How to overcome the limitation of the interscalene block in covering the ulnar nerve?

Overcoming Ulnar Nerve Coverage Limitations with Interscalene Block

Add a supplemental distal ulnar nerve block at the wrist or elbow when ulnar nerve coverage is required for surgery, as interscalene blocks consistently miss the ulnar nerve in 13-45% of cases.

Understanding the Problem

The interscalene block has a well-documented anatomical limitation in covering the ulnar nerve distribution, which is critical to recognize before proceeding with upper extremity surgery 1, 2. This occurs because:

• The ulnar nerve (C8-T1) derives from the lower trunk of the brachial plexus, which lies deeper and more caudal in the interscalene groove 1
• Studies demonstrate ulnar nerve sparing in 13-45% of interscalene blocks, making this a predictable rather than occasional problem 1, 2
• The posterior approach to interscalene block provides better ulnar coverage than the lateral approach, but still remains unreliable for consistent ulnar anesthesia 2

Primary Solutions

For Shoulder Surgery (Ulnar Coverage Not Critical)

Continue with standard interscalene block alone, as the surgical field is primarily innervated by suprascapular and axillary nerves which are reliably blocked 3. The missed coverage of posterior arm cutaneous nerves is typically not clinically significant for shoulder procedures 3.

For Forearm/Hand Surgery (Ulnar Coverage Essential)

Do not rely on interscalene block alone for forearm and hand surgery 1. Instead, use one of these approaches:

Option 1: Switch to Supraclavicular Block with Intertruncal Approach

• The intertruncal (IT) approach for supraclavicular block provides superior ulnar nerve blockade compared to traditional corner pocket approach 4
• Complete sensory blockade of the ulnar nerve occurs in 75.9% with IT approach versus only 43.3% with corner pocket approach (P = 0.023) 4
• Onset time for ulnar nerve block is significantly faster: 15 minutes with IT approach versus 20 minutes with corner pocket (P = 0.012) 4
• Supraclavicular blocks achieve 92% success rates compared to 56-86% for axillary blocks 5

Option 2: Combined Infraclavicular Plus Distal Nerve Blocks

• Add supplemental distal median, radial, and ulnar nerve blocks to an infraclavicular block, which accelerates onset by approximately 6 minutes (40% treatment effect) and improves block consistency 6
• Use 30 ml lidocaine 1.5% with epinephrine for infraclavicular block, followed by 12 ml of 50:50 mixture of lidocaine 2% and ropivacaine 0.75% for distal blocks 6
• This combined approach reduces total aggregate block scores at 15 minutes (6.7 vs. 9.9, P = 0.01) and demonstrates reduced variance, indicating more consistent results 6

Option 3: Costoclavicular Block

• Consider costoclavicular block as a phrenic-sparing alternative that provides comprehensive upper extremity coverage including ulnar distribution 7, 8
• This approach reduces hemidiaphragmatic paralysis to 5.9% compared to 84.4% with interscalene block while maintaining equivalent surgical anesthesia 7

Critical Pitfalls to Avoid

• Never assume interscalene block will provide adequate ulnar nerve coverage for forearm/hand surgery—this approach "did not provide satisfactory anesthesia" in these cases 1
• Do not attempt to compensate by using the posterior approach to interscalene block, as it still causes the same hemidiaphragmatic paresis as lateral approach while remaining unreliable for ulnar coverage 1
• Recognize that even when posterior interscalene approach provides better ulnar coverage than lateral approach, the distribution patterns are fundamentally different and neither is consistently reliable 2

Multimodal Analgesia Support

Regardless of block choice, initiate regular paracetamol and NSAIDs/COX-2 inhibitors preoperatively, add single-dose IV dexamethasone to prolong block duration, and reserve opioids for rescue only 9, 7. This becomes especially important when block resolution occurs, as inadequate multimodal analgesia leads to significant breakthrough pain 9.