Diagnosis of humeral dislocations
Posterior shoulder dislocation is easy to miss if one is unaware of its specific manifestations. On an anteroposterior (AP) radiograph, the humeral head is rotated and visually resembles a "light bulb" (light-bulb shape). Meanwhile, medial displacement is significantly less pronounced than in anterior dislocations. An axial view is strictly required for definitive confirmation of the diagnosis. Such injuries may be accompanied by fractures of the posterior glenoid rim and the formation of a reverse Hill-Sachs lesion (reverse Hill-Sachs defect)—damage to the anterosuperior aspect of the humeral head.
Significantly less common is inferior dislocation (luxatio erecta), which occurs under the influence of extreme force leading to hyperabduction. In this case, the head is displaced inferiorly, presenting the highest risk of injury to the rotator cuff and the neurovascular bundle.
Following reduction of a dislocation, radiography is strictly mandatory. Anteroposterior (AP) and axial views are obtained. If the articular surfaces appear congruent, but displacement persists (articular offset), the patient is referred for an MRI to check for entrapped tissues (typically the subscapularis muscle or the long head of the biceps tendon).
Fractures of proximal humerus
Unlike young individuals, whose bones are stronger and whose trauma more frequently results in dislocations, humeral fractures are characteristic of elderly patients. Fracture lines typically follow the contours of fused growth plates (fused growth plates), passing through the anatomical or surgical neck, or separating the lesser and greater tuberosities.
To assess the severity of injuries, the Neer classification (Neer classification) is used. It is based on the number of bone fragments and the degree of their displacement. Fragment displacement greater than 1 cm or rotation exceeding 45 degrees is considered clinically significant. Most simple two-part fractures are successfully reduced via closed reduction.
Bony defects and labral lesions
Anterior joint instability frequently leads to combined osteochondral injuries:
- Bony Bankart lesion (Bony Bankart Lesion): occurs in anterior dislocation. Characterized by medial displacement of the avulsed glenoid rim along with the anterior fibrocartilaginous labrum.
- Hill-Sachs lesion (Hill-Sachs Deformity): a secondary compression fracture of the humeral head following impact against the glenoid rim. It is important to identify off-track configurations (off-track), as simply repairing the labrum is insufficient in these cases—surgical bone correction is required.
Separately, SLAP lesions (Superior Labrum from Anterior to Posterior) are distinguished, which are typical for athletes who perform frequent overhead throws. Abnormal traction at the biceps attachment site leads to a tear of the superior labrum from anterior to posterior. An accurate diagnosis is made using MRI or arthrography upon fluid leakage into the thickness of the cartilaginous labrum. The extent of the tear is described using the clockface terminology.
Rotator cuff and impingement syndrome
Chronic tears of the rotator cuff tendons lead to secondary bone changes—arthropathy (rotator cuff arthropathy) develops. On a standard radiograph, this presents as marked narrowing of the subacromial space and signs of bone impingement.
On MRI scans (in the oblique coronal plane with fat suppression), external impingement manifests as fluid accumulation in the subacromial bursa (bursitis) and thickening of the supraspinatus tendon (tendinopathy). If the tendon tear progresses to full-thickness, fluid begins to be detected simultaneously in the subacromial bursa and around the synovial sheath of the biceps within the glenohumeral joint cavity. This is a clear sign of a pathological communication forming between the two spaces.
Capabilities of ultrasound and tomosynthesis
Traditional radiography provides excellent contrast between bone and soft tissues, but is insensitive to bone loss. Alternatively, digital tomosynthesis (digital tomosynthesis) can be used—a series of low-dose images acquired along an arc and reconstructed into planar images (similar to CT). The method is good for evaluating erosions and fractures, but has not replaced more precise modalities.
Ultrasound examination using a high-frequency transducer surpasses MRI in soft-tissue spatial resolution. The method allows for dynamic testing, evaluation of ligament laxity, and detection of hyperemic blood flow. The primary value of ultrasound is guidance during injections. If ultrasound-guided administration of an anesthetic into the subdeltoid bursa does not relieve the pain, this reliably rules out rotator cuff impingement as the cause of symptoms. Ultrasound is also the first-line method for evaluating non-aggressive cysts, hematomas, and bursitis.
To memorize the four typical proximal humeral fracture lines along the growth plates (Neer classification), remember the mnemonic MALE: Greater tuberosity (Greater), Lesser tuberosity (Lesser), Anatomical neck, Surgical neck (Anatomical, Surgical).
Class and exam questions
Why perform an MRI if the joint is reduced and the articular surfaces are congruent, but minor displacement persists?
This is necessary to rule out interposition (entrapment) of soft tissues within the joint space. Most commonly, the subscapularis muscle or the long head of the biceps tendon becomes trapped between the articular surfaces.
How to distinguish a full-thickness supraspinatus tear on MRI?
The primary sign is the presence of fluid with high MR signal intensity that simultaneously fills the subacromial bursa and the joint cavity. This proves the presence of a pathological communication between these spaces.
What is the main value of ultrasound guidance during shoulder joint injections?
In its diagnostic accuracy. If local anesthetic administration under ultrasound guidance provides not even temporary relief, impingement can be ruled out as a source of pain with a high degree of confidence—something that cannot be achieved with blind injections.
What else to study on this topic
- Acromioclavicular joint injuries: Rockwood classification and surgical management
- Acute calcific bursitis: imaging of hydroxyapatite deposits and simulation of septic arthritis
- Radiological signs of rheumatoid arthritis of the shoulder and elbow: erosions and fat pad displacement
- Post-traumatic osteolysis of the clavicle in weightlifting athletes
- Principles of ultrasound-guided biopsy of soft tissue masses
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