Anatomical and biomechanical features
Understanding the biomechanics of the shoulder joint is essential for proper diagnosis and treatment. An important role is played by Rouviere's recess, a fold of the shoulder joint capsule in the axillary region. During a fracture, blood and fibrin effuse into this space. If the fold adheres ("glues" together), it becomes a serious obstacle to the full restoration of the range of motion.
In addition, the external rotators of the shoulder attach to the proximal part of the bone: supraspinatus, infraspinatus, and teres minor muscles. When the greater tubercle is avulsed, these muscles can displace the fractured fragment under the acromion of the scapula. Such displacement is considered an indication for surgical intervention.
When evaluating radiographs, it is important to remember the neck-shaft angle (the angle between the head and the shaft of the humerus), which is normally 135°.
Classification and injury mechanisms
The injury can result from either a direct blow to the lateral surface of the shoulder or an indirect mechanism (more common), such as a fall on an outstretched hand or elbow.
According to the AO/ASIF classification, fractures are divided into three types depending on the involvement of the metaphysis and articular surface:
- Type A (unifocal): isolated fracture of the tuberosities or metaphysis without extension into the articular surface.
- Type B (bifocal): combined fracture of the tuberosities and metaphysis, not involving the epiphysis.
- Type C (bifocal intra-articular): fracture of the head and anatomical neck. This is the only type that extends to the articular surface.
The most frequent are surgical neck fractures of the humerus, especially in the setting of senile osteoporosis and age-related cortical thinning. Depending on the position of the arm at the moment of the fall, they are divided into:
- Adduction fractures: the central fragment is abducted, the distal fragment is adducted. Unimpacted fragments form an angle open medially and posteriorly. Sharp edges can damage the axillary nerve.
- Abduction fractures: the central fragment is adducted, the distal fragment is abducted. The angle is open posteriorly and laterally. Often combined with a greater tubercle injury.
- Impacted fractures without axial displacement: uniform impaction of the distal fragment into the proximal one.
Differential diagnosis of humeral neck fractures
It is crucial to distinguish an impacted fracture from an unimpacted one. In an impacted fracture, symptoms may be mild, and it is often mistaken for a contusion. A distinguishing feature of an impacted fracture is the movement of the humeral head together with the shaft during passive rotational movements, as well as tenderness upon axial loading (tapping on the elbow).
| Sign | Impacted fracture | Unimpacted fracture |
|---|---|---|
| Pain | Minimal (maximum in the neck region) | Pronounced (in the area of the protruding fragment) |
| Joint function | Minimally impaired | Active movements are impossible |
| Head movement during rotation | Moves together with the shaft | Remains in place |
| Fragment crepitus | Absent | May be detected |
| Change in the shoulder axis | Negligible | Noticeable (axis projects onto the clavicle or lateral to the acromion) |
Radiological diagnosis and management
For accurate diagnosis, radiography is performed strictly in two projections: anteroposterior and lateral (axial). If shoulder abduction is impossible due to the risk of displacement, a transthoracic view is performed: the patient stands, the cassette is pressed against the injured joint, and the beam is directed through the axilla of the raised healthy arm. CT and MRI are used if necessary.
Pre-hospital care includes the administration of general analgesics and transport immobilization. A Cramer wire ladder splint (modeled on the healthy arm and immobilizing three joints) or soft bandages are used: Desault bandage (with an axillary roll), Velpeau bandage (arm flexed at an acute angle), or a simple sling.
Briefly: answers to topical questions
What are the differences between adduction and abduction surgical neck fractures of the humerus?
Adduction and abduction surgical neck fractures of the humerus differ in fragment displacement biomechanics, the direction of the deformity angle, and associated injuries.
| Sign | Adduction fracture | Abduction fracture |
|---|---|---|
| Position of the central fragment | Lead | Adduction |
| Position of the distal fragment | Adduction | Lead |
| Impaction (in impacted fractures) | Medial margin | Lateral margin |
| Angle (in unimpacted fractures) | Open medially and posteriorly | Open posteriorly and laterally |
| Shoulder axis | Lateral to the acromion | Projects onto the clavicle |
| Complications and associations | Damage to the deltoid muscle and axillary nerve | Greater tubercle fracture |
What are the clinical symptoms and specific shoulder positions in greater and lesser tubercle fractures?
The clinical presentation of tuberosity fractures includes general symptoms and specific changes in shoulder position depending on the injured structure.
- General signs include pain and swelling in the shoulder joint area.
- Greater tubercle fracture — the shoulder is internally rotated, attempts at external rotation cause pain. In combined injuries, it is usually not clinically apparent and requires radiographic control.
- Fracture of the lesser tubercle — the shoulder is rotated externally, and active internal rotation is impossible.
Class and exam questions
Why does the humeral head move together with the arm in an impacted fracture?
Because one bone fragment is tightly impacted into the other, they temporarily function as a single bony unit. Therefore, during passive rotation of the diaphysis, the head also moves.
Which radiographic projections are mandatory for humeral fractures?
Anteroposterior and lateral (axial) projections are mandatory. If the axial view cannot be performed due to pain or risk of displacement, a transthoracic chest radiograph is taken.
What clinical sign can be used to identify a tubercle fracture?
In a fracture of the greater tubercle, the shoulder is rotated internally, and attempts at external rotation cause severe pain. In a fracture of the lesser tubercle, the shoulder is rotated externally, and active internal rotation is impossible.
What else to study on this topic
- Technique and indications for osteosynthesis in tubercle fractures
- Specifics of applying Desault and Velpeau bandages at the prehospital stage
- Conservative management strategy for impacted fractures
- Pathogenesis of senile osteoporosis as a risk factor for fractures
- Axillary nerve injuries: diagnostics and consequences
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