Shoulder anatomy and function 1

Each lab group needs:

  1. Locate on yourself and on a partner the palpable structures that your texts lists (Smith, Weiss, & Lehmkuhl, 1996, pp.224-226) for the shoulder complex

    sternum, including xiphoid process, manubrium, sternoclavicular joint
    clavicle
    scapula, including

    scapular spine
    acromion process
    the scapula's attachment to the clavicle at the acromioclavicular (AC) joint
    supraspinous and infraspinous fossae
    vertebral and axillary borders
    inferior angle
    coracoid process

    humerus, including greater and lesser tubercles, intertubercular (bicipital) groove

  2. On a laboratory skeleton,

    Note the scapula's glenoid fossa, including the supraglenoid and infraglenoid tubercles, which are important sites of muscle attachment.

    Locate the coracoacromial ligament, the coracoclavicular and the coracohumeral ligaments.

    Locate the sternoclavicular joint and the site of the costoclavicular ligament.

  3. Palpate several lab partners' scapular positions as they stand. Using the base of the scapular spine and the inferior angle as landmarks, note the following:

    Is the scapular spine at the level of the T4 spinous process, a typical position?

    Is the scapula's inferior angle at the level of the T8 spinous process, a typical position?

    Is either scapula rotated? The base of the scapular spine and the scapula's inferior angle are typically aligned vertically.

    Is one scapula more abducted or elevated than the other?

    Is either scapula "winged?" Therapists generally attribute a winged scapula, one whose vertebral border rests away from the thorax, to an elongated serratus anterior. Investigate the attachments of the serratus anterior to see why elongation of this muscle permits the scapula's vertebral border to rest off of the ribcage.

  4. Because of postural compensations that we studied in an earlier lab, asymmetries in scapular position may be associated with an unlevel pelvis.

    If you detect scapular asymmetry in one of your lab partners, check the pelvic level to see whether the two findings are correlated.

  5. Observe scapulohumeral rhythm by observing your lab partner's motion as he or she elevates the shoulder. ("Shoulder elevation," which refers to movements that place the glenohumeral joint in full flexion or abduction, combines glenohumeral and scapulothoracic movements, along with thoracic extension.)

    As your partner slowly elevates the shoulder through a "goniometric" arc of 180 degrees (using any combination of flexion and abduction), follow the scapula's upward rotation. Palpate two landmarks, the base of the scapular spine and the inferior angle, and note the following:

    • The first 30 degrees of shoulder elevation involves largely glenohumeral movement. The scapula's movement is inconsistent. This is termed the setting phase.

    • Thereafter, shoulder elevation involves an overall 2:1 ratio of glenohumeral to scapulothoracic movement.

    What purposes does scapulohumeral rhythm serve?

  6. During the first 90 to 100 degrees of shoulder elevation, the clavicle's distal ends moves superiorly. Palpate this "clavicular elevation" while your lab partner slowly moves the limb overhead.

  7. At around 90 to 100 degrees of shoulder elevation, the clavicle ceases its elevation and begins to rotate backward (Smith, Weiss, & Lehmkuhl, 1996, p.229). Palpate this clavicular rotation by placing your fingers on the portion of the clavicle that is anteriorly convex. While your partner slowly moves the limb overhead, determine the point in the range of motion when the clavicle's superior surface begins to move backward.

  8. At least a portion of shoulder elevation involves thoracic movement. To convince yourself of the dependence of shoulder movement on thoracic position, elevate your shoulder as you sit with an erect, extended lumbar spine. Do the same while sitting with a more flexed or slumped lumbar posture. What differences do you notice in the extent of your shoulder movement?

  9. Acting together (in a synergy), serratus anterior and upper trapezius produce the scapular upward rotation that is part of scapulohumeral rhythm during the initial phase of shoulder elevation.

    Verify this fact by finding the muscles' lines of application and assessing their effect on an AP axis that projects through the sternoclavicular joint to the base of the scapular spine.

  10. Identify lines of application for the other scapulothoracic muscles:
    • middle trapezius
    • lower trapezius
    • rhomboideus major and minor
    • levator scapulae

    and predict each muscle's effect on scapular upward or downward rotation around the same AP axis that the previous problem specified.

    Predict also each muscle's effect on causing the scapula to:

    • elevate (move superiorly) or depress (move inferiorly).
    • abduction (move away from the vertebral column) or adduct (move toward the vertebral column).

Last updated 11-8-01 Dave Thompson PT
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