Understanding Congenital Pseudarthrosis of the Clavicle

Finding a lump on your child’s collarbone (clavicle) can be frightening, especially when the word “pseudarthrosis” is used. It is important to know that congenital pseudarthrosis of the clavicle (CPC) is a rare, benign (non-cancerous) developmental condition that is present at birth ^[1][2]. It is not the result of anything you did during pregnancy, nor is it caused by a “broken bone” during birth ^[3].

What is Congenital Pseudarthrosis of the Clavicle?

The word pseudarthrosis literally means “false joint.” In children with this condition, the collarbone does not form as one solid piece. Instead, the middle third of the bone remains in two separate pieces that are connected by flexible fibrous tissue rather than solid bone ^[1][3].

This is a localized anomaly, meaning it usually only affects that one specific bone and does not mean your child has a systemic (whole-body) disease ^[1]. While it can look like a fracture on an X-ray, doctors distinguish CPC from a birth injury because it does not show a callus (the hard bridge of “new bone” that typically forms when a fracture is healing) ^[4][3].

Why Did This Happen?

To understand why CPC occurs, it helps to look at how a baby’s bones grow before birth. The collarbone is unique because it starts as two separate “growing zones” called primary ossification centers ^[5].

• Normal Development: Usually, these two centers grow toward each other and fuse into one solid bone during the seventh week of fetal development.
• CPC Development: In children with CPC, these two centers fail to fuse ^[1].

The most widely accepted theory for why they don’t fuse involves the subclavian artery, a major blood vessel that sits right behind the collarbone. In most people, this artery sits slightly higher on the right side than the left. Experts believe the physical “pulsing” of this artery during early development may physically prevent the two halves of the bone from joining together ^[6]. This explains why the condition occurs on the right side in about 95% of cases ^[1][3]. When it occurs on the left side, it is often because the child’s internal organs are mirrored (a condition called situs inversus) ^[6]. In rare instances (roughly 5-10%), it can affect both collarbones (bilateral). Doctors will evaluate bilateral cases closely to rule out other genetic conditions ^[4][7].

Daily Life and Handling Your Newborn

It is completely normal to be terrified of hurting your child when you first discover the bump. However, because CPC is a painless, benign anomaly and not an active fracture, you can handle your baby normally ^[3].

• Car Seats: It is safe to buckle car seat straps securely over the collarbone.
• Tummy Time: Your baby can and should participate in regular tummy time.
• Handling: You do not need to support their head or shoulder differently than you would any other infant.

Is It Serious?

While the word “congenital” can sound heavy, CPC is a benign condition. Most children experience the following:

• Painless Lump: The most common sign is a noticeable, painless bump over the middle of the collarbone that grows as the child grows ^[3].
• Normal Movement: Most children have a full range of motion in their shoulder and arm ^[3].
• Functional Strength: While the shoulder may appear slightly lower or closer to the chest, most children do not experience significant weakness.

In rare cases, as a child grows, the “false joint” can cause some discomfort or, very rarely, press on nearby nerves or vessels (thoracic outlet syndrome) ^[8][9]. Because of this, your care team will monitor the site to ensure your child remains comfortable and functional as they reach school age.

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