Chapter 33

### Big Picture

The fascia of the hand is continuous with the fascia of the forearm (antebrachium). In the hand, the fascia varies in thickness and divides the hand into five separate compartments that correspond with the five digits and have similar blood supply, innervation, and actions.

### Fascial Layers of the Palmar Side of the Hand (Figure 33-1A)

• Palmar aponeurosis. Located over the palm of the hand and covers the flexor tendons and deeper structures of the hand. The palmar aponeurosis extends distally and becomes continuous with the fibrous digital sheaths.
• Fibrous digital sheaths. Form a tunnel that encloses the flexor tendons of digits 2 to 5 and the tendon of the flexor pollicis longus muscle and their associated synovial sheaths.
• Flexor retinaculum (transverse carpal ligament). Forms a roof over the concavity created by the carpal bones, forming a tunnel (i.e., the carpal tunnel). The median nerve and the tendons of the flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus muscles, and their associated synovial sheaths, pass through this tunnel. The flexor retinaculum anchors medially to the pisiform and the hook of the hamate. Laterally, the flexor retinaculum is anchored to the scaphoid and trapezium.
• Transverse palmar ligament. Continuous with the extensor retinaculum from the dorsal side of the wrist and wraps around, anteriorly, to form a fascial band around the flexor tendons. This ligament should not be confused with the flexor retinaculum, which is located deeper to the transverse palmar ligament.

###### Figure 33-1

A. Fascia of the palm of the hand and carpal tunnel. B. Fascia of the posterior hand and extensor compartments. C. Actions of digits 2–4. D. Actions of digit 1 (thumb).

### Fascial Compartments of the Palmar Side of the Hand

The fascial layers divide the palmar side of the hand into the following five compartments (Figure 33-1A):

• Thenar compartment. Contains three muscles that act on digit 1 (thumb).
• Hypothenar compartment. Contains three muscles that act on digit 5.
• Central compartment. Located between the thenar and hypothenar compartments and contains the flexor tendons and the lumbrical muscles.
• Interosseous compartment. Located between the metacarpals and contains the dorsal and palmar interossei muscles.

### Fascial Layers of the Dorsal Side of the Hand

• Extensor retinaculum. Continuous with the fascia of the forearm and attached laterally to the radius and medially to the triquetrum and pisiform bones. The extensor retinaculum works to retain the tendons that are near the bone while allowing proximal and distal gliding of the tendons (Figure 33-1B).
• Dorsal digital expansions. An aponeurosis covering the dorsum of the digits ...

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