Structure
Associated pathology
GH joint
GH osteoarthritis
Rotator cuff/SASD bursa
Supraspinatus tendinopathy/partial tear, SASD bursitis
Long head of biceps tendon
Biceps tendinopathy, biceps tendon instability
GH joint capsule/ligaments
Frozen shoulder
AC joint
AC osteoarthritis
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 GH joint capsule and surrounding ligaments are pictured. Notably, the coracohumeral ligament (CHL) is a thick fibrous band arising from the coracoid process and inserting on the greater and lesser tuberosities of the humerus. The CHL assists with reinforcing the joint capsule and stabilizing the LHB tendon. Outlined in green, the superior fibers of the glenohumeral ligament are called the superior glenohumeral ligament (SGHL). The CHL and SGHL are important structures within the rotator interval, discussed below. The acromioclavicular joint and associated stabilizing ligaments are also pictured. The inset picture shows the joint’s articular surface, glenoid and labrum. (Reproduced with permission from Philip Peng Educational Series)
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).
There are four rotator cuff muscles: supraspinatus, infraspinatus, subscapularis, and teres minor. The supraspinatus passes under the coracoacromial arch (outlined in yellow), which consists of the bony acromion and coracoid process bridged by the coracoacromial ligament. The SASD bursa is a synovium-lined potential space located deep to the acromion and deltoid muscle and superficial to the supraspinatus and infraspinatus tendons. The clinical finding of subacromial impingement is often associated with poor shoulder biomechanics, rotator cuff tendinopathy/tears, SASD bursitis, and/or abnormal coracoacromial arch anatomy. (a) Anterior view of the rotator cuff muscles with anterior deltoid muscle reflected away. (b) Posterior view of the rotator cuff muscles with posterior deltoid muscle partially resected. (Reproduced with permission from Philip Peng Educational Series)
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 joint capsule (not pictured) extends from the medial glenoid cavity and base of the coracoid process to the anatomic neck of the humerus. The synovial membrane lines the deep surface of the capsule and the outer surface of the biceps tendon. As one of three main synovial recesses, the biceps tendon sheath extends along the extra-articular portion of the LHB tendon. The rotator interval is a triangular space (outlined in yellow) located in the anterosuperior portion of the GH joint with complex anatomical relationships. The boundary is defined superiorly by the supraspinatus tendon, inferiorly by the subscapularis tendon, and medially, at its base, by the coracoid process. The rotator interval contains the CHL, SGHL, LHB tendon, and rotator interval joint capsule. (a) The three main synovial membrane recesses are pictured. (b) Diagram of the rotator interval. Slices x and y mark ultrasound positions applicable to Figs. 19.6a and 19.6b. (Reproduced with permission from Philip Peng Educational Series)
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 joint is a synovial joint with the articular surfaces separated by a wedge-shaped fibrocartilaginous disk (asterisk). The inferior surface of the joint is in direct contact with the subacromial bursa and supraspinatus muscle and may play a role in the development of the impingement syndrome. (Reproduced with permission from Philip Peng Educational Series)
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.
Patient Selection
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
Diagnosis | Pertinent history |
|---|---|
GH joint osteoarthritis | Advanced age, associated stiffness, pain with putting on a seat belt and reaching behind the back |
Frozen shoulder | 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
Test | Site of pathology | Description |
|---|---|---|
Cross-body adduction | AC joint | Arm flexed 90°, forced into horizontal adduction, pain localizes over AC joint |
Speed’s | LHB tendon | Arm flexed 90°, elbow extended and forearm supinated (palm up), downward force applied Pain localizes over the bicipital groove |
Empty can | Supraspinatus | Arm flexed 90° in scapular plane (relatively abducted), internally rotated (thumb pointing down), downward force applied |
O’Brien’s | Labrum | Arm flexed 90°, horizontally adducted 15°, internally rotated (thumb pointing down), downward force applied |
A simplified algorithm is provided to guide the reader through the physical examination of the shoulder. Palpation is omitted because tenderness of various structures, especially the LHB tendon, is common and non-specific. AC joint tenderness worse on the affected side and that reproduces the patient’s typical pain supports a diagnosis of AC joint pathology. If marked stiffness and pain is apparent on range of motion examination in a middle-aged adult, the diagnosis of frozen shoulder is likely. In this case, the remaining exam can be abbreviated, as most of the provocative maneuvers will be painful and non-specific. A normal x-ray to rule out early osteoarthritis or bony pathology essentially confirms the diagnosis of frozen shoulder. ROM, range of motion; RTC, rotator cuff; ER, external rotation; IR, internal rotation; OA, osteoarthritis. (Reproduced with permission from Dr. Jennifer McDonald)
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.
Ultrasound Scan
LHB tendon and rotator interval | |
|---|---|
Position: | Supine, arm supinated |
Probe: | Linear, 5–13 MHz |
Short-axis scan of long head of biceps (LHB). (Figure reproduced with permission from Jennifer McDonald)
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.
