● Palmaris longus. ● Flexor digitorum superficialis. ● Flexor digitorum profundus. ● Flexor pollicis longus. ● Pronator quadratus. ● Thenar musculature. ● First and second lumbrical muscles.
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 three and half digits, as well as the lateral two lumbrical muscle units. Figure 5: Spinal Nerves
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 nerve , which supplies the skin of the middle and lateral palm. Anomalies of the median nerve On occasion, rare anomalies may be witnessed in cadavers. 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 : May remain present upon birth. This creates an extra artery in the antebrachium and the hand. ● The median nerve : May bifurcate proximal to the carpal tunnel and/or carpal bones, rather than after exiting the carpal tunnel itself.
Hilton’s Law states that a nerve that innervates a muscle will also supply the skin, adjacent joints, and the surrounding tissues with nervous signals. This law is important to understand for several reasons: First, knowing that the adjacent joint to a muscle is affected indicates that the musculotendon load at the neighboring joint region will likely carry additional stress with the injured nerve and muscle tissues, thus leading to strain injuries. Second, CTS may not initially be experienced with obvious pain, tingling, or weakness 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 a region may need to be examined. This significant anatomical law, defined by John Hilton in 1860, demonstrates a key understanding about how one may interact with the nervous system in the care of neurological conditions such as CTS.
SIGNS AND SYMPTOMS
Major signs and symptoms of carpal tunnel syndrome include these prominently witnessed phenomena: 1. Atrophy of the thenar muscles. There are four thenar muscles, located at the radial (thumb) side of the hand. When one presses his/her thumb next to the index finger, the thenar muscles create a bulge in this region. 2. The four thenar muscles are the abductor pollicis brevis, the flexor pollicis brevis, the opponens pollicis, and 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 the thumb toward the other digits. ○ Adductor pollicis pulls the thumb back toward the palm. 3. 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. Diagnostic features 1. Compression of the anterior wrist, recreating the symptoms: ○ Compression does not need to be deep; as little as one pound of pressure is enough to illicit a neurological or a pain response. 2. Examination of the wrist circumference itself. If wrist circumference is less than six inches, one is more at risk of acquiring CTS.
4. Tingling, numbness of first 3½ digits (thumb, index, middle and radial half of ring fingers): This is often referred to as paresthesia , a “pins and needles” sensation, and may often accompany the tingling and numbness experience by CTS patients. 5. Pain in the wrist and hand: This pain usually worsens when the wrist is brought into a flexed (bent) position. It is experienced by a sharp, shooting pain radiating through the antebrachium. Chronic pain becomes nuanced as treatments and self-care become less effective or if the condition worsens over time. 6. Loss of gripping and/or pinching strength: Lifting, carrying, and moving objects becomes more challenging as hand strength weakens over time. Supportive wrist guards become a useful tool for the patient to supplement his/her lost strength. 7. Interference with sleep: The paresthesia and similar sensations experienced often wake up patients several times per night. The lack of sleep creates a secondary list of health challenges and occupational concerns. 3. X-rays that determine inflammation or structural damage to carpal bones can be a powerful diagnostic tool. 4. Electromyogram tests will determine muscular activity within a region. Improper nerve supply causes the muscles to atrophy and the activity to diminish. 5. A nerve conduction study to determine electrical impulse flow through the wrist: This exam, combined with prior mentioned diagnostic tools, can become a powerful measure for CTS potential, as well as current diagnosis.
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