Medial Clavicle Physeal Injury (Pseudodislocation) — Pattern

Medial clavicle injuries in children and adolescents are frequently misdiagnosed and mismanaged because they are not what they appear to be. What presents as a `sternoclavicular (SC) joint dislocation` in a skeletally immature patient is almost invariably a physeal injury — a Salter-Harris fracture through the medial clavicular physis — and NOT a true dislocation of the SC joint. This distinction has profound implications for management, imaging interpretation, prognosis, and surgical decision-making. The medial clavicular physis is the last physis in the body to ossify and the last to fuse — it does not appear radiologically until age 18–25 years and does not fuse until age 22–25 years — meaning that apparent `SC dislocations` in patients up to the age of 25 years must be presumed to be physeal injuries until proven otherwise.

• The medial clavicular physis: the last secondary ossification centre to appear in the human body (~age 18–22 years) and the last to fuse (~age 22–25 years); the thick ligamentous structures of the sternoclavicular joint (anterior and posterior SC ligaments, costoclavicular ligament, interclavicular ligament) are significantly stronger than the immature physeal cartilage; therefore, when significant force is applied to the medial clavicle in a skeletally immature patient, the physis fails (physeal fracture) BEFORE the ligaments fail (true SC joint dislocation); the result is a Salter-Harris Type I or II physeal fracture — the medial clavicle ossification centre (epiphysis) remains in the SC joint while the metaphysis displaces; the displacement direction (anterior or posterior) depends on the mechanism
• Clinical importance: posterior displacement of the medial clavicular metaphysis (what appears to be posterior SC joint dislocation) is a potentially life-threatening injury — the posterior displacement can compress or lacerate the trachea, oesophagus, subclavian vessels, brachial plexus, and the innominate (brachiocephalic) vein; anterior physeal injury (far more common and benign) displaces anteriorly and is easily visible as a prominent medial clavicle but poses no threat to adjacent vital structures

• Plain X-ray limitations: the medial clavicular physis does not ossify until age 18–22 years; therefore, on standard AP chest X-ray or clavicle views, the medial clavicle epiphysis is not visible (it is entirely cartilaginous); there is NO bony ossification centre to demonstrate the physeal fracture; the X-ray may appear normal OR may show asymmetry of the medial clavicle position relative to the manubrium — but this asymmetry is difficult to appreciate on standard views because of the complex 3D anatomy of the SC joint and the overlapping structures in the mediastinum; the Rockwood serendipity view (a 40° cephalic tilt AP view of the SC joint) can help demonstrate anterior vs posterior displacement — a superior position of the medial clavicle = anterior displacement; an inferior position = posterior displacement; but CT is far superior
• CT scan (gold standard): the investigation of choice for medial clavicle injuries in all age groups; CT clearly demonstrates: (1) the direction of displacement (anterior vs posterior); (2) the presence of a physeal fracture vs true SC joint dislocation (in adolescents, the thin cartilaginous epiphysis may occasionally be visible on CT); (3) proximity to vital mediastinal structures; (4) vascular compromise (CT angiography if vascular injury suspected); CT should be obtained urgently for any suspected posterior SC dislocation or medial clavicle injury with cardiorespiratory symptoms
• MRI: superior to CT for visualising the cartilaginous epiphysis and confirming the physeal fracture diagnosis; used in selected cases, particularly when distinguishing a physeal injury from a true SC dislocation has management implications; MRI arthrography can demonstrate the intact SC joint ligaments in a physeal fracture (confirming the ligaments are NOT the injured structure)

• Anterior displacement — non-operative: the vast majority of anterior medial clavicular physeal injuries in children can be managed non-operatively with excellent outcomes; the medial clavicular physis has exceptional remodelling potential (the last physis to fuse — significant growth remaining until age 22–25); even with apparent residual anterior protrusion, the cosmetic result is typically acceptable and function is unaffected; management: arm sling for 3–6 weeks for pain relief; gradual return to activity; reduction of an anterior physeal injury is possible but rarely maintained; since the deformity is cosmetically acceptable and function is unaffected, operative reduction is almost never indicated for anterior displacement; the protrusion remodels significantly over 2–3 years
• Posterior displacement — urgent management: posterior displacement with symptoms (dyspnoea, dysphagia, hoarseness, venous congestion, neurological deficit) = URGENT surgical emergency; management: (1) Closed reduction first (in the operating room with vascular surgery on standby — NOT in the ED); the patient is positioned supine with a roll between the scapulae; a towel clip is placed around the medial clavicle shaft and used to pull the clavicle anteriorly while the arms are held in abduction and extension; a `clunk` is felt when reduction is achieved; post-reduction check for vascular and neurological function; (2) Stabilisation after reduction — the reduced physis is typically stable and can be immobilised in a figure-of-eight bandage or sling; (3) Open reduction if closed fails — direct anterior incision over the SC joint with vascular surgery standby; care to avoid the underlying mediastinal structures; plate or suture fixation across the SC joint is rarely required and carries risk
• Vascular surgery standby: this is a MANDATORY requirement for attempted reduction of posterior medial clavicle physeal injuries; the retrosternally displaced clavicle may be adherent to or compressing the innominate vein, subclavian artery, or aorta; blind attempts at reduction without vascular backup can cause catastrophic haemorrhage; the reduction manoeuvre must ALWAYS be performed in an operating room with a vascular surgeon immediately available; any attempt at reduction in the emergency department without vascular backup is contraindicated

• Medial clavicular physis: last secondary ossification centre to ossify (age 18–22 years) and last to fuse (age 22–25 years); therefore any apparent `SC joint dislocation` in patients up to age 25 = assume physeal fracture (Salter-Harris I or II) until proven otherwise
• Why physeal injury not SC dislocation in children: SC ligaments are stronger than the immature physis; force fails the physis before the ligaments; the medial clavicle epiphysis stays in the SC joint; the metaphysis (clavicle shaft) displaces anteriorly or posteriorly
• Anterior displacement (70%): anterior protrusion, palpable; benign; non-operative; sling 3–6 weeks; excellent remodelling; reduction not maintained and usually not required; good functional outcome
• Posterior displacement (30%): retrosternal clavicle; EMERGENCY — threatens trachea (stridor, dyspnoea), oesophagus (dysphagia), subclavian vessels (vascular compromise), innominate vein (venous congestion), brachial plexus; urgent CT mandatory
• Posterior displacement management: ALWAYS in operating room; vascular surgery on standby MANDATORY; closed reduction with towel clip (abduction + extension + anterior pull on clavicle); open reduction if closed fails; NEVER attempt reduction in ED without vascular backup
• Imaging: plain X-ray unreliable (epiphysis is cartilaginous — not visible); CT scan is gold standard; Rockwood serendipity view (40° cephalic tilt) helps but less accurate than CT; MRI shows cartilaginous epiphysis and intact SC ligaments confirming physeal injury
• Key distinguishing feature from true SC dislocation: SC ligaments are INTACT in physeal fracture; the physis has failed; in a true dislocation, the ligaments rupture; distinguish on MRI or intraoperatively; management implications: physeal injuries remodel (non-operative anteriorly); true SC dislocations in adults = operative for posterior; chronic SC dislocations = figure-of-eight reconstruction
• Complications of posterior displacement: tracheal compression (most common), venous thrombosis, pneumothorax, oesophageal injury, death (rare); missed diagnosis = catastrophic outcome; high index of suspicion for ANY medial clavicle injury with cardiorespiratory symptoms