Clinical presentation and the "piano key" sign
The leading manifestation of an acromioclavicular joint injury is the "piano key" sign. To detect it, support the patient's elbow while simultaneously pressing down on the prominent distal end of the clavicle.
In the case of a positive sign, the clavicle easily depresses back to its anatomical position. However, as soon as the physician stops applying pressure, the acromial end immediately springs back upward, much like a piano key. This indicates disruption of the ligamentous apparatus holding the clavicle.
Differential diagnosis: complete dislocation and subluxation
The severity of the injury directly affects the prominence of symptoms. In complete dislocation, the clinical presentation is always more pronounced.
- Complete dislocation: There is absolute dissociation of the articular surfaces of the scapula and clavicle. The acromial end is displaced upward to such an extent that the physician can clearly palpate its articular margin. Biomechanically, this manifests as complete independence of movement: the scapula moves on its own, while the position of the clavicle remains unchanged.
- Subluxation: The articular surfaces are not fully dissociated, as the coracoclavicular ligament remains intact (undamaged). Because of this, it is impossible to palpate the articular end of the clavicle. Biomechanically, the connection between the bones is preserved: any movements of the scapula are accompanied by normal synchronous displacement of the distal end of the clavicle.
Features of neglected dislocations
Over time, the clinical presentation of the injury may evolve. In some cases, symptoms diminish and become less noticeable; in others, conversely, they become even more pronounced.
Over time, the protrusion of the acromial end of the clavicle may gradually increase. At the same time, the classic "piano key" sign often becomes incomplete: due to scar tissue changes or tissue interposition, pressing on the clavicle no longer allows it to fully depress.
Radiological diagnostics
The main method of objective visualization is radiography. The study is mandatory performed in the anteroposterior projection, capturing both shoulder girdles to allow a comparison between the healthy and injured joints.
The main radiological criterion for injury is the displacement of the lower contour of the clavicle in the joint area upward relative to the corresponding contour of the acromion.
Functional stress study
If the standard radiograph does not provide a definitive answer, stress radiography is used for precise differential diagnosis between dislocation and subluxation.
Procedure technique:
- The patient is in a standing position.
- A weight ranging from 3 to 5 kg is suspended or fixed to both upper extremities.
- An X-ray of both shoulder girdles is taken (ideally on a single film for precise positioning).
The weight pulls the arms and scapulae downward. If the ligaments are injured, the clavicle remains in place while the scapula drops down, making the displacement obvious.
Evaluation criteria:
- Subluxation: The distance from the coracoid process of the scapula to the clavicle increases slightly (less than 0.5 cm).
- Complete dislocation: The distance between the coracoid process and the clavicle increases by 0.5 cm or more.
Briefly: answers to topical questions
Which specific ligaments are torn in a complete dislocation of the acromial end of the clavicle?
In a complete dislocation of the acromial end of the clavicle, there is a combined rupture of two ligaments that ensure joint stability.
- Acromioclavicular ligament — located internally, enveloping the joint.
- Coracoclavicular ligament — located outside the joint, connecting the coracoid process of the scapula to the distal end of the clavicle in the region of its tubercle, and consisting of two portions (conoid and trapezoid).
What mechanism of injury most frequently leads to an acromioclavicular joint rupture?
The sources do not specify which mechanism of injury occurs most frequently, but two main types of impact are distinguished.
| Mechanism | Description |
|---|---|
| Direct | The load vector is directed from top to bottom directly onto the acromion process. |
| Indirect | Impact from the outside onto the shoulder joint with the arm adducted and internally rotated, or an axial load on an abducted arm. |
What types of immobilizing bandages are used for the conservative treatment of an acromioclavicular subluxation?
For the conservative treatment of an acromioclavicular subluxation, bandages and splints that provide external vertical pressure are used. The following types of immobilization are employed:
- Plaster cast (splint) — applied with pressure on the acromial end of the clavicle.
- Abduction splint — used with the application of a pressure pad on the acromial end of the clavicle.
- "Harness" plaster bandage — acts as an alternative method of fixation.
- Thoracobrachial bandage with a ShimBARETSKY compression screw — used to create external vertical pressure.
What surgical methods exist for treating neglected complete dislocations of the acromial end of the clavicle?
For complete dislocations of the acromial end of the clavicle, the following are used:
- repair of both damaged ligaments;
- coracoclavicular ligament repair with transarticular fixation;
- internal splinting with a shape-memory structure made of titanium nickelide;
- fixation with a hook plate.
For neglected complete dislocations, a specific surgical technique is not separately specified in the provided sources.
Remembering the difference in biomechanics is simple: in a COMPLETE dislocation, the clavicle completely "forgets" about the scapula (they move separately), whereas in a SUBLUXATION, it submits to it (they move synchronously).
Class and exam questions
Is it possible to palpate the articular end of the clavicle in subluxation?
No, this is only possible in a complete dislocation, when the acromial end is displaced significantly higher.
What is the purpose of using a load during radiography?
A weight of 3–5 kg pulls the scapula downward. In the event of a complete ligament rupture, this leads to a visible increase in the distance between the scapula and the clavicle on the radiograph (greater than 0.5 cm), which makes it possible to distinguish a dislocation from a subluxation.
How does the "piano key" sign change in chronic injury?
It may become incomplete — when pressure is applied, the clavicle does not fully depress back into its place.
What else to study on this topic
- Anatomy of the coracoclavicular ligament and its role in stabilization
- Reasons for the increasing prominence of the clavicle in neglected injuries
- Technique for correct weight fixation in functional radiography
- Assessment of acromion and clavicle contours on comparative radiographs
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