Rotator cuff/SASD bursa
Supraspinatus tendinopathy/partial tear, SASD bursitis
Long head of biceps tendon
Biceps tendinopathy, biceps tendon instability
GH joint capsule/ligaments
The shoulder consult can be formidable due to the multiple potential pain generators (Table 19.1).
The relevant shoulder girdle anatomy and corresponding pain generators will be briefly reviewed.
The glenohumeral (GH) joint is a synovial ball-and-socket joint consisting of the humeral head and shallow glenoid fossa. The fibrocartilaginous glenoid labrum and surrounding ligamentous structures are instrumental in stabilizing the joint (Fig. 19.1). Chronic pain localizing to the GH joint is often related to degenerative labral pathology and/or cartilage loss (GH joint osteoarthritis).
The four rotator cuff muscles, which create a tight layer of tendons around the GH joint, also play an important role in joint stabilization (Fig. 19.2). The rotator cuff helps to keep the humeral head centered on the glenoid during arm elevation. The subacromial subdeltoid (SASD) bursa lies sandwiched between the deeper rotator cuff tendons and the superficial deltoid muscle and coracoacromial arch. The SASD bursa allows the rotator cuff tendons to glide smoothly under the deltoid and arch. Subacromial impingement, an important clinical sign, occurs when the superior aspect of the humeral head and rotator cuff tendons impinge on the undersurface of the coracoacromial arch. The clinical finding of subacromial impingement is often seen together with the clinical diagnoses of rotator cuff pathology and SASD bursitis.
The long head of biceps (LHB) tendon originates at the superior aspect of the glenoid and labrum. The intra-articular proximal tendon travels over the anterosuperior humeral head and then takes a sharp turn to become extra-articular within the bicipital groove of the humerus (Fig. 19.3a, b). LHB tendinopathy and/or instability are additional causes of shoulder pain. Isolated LHB tendon pathology is rare. Biceps tendinopathy is often associated with other shoulder pathology, especially superior labral tears and anterosuperior rotator cuff tears in the region of the rotator interval.
The rotator interval is a triangular space where the anterior supraspinatus fibers and lateral subscapularis fibers border the intra-articular portion of the biceps tendon (Fig. 19.3a, b). Frozen shoulder, another common cause of shoulder pain and stiffness, is thought to be related to inflammation and thickening of the rotator interval structures.
The acromioclavicular (AC) joint, located at the superior aspect of the shoulder complex, is a small synovial joint between the lateral aspect of the clavicle and the acromion process of the scapula (Fig. 19.4). It has limited range of motion. A wedge-shaped fibrocartilaginous disk separates the articular surfaces of the joint. Several surrounding ligaments reinforce the AC joint capsule. Chronic AC joint pain is often related to degenerative changes with cartilage loss and bone spurring.
One of the more challenging aspects of ultrasound-guided shoulder injections is choosing the appropriate patient and anatomical target. The clinical history is an important part of the shoulder pain consult and provides clues about the primary pain generator. Associated with each of the major shoulder pain diagnoses, a few key symptoms are often elicited on history (Table 19.2). Pain with sleeping, especially when lying on the affected shoulder, is often reported and is a non-specific finding.
Clues on shoulder history
GH joint osteoarthritis
Advanced age, associated stiffness, pain with putting on a seat belt and reaching behind the back
Middle age, progressive marked stiffness, pain with putting on a seat belt and reaching behind the back
Rotator cuff pathology/SASD bursitis
Pain referral to lateral upper arm, pain with overhead activities
Long head of biceps tendinopathy/instability
Anterior shoulder pain, pain with putting on a seat belt and reaching behind the back
AC joint osteoarthritis
Superior shoulder pain, variable referral pattern, pain with reaching across the chest and overhead
The shoulder physical examination can also be challenging. Most of the special tests are not sensitive or specific. A simplified algorithm is provided to assist the pain physician in interpreting the physical examination findings (Fig. 19.5). A simple explanation of the included tests is seen in Table 19.3. In many cases, the primary pain generator will remain unclear despite a detailed history and physical. In these instances, US-guided injection of the most likely target with local anesthetic can assist with diagnostic clarification.
Shoulder physical examination special tests
Site of pathology
Arm flexed 90°, forced into horizontal adduction, pain localizes over AC joint
Arm flexed 90°, elbow extended and forearm supinated (palm up), downward force applied
Pain localizes over the bicipital groove
Arm flexed 90° in scapular plane (relatively abducted), internally rotated (thumb pointing down), downward force applied
Arm flexed 90°, horizontally adducted 15°, internally rotated (thumb pointing down), downward force applied
A simple explanation of the tests is seen in Table 19.3.
When in doubt, or if the injection is not providing the expected benefit, seeking the opinion of a shoulder surgeon or musculoskeletal medicine specialist for diagnostic clarification is recommended. In addition, clinical findings suggestive of acute trauma, marked weakness, instability, or significant mechanical symptoms (i.e., locking) should trigger a referral for diagnostic clarification and to rule out the need for surgical management.
LHB tendon and rotator interval
Supine, arm supinated
Linear, 5–13 MHz
Scan 1: Extra-articular LHB tendon, transverse view (Fig. 19.6a). Probe position corresponds to Fig. 19.3 slice “x.” Note the greater and lesser tuberosities (GT and LT, respectively) of the humerus and LHB tendon within the bicipital groove. Depicted in purple, the synovial-lined biceps tendon sheath surrounds the tendon and is the target (marked by a star) for injection. The accompanying ascending branch of the anterior circumflex artery should also be located. The transverse humeral ligament (THL), an extension of the subscapularis tendon, is the roof of the bicipital groove.