Introduction:
It is a condition caused due to failure in the formation (ossification) of the central portion of the clavicle. The clavicle, also known as the collarbone, is a sigmoid-shaped bone that connects the sternum (partially T-shaped vertical bone that forms the anterior portion of the chest) to the shoulder blade (scapula).
The condition is typically observed just after birth or during the first days of life as a painless swelling in the middle third or the lateral aspect of the clavicle. The right clavicle is the most commonly affected side, and it is more common in girls than boys.
Based on the anatomical, clinical, and pathological differences, the condition can be divided into two types:
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Congenital Failure of Two Segments of the Clavicle to Unite - This is observed at birth and is caused due to hypoplasia (arrested development) of the distal fragment of the clavicle. When observed clinically, it causes pain on the application of pressure, and radiographically the medial fragment (part of the clavicle towards the middle or center) is bigger than the lateral fragment (the part away from the middle of the body) with a space in between them.
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Congenital Bone Deficiency - In this type of defect, the clavicle is normal at birth but later on fractures even with the slightest trauma due to the underlying bone deficiency. It can be treated surgically, unlike the first type.
The condition normally does not cause any functional incapacity, and most of the shoulder movements remain normal; however, occasionally, it may be associated with pain while performing activities that involve movements above the head level.
Diagnosis can be made with clinical examination and imaging. The condition can be treated surgically by resecting and approximating the edges or using bone grafts. The prognosis is good if the surgery is followed up with stabilization by means of osteosynthesis.
What Causes Congenital Pseutdoarthrosis of the Clavicle?
The clavicle is the first bone to ossify (become bony) in the fetus through a process called membranous ossification. The clavicle begins as one cartilaginous mold, which then divides into two parts separated by a pre-cartilaginous interval. When the embryo reaches the length of 17 mm, the two parts start to ossify, which is complete by the time the embryo reaches the length of 19 mm. The two ossified parts, now known as the primary ossification centers, fuse and form one bone called the clavicle.
Any anatomical, environmental, or mechanical disturbances during any stage of the entire process will lead to failure in the fusion of the primary ossification centers leading to pseudoarthrosis of the clavicle. Anatomical disturbances include a higher position of the right subclavian artery (artery located just below the clavicle) than its contralateral one or an abnormal position of the fetus in the womb. Mechanical and environmental disturbances, on the other hand, put excess pressure on the right subclavian artery during clavicle formation resulting in its failure to fuse.
The condition can occur on its own or be associated with other genetic conditions like:
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Ehler-Danlos Syndrome - They are a group of inherited conditions caused due to genetic mutations (alterations) that primarily affect the body's connective tissue.
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Al-Awadi/Raas-Rothschild Syndrome - It is a rare phocomelia (a condition where the hand or foot is directly attached to the trunk) syndrome characterized by limbic and pelvic hypoplasia (reduced development) or aplasia (no development) and renal and facial abnormalities.
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Kabuki Syndrome - It is a congenital condition characterized by abnormal facial features, mental impairment, and growth problems.
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Prader-Willi Syndrome - Also a genetic condition that can cause delayed development, behavioral issues, and altered physical appearance.
Other less common conditions associated with congenital pseudoarthrosis of the clavicle are thoracic outlet syndrome (a condition caused due to compression of blood vessels located between the clavicle and the first rib) and multiple vertebral malformations.
How Is Congenital Pseudoarthrosis of Clavicle Diagnosed?
The condition can be diagnosed with the help of clinical manifestations, radiographs, and histopathological studies.
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Clinical Manifestations - It is often seen as a painless protuberance in the middle of the clavicle, along with hypermobility, which starts after a few days of birth. As the child grows older and becomes more active, it may cause pain and functional incapacity.
The condition causes the shoulder to droop, which will become an esthetic concern, especially if the child is female.
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Radiographic Examinations - The radiographs will show a characteristic clear gap between the medial fragment and the lateral fragment. The former is located above the latter due to tractional forces exerted by the upper limb. The lateral aspect of the clavicle will be enlarged, while its medical aspect will atrophy with fibrous cartilage in the middle.+
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Histopathological Studies - The histopathological features of pseudoarthrosis demonstrate chondrocytes (cartilage-producing cells) arranged in a columnar fashion at different maturation levels similar to that seen in the long bones.
What Is the Treatment for Congenital Pseudoarthrosis of the Clavicle?
Although the clavicle is the first bone to calcify in the body, it takes approximately 20 years for it to complete the process, which is why the clinician typically delays any congenital repair of the clavicle for a later age.
Treatment primarily involves surgery, during which the surgeon will resect and approximate the ends of the clavicle and place a graft to fill the gap. The graft can be taken from the iliac crest of the patient's own body, or it can be a bovine xenograft. The approximated bones will be fixed with the help of screws or wires until stabilization is achieved.
The procedure is done under anesthesia, and the patient will be given prophylactic antibiotics prior to prevent postoperative infection. Post-op, the patient will be immobilized with a sling and a swath or a shoulder spica cast (if internal fixation is not possible). The clavicle is protected until the stabilization is confirmed radiologically.
Failure of the clavicle to unite is the major complication seen after the surgery; however, this can be avoided by using the aforementioned plates and screws.
Conclusion:
It is a rare condition caused due to failure of the union of the primary ossification centers of the clavicle. Most cases are diagnosed at birth; diagnosis at a later stage is not uncommon. The primary concern is aesthetics because the condition does not cause functional incapacity. Selective surgery is the preferred mode of treatment, and the prognosis is excellent if the union is stabilized with pins and screws.
