Wrist and hand anatomy and function

Each lab group needs:

  1. Locate on yourself and on a partner the palpable structures that your text (Smith, Weiss, & Lehmkuhl, 1996, pp.158-159) lists for the elbow and radioulnar joints.

    • medial and lateral humeral epicondyles; note that the two bony landmarks identify the elbow's single, lateral axis (Smith, Weiss, & Lehmkuhl, 1996, Fig.5-1, p.159).

    • olecranon process; verify that you can palpate activity in the triceps brachii by palpating its tendon just proximal to the olecranon process

    • head of the radius; palpate movement of the radial head as you pronate and supinate the radioulnar joint. Two landmarks, the radial head and the distal end of the ulna, identify the radioulnar jont's oblique axis Smith, Weiss, & Lehmkuhl, 1996, Fig.5-2, p.161).

    • biceps tuberosity (the site of the biceps brachii's common attachment on the proximal radius). This structure is not palpable, but you should locate it on the laboratory skeleton so you can appreciate why the biceps brachii supinates the radio-ulnar joint.

  2. Because of the elbow and radioulnar joints' proximity, certain muscles cross and, therefore, act at both joints. The presence of multi-joint muscles necessitates true synergies among some of the muscles that cross elbow and radioulnar joints.

    Palpate the triceps brachii just superior to the olecranon process, and note that it is active when rapidly pronate or supinate your radio-ulnar joint. Your text (Smith, Weiss, & Lehmkuhl, 1996, Fig. 4-4, p.134) illustrates EMG evidence that the triceps also acts when you supinate (Fig 4-4A) or pronate (Fig. 4-4B) against resistance.

    Explain the triceps' activity in rapid or forceful pronation.
    Explain the triceps' activity in rapid or forceful supination.

  3. Locate the lateral and antero-posterior (AP) axes for wrist motion, using the landmarks illustrated in Smith, Weiss, & Lehmkuhl (1996, pp. 181,188).

  4. Locate on yourself and on a partner the palpable structures that your text (Smith, Weiss, & Lehmkuhl, 1996, pp.181-184) for the wrist and hand.
    • styloid process of the ulna
    • styloid process of the radius
    • capitate
    • scaphoid
    • lunate
    • 1st through 5th metacarpals and metacarpophalangeal (MCP) joints.
    • first carpo-metacarpal (CMC) joint

  5. The course's objectives direct you to learn about the muscles that your text (Smith, Weiss, & Lehmkuhl, 1996, pp.191-197) lists for the wrist and hand. Use skin pencils to draw lines of application, local to the wrist, for the following muscles. Predict and verify each muscle's effect on wrist movement. Consider both of the joint's axes.
    • Carpal muscles

      • extensor carpi radialis longus
      • extensor carpi radialis brevis
      • extensor carpi ulnaris

      • flexor carpi radialis
      • flexor carpi ulnaris
      • palmaris longus

    • Extrinsic hand muscles

      • extensor digitorum (communis)
      • extensor indicis (proprius)
      • extensor digiti minimi (proprius)

      • flexor digitorum superficialis
      • flexor digitorum profundus

  6. Refer to the list of carpal muscles that appears in the right hand column in the table below. In the left hand column, write in the blanks the muscle pairs that can act in helping synergies to produce:

    Wrist flexion:
    _________ and _____________

    Wrist extension:
    _________ and _____________

    Ulnar deviation:
    _________ and _____________

    Radial deviation:
    _________ and _____________

    Extensor Carpi Radialis Longus
    Extensor Carpi Radialis Brevis
    Extensor Carpi Ulnaris

    Flexor Carpi Radialis
    Flexor Carpi Ulnaris
    Palmaris Longus

  7. Palpate the tendon of extensor carpi radialis longus as you grasp a hand tool, the handle of a cooking utensil or pot, or some other "graspable" object. Verify that you can palpate activity in this muscle regardless of the wrist's orientation with respect to the line of application of gravity. In other words, activity in the extensor carpi radialis longus is not just to control the wrist against the force of gravity. When you grasp any object firmly, the wrist extends. The wrist also extends when you make a fist, especially if you do so quickly.

    To grasp firmly, you must flex the DIP joints of the second through fifth digits. The hand possesses only one muscle that can accomplish this task. This muscle is the _______________________.

    However, this muscle also flexes or extends (choose one) the wrist. Activity in the wrist extensors, including the extensor carpi radialis, prevents wrist movement.

    Why do we activate these muscles in a synergy? If the muscle that flexes the DIP joints also flexes the wrist, it becomes very short or long (choose one). The change in the muscle's length decreases its ability to develop force for the task of grasping an object.

    Compare your analysis of the role of the wrist extensors during grasp with that of your text (Smith, Weiss, & Lehmkuhl, 1996, pp.195-196).

  8. Choose a pair of activities from the list, and analyze the forces that act at the glenohumeral, elbow, and wrist joints. Don't forget to analyze one joint at a time, accounting first for the effect of gravity before predicting which muscles are active. Comment on how the change in posture influences gravitational and muscle forces and moments.

    1. write a sentence on a piece of paper, then on a blackboard

    2. stir the contents of a pot while standing at the stove, then while seated in a chair or wheelchair

  9. Permit the muscles in your hand to relax and note the following in the second through fifth digits.

    1. The metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints are all slightly flexed.

      Why? Because the resting lengths of the long finger flexors (the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) are shorter or longer (choose one!) than the resting lengths of the long extensors (extensor digitorum communis, extensor indicis, and extensor digiti minimi).

    2. Passive wrist extension increases flexion in the MCP, PIP, and DIP.

      Why? Because wrist extension shortens or elongates (choose one!) the FDP and FDS. This change in length increases passive force in the FDP and FDS, so they produce finger flexion.

    3. Passive wrist flexion extends (decreases flexion) in the MCP,PIP,and DIP.

      Why? Because wrist flexion shortens or elongates (choose one!) the FDP and FDS. This change in length decreases passive force in the FDP and FDS, decreasing their contribution to finger flexion. Wrist flexion also shortens or elongates (choose one!) the extensor digitorum. This change in length increases passive force in that muscle, producing finger extension.

Last updated 11-19-01 Dave Thompson PT
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