The clavicle, commonly known as the collarbone, is the single bony bridge connecting the upper limb to the main trunk of the body. This S-shaped bone acts as a rigid support that positions the shoulder joint laterally away from the chest wall. Compromising the integrity of the clavicle, whether through severe trauma or a surgical cut (osteotomy), creates complex problems due to its unique location and function. The consequences affect the function of the entire arm and can damage adjacent vital structures.
The Clavicle’s Essential Role in Shoulder Mechanics
The clavicle’s primary function is to serve as a spacer, holding the shoulder blade (scapula) and arm at an optimal distance from the torso. This arrangement permits the wide range of motion the human arm is capable of, especially for lifting the arm overhead. Without this bony strut, the shoulder would collapse inward and forward toward the midline of the body, severely limiting mobility.
The bone also transmits mechanical forces from the arm to the axial skeleton. When a person falls on an outstretched hand, the impact force travels up the arm and is channeled through the clavicle to the rest of the body. The clavicle’s double-curve shape gives it resilience, but the middle section is often the weakest point, making it the most commonly fractured bone. It links to the sternum at the sternoclavicular joint and the scapula at the acromioclavicular joint, providing structural anchors for the shoulder complex.
Risks to Adjacent Neurovascular Structures
A severe break or surgical manipulation of the clavicle poses an immediate threat to the nerves and vessels passing beneath it. The clavicle forms a protective roof over the cervicoaxillary canal, a passageway for the neurovascular bundle supplying the entire upper limb. Damage to the bone risks puncturing or compressing these delicate structures.
The brachial plexus, a complex network of nerves originating from the neck, passes directly under the clavicle, providing motor and sensory function to the arm and hand. An injury to this plexus can lead to plexopathy, resulting in severe weakness, numbness, or even paralysis of the entire arm. This damage can occur from sharp bone fragments during trauma or from scar tissue formation or compression by a shortened bone after healing.
The subclavian artery and subclavian vein also lie in close proximity, particularly near the medial third of the clavicle. The subclavian vein can be as close as a few millimeters to the bone, making it vulnerable during trauma or hardware placement in surgery. Damage to these major vessels can cause life-threatening hemorrhage or lead to complications like pseudoaneurysms (localized collections of blood outside the vessel wall) or deep vein thrombosis.
Consequences for Shoulder Stability and Movement
Compromising the clavicle’s length or alignment alters the biomechanics of the shoulder, reducing its strength and range of motion. When the clavicle is shortened, often by more than a centimeter, the scapula is pulled closer to the chest wall. This inward and forward shift, known as shoulder protraction, disrupts the natural alignment of the shoulder socket (glenoid).
The altered position decreases the distance between the rib cage and the shoulder blade, causing muscles to function less efficiently. A shortened clavicle reduces the ability of upper extremity muscles to generate force for movements like abduction (lifting the arm out to the side) and internal rotation. This functional deficit can lead to chronic pain and difficulty with everyday tasks requiring reaching overhead. The absence of the clavicular strut also affects scapular rotation, which is necessary for full arm elevation, potentially contributing to rotator cuff dysfunction and shoulder impingement.
Challenges in Bone Healing and Recovery
The recovery process after a severe clavicle injury or osteotomy is often complicated by high rates of non-union or malunion. Non-union is the failure of the bone ends to heal together, while malunion is healing in a deformed or shortened position. The incidence of non-union after non-operative treatment for certain displaced fractures can be as high as 15%.
The clavicle’s location makes it difficult to immobilize completely, as it is constantly subjected to tension from strong muscles like the sternocleidomastoid, trapezius, and pectoralis major. This constant pulling force can displace the bone fragments, hindering healing. When the bone heals in a shortened or angulated position, the resulting malunion can cause ongoing symptoms like a palpable bump, chronic pain, and restricted movement. Surgical repair, while often necessary, introduces risks including hardware failure, infection, and a prominent bone lump that can be cosmetically bothersome.