What is the recommended management for an acromioclavicular (AC) joint separation with posterior displacement of the clavicle?

AC Separation with Posterior Displacement of the Clavicle

Posterior displacement of the clavicle in AC joint separation requires urgent surgical intervention, as this represents a Type IV or higher injury that is associated with significant instability and poor functional outcomes without operative stabilization.

Understanding the Injury Pattern

Posterior displacement of the clavicle indicates disruption of both the AC ligaments and the coracoclavicular (CC) ligaments, with the clavicle being driven posteriorly through the deltotrapezial fascia 1. This is classified as a Rockwood Type IV injury (or higher), which represents a severe injury pattern requiring different management than standard AC separations.

The biomechanical significance is critical: the superior and posterior AC capsular ligaments normally contribute 56% and 25% respectively to restraining posterior translation of the clavicle 2. When these structures are disrupted along with the CC ligaments, the clavicle becomes unstable in multiple planes.

Initial Imaging Approach

• Standard radiographs should include AP views in internal and external rotation PLUS an axillary or scapula-Y view 3, 4

  • The axillary view is essential because posterior displacement can be completely missed on AP views alone 3
  • Radiographs should be performed upright as malalignment can be underrepresented on supine films 3

• CT imaging may be appropriate if fracture complexity needs characterization or if radiographs are equivocal 3

Treatment Algorithm

Type IV, V, and VI Injuries (Including Posterior Displacement)

Surgery is almost always recommended 1. The evidence strongly supports operative management for these injury patterns:

1. Timing: Acute surgical treatment is preferred

   • Better outcomes with acute repair versus delayed reconstruction
   • Allows for direct repair of native ligaments when possible

2. Surgical Technique Options:

   • Arthroscopically-assisted anatomic CC ligament reconstruction using suture-button devices provides satisfactory outcomes at midterm follow-up (58 months) with minimal loss of reduction 5
   • The procedure should include:
     • True suture of the CC ligaments (conoid and trapezoid)
     • Release/desincarceration of AC ligaments from the joint 6
     • Reduction under direct visualization to ensure proper anterior-posterior alignment 5

3. Critical Technical Points:

   • Preserve the posterior and superior AC capsular ligaments whenever possible, as these are the primary restraints to posterior translation 2
   • Address the posterior displacement specifically during reduction - this requires careful attention as 2 of 23 patients in one series showed increased posterior subluxation at later follow-up despite initial correction 5
   • Consider double adjustable loops with triple-button fixation for anatomic CC ligament reconstruction 7

Common Pitfalls to Avoid

1. Missing the diagnosis: Failing to obtain axillary or Y-views will miss posterior displacement on standard AP radiographs 3

2. Undercorrection of posterior displacement: Even with surgical treatment, posterior displacement can persist or recur 5. Intraoperative verification of reduction in all planes is essential.

3. Attempting conservative management: Unlike Type III injuries where treatment remains controversial, Type IV injuries with posterior displacement have poor outcomes with non-operative treatment 1, 8

4. Inadequate capsular preservation: Surgical techniques that fail to preserve or reconstruct the posterior and superior capsular structures risk persistent posterior instability 2

Post-Operative Management

• Shoulder brace immobilization for 6 weeks 6
• Radiographic follow-up to monitor for loss of reduction, particularly posterior subluxation
• Physical therapy initiation after immobilization period

The key distinction is that posterior displacement represents a qualitatively different injury than simple superior displacement, requiring recognition of the specific biomechanical instability pattern and surgical planning that addresses the posterior translation component specifically.