C5, C6, C7, C8: which fingers tell you which nerve

WHICH NERVE ROOT

C5 covers the outer shoulder with no fingers, C6 the thumb and index finger, C7 the middle finger, and C8 the ring and little fingers. Which fingers are numb narrows the level before anyone books imaging. It is the single most useful sentence you can bring to an appointment.

Which fingers go with which cervical nerve root?

Each cervical nerve root carries sensation from a defined strip of skin and power to a defined set of muscles. When one root is irritated, the pattern it produces is not random and it is not “the whole arm.”

• C5 — the outer shoulder and upper arm, stopping around the elbow. No fingers. Weakness shows up lifting the arm out to the side. This is the level most often mistaken for a shoulder problem. That is because in every practical sense it looks like one.
• C6 — down the thumb side of the forearm into the thumb and index finger. Biceps weakness, and a reduced biceps or brachioradialis reflex.
• C7 — the back of the arm into the middle finger. Triceps weakness, a reduced triceps reflex. The most commonly affected root of the four.
• C8 — the little finger side of the forearm into the ring and little fingers. Weak grip and weak finger spread, because the small muscles inside the hand run on this level.

Two fingers and a movement you have lost are more specific data than most of what gets collected at a first appointment. If you take nothing else from this: write down which fingers, before you go.

How accurate are dermatome charts and Spurling’s test?

Dermatome charts (maps of the skin each nerve root supplies) are drawn with hard borders. Real people have overlap between neighboring roots. They have meaningful variation in how the brachial plexus (the nerve network into the arm) is put together. And there is a fair amount of individual difference in where a given root’s territory actually ends. A C6 pattern that spills into the middle finger has not disproved anything.

The provocation tests have the same character. Spurling’s test means extending and rotating the neck toward the painful side under gentle compression. It is a truly useful confirming test when it brings on the arm symptom, because it is fairly specific. It is not sensitive. A negative Spurling’s in a patient with a clear dermatomal story does not clear the root. Systematic reviews of the physical exam in cervical radiculopathy (a pinched nerve root in the neck) have been consistent about this for years.

So the map is a hypothesis generator (a source of ideas to test), not a verdict. Used that way, it is excellent. Used as proof, it produces confident errors.

What does an EMG show that a dermatome map cannot?

The dermatome tells you where the symptom is. It cannot tell you where along the nerve the problem sits, and that is the question that changes the treatment. Needle EMG looks for denervation (muscle cut off from its nerve supply) in a myotomal distribution. That means muscles supplied by one root but by different peripheral nerves. If C7-innervated muscles are affected across two different peripheral nerve territories, the lesion is at the root. If the abnormality follows a single peripheral nerve instead, it is not a neck problem at all.

Two honest limitations. Needle findings take one to three weeks after onset to appear. So an early study can be normal in a truly compressed root. And a purely sensory radiculopathy (pain and numbness with no motor, or muscle, involvement) may never produce a positive needle study. That is because the sensory cell body sits outside the compression. A normal EMG narrows the field. It does not empty it.

Why does the exact nerve root level matter for treatment?

Because everything downstream is level-specific. A cervical epidural steroid injection is delivered to a segment, not to a neck. The same is true of a transforaminal approach and of surgical decompression. It is also true of the decision about whether the finding on the scan is the finding that matters. Getting the level wrong is not a small miss. It is a treatment delivered next to the problem.

This is also where the imaging finally earns its place. Once the exam has produced a level, the scan is asked a narrow question it can answer. It is not asked an open one it cannot. Read in the other order it is much less useful.

What should you tell the doctor about your numb fingers?

Three sentences, prepared in advance, and you will have contributed more to the diagnosis than most first visits manage:

• Which fingers, specifically. Not “my hand” — which fingers.
• What position makes it worse, and what makes it stop. Overhead, bent elbow, at night, turning the head.
• Whether anything has actually become weaker. Dropping things, jars, a key in a lock, buttons.

The fear underneath this is usually not the pain. It is whether the numbness is going to be permanent. That question has an answer, and getting the level right is the first step toward it.

Biceps tendonitis. Tennis elbow.

Frequently asked questions about C5 to C8 nerve roots

What fingers are affected by C6 and C7?

C6 runs down the thumb side of the forearm into the thumb and index finger. C7 runs down the back of the arm into the middle finger. Real people have overlap between neighboring roots, so a C6 pattern that spills into the middle finger does not rule anything out. The finger pattern points to a level; the examination confirms it.

What are the symptoms of a C7 pinched nerve?

A C7 root sends symptoms down the back of the arm into the middle finger. It also weakens the triceps, the muscle that straightens the elbow, and reduces the triceps reflex. C7 is the most commonly affected of the four lower neck roots, so middle-finger numbness with a weaker push is one of the patterns we see most often.

What does the C8 nerve root control?

C8 carries feeling from the little-finger side of the forearm into the ring and little fingers. It also powers the small muscles inside the hand. That is why a C8 problem shows up as a weak grip and trouble spreading the fingers, often noticed as dropping things, struggling with jars, turning a key or doing buttons.

Can a C5 pinched nerve feel like a shoulder problem?

Yes. C5 covers the outer shoulder and upper arm, stops around the elbow and involves no fingers. Its weakness shows up when you lift the arm out to the side. In every practical sense it looks like a shoulder problem, which makes C5 the level most often mistaken for one. An examination of the neck and the shoulder together sorts it out.