Sternoclavicular instability

1. High-Yield Summary

• Sternoclavicular (SC) joint instability represents less than 3% of all shoulder girdle dislocations, with anterior dislocations outnumbering posterior dislocations by approximately 9:1.
• Posterior SC joint dislocation is a true orthopaedic and thoracic emergency due to immediate proximity to vital mediastinal structures (innominate vessels, trachea, esophagus, and vagus/phrenic nerves), with serious complications occurring in up to 30% of cases.
• In patients younger than 25 years, medial clavicle displacement almost universally represents a Salter-Harris Type I or II physeal fracture rather than a true capsular dislocation, as the medial clavicular physis is the last in the human body to fuse (ages 23–25).
• Contrast-enhanced computed tomography (CT) is the non-negotiable gold standard imaging modality to definitively differentiate anterior from posterior translation, rule out physeal fractures, and evaluate retrosternal vascular compression.
• Closed reduction of an acute posterior dislocation mandates general anesthesia and immediate operating room standby by a cardiothoracic or vascular surgical team with an open sternotomy tray.
• The use of smooth or threaded transfixing Kirschner wires or pins across the sternoclavicular joint is absolutely contraindicated due to lethal complications from trans-mediastinal and intracardiac migration.

2. Anatomy

The sternoclavicular joint is the sole true skeletal articulation connecting the upper extremity axial appendicular skeleton to the trunk. It is classified biomechanically as a diarthrodial, saddle-shaped (sellar) joint, characterized by marked bony incongruity: less than 50% of the medial clavicular articular surface articulates with the shallow clavicular notch of the manubrium sterni at any point in range of motion. Intrinsic osseous stability is negligible; structural integrity depends entirely on its robust capsular and ligamentous envelope.

A complete intra-articular fibrocartilaginous disc divides the joint space into two distinct non-communicating synovial cavities. The disc attaches superiorly and posteriorly to the posterosuperior border of the medial clavicular articular margin and inferiorly to the junction of the first costal cartilage and the sternum. It functions as a substantial shock absorber against compressive axial loads and acts as a primary checkrein preventing medial migration of the clavicle over the manubrium.

Ligamentous Stabilizers

• Posterior Sternoclavicular Capsular Ligament: The thickest, strongest, and most critical stabilizing component of the SC complex. Biomechanical studies confirm it provides the primary restraint against both anterior and posterior translation of the medial clavicle. Rupture of the posterior capsule is the hallmark biomechanical lesion in persistent posterior instability.
• Anterior Sternoclavicular Capsular Ligament: Anteromedial thickening of the fibrous joint capsule. Provides secondary resistance to anterior translation and excessive superior displacement during arm elevation.
• Costoclavicular (Rhomboid) Ligament: Situated 10 to 15 mm lateral to the sternal articular margin, running from the upper surface of the first rib and costal cartilage to the costal tuberosity on the inferior clavicle. Composed of two distinct laminae (anterior fascicle directing superiorly and laterally; posterior fascicle directing superiorly and medially). Acts as the primary restraint against superior translation and lateral displacement, serving as the pivot fulcrum for clavicular rotation during shoulder abduction.
• Interclavicular Ligament: Spans across the suprasternal (jugular) notch, connecting the superomedial aspects of both clavicles. Tightens during arm depression, protecting against inferior displacement of the clavicle.

Retrosternal Neurovascular Danger Zones

The space directly posterior to the manubrium and medial clavicles is dense with vital cardiopulmonary and neurovascular conduits separated by only millimeters of loose connective tissue:

• Great Vessels: The right brachiocephalic (innominate) artery bifurcates directly behind the right SC joint into the right common carotid and right subclavian arteries. The left common carotid artery and left subclavian artery arise directly from the aortic arch posterior to the left SC joint. The left brachiocephalic vein courses obliquely across the retrosternal space immediately posterior to the manubrium to merge with the right brachiocephalic vein into the superior vena cava.
• Neurologic Structures: The vagus nerve (cranial nerve X), recurrent laryngeal nerve, and phrenic nerve descend directly through the superior thoracic inlet adjacent to the internal mammary (internal thoracic) vessels.
• Visceral Structures: The trachea lies in the midline posterior to the great vessels, bordered posterolaterally by the cervical esophagus. The pleural cupola (dome of the pleura) and apical lung segments extend 2 to 3 cm above the level of the first rib and medial clavicle.

Surgical Exposure and Internervous Plane

The surgical approach to the sternoclavicular joint exploits the natural anatomic intermuscular interval between the clavicular head of the sternocleidomastoid muscle superiorly (innervated by the spinal accessory nerve, cranial nerve XI, and cervical plexus branches C2–C3) and the clavicular origin of the pectoralis major muscle inferiorly (innervated by the medial and lateral pectoral nerves). Dissection must remain strictly subperiosteal along the posterior clavicular and sternal cortex, utilizing a malleable retractor or Hohmann retractor directly on bone to avoid retrosternal soft tissue penetration.

3. Pathogenesis

Traumatic sternoclavicular instability results from high-energy mechanical forces transmitted through the pectoral girdle or direct focal impacts. Two distinct biomechanical mechanisms account for the majority of acute injuries:

• Indirect Compressive Force (Most Common): When the lateral aspect or tip of the shoulder receives a severe axial compressive load (such as a motor vehicle rollover or compression under an athlete pile-up). If the anterolateral shoulder is driven forcibly backwards, the clavicle pivots across the first rib/costoclavicular ligament complex as a fulcrum, levering the medial clavicle anteriorly out of the manubrial socket and resulting in an anterior SC dislocation. Conversely, if the posterolateral shoulder is driven forcibly forwards, the medial clavicle levers posteriorly into the superior mediastinum, producing a posterior SC dislocation.
• Direct Force: A localized high-velocity impact directed straight against the anterior medial clavicle (such as a dashboard collision, steering wheel strike, or helmet blow in football) punches the medial clavicular head directly backward into the mediastinum, causing an acute posterior dislocation.
• Physeal Fractures in Adolescents and Young Adults: The medial clavicular epiphysis is uniquely the last secondary ossification center to appear radiographically (between ages 18 and 20) and the last to undergo complete physeal fusion with the clavicular diaphysis (typically between ages 23 and 25). Prior to complete skeletal maturity, the cartilaginous physis represents the mechanical weak link of the medial clavicle. High-energy displacement in patients under 25 years of age represents a Salter-Harris Type I or II physeal fracture with periosteal sleeve disruption rather than a true capsuloligamentous dislocation. The thick posterior periosteal sleeve often remains intact within the articular socket.
• Atraumatic and Voluntary Instability: Characterized by benign multi-directional ligamentous hyperlaxity (generalized ligamentous laxity or connective tissue disorders such as Ehlers-Danlos syndrome). Subluxation typically occurs spontaneously or voluntarily upon shoulder elevation, forward flexion, and internal rotation, accompanied by an audible, palpable pop with minimal pain and rapid self-reduction upon arm return.

4. Natural History

Sternoclavicular joint injuries follow divergent natural histories determined by direction of displacement, patient age, and underlying etiology. Traumatic SC dislocations occur predominantly in young active males (male-to-female ratio exceeding 4:1), with motor vehicle collisions accounting for 45% to 50% and contact sports accounting for 30% to 40% of cases.

Acute anterior dislocations carry an excellent prognosis for life, but a notoriously poor natural history for maintaining stable closed reduction. Over 70% to 80% of anterior dislocations redislocate or persist as chronic anterior subluxations. Chronic, unreduced anterior instability is frequently asymptomatic or cosmetically prominent without long-term functional impairment in recreational patients, demonstrating minimal loss of shoulder strength or motion.

In contrast, posterior sternoclavicular dislocations carry substantial morbidity and potential mortality. Left unrecognized or unreduced, retrosternal compression produces progressive venous occlusion, superior vena cava syndrome, subclavian steal syndrome, late pseudoaneurysms, erosion into the pulmonary arterial trunk, recurrent pulmonary infections, tracheal stenosis, and tracheoesophageal fistulae. Acute prompt anatomic reduction of traumatic posterior dislocations, conversely, produces durable stability with capsular healing and low redislocation rates.

Atraumatic and voluntary subluxations exhibit a benign natural history that typically resolves spontaneously or stabilizes with skeletal maturity and nonoperative postural conditioning. Surgical intervention in atraumatic multi-directional instability historically yields catastrophic failure rates with recurrent instability, surgical scarring, and persistent pain.

5. Clinical Presentation

History

Patients typically present with severe focal pain over the sternoclavicular junction, supporting the injured arm across the abdomen with the contralateral hand. Active abduction or forward elevation of the ipsilateral upper extremity markedly exacerbates pain. In all suspected SC injuries, clinicians must perform a systematic review of systems targeting mediastinal compression:

• Dyspnea and Stridor: Suggests tracheal compression, subglottic impingement, or pneumothorax.
• Dysphagia and Odynophagia: Indicates posterior esophageal compression or retrosternal hematoma.
• Dysphonia and Hoarseness: Signals traction or compression on the recurrent laryngeal nerve.
• Sensation of Choking or Fullness: Common herald sign of acute retrosternal mass effect.
• Upper Extremity Paresthesias and Venous Engorgement: Reflects compression of the subclavian/innominate vessels or brachial plexus roots.

Physical Examination

Physical examination begins with visual inspection from the head of the bed looking tangentially down across the manubrium. An anterior dislocation demonstrates an obvious focal asymmetry, with the medial clavicular head visibly and palpably protruding anterior to the sternum. In a posterior dislocation, the normal medial clavicular contour is absent, replaced by a hollow depression, though post-traumatic swelling or hematoma can obscure the depression. The medial clavicle is tender to direct palpation, and lateral compression of both shoulders toward the midline elicits acute mechanical crepitus.

6. Imaging and Diagnostic Studies

Accurate radiographic visualization of the sternoclavicular joint on standard chest and shoulder projections is notoriously difficult due to superimposition of the ribs, sternum, thoracic spine, and mediastinal soft tissues.

Plain Radiography

• Serendipity View (Rockwood Projection): The most informative specialized plain projection. The patient is placed supine with a 40-degree cephalic tube angulation centered directly on the manubrium sterni. If the medial clavicle is dislocated anteriorly, it projects superior to the interclavicular trans-axial reference line; if dislocated posteriorly, it projects inferior to the line.
• Heinig View: Tangential lateral projection through the sternoclavicular articulation with the central beam directed across the manubrium perpendicular to the long axis of the body.
• Hobbs View: A cephalocaudal 90-degree projection with the patient seated and leaning forward over the cassette; frequently impossible to obtain in acute trauma due to severe pain.

Computed Tomography (CT)

Computed tomography with intravenous contrast is the non-negotiable gold standard imaging modality for all suspected sternoclavicular pathology. Standard thin-cut axial helical CT with multiplanar coronal, sagittal, and 3D volume-rendered reconstructions provides:

• Definitive confirmation of anterior versus posterior translation, quantifying articular displacement in millimeters.
• Precise differentiation between true capsular dislocation and Salter-Harris Type I/II medial clavicular physeal fractures in individuals younger than 25 years.
• Mapping of retrosternal hematomas and clear evaluation of clearance between the posterior medial clavicle and adjacent great vessels (brachiocephalic trunk, internal jugular vein, subclavian artery).
• Identification of intra-articular osteochondral fragments or associated first rib and manubrial fractures.

Magnetic Resonance Imaging (MRI)

MRI is reserved primarily for chronic instability, recurrent subluxation, or diagnostic dilemmas. High-resolution non-contrast MRI accurately depicts tears of the fibrocartilaginous intra-articular disc, anterior and posterior capsular ligament attenuation, disruption of the costoclavicular ligament, and focal bone marrow edema indicative of occult physeal injury or avascular necrosis.

7. Classification

Management of sternoclavicular instability depends on structured anatomical classification systems integrating mechanical displacement with clinical etiology.

8. Treatment

Medical / Nonoperative Management

Nonoperative management is the standard of care for Rockwood Type I sprains, Type II subluxations, chronic asymptomatic anterior dislocations, and atraumatic voluntary subluxation:

• Acute Sprains & Subluxations: Simple arm sling immobilization for 1 to 2 weeks for symptom relief, followed by active-assisted range of motion below 90 degrees of elevation. Progressive periscapular strengthening begins at 3 to 4 weeks, with unrestricted return to sports permitted once full painless motion is restored (typically 6 weeks).
• Atraumatic and Voluntary Instability: Strict prohibition of surgical intervention. Management focuses on structured physical therapy targeting periscapular stabilizers (trapezius, serratus anterior, rhomboids), postural biofeedback, and psychological counseling where voluntary dislocating behaviors exist. Patients achieve compensation without functional deficit.
• Chronic Asymptomatic Anterior Dislocation: Benign neglect is preferred. Due to substantial operative morbidity and high redislocation rates after anterior reconstruction, patients with painless chronic anterior prominence should be managed conservatively, experiencing minimal functional impairment in activities of daily living.

Operative Management

Operative management is reserved for acute posterior dislocations failing closed reduction, posterior dislocations with mediastinal impingement, chronic symptomatic anterior or posterior instability failing extensive conservative rehabilitation, and post-traumatic degenerative osteoarthritis.

Acute Posterior Dislocation Closed Reduction Protocol:

• Operating Room Configuration: Must be performed under general endotracheal anesthesia with full muscle relaxation. A cardiothoracic or vascular surgery team must be present in the room with a sternotomy set open and prep extended to include the neck, chest, and groin for femoral vascular access.
• Patient Positioning: Supine position with a dense sandbag or rolled towels positioned longitudinally between the medial borders of the scapulae.
• Traction Maneuver: The ipsilateral arm is abducted to 90 degrees and extended slightly backward while continuous longitudinal arm traction is applied. An assistant simultaneously applies gentle posterior pressure to both lateral acromia.
• Percutaneous Clamp Technique: If traction alone fails, sterile preparation of the medial clavicle allows percutaneous grasping of the clavicular diaphysis with a sterile towel clip or reduction clamp, exerting anterior traction directly perpendicular to the chest wall. Successful reduction is signaled by an audible and palpable clunk.

Open Stabilization and Reconstruction Options:

• Figure-of-8 Semitendinosus Autograft / Allograft (Spencer Technique): The recognized gold standard for anatomic ligamentous reconstruction. Drill tunnels are placed through the anterior-to-posterior cortex of the medial clavicle and through the anterior cortex to superior margin of the manubrium. A free hamstring tendon graft is passed in a figure-of-8 configuration and tensioned with the arm in neutral, restoring both anterior and posterior translational resistance.
• Subclavius Tenodesis (Burrows Technique): Dynamic tenodesis mobilizing the subclavius tendon or costoclavicular ligament remnant through a transosseous drill hole in the medial clavicle.
• Medial Clavicle Resection Arthroplasty: Indicated for post-traumatic degenerative arthritis or non-reconstructable articular comminution. Critical surgical guideline: Resect no more than 10 to 15 mm of the medial clavicle, and strictly avoid detaching or compromising the costoclavicular ligament. Disruption of the costoclavicular ligament destabilizes the remaining clavicle superiorly and laterally, causing chronic shoulder girdle dysfunction.
• Absolute Contraindication Warning: Kirschner wires, Steinmann pins, or smooth transfixing metallic hardware must NEVER be utilized across the sternoclavicular joint. Historical literature documents catastrophic fatalities resulting from pin breakage and rapid migration into the aorta, pulmonary artery, pericardium, cardiac ventricles, and lung parenchyma.

Indications and Contraindications

• Absolute Indications for Emergent Surgery: Irreducible acute posterior dislocation; posterior dislocation presenting with vascular insufficiency, airway compromise, progressive dysphagia, or hemothorax; open sternoclavicular dislocation.
• Relative Indications for Elective Reconstruction: Chronic, recurrent symptomatic anterior or posterior subluxation in high-demand throwing or contact athletes with persistent pain and functional disability after at least 6 months of supervised physical therapy; post-traumatic SC osteoarthritis refractory to conservative care.
• Absolute Contraindications to Surgery: Atraumatic multi-directional instability or voluntary dislocation without structural capsular rupture; systemic connective tissue hyperlaxity without localized traumatic structural pathology; active systemic or regional infection; asymptomatic chronic anterior dislocation.

9. Outcome

Functional outcomes following sternoclavicular instability treatment are measured using validated patient-reported outcome measures including the American Shoulder and Elbow Surgeons (ASES) score, the QuickDASH (Disabilities of the Arm, Shoulder, and Hand), and the Rockwood SC Joint scoring system.

Anatomic figure-of-8 tendon graft reconstruction delivers superior biomechanical and clinical survivorship compared to historic non-anatomic soft tissue transfers. Systematic reviews demonstrate successful joint stabilization in over 88% to 92% of patients undergoing autograft or allograft reconstruction for chronic instability, with significant post-operative improvements in ASES scores (mean improvement >30 points) and return to baseline sports activities between 4 and 6 months post-operatively.

Closed reduction of acute posterior dislocations achieved within 48 hours demonstrates a long-term stability rate exceeding 85%, with capsular healing maintaining joint congruence and near-zero recurrence. Conversely, acute closed reduction of anterior dislocations is associated with recurrent subluxation in over 75% of cases; however, subjective satisfaction among non-operative patients remains high (80–85%) despite persistent anatomic asymmetry.

10. Complications

Complications associated with sternoclavicular joint instability range from benign cosmetic asymmetry to life-threatening intraoperative mediastinal catastrophic events.

11. Pearls and Pitfalls

Managing sternoclavicular instability requires clinical vigilance and adherence to surgical safety corridors:

• The CT Red Rule: Never attempt closed or open reduction of a suspected posterior dislocation without a prior contrast-enhanced CT scan confirming the location of the great vessels and excluding an underlying vascular laceration tamponaded by the medial clavicular head.
• The Cardiothoracic Co-Surgeon Pearl: Never attempt closed or open reduction of a posterior dislocation in an emergency department or clinic treatment room. Schedule in the main operating room with general anesthesia, full muscle relaxation, an open sternotomy tray, and a cardiothoracic surgical team present in the room.
• The Costoclavicular Ligament Preservation Rule: When performing medial clavicle resection arthroplasty for post-traumatic degenerative arthritis, measure precisely and resect no more than 10 to 15 mm of bone. Never extend the resection lateral to the costoclavicular (rhomboid) ligament insertion, as sacrificing this ligament creates severe superior instability of the remaining clavicular stump.
• The Physeal Awareness Pearl: In any patient under 25 years old presenting with medial clavicle deformity, maintain high index of suspicion for a Salter-Harris physeal fracture. The periosteal sleeve is frequently intact, and anatomical closed reduction or gentle open reduction often heals rapidly with robust bone remodeling.
• The Hardware Prohibition Rule: Do not transfix the sternoclavicular joint with metallic smooth pins, Steinmann pins, or Kirschner wires under any circumstances. Multiple fatal events are documented in the literature from trans-cardiac and trans-aortic pin migration driven by respiratory and shoulder motion.

12. Controversy

Several clinical dilemmas continue to stimulate active debate within shoulder surgery:

• Acute Anterior Dislocation: Closed Reduction vs Nonoperative Acceptance: Many surgeons advocate attempting an acute closed reduction within the first 10 to 14 days under sedation. However, counter-arguments cite redislocation rates exceeding 70% to 80% once the arm is mobilized. Proponents of primary nonoperative management emphasize that chronic anterior prominence carries negligible functional deficit in non-throwing athletes, arguing that closed reduction attempts expose patients to unnecessary procedural and anesthetic risks.
• Biologic Autograft vs Synthetic Augmentation: Anatomic figure-of-8 reconstruction with semitendinosus or gracilis tendon remains the benchmark. Recently, synthetic non-absorbable ultra-high-molecular-weight polyethylene (UHMWPE) tape with knotless cortical buttons has gained traction to avoid donor-site morbidity and tunnel enlargement. Long-term comparative registry data are ongoing regarding foreign body granuloma risks and long-term survivorship.
• Sternal Tunnel Drilling vs Sternal Docking: Full-thickness transosseous drilling of the manubrium carries inherent risk to underlying retrosternal structures. Technique modifications utilizing anterior sternal docking cortical buttons or unicortical anchor fixation aim to minimize mediastinal penetration while achieving equivalent biomechanical fixation strength.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Willinger L, Schanda J, Herbst E et al. Outcomes and complications following graft reconstruction for anterior sternoclavicular joint instability. Knee Surg Sports Traumatol Arthrosc. 2016. doi:10.1007/s00167-015-3770-x [Level I: Systematic Review / Meta-Analysis]
• Martetschläger F, Warth RJ, Millett PJ. Instability and degenerative arthritis of the sternoclavicular joint: a current concepts review. Am J Sports Med. 2014. doi:10.1177/0363546513498990 [Level I: Systematic Review / Meta-Analysis]
• Thut D, Hergan D, Dukas A et al. Sternoclavicular joint reconstruction–a systematic review. Bull NYU Hosp Jt Dis. 2011. doi:PMID:22035392 [Level I: Systematic Review / Meta-Analysis]
• C. M. Robinson. Fractures of the clavicle in the adult. Journal of Bone and Joint Surgery – British Volume. 1998. doi:10.1302/0301-620x.80b3.8079 [Level IV (Prognostic / Case Series): Seminal Conceptual / Observational Study]
• Caroline Anne Mitchell, Ade Adebajo, Elaine M. Hay et al. Shoulder pain: diagnosis and management in primary care. BMJ. 2005. doi:10.1136/bmj.331.7525.1124 [Level IV (Prognostic / Case Series): Seminal Conceptual / Observational Study]

15. Master Class Pro-Tip

When performing open figure-of-8 graft reconstruction of the sternoclavicular joint, the most hazardous maneuver is placing the transosseous drill holes through the manubrium. Place a broad malleable retractor directly against the posterior sternal cortex through a strictly subperiosteal corridor before passing any drill bit. Angle the drill strictly anterior-to-posterior and slightly superiorly, aiming into the palpable notch of the retractor. Maintain visual and tactile contact between the drill bit tip and the metal shield at all times to prevent sudden penetration into the left brachiocephalic vein or trachea.

Master Class Surgical Pearl: Sternoclavicular Joint Stabilization