's called a brachial radialis reflex. That's when the doctor hits your forearm and the hand moves. And it's also associated with sensation that typically goes to your thumb. There's also the C7 nerve pattern is associated with strength to your triceps muscle, the ability to straighten out. It's associated with the reflex along the triceps where you hit the end of the elbow and the arm moves and it's also associated with sensation. The C7 nerve pattern is the middle finger. So as you can see each individual nerves typically follow a pattern in a nerve in the neck and are associated with specific muscle groups, specific areas sensation and for some associated with certain reflexes. This is Dr. Shim talking about nerve patterns. I hope you got some information that was useful to your studies.
Many people with neck and back problems are often disturbed by the fact that they have pain but the physician tells them that the herniated disc on the MRI is not causing the pain they are feeling. How does he know?
A dermatome refers to an area of skin that is innervated by a single spinal nerve. These areas of skin carry sensation, including pain, from that area, to the brain. When a patient complains of pain in a certain part of their body the physician will first look at the radiological studies to see if there is any type of disruption in the spine in the area that correlates with the dermatome. For example, if the patient has pain in his low back that goes down the back of the leg to the bottom of the foot, the physician will look at the L5/S1 area of the spine as that is the nerve that usually serves that area. If the pain goes across the front of the thigh, the problem is usually higher up in the spine (see picture) such as L2 or L3.
The same works with neck problems. If the pain, numbness or tingling go into the thumb on the right, the disruption is probably at the C6 nerve on the right. The physician will test the sensory pathways that enervate a certain dermatome in several different ways. You will have a sharp object used as a “pinprick” test and something softer such as a cotton swab used to check “light touch”. These are all compared to other parts of the body to see if there are changes in sensation. This should be a part of any neuro/ spine exam.
This sounds simple but, because we are dealing with the human body, it is not. Much variability exists between dermatome maps in standard anatomy and medical guideline textbooks. A review of 14 different dermatome maps by Lee et al showed variations within each individual map. Each individual will also have their own variation but the above map will give you some idea of what to expect.
Most areas of the skin are innervated by 2 or more spinal nerve roots, which may be the reason for variability between individuals. We also frequently see people who are “wired differently”. They show signs that the nerves expected in one area can be one level above or below the expected level. This is why some people with a C5 spinal cord injury can breathe on their own and some need to be on a ventilator.
So if you see the doctor for your herniated disc at L4/5 and your pain is in your groin area, the chances are, fixing the L4/5 level will do nothing to relieve your pain.
- Kim J, Choi JG, Son BC. Bilateral Ganglion Cysts of the Ligamentum Flavum in the Cervical Spine Causing a Progressive Cervical Radiculomyelopathy and Literature Review. Case Rep Neurol Med. 2017;2017:3953641. PubMed PMID: 28831319
- Dietrich C, Blume KR, Franz M, Huonker R, Carl M, Preißler S, Hofmann GO, Miltner WHR, Weiss T. Dermatomal Organization of SI Leg Representation in Humans: Revising the Somatosensory Homunculus. Cereb Cortex. 2017 Sep 1;27(9):4564-4569. PubMed PMID: 28119344