Lab Manual - Extensor Compartment of the Forearm, Deep Hand, Wrist and Hand Joints

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Identify the extensor compartment; nerves and vessels supplying their contents; functional significance. (explanation)
  2. Describe the position of tendons, associated bursae, nerves, and vessels beneath the palmar carpal ligament. (explanation)
  3. Identify the prominent features of carpals, metacarpals and phalanges associated with the hand as listed in the lab manual. (explanation)
  4. Define the thenar, hypothenar, central, and adductor-interosseous compartments of the hand and the functional significance of each. (explanation)
  5. Correlate any fractures or deep cuts of the hand with functional disruptions of associated muscular and neurovascular structures. (explanation)
  6. Describe the movements of the fingers and thumb. (explanation)
  7. Describe the collateral circulation of the hand. (explanation)

Readings and Modules:

Procedure:

1. Review the bony landmarks. (Play movie; View images: N 420, 421, 436, 439, 440, 450, 451, 452, 456, TG 2-03A, 2-03B, 2-04, 2-21, 2-22, 2-31, 2-32)

Review bony processes of the humerus, radius and ulna previously examined. Identify supinator crest, posterior border, and interosseous crest of ulna. Identify the dorsal radial tubercle and interosseous crest of radius. Locate grooves at the distal end of radius which accommodate tendons as they cross the wrist. Examine an articulated hand, noting arrangements of carpals, metacarpals, and phalanges. Identify proximal, middle and distal phalanges.

Bones of the wrist
Wrist bones

2. Remove the superficial fascia from the dorsum of the forearm. (Play movie; View images: N 444, 480, TG 2-02, 2-23, 2-29)

Remove the superficial fascia from the forearm, wrist and hand, leaving the cutaneous nerves and veins intact. Observe the posterior part of the antebrachial fascia, noting continuity with brachial fascia and its thickening at the distal end of radius and ulna and wrist, the extensor retinaculum. Note its continuation onto the hand as the fascia of the dorsum of the hand. Remove the posterior antebrachial fascia leaving the extensor retinaculum intact. As you reflect, note that some muscles use this fascia as an origin. Do you see intermuscular septa? If not, why? Note the superficial position of the posterior border of the ulna.

3. On the extensor side of the forearm, separate and dissect the superficial extensor muscles. (Play movie; View images: N 444, 446, 450, 451, TG 2-21, 2-22, 2-23, 2-29)

The muscles of the posterior forearm region lie in two layers, superficial and deep. The superficial layer arises from the lateral epicondyle of the humerus via a common extensor tendon. The muscles of the deep layer arise collectively from the posterior surface of the radius and ulna and the intervening interosseous membrane. Emphasize these general common origins. Note functional arrangements of muscles. Note that muscles use adjacent muscles as part of their origin.

Dissect each muscle by picking up its tendon at the proximal border of the extensor retinaculum and separating it toward its origin as far as possible, in the following order: brachioradialis (note attachment to lateral supracondylar ridge), extensor carpi radialis longus (note attachment to lateral supracondylar ridge), extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris.

4. Examine extensor expansion on dorsum of fingers. (Play movie; View images: N 441, 451, 463, 464, 465, 470, TG 2-22, 2-32, 2-34, 2-35, 2-40, 2-41A, 2-41B, 2-45)

Remove the deep fascia from the dorsum of the hand distal to the extensor retinaculum. Identify tendons of extensor digitorum and extensor digiti minimi muscles. Trace an exemplary tendon to any digit (2-4) and examine the manner of insertion on the middle and distal phalanges. Expose completely an extensor expansion, demonstrating its lateral borders, interossei and lumbrical tendons. Do not trace these tendons into the palm. Note transverse fibers uniting all tendons and capsular attachments at the joints. Note tendinous cross bridges.

Return to the wrist and locate insertions of the extensor carpi radialis longus and brevis and extensor carpi ulnaris.

5. Dissect the deep extensor muscles of the forearm. (Play movie; View images: N 439, 441, 444, 445, 447, 451, 452, 454, 456, 459, 460, 461, 462, 468, 470, 472, 476, 478, TG 2-24, 2-27, 2-29, 2-30, 2-31, 2-32A, 2-32B, 2-34, 2-35, 2-39A, 2-39B, 2-40A, 2-40B, 2-41, 2-50)

Return to the forearm and make an incision between the extensor carpi radialis brevis and extensor digitorum as far proximal as the lateral epicondyle of the humerus. Separate these muscles to expose the deep layer.

Clean and identify the following muscles: supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. Trace the tendons to the extensor retinaculum and then, distal to the extensor retinaculum, to their ultimate insertions. Note the course of some of these tendons across the tendons of extensor carpi radialis longus and brevis.

Examine the extensor retinaculum, noting medial and lateral attachments, proximal and distal extents, and orientation. Open each compartment with a longitudinal incision and note: (1) tendons contained, (2) deep attachments of septa, (3) relation of tendons to grooves in bone, (4) synovial bursae (sheaths), (5) sequence of tendons (from radial to ulnar side).

Synovial bursa (sheath). Carefully open a compartment and distinguish parietal and visceral layers. Where do they become continuous? Note extent of synovial bursae proximal and distal to the extensor retinaculum. How do bursae function?

Radial nerve. Return to the cubital fossa. Locate the radial nerve beneath the brachioradialis muscle. Identify branches of the radial nerve to forearm muscles. Note point of division into superficial and deep radial nerves. Follow the superficial radial nerve, noting course and relations to brachioradialis, and point of emergence into the superficial fascia. What does it accompany? Follow the deep radial nerve as it pierces the supinator muscle. Trace by incising through the muscle. Observe branches of the deep radial nerve to supinator and superficial extensor muscles. Trace its branches to the muscles of the deep layer. What is the posterior interosseous nerve? Note accompanying posterior interosseous artery and vein, and the posterior branch of the anterior interosseous artery and vein joining the posterior interosseous artery on the interosseous membrane near the wrist.

Find and save the dorsal cutaneous branch of the ulnar nerve as it passes around the distal end of the ulna onto the dorsum of the hand. Identify its dorsal digital branches.

Review radius and ulna and general arrangement of carpals, metacarpals, and phalanges in an articulated hand. Identify the scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate, and hook of hamate. (Handy Mnemonic: Some Lovers Try Positions That They Can't Handle)

Surface anatomy of the anatomical snuffbox

Pull the tendons of the long flexors distally to expose the adductor-interosseous compartment. Clean the adductor pollicis muscle and identify its oblique and transverse heads. Clear the anterior interosseous fascia from interosseous muscles and identify the deep palmar arterial arch; note the accompanying deep branch of the ulnar nerve.

6. Follow the radial artery through the anatomical snuffbox and through the 1st dorsal interosseous m. (Play movie; View images: N 464, 465, 466, 469, TG 2-35A, 2-35BC, 2-37A, 2-37B, 2-41, 2-45, 2-46, 2-48, 2-49, 2-50, 2-52)

Return to the wrist and pick up the radial artery in the "anatomical snuff box". Identify dorsal metacarpal arteries and dorsal digital branches.

Trace the radial artery to the interval between the first and second metacarpal bones. Reflect the first dorsal interosseous muscle from its attachment to the first metacarpal and continue tracing the radial artery into the deep palmar arterial arch. Identify princeps pollicis and radialis indicis arteries.

Angiogram of the wrist and hand

Reflect the origin of adductor pollicis. Dissect dorsal and palmar interosseous muscles; determine position, structure, dual insertion, and action. Observe these muscles on both the palmar and dorsal sides of the hand. Follow these muscles to their insertions on proximal phalanges and extensor expansions.

Consider the complete blood supply to the hand: sources, arches (how many and how formed?). How do the dorsal and palmar proper digital arteries differ in their formation? What are perforating arteries? Where are they found? Function?

Organize the motor innervation to intrinsic muscles of the hand and review sensory distribution. Organize the actions of both the intrinsic and extrinsic muscles of the hand.

Growth plates at the wrist
Colles' fracture

 

Updated: 31 Oct 2011