Congenital Pseudarthrosis of the Clavicle

Congenital pseudarthrosis of the clavicle (CPC) is a rare congenital failure of fusion of the two primary ossification centres of the clavicle. It is present from birth, though often noticed only in infancy or early childhood.

How rare. The literature consists almost entirely of case reports and small series. The Depaoli systematic review pooled the entire published experience and found only 231 patients (240 clavicles) across 21 articles; no population incidence was retrievable, so none is quoted.

Who. The condition is typically right-sided (Depaoli review), and bilateral cases are uncommon. The pooled data show no sex predominance, an important correction to older teaching drawn from individual series.

Predisposing factors. None is clearly established. In particular CPC is not associated with neurofibromatosis, the distinction that matters most against congenital pseudarthrosis of the tibia.

Behaviour. CPC is usually painless and non-progressive, causes little functional deficit, and is compatible with normal shoulder function. That is why observation is legitimate, and why most published surgery was undertaken for cosmesis.

The clavicle is unique. It is the first bone in the body to begin ossifying, around the fifth to sixth week of gestation, and it ossifies largely by intramembranous ossification from two primary centres, one medial and one lateral, that normally coalesce in the mid-shaft. The bony ends then form by endochondral ossification, and the medial physis is the last in the body to fuse, in the early-mid twenties (relevant to medial physeal injuries, covered in our Clavicle Fractures topic). The general process of ossification is covered in our Intramembranous/Endochondral Ossification topic.

CPC is the failure of those two primary centres to coalesce. The non-union therefore sits in the middle third and is present without any trauma.

Why the right. The subclavian artery sits higher on the right, just beneath the clavicle, and its pulsation is thought to disturb coalescence: the pulsation theory. On the left the artery is lower, and left-sided CPC is associated with dextrocardia/situs inversus, where the arterial anatomy is mirrored. Bilateral cases are associated with bilaterally elevated or anomalous subclavian arteries (for example, cervical ribs).

The child presents in infancy or early childhood with a painless, mobile, non-tender lump over the middle third of the clavicle.

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The plain radiograph is the diagnostic test. It shows a gap in the middle third of the clavicle with smooth, rounded, sclerotic non-united bone ends and no callus, the appearance that separates CPC from a healing birth fracture at a glance. The diagnosis is clinical, a painless mid-clavicular mass, plus that radiograph.

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Nothing else is needed routinely. CT or MRI adds nothing to the diagnosis in a typical painless right-sided case; reserve cross-sectional imaging for pre-operative planning or atypical presentations. No laboratory work-up is required, because inflammatory markers and calcium metabolism are irrelevant to this structural diagnosis.

When the pattern is atypical, look further.

• Left-sided lesion: a chest radiograph and cardiac assessment for dextrocardia/situs inversus
• Bilateral lesions: a skeletal survey and consideration of cleidocranial dysplasia (RUNX2) rather than simple CPC
• Phenotype beyond an isolated unilateral clavicle defect: genetic testing, which is reserved for this situation

Confirm that the lesion is neither a fracture nor cleidocranial dysplasia.

• Clavicle birth fracture is the main differential. It follows birth trauma, is initially painful, and heals with abundant callus and simple immobilisation; CPC is painless, atraumatic and does not heal.
• Cleidocranial dysplasia is suspected when the clavicular defects or absence are bilateral, or when there are cranial features (delayed closure of the fontanelles, Wormian bones), dental anomalies and other skeletal signs. It is a RUNX2 disorder.
• Congenital pseudarthrosis of the tibia is strongly NF1-associated and notoriously difficult to treat, whereas CPC treats well; reserve concern about neurofibromatosis for the tibia.

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Observation. Given that natural history, many children need only reassurance and observation. Most untreated children remain asymptomatic. The rare downsides of leaving it are a prominent cosmetic lump, occasional aching or fatigue with activity or a drooping shoulder, and, rarely, thoracic-outlet-type symptoms from the bony prominence (see our Thoracic Outlet Syndrome topic).

Indications for surgery.

• Symptoms: pain, shoulder fatigue
• Troublesome cosmetic prominence
• Functional limitation

Timing. Surgery is typically undertaken around age 3-6 years: old enough for safe anaesthesia and surgery and to harvest iliac-crest graft, yet young enough for good remodelling and union, and before the lump or any functional or cosmetic concern becomes established. Some surgeons favour earlier intervention for easier union and remodelling. The Kim series is the caution against going too early with too little: infants operated under 18 months with suture fixation alone had a 43% nonunion rate, against 13% in older children treated with plate fixation, so stable fixation at an older age unites more reliably.

Technique.

1. Resect the pseudarthrosis back to healthy bleeding bone
2. Bridge the gap with autologous iliac crest graft
3. Stabilise with a plate, or an elastic stable intramedullary nail (ESIN) or K-wire

Graft and fixation. Autograft is preferred; union is more reliable with it, and the reported failures cluster where allograft was used. The Li multicentre comparison found that intramedullary devices gave shorter union time and easier implant removal than plates, with no difference in complications or outcome.

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The anatomy at risk. Directly beneath the middle third of the clavicle run the subclavian/axillary vessels and the brachial plexus, crossing over the first rib between the scalenes, with the lung apex medially. A mid-clavicular resection is therefore done with careful subperiosteal dissection, staying on bone and protecting these structures (full anatomy in our Brachial Plexus Anatomy topic). This is why a series reporting no neurovascular complications is making a substantive claim rather than a routine one.

What to promise the family. Published series are small and range from roughly three-quarters to near-universal healing (see Evidence below), so "it almost always unites" overstates it. Even where the bone fails to unite radiologically, operated children are typically pain-free with full movement. The functional result and the radiographic result are not the same endpoint, a distinction worth making explicitly when consenting a family whose concern is usually cosmetic; define success with them before operating.

• Nonunion is the main complication. The systematic review puts overall surgical union at 87.4%, a nonunion rate of 12.6%, rising to 44.4% when allograft was used (Depaoli review); the infants treated with suture fixation alone fared worst (Kim series, above).
• Major complications had a 15.7% prevalence across the published surgical experience, the figure to quote in consent rather than the reassuring individual series.
• Reoperation for implant removal: plates typically require a second procedure; intramedullary devices are removed more easily and earlier.
• Neurovascular injury: the subclavian vessels and brachial plexus lie directly beneath the resection field, and the benchmark series reporting no such injuries achieved that with careful subperiosteal technique.