Shoulder joint dislocations and associated injuries
The most common type is anterior dislocation, where the humeral head is displaced beneath the coracoid process. When evaluating a standard AP radiograph, one should specifically look for typical bone defects:
- Hill-Sachs lesion (Hill-Sachs lesion): a wedge-shaped impacted defect of the posterosuperior humeral head. It appears as a radiopaque line, but is more accurately assessed on axial views or MRI (bone bruise zone).
- Bony Bankart lesion (Bony Bankart): avulsion of the anteroinferior glenoid rim. Fragments larger than 5 mm significantly increase the risk of recurrent dislocations.
Posterior dislocation is rare (less than 5% of cases). Due to internal rotation, the humeral head acquires a light-bulb shape on the AP projection, without significant medial displacement. It is definitively confirmed on the axial projection.
A rare and dangerous variant is inferior dislocation (luxatio erecta). The arm is fixed in hyperabduction. It carries the maximum risk of neurovascular bundle and rotator cuff injury.
Fractures of proximal humerus
These fractures are typical in elderly patients. Fracture lines usually pass through fused growth plates: the anatomical and surgical necks, and the greater and lesser tuberosities.
Severity is assessed using the Neer classification (Neer classification). Fragment displacement of more than 1 cm or rotation of more than 45 degrees is considered significant. In 85% of cases, the fracture is comminuted yet non-displaced (single-part), and therefore reduced closed.
It is important to remember complications: in fractures of the surgical neck, the sharp edges of the diaphysis can injure the axillary artery and brachial plexus. The pectoralis major muscle pulls on the diaphysis, causing medial displacement.
Acromioclavicular joint (ACJ) injuries
ACJ stability is provided by the acromioclavicular (AC) and coracoclavicular (CC) ligaments. Normally, the inferior cortical margins of the clavicle and acromion should lie on the same line, and the coracoclavicular distance should not exceed 13 mm.
Rockwood injury grades:
- Grade 1: Ligament sprain, no joint displacement.
- Grade 2: AC ligaments are torn, but CC ligaments are intact. The clavicle is elevated but does not exceed the superior border of the acromion. Coracoclavicular distance is normal.
- Grade 3: All ligaments are torn. Coracoclavicular distance is >13 mm, and the clavicle rises above the acromion. Surgery is indicated.
To differentiate between grades 2 and 3, stress radiography with weights suspended from the wrists may be used.
Elbow joint and occult fractures
In elbow injuries, soft tissue evaluation is critically important. The main marker is the fat pad sign (Fat pad sign). When fluid (effusion) appears, fat is displaced from the humeral fossae and becomes visible on the lateral view as a radiolucent area. Visibility of the posterior fat pad is always pathological and requires searching for an occult fracture.
In children, the most common injury is an occult supracondylar fracture (often greenstick). To detect it, the anterior humeral line rule is used: on the lateral radiograph, a line drawn along the anterior cortex of the humerus must intersect at least the anterior third of the capitellum. If the line passes entirely anteriorly, it means the distal fragment is displaced posteriorly. This is a dangerous condition, as the proximal bone edge can lacerate the brachial artery, median nerve, or ulnar nerve.
Briefly: answers to topical questions
Which anatomical structures form the rotator cuff of the shoulder, and which of them are most frequently injured during dislocations?
The complete anatomical composition of the rotator cuff is not specified in the cited sources.
- Supraspinatus muscle (supraspinatus) — in anterior dislocation, its tendon may cause a traction avulsion of the greater tuberosity; the tendon itself remains intact and attached to the avulsed bone fragment.
- Subscapularis muscle (subscapularis) — may become entrapped within the joint space following reduction of a dislocation.
- In inferior dislocation (Luxatio erecta), there is the highest risk of injury to the neurovascular bundle, ligaments, and rotator cuff.
Which vessels and nerves are most vulnerable in surgical neck fractures of the humerus?
Surgical neck fractures of the humerus can be complicated by injuries to the axillary artery and brachial plexus.
For posterior shoulder dislocation: the "light-bulb" sign on the AP projection — due to rotation, the humeral head appears perfectly round, like an incandescent lamp.
Class and exam questions
Why take an X-ray after shoulder dislocation reduction?
Control radiography (in two projections) is strictly mandatory to confirm correct bone alignment and to check for small fragments that may have arisen during reduction.
What is a reverse Hill-Sachs lesion?
This is an impacted defect on the anterior surface of the humeral head. Unlike the classic lesion, it occurs as a complication of posterior shoulder dislocation.
Why perform stress radiography of the ACJ?
Weights attached to the wrists create downward traction (distraction). This helps visualize occult separation of the clavicle and coracoid process to differentiate grade 2 from grade 3 Rockwood injuries.
When is MRI indicated after dislocation reduction?
MRI is prescribed if the articular surfaces are reduced but displacement persists (joint space widening). This is done to check for entrapped soft tissues, such as the subscapularis muscle.
What else to study on this topic
- Specifics of detecting lateral epicondyle fractures in children (ossification centers).
- Differential diagnosis between os acromiale (developmental anomaly) and fracture.
- Mechanism of greater tuberosity avulsion by supraspinatus tendon traction.
- Assessment of multiplanar shoulder instability signs on MRI.
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