The mnemonic LOAF helps one remember innervation of the hand supplied by the median nerve: L = lumbricals 1 and 2; O = opponens pollicis; A = abductor pollicis brevis; F = flexor pollicis brevis. Further dissecting the median nerve, we observe as this nerve travels between the flexor digitorum profundus and the flexor digitorum superficialis muscles. This branches into two main segments: The anterior interosseous nerve , which supplies the deeper anterior antebrachial muscles, and the palmar cutaneous nerv e, which supplies the skin of the middle and lateral palm. When the median nerve travels through the carpal tunnel arch, the nerve splits into two other branches: The recurrent branch , which innervates the four thenar muscles, and the palmar digital branch , which innervates the palmar surface and fingertips of the lateral 3.5 digits, as well as the lateral two lumbrical muscle units. Anomalies of the median nerve On occasion, rare anomalies may be witnessed. Some of these occurrences that affect the median nerve structure include: ● Riche-Cannieu anastomoses, which result in a connection between the recurrent branch of the median nerve and the deep branch of the ulnar nerve within the hand. ● Martin-Gruber anastomoses, which result when median nerve branches cross each other in the antebrachium merging with the ulnar nerve, causing sensory and motor abnormalities in the anterior antebrachium. ● An extra artery, called the median artery, that may remain present upon birth, which creates an extra artery in the antebrachium and the hand. ● The median nerve bifurcating proximal to the carpal tunnel and/or carpal bones, rather than after exiting the carpal tunnel itself. Hilton’s law states that a nerve innervating a muscle also supplies the skin, adjacent joints, and surrounding tissues with nervous signals. This law is important to understand for several reasons. First, knowing that the joint adjacent to a muscle is affected indicates that the musculotendon load at the neighboring joint region will likely carry additional stress on the injured nerve and muscle tissues, thus leading to strain injuries. Second, CTS may not initially be experienced with the obvious pain, tingling, or weakness that is typical of CTS; rather, vague skin sensations may initially be experienced. These sensations can clue a practitioner toward a CTS diagnosis. Third, if one presents with CTS symptoms (not merely the wrist), all joints within the region may need to be examined. This significant anatomical law, defined by John Hilton in 1860, demonstrates a key understanding about how healthcare professionals may interact with the nervous system when caring for individuals with neurological conditions such as CTS.
Figure 5: Brachial Plexus Nerves
Spinal nerves that emanate from spinal column bones C4 through T1 innervate the superior limbs. These nerves stem from the inferior portion of the brachial plexus—a bundle of nerves innervating the musculature of the superior limb and upper torso. As illustrated in Figure 5, the median nerve is a convergence of the lateral and medial cords of the brachial plexus unit. Nerve signal interference along the lateral and/ or medial cord pathways can cause intermittent disruptions of signals along the median nerve. This interference can be witnessed along the spinal column or along the tracks of nerve traveling through the axilla, as well as along the anterior superior limb. Here are a few mnemonics students may use to learn the subdivisions associated with the brachial plexus:* ● Read that Dastardly Cadaver Book ● Rugby Teams Drink Cold Beer ● Reach to Drink Cold Beer * (R = roots; T = trunks; D = divisions; C = cords; B = branches) Branching from the brachial plexus, the median nerve descends distally within the superior limb bilaterally. The median nerve initially travels lateral to the brachial artery that crosses medially just proximal to the elbow (cubital fossa) region. This nerve innervates the following muscles: ● Pronator teres ● Flexor carpi radialis ● Palmaris longus
● Flexor digitorum superficialis ● Flexor digitorum profundus ● Flexor pollicis longus ● Pronator quadratus ● Thenar musculature ● First and second lumbrical muscles
SIGNS AND SYMPTOMS
the thumb toward the other digits. Adductor pollicis pulls the thumb back toward the palm. If the hypothenar muscles are located at the ulnar (pinky) side of the hand atrophy, this indicates Guyon’s canal syndrome—an impingement of the ulnar nerve. ● Tingling, numbness of first 3.5 digits (thumb, index, middle, and radial half of ring fingers ): This is often referred to as paresthesia, a “pins and needles” sensation, and often accompanies the tingling and numbness experience by CTS patients. ● Pain in the wrist and hand : This pain usually worsens when the wrist is brought into a flexed (bent) position. It is experienced as a sharp, shooting pain radiating through the antebrachium. Chronic pain becomes
Major signs and symptoms of carpal tunnel syndrome include these prominently witnessed phenomena: ● Atrophy of the thenar muscles : There are four thenar muscles located at the radial (thumb) side of the hand. When one presses their thumb next to the index finger, the thenar muscles create a bulge in this region. The four thenar muscles are: ○ the abductor pollicis brevis ○ the flexor pollicis brevis ○ the opponens pollicis ○ the adductor pollicis muscles ● The term pollicis refers to the thumb : Abductor pollicis brevis pulls the thumb away from the palm in a lateral manner. Flexor pollicis brevis pulls the thumb away from the palm in an anterior manner. Opponens pollicis pulls
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Book Code: MGA1226
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