This model allows for the position of the bones of the shoulder to be observed in relation to the underlying rib cage. Due to its positioning on the rib cage, the scapula is offset 30 degrees from the frontal plane — this is called the scapular plane.
In the following models, the shoulder is isolated from the rib cage for emphasis — and the purpose of this model is to show the actual spatial arrangement of those anatomical entities.
It is important to note that the scapula does protract, retract and rotate along the rib cage, and is responsible for much of the motion associated with the shoulder. Furthermore, much of the pathology associated with the shoulder joint may be caused by improper scapular movement.
This model displays the anterior view of the shoulder. It is especially good for observing the bones of the shoulder and the origins and/or insertion points of the subscapularis, supraspinatus, and biceps muscles.
This model displays the posterior view of the shoulder. In addition to the bony structures shown, this model clearly shows the deltoid, supraspinatus, and triceps muscles.
This model is another anterior view of the shoulder. It clearly displays the acromioclavicular, corocoacromial, coraco-humeral, and capsular ligaments, as well as the bones to which they attach. The superior, middle, and inferior glenohumeral ligaments are collectively referred to as the capsular ligaments.
This model is another posterior view of the shoulder. The acromioclavicular ligament is more clearly displayed, and the posterior aspects of the capsular ligments may be seen.
This picture shows a sagittal cut of the shoulder and displays the major entities of the rotator cuff. This view displays the capsule in which the head of the humerus sits, and the 4 major muscles (i.e. the rotator cuff) that are involved in stabilizing the humerus in its socket (function described in detail below).
Functions of the Components of the Shoulder
- Coracoacromial ligament: controls anterior and posterior translation of the lateral clavicle
- Coracoclavicular ligament: controls vertical stability; restrains superior and anterior displacement
- Acromioclavicular ligament: provides stability across the joint; restrains posterior translation and displacement of the clavicle
- Capsular ligaments: joins the glenohumeral joint capsule anteriorly, inferiorly, and posteriorly
- Coracohumeral ligament: provides stability superiorly, preventing superior translation
Muscles of the Rotator Cuff
- The four major muscles of the rotator cuff rotate the humerus and properly orient the humoral head in the glenoid fossa (socket). The tendons of these four muscles merge, forming a cuff around the glenohumeral joint.
- Supraspinatus: abducts the humeral head and acts as a humeral head depressor
- Infraspinatus: externally rotates and horizontally extends the humerus
- Teres minor: externally rotates and extends the humerus
- Subscapularis: internally rotates the humerus
Physical Evaluation of the Shoulder
Range of Motion (ROM) Tests
The following ROM tests should be conducted both actively (patient’s own strength) and passively (performed by examiner), and the results should be considered separately. The reason for this is that if the patient is experiencing pain, he/she may restrict movement. Furthermore, the opposing limb should be examined in an identical fashion in order to evaluate bilateral symmetry. Note that all pictures shown here are performed passively, unless specifically noted as active.
The patient is positioned sitting and the elbow is flexed 90 degrees. While the elbow is held against the patient’s side, the examiner externally rotates the arm as permitted.
The patient should be positioned sitting. Again with the elbows at the patient’s side, the examiner should raise the thumb up the spine, and record the position in relation to the spine (reaching T7 is normal, unless bilateral symmetry is observed).
Internal Rotation at 90 degrees of Forward flexion
The patient is positioned sitting with the elbow and shoulder supported to prevent muscle contraction. The arm is at 90 degrees with the fingers pointing downward and palm facing posteriorly. The examiner attempts to rotate the forearm posteriorly as far as possible.
The arm is kept straightened and brought upward through the frontal plane, and moved as far as the patient can go above his head. Note: for recording purposes, 0 degrees is defined as straight down at the patient’s side, and 180 degrees is straight up.
Shoulder Abduction: Active Test
The arm is again kept straightened, while raised and abducted. Observe the twisting of the hand–facing outward, not forward, as in forward flexion. The ROM is measured in degrees as decribed for forward flexion. As pictured, this test is being done actively by the patient, but may be performed by the examiner as well.
Acromioclavicular (AC) Joint Testing
Palpation of AC Joint
The patient’s arm is kept at his side and the examiner palpates the AC joint for discomfort/pain and gapping.
Cross-Arm Horizontal Adduction Test
The patient places his hand on the opposite shoulder, while the examiner exerts force horizontally. Again, the presence of pain indicates possible pathology.
Glenohumeral Laxity and Apprehension
Have the patient in the supine position, with the arm abducted 90 degrees. Rotate the shoulder externally by pushing the forearm posteriorly. If patient feels instability, they typically will balk when the test is performed.
Have the patient in the supine position. Stabilize the scapula, and slide the humeral head anteriorly and posteriorly within the glenoid fossa to evaluate the stability of the joint. Note the axial load being applied to the elbow.
Position the patient sitting. Internally rotate the arm with the thumb facing downward, and abduct and forward flex the arm. If impingement is present, the patient will experience pain as the arm is abducted.
Position the patient standing with the shoulder abducted 90 degrees, and internally rotate the forearm. The presence of pain with movement is indicative of possible pathology.
External Rotator Cuff (RC) Strength
Position the patient sitting, with his arms at his sides and elbows at 90 degrees. It is important to maintain the elbow positioning at the sides while the external rotation is attempted by the patient (the examiner applies internal resistance).
Internal RC Strength
Same as above, but the patient is attempting to rotate internally (and examiner resisting externally).
The patient is positioned sitting with arms straight out, elbows locked, thumbs down, and arm at 30 degrees (in scapular plane). The patient should attempt to abduct his arms against the examiner’s resistance.
Palpation of Bicipital Groove
Position the patient sitting, beginning with the arm straightened. The patient should then flex his arm to contract the biceps muscles. The examiner palpates the bicipital groove to attempt to illicit pain.