Illustrated Encyclopedia of Human Anatomic Variation: Opus III: Nervous System: Plexuses

Radial Nerve

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

The radial nerve may communicate with the ulnar nerve in the arm.

The radial nerve may (a) supply a small branch to the lateral portion of the brachialis muscle; (b) be the motor supply to extensor carpi radialis brevis (56% of cases by the deep radial); (c) supply dorsal distal nerves to the little finger and ulnar side of the third finger (instead of the ulnar nerve); and (d) supply the middle and index fingers through its posterior interosseous branch.

The dorsal lateral antebrachial cutaneous branch of the nerve may extend to the first phalanx of the third finger and the second phalanx of the little finger; it may send a branch to the palm.

The radial nerve may supply the entire dorsum of the hand including the dorsal aspect of all the fingers.

Cases have been reported in which the radial nerve is absent, its area of supply receiving branches from the musculocutaneous nerve (lateral antebrachial cutaneous for the thumb) and the ulnar nerve (remainder of the digits).

The radial branch to anconeus may run in the sheath of the ulnar; leaving the sheath it may reach the muscle in company with the superior ulnar collateral artery.

The superficial branch of the radial nerve may be doubled.

The superficial branch supplies the extensor carpi radialis brevis in 32% of cases, by a separated branch in 12%.

When the dorsoepitrochlearis muscle is present (18-20% of cases) it is innervated by the radial nerve.

Riche-Cannieu anastomoses (between the median and ulnar nerves in the palm of the hand) may exist in 70% of individuals. Martin-Gruber (median-ulnar nerves) anastomoses in the forearm have a reported frequency of 15%. It should be remembered that the "anastomoses" occur between the median, ulnar, radial, and musculocutaneous nerves, as well as between other nerves. These are errors in the pathway (course) of some, inappropriately placed nerve fibers. In order for these nerve fibers to get to their proper end-point, the bundle of nerves fibers leave the inappropriate trunk and join the proper nerve trunk. Both Martin-Gruber and Riche-Cannieu "anastomoses" are examples of nature's correction of nerve fibers located in inappropriate nerve pathways. Certainly a mystery, these "anastomoses". On a broader and larger scale, the brachial plexus and sacral plexuses are other examples of neuronal sorting.

Image 58 Image 59 Image 60 Image 61 Image 62A

Image 62B

References

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