What is the role of the Peng block in managing shoulder pain?

The Role of the Peng Block in Managing Shoulder Pain

The Peng block (pericapsular nerve group block) may be considered as an alternative analgesic technique for shoulder pain in selected cases, particularly when avoiding respiratory complications is critical, but it is not yet established as a first-line intervention for shoulder pain management. 1

Diagnostic Evaluation for Shoulder Pain

Before considering any nerve block technique, proper evaluation is essential:

• Plain radiography is the preferred initial imaging study for shoulder pain, especially with trauma history
• Clinical assessment should include:
  • Musculoskeletal evaluation
  • Evaluation of spasticity
  • Identification of any subluxation
  • Testing for regional sensory changes 2, 3

Established Nerve Block Techniques for Shoulder Pain

First-Line Regional Techniques:

1. Interscalene Brachial Plexus Block:

   • Considered the gold standard analgesic technique for shoulder surgery 1
   • Provides superior analgesia compared to systemic analgesics 2
   • Limitations: Associated with hemidiaphragmatic paresis, which may be problematic for patients with respiratory issues 1

2. Suprascapular Nerve Block:

   • Well-established technique with strong evidence base
   • Effective for reducing shoulder pain through both nociceptive and neuropathic pain mechanisms 2
   • Superior to placebo injections for hemiplegic shoulder pain for up to 12 weeks 4
   • Number needed to treat of 4 to reduce pain by 50% at 4 weeks 4
   • Improves shoulder function and reduces pain in chronic shoulder pain 5
   • Can be performed using posterior, superior, or anterior approaches 6

3. Combined Suprascapular and Axillary Nerve Block ("Shoulder Block"):

   • Alternative to interscalene block that targets the two main nerves supplying the shoulder 7
   • Favored over no block or suprascapular nerve block alone when interscalene block is not possible 2

The Peng Block: Emerging Alternative

The Peng block is a relatively new technique that:

• Targets the pericapsular nerve group around the shoulder
• May provide analgesia without causing motor block or pulmonary complications
• Does not result in muscle laxity, blocking only the shoulder and upper third of humerus
• Can be safely applied for partial anesthesia and analgesia in selected shoulder surgery cases
• Alone is not sufficient for complete surgical anesthesia 1

Comprehensive Shoulder Pain Management Algorithm

1. First-line treatments:

   • Patient education on positioning and range of motion exercises 2
   • Analgesics (acetaminophen, NSAIDs) if no contraindications 2, 3
   • Physical therapy with gentle stretching and mobilization techniques 2, 3

2. For moderate to severe pain:

   • Subacromial or glenohumeral corticosteroid injections for inflammation 2, 3
   • Botulinum toxin injections for pain related to spasticity 2

3. For perioperative pain management:

   • Interscalene brachial plexus block (first choice) 2, 1
   • If interscalene block contraindicated (respiratory concerns):
     • Consider combined suprascapular and axillary nerve block 2, 7
     • Consider Peng block in selected cases 1

4. For refractory cases:

   • Suprascapular nerve block 2, 3, 6, 4
   • Neuromuscular electrical stimulation 2, 3

Important Considerations and Pitfalls

• Avoid shoulder immobilization with arm slings or wraps as it can lead to frozen shoulder 3
• Begin physical therapy early to prevent development of frozen shoulder 3
• The Peng block is still emerging as a technique and requires further research to establish its role in routine clinical practice 1
• When selecting a nerve block technique, consider:
  • Patient's respiratory status (avoid interscalene block in patients with respiratory compromise)
  • Need for motor preservation
  • Duration of analgesia required
  • Available expertise with different block techniques

While the Peng block shows promise as an alternative technique that avoids respiratory complications, current guidelines and evidence still favor interscalene block as first-line regional technique for shoulder surgery, with suprascapular nerve block (alone or combined with axillary nerve block) as the main alternative when respiratory concerns exist.