How should a cyst over the acromioclavicular (AC) joint be evaluated and managed?

Acromioclavicular Joint Cyst Management

A cyst over the AC joint should be evaluated with MRI to identify the underlying rotator cuff pathology that is almost always present, and definitive treatment requires arthroscopic or open cyst excision combined with distal clavicle resection—aspiration alone is ineffective and should be avoided.

Initial Evaluation

When you encounter an AC joint cyst, you're looking at a soft, non-mobile mass directly over the AC joint that typically signals significant underlying shoulder pathology. The key diagnostic principle is that AC joint cysts are almost never isolated findings—they represent a "geyser sign" where synovial fluid escapes through a rotator cuff tear, crosses the subacromial bursa, and decompresses through a degenerated AC joint 1.

Imaging Strategy

• Start with plain radiographs to assess for glenohumeral arthritis, superior humeral head migration, and AC joint degeneration 2, 3
• MRI is essential for definitive diagnosis and surgical planning 1, 3
  • Look for the "geyser sign": fluid tracking from the glenohumeral joint through the cuff defect, across the subacromial bursa, and into/through the AC joint
  • Assess rotator cuff integrity—complete supraspinatus tears are the most common association 4, 5
  • Evaluate cyst size, extent, and relationship to surrounding structures 6

Treatment Algorithm

Surgical Management (Preferred)

The evidence strongly supports surgical intervention over conservative measures 1, 7. Your approach should follow this hierarchy:

1. If rotator cuff is reparable: Perform rotator cuff repair + cyst excision + distal clavicle resection 1, 5

2. If rotator cuff is irreparable (most common in elderly patients): Arthroscopic or open cyst excision + distal clavicle resection 8, 7

   • Recent evidence from 2024-2025 shows arthroscopic decompression with distal clavicle resection achieves minimal recurrence 8, 7
   • This approach addresses both the cyst and the underlying AC joint pathology

3. For massive cysts with atypical extension (>7-12 cm extending into trapezius): Open resection through dual incisions may be necessary 6

What NOT to Do

Aspiration with or without steroid injection is futile and should be avoided 9, 1. The 2016 study of high-risk (ASA 3-4) elderly patients showed:

• 100% recurrence to original size within one month 9
• No meaningful improvement in pain or function
• High risk of creating a draining sinus tract 1
• Only theoretical benefit of temporarily reducing skin tension 9

Critical Pitfalls

• Don't mistake these for tumors: The atypical presentation, especially when extending medially into the trapezius, can mimic neoplastic processes 6, 3
• Don't treat the cyst in isolation: Failure to address the underlying rotator cuff pathology guarantees recurrence 4
• Don't assume pain correlates with pathology: These cysts can be painless despite massive underlying rotator cuff tears and glenohumeral arthritis 3

Special Considerations for High-Risk Patients

In ASA 3-4 patients where surgery poses prohibitive risk, observation is the only reasonable option 9. Aspiration provides no durable benefit and should not be offered as a temporizing measure unless there is imminent skin breakdown—even then, the benefit is questionable 9.