Can a coronary artery bypass graft (CABG) cause numbness in the left hand, particularly in the 4th and 5th digits?

Numbness in the 4th and 5th Digits After CABG

Yes, CABG can cause numbness in the left hand, particularly the 4th and 5th digits, most commonly due to brachial plexus injury during surgery or ulnar nerve compression from positioning, though this is not a typical or expected complication.

Mechanism of Nerve Injury During CABG

The numbness pattern you describe—affecting the 4th and 5th digits specifically—suggests ulnar nerve involvement, which can occur through several perioperative mechanisms:

• Positioning injury: Prolonged arm abduction and external rotation during the lengthy CABG procedure can stretch or compress the brachial plexus or ulnar nerve at the elbow 1
• Sternal retraction: Aggressive sternal spreading can cause traction on the brachial plexus, particularly affecting the lower trunk (C8-T1), which supplies the ulnar nerve distribution 1
• First rib fracture: Rarely, sternal retraction can fracture the first rib, directly injuring the lower brachial plexus 1

Harvest Site Complications vs. Central Nerve Injury

It's critical to distinguish between two different sources of numbness:

If the radial artery was harvested from the left arm, harvest-site sensory disturbances are extremely common and affect approximately 32% of patients at long-term follow-up (median 2.5 years), with an additional 14% experiencing paresthesia/dysesthesia 2. However, radial artery harvest typically causes numbness along the radial (thumb) side of the forearm and hand, not the ulnar (pinky) side 2.

Ulnar distribution numbness (4th and 5th digits) is more consistent with:

• Ulnar nerve compression at the elbow or wrist from positioning
• Lower brachial plexus injury from surgical positioning or retraction
• These are not related to graft harvest sites 2

Neurological Complications of CABG

While the guidelines focus primarily on cerebral complications rather than peripheral nerve injuries, the evidence shows:

• Neurologic complications from CABG are well-documented, though most literature focuses on stroke and cognitive decline rather than peripheral neuropathies 3, 4, 5
• Subclinical cerebral complications occur in approximately 21% of CABG patients (new MRI lesions), but these would not cause isolated hand numbness 3
• Focal neurologic deficits from CABG are typically due to embolic stroke or watershed infarction, not peripheral nerve injury 5

Clinical Approach

Immediate evaluation should include:

• Detailed motor examination of the hand: test finger abduction (dorsal interossei), finger adduction (palmar interossei), and thumb adduction (adductor pollicis)—all ulnar nerve functions
• Assess for Froment's sign (compensatory thumb flexion when attempting to pinch paper between thumb and index finger)
• Check for sensory loss in the ulnar nerve distribution: entire 5th digit and ulnar half of 4th digit
• Examine for Tinel's sign at the elbow (cubital tunnel) and wrist (Guyon's canal)

Common pitfall: Do not assume all post-CABG numbness is from graft harvest. The distribution matters—radial artery harvest causes radial-sided symptoms, while ulnar-sided symptoms suggest positioning injury 2.

Prognosis and Management

Most positioning-related nerve injuries from cardiac surgery are neurapraxic (temporary demyelination without axonal loss) and recover spontaneously over weeks to months. However:

• If symptoms persist beyond 3 months or worsen, nerve conduction studies and EMG are indicated
• Severe cases may require surgical decompression if there is evidence of ongoing nerve compression
• Physical therapy and occupational therapy can help maintain hand function during recovery

The fact that persistent sensory disturbances occur in approximately 32-39% of patients at harvest sites suggests that some degree of chronic numbness may be permanent, though this data specifically relates to harvest sites rather than positioning injuries 2.