Clavicle Fractures and Classification

A broken collarbone is one of the most frequent skeletal injuries you will encounter, from the playground to the sports field. Understanding clavicle fractures is crucial because while many heal uneventfully, mismanagement can lead to chronic pain, shoulder dysfunction, and disability.

Anatomy and Mechanism of Injury

The clavicle is an S-shaped long bone that acts as a strut, connecting the sternum to the scapula and stabilizing the upper extremity. Its unique shape and subcutaneous position make it vulnerable to injury. Anatomically, it is divided into thirds: the medial (sternal) third, the middle third, and the distal (lateral or acromial) third.

The vast majority of fractures—approximately 80%—occur in the middle third. The two primary mechanisms explain this pattern. A fall onto an outstretched hand (FOOSH) transmits force up the arm through the shoulder to the clavicle, which fails at its structurally weakest point—the junction of its two curves. The second mechanism is a direct impact to the shoulder, such as in a sports collision or a fall directly onto the lateral shoulder, which drives the acromion downward and bends the clavicle over the first rib until it fractures.

Classification Systems: Allman and Neer

To standardize communication and guide treatment, fractures are classified. The classic Allman classification is straightforward, dividing fractures by location into Group I (middle third), Group II (distal third), and Group III (medial third).

For the clinically complex distal third fractures, the Neer classification is indispensable, as it accounts for ligamentous integrity. This system hinges on the coracoclavicular ligaments (the conoid and trapezoid), which tether the clavicle to the coracoid process of the scapula. A Neer Type I fracture is stable, occurring lateral to the ligaments, which remain intact. A Neer Type II fracture is unstable; the fracture occurs medial to the ligaments, which are detached from the medial fragment. This allows the medial fragment to displace superiorly due to unopposed pull from the sternocleidomastoid muscle, while the lateral fragment drops due to the weight of the arm. Neer Type III involves the articular surface of the acromioclavicular joint.

Clinical Presentation and Diagnostic Workup

A patient typically presents supporting the injured arm with the opposite hand, with the head tilted toward the injury to relax the sternocleidomastoid. Examination reveals localized tenderness, swelling, bruising, and often a visible deformity or "bump" at the fracture site. A thorough neurovascular exam is mandatory to assess for injury to the nearby brachial plexus or subclavian vessels, though this is rare.

Diagnosis is confirmed with radiographs. A standard anteroposterior (AP) view of the clavicle is the first step. For distal third fractures, a Zanca view (AP with 10-15° cephalic tilt) clears the acromion to better visualize the AC joint. An axillary lateral view can help assess displacement and articular involvement. CT scanning is reserved for complex or intra-articular fractures where plain films are insufficient.

Management: Conservative vs. Surgical

The treatment paradigm is dictated by fracture location, displacement, and patient factors.

Most middle third fractures are treated successfully with conservative management. This involves immobilization in a simple sling or figure-of-eight brace for comfort, with the goal of early pendulum exercises to prevent shoulder stiffness. Healing typically takes 6-8 weeks in adults, with union rates historically cited as high as 95% for non-displaced fractures.

Surgical fixation is indicated for specific scenarios where non-operative treatment yields poor outcomes. Absolute indications include open fractures, tenting of the skin with impending perforation, and associated neurovascular injury. Relative surgical indications, based on evidence of better functional outcomes, include:

• Shortening of >2 cm in displaced midshaft fractures.
• Comminution (multiple bone fragments).
• Displaced distal fractures (Neer Type II), which have a high rate of nonunion with sling treatment alone due to the coracoclavicular ligament disruption.

Surgical options include plate osteosynthesis (most common for midshaft) or intramedullary fixation. For Neer Type II distal fractures, fixation often involves a hook plate or a locking plate with suture augmentation to reconstruct the coracoclavicular ligaments.

Clinical Vignette and Case Application

Consider a 25-year-old cyclist who falls directly onto his right shoulder. He presents in a sling, with an obvious superior prominence of his medial clavicle near the AC joint. An AP and Zanca view show a fracture of the distal third, with the medial fragment significantly displaced upward. The lateral fragment appears inferior. This is a classic presentation of an unstable Neer Type II distal clavicle fracture due to ligament disruption. Given the high nonunion rate with non-operative treatment, you would discuss the relative benefits and risks of surgical fixation versus a trial of conservative management with this patient.

Common Pitfalls

1. Missing Ligamentous Instability in Distal Fractures: Treating all distal fractures with a sling can lead to nonunion. You must actively look for signs of coracoclavicular ligament disruption on X-ray (significant superior displacement of the medial fragment) and apply the Neer classification.
2. Over-reliance on Figure-of-Eight Braces: These braces are often uncomfortable and do not provide better reduction or outcomes than a simple sling. They can increase skin pressure and risk of neuropraxia. The sling is preferred for comfort and compliance.
3. Inadequate Follow-up for Displaced Midshaft Fractures: Assuming all midshaft fractures heal perfectly can miss symptomatic malunions or nonunions. Patients with significant displacement or shortening should be monitored closely, and early surgical referral considered if they are young, active individuals.
4. Neglecting Early Motion: Prolonged, strict immobilization leads to a "frozen shoulder." Educate patients to begin gentle, pain-free pendulum exercises within the first 1-2 weeks to maintain glenohumeral range of motion even while the fracture is healing.

Summary

• The clavicle is the most commonly fractured bone, with the middle third being the most frequent site due to FOOSH or direct impact mechanisms.
• The Neer classification is critical for distal third fractures, as a Type II fracture with coracoclavicular ligament disruption is unstable and has a high nonunion rate with conservative care.
• Most middle third fractures are managed successfully with a simple sling, early pendulum exercises, and time.
• Surgical fixation is strongly considered for displaced midshaft fractures with >2 cm shortening, comminution, and for displaced distal (Neer Type II) fractures.
• Always perform a thorough neurovascular exam and use appropriate radiographic views (AP clavicle, Zanca view) for an accurate diagnosis and classification.