OBSERVATIONS OF THE POSTERIOR AXILLARY WALL, SCAPULA, AND SHOULDER
Dr. Robert J. Cowie
Problems or Scenario:
With the cadaver in the prone position, the student should observe and study the shoulder and posterior axillary wall, keeping the following problems and concepts in mind:
1. In what ways is the shoulder adapted for non-weight bearing functions of the upper extremities, i.e., manipulation, carrying, and bipedal locomotion?
2. How does the organization of the shoulder and posterior axillary regions enhance, breathing, coughing, climbing, swimming, throwing, (and tickling)?
3. How does the anatomical organization restrict or diminish weight bearing?
Prior to Dissection:
Osteology:
Review the structure of the scapula, clavicle, and proximal head of the humerus with disarticulated bones. Be able to identify the landmarks such as the angles, margins, spine, greater notch, acromion, and acromial fossa of the scapula; the distal head of the clavicle, and the anatomical and surgical heads, greater & lesser tubercles, intertubercular groove, and radial groove of the humerus. Also, articulate the bones accurately (as shown in your Atlas).
On an articulated skeleton, study the relationships of the bones, and their joints, capsules, and ligaments. Describe the related structural mechanisms important for flexibility of the joint. What is the functional importance of the margins and spine of the scapula for upper limb mobility?
Surface Anatomy:
Before you begin to dissect, identify and palpate the surface landmarks of the shoulder and posterior axillary wall on yourself, on a consenting colleague (develop your professional attitude), and on your cadaver. It is essential for clinical understanding that each student be able to locate accurately the axillary folds, point of acromion, spine of scapula. (See your Atlas)
Imaging:
At some point between studying the bones and completing the dissection, you should study X-rays, crossections and MRI/CTs available in the lab, as well as in your Atlas.
Dissection:
Turn to Sauerland's Dissector, page 186-192.
-Dissect in layers, from superficial to deep in order to maintain your understanding of the organization and layers of the shoulder.
-Expose and dissect the posterior axillary wall and observe the deltoid, teres major and minor, and latissimus dorsi muscles.
-Open the quadrangular space (list boundaries) and observe the axillary n. and posterior humeral circumflex a.
-Open the triangular interval (list boundaries) and observe: the radial n., and profunda brachii a.
-In view of the above Problems and Concepts concerning the posterior axillary wall, each dissecting group should prepare a list of structures and characteristics which contribute to the function of the upper limb during bipedal locomotion, forced breathing and coughing, while carrying a heavy object, lifting a feather over your head, or doing "pull-ups" while hanging by the hands.
- As you dissect, identify the blood and nervous supplies to the muscles of the region. What is their origin, course and distribution? How are these structures protected within the shoulder? Identify and display the suprascapular vessels and nerve as it traverses the suprascapular notch. Suggest specific functional deficits from disruption of these supplies at different levels. Be aware that these vessels provide an important arterial anastomoses around blockage in the axillary a.
-Does your cadaver reveal any evidence of prior surgery, structural anomalies, or prosthetic devices? If so, be careful to observe: The location of, or surgical approach to, the condition. Which structures are involved? Are there any apparent changes in fascial, musculotendinous, skeletal, or "postural" relations of the thorax? Suggest a probable "cause" of the observed anomaly or surgical intervention, and any possible limitation or facilitation of function due to the observed condition.
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REFERENCES: Agur, A., Grant's Atlas, 9th Edition, 1991.
Moore, K. and Agur, A., Essential Clinical Anatomy, 1st Edition, 1996; pgs. 281-284, &301-307
Warwick & Williams, Gray's Anatomy. 35th Edition, 1973