Sternoclavicular Joint Dislocation

The sternoclavicular joint is the only true articulation between the upper limb and the axial skeleton, and the least stable major joint in the body. Dislocation is rare, under 1% of all joint dislocations.

Direction. Anterior dislocation is about nine times commoner than posterior, and posterior dislocation accounts for under 1% of shoulder girdle injuries. The anterior injury is a cosmetic prominence with mild pain and is often well tolerated. The posterior injury is rare but life-threatening: the medial clavicle is driven towards the mediastinum, and dyspnoea, dysphagia or vascular compromise make it an emergency.

Mechanism. Indirect high-energy trauma, a force applied to the lateral shoulder, is the most common cause.

• Fall onto the shoulder - indirect force through the clavicle
• Road traffic collision - restrained driver or passenger, lateral compression; a high-energy restraint injury
• Contact and collision sport - a direct blow to the medial clavicle or shoulder
• Fall onto the outstretched hand - force transmitted medially through the clavicle, levering its medial end
• Atraumatic subluxation - multidirectional laxity in young patients

Who it matters in. Chronic instability limits overhead athletes. In adolescents, and in anyone under 25 years, a medial clavicular physeal separation often mimics dislocation.

The joint. A saddle-type (sellar), ginglymoarthrodial synovial joint with a complete intra-articular disc of fibrocartilage that divides it in two. The medial clavicle is larger than the manubrial fossa: more than 50 percent of its articular surface sits outside the socket, and only a small portion articulates. There is no bony constraint, so stability is entirely ligamentous. The range is small: 40 degrees of elevation and 30 degrees of rotation.

The restraints. The extra-articular ligaments (interclavicular, costoclavicular and capsular) and the disc hold the joint reduced. The posterior capsule is the strongest single restraint, and the anterior capsule is the weakest; anterior dislocations are the commoner. The interclavicular ligament crosses the suprasternal notch between the two clavicles, and the costoclavicular (rhomboid) ligament runs from the clavicle to the first rib.

The costoclavicular ligament. It is the primary restraint to superior and medial-lateral displacement, but sectioning studies show it contributes little to the anterior-posterior translation that produces a dislocation. That is why the capsular ligaments, not the costoclavicular, are what modern reconstruction recreates.

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How it dislocates. An indirect force to the lateral shoulder drives the medial clavicle, which pivots at the costoclavicular ligament.

• Anterior force vector (most common) - the clavicle is levered forwards out of the manubrium, tearing the anterior capsule, costoclavicular and interclavicular ligaments, with the posterior capsule intact
• Posterior force vector (less common, high-energy) - posterior dislocation, with the posterior capsule torn
• Direct blow to the medial clavicle - can drive it posteriorly

What lies behind the joint. A posteriorly displaced clavicle can compress any of these, and the internal jugular vein as well:

• Immediately posterior to the medial clavicle - brachiocephalic vein, common carotid, subclavian artery and vein
• Deeper plane - trachea, oesophagus, vagus nerve, phrenic nerve, and on the left the thoracic duct

The physis. The medial clavicular physis is the last to fuse, at 23-25 years, and in adolescents it is the weakest link. A physeal injury in an adolescent often mimics a posterior dislocation on imaging.

The injury is described by the direction of displacement, the time since injury, and the severity of the ligament disruption.

Severity grade. Direction and timing are two axes; the severity grade of the ligamentous injury is the third, and it dictates whether the joint is stable.

• Grade I, sprain - the capsular ligaments are stretched but intact; the joint is stable and minimally displaced, with tenderness and mild swelling only. Sling and analgesia.
• Grade II, subluxation - partial capsular and ligament disruption with the costoclavicular ligament still intact; the joint subluxes but is not frankly dislocated, and is partially stable. Sling, analgesia, and avoidance of provocative positions.
• Grade III, dislocation - complete disruption of the capsular ligaments (and usually the costoclavicular ligament); the joint is frankly dislocated anteriorly or posteriorly and unstable. This is where the anterior-versus-posterior distinction and the mediastinal emergency apply.

A Grade I-II injury does not need reduction, only symptomatic care. The dramatic management decisions (urgent CT, theatre reduction, reconstruction) belong to the Grade III dislocation, so do not over-treat a sprain or subluxation.

History. Establish the mechanism: high-energy trauma, contact sport, a road traffic collision or a fall. Then ask for the posterior red flags - dyspnoea, stridor, dysphagia, voice change, arm paraesthesia or ischaemia. Previous episodes of recurrent subluxation suggest multidirectional laxity, and in a patient under 25 years consider a physeal injury rather than a true dislocation.

Examination. Look for asymmetry, swelling, ecchymosis and skin tethering, and palpate the position of the medial clavicle relative to the suprasternal notch and the other side. Elevating the arm in extension stresses the joint. In a suspected posterior injury, look for neck vein engorgement and tracheal deviation, and check the pulses and the neurology.

Differential diagnosis. Not every painful or deformed medial clavicle is a dislocation.

Septic arthritis. A swollen, warm, tender SC joint is not always traumatic. Septic arthritis of the SC joint is a distinct, examinable entity that is easily missed, and because the joint sits over the mediastinum, untreated infection can spread to a chest-wall abscess, sternoclavicular osteomyelitis and mediastinitis, a potentially life-threatening complication.

• Host risk factors - intravenous drug use (classic), diabetes, immunosuppression, chronic kidney disease, an indwelling central line or catheter, and a distant source of bacteraemia; it can also occur with no obvious risk factor
• Organisms - Staphylococcus aureus is commonest overall; Pseudomonas aeruginosa is classically associated with intravenous drug use
• Diagnosis - raised inflammatory markers, blood cultures, CT or MRI to define abscess, osteomyelitis or retrosternal extension, and joint aspiration for Gram stain and culture
• Management - targeted IV antibiotics for early disease; established septic arthritis with abscess or osteomyelitis usually needs surgical debridement or en bloc resection of the SC joint (medial clavicle and manubrial portion), which is generally well tolerated functionally

In an IV drug user or immunocompromised patient with a hot, painful medial clavicle and fever, think SC septic arthritis with possible mediastinal extension: image and aspirate, and do not treat it as a sprain.

Atraumatic subluxation. Common in young, hypermobile women, and not a dislocation. The medial clavicle subluxes spontaneously or with minor movements and reduces again. It needs no reduction, immobilisation or surgery; education, reassurance and avoidance of provocative positions are the management, and operating on it has high failure and complication rates.

Plain radiographs. A limited role: the AP chest film is the initial screen and excludes associated rib or lung injury. Plain films are notoriously hard to interpret here and miss up to 50 percent of SC dislocations; they cannot define the direction accurately or show the relationship to the mediastinum. The serendipity view (40-degree cephalic tilt) is now largely superseded, a historical curiosity.

CT with IV contrast is the investigation of choice, indicated in all suspected SC dislocations. Acquire thin slices (1 mm) from chin to diaphragm with IV contrast, and add 3D and multiplanar reformats for surgical planning. It gives the definitive diagnosis and maps the vessels:

• Direction of dislocation and distance displaced
• Relationship to the mediastinal vessels, trachea and oesophagus, including tracheal or vessel deviation

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CT angiography is added for a posterior dislocation with a pulse deficit, an expanding haematoma or asymmetry. It shows vessel compression, intimal injury, pseudoaneurysm or occlusion, and the surgical plan is made jointly with vascular surgery, with image sharing and on-table angiography as needed.

MRI distinguishes a physeal injury from a true dislocation in adolescents. Physeal oedema with intact ligaments and no true joint disruption justifies conservative treatment and avoids an operation on the physis.

Prognostic factors. The best prognosis belongs to an acute anterior dislocation treated conservatively, an acute posterior dislocation reduced within 24 hours with an intact costoclavicular ligament, and a low-demand patient. The poor prognosis belongs to a delayed posterior dislocation, failed closed reduction, multiple reconstruction attempts, hypermobility syndromes, and contact athletes returning to high-impact sport.