What nerve is likely injured in a 22-year-old right-handed (rt handed) male with no past medical history, who presents with a 7cm laceration on his distal right forearm from a skill saw injury, and is unable to cross his fingers with decreased sensation in his little finger?

Ulnar Nerve Injury

Based on the clinical presentation of inability to cross fingers (loss of intrinsic hand muscle function) and decreased sensation in the little finger, this patient has sustained an ulnar nerve laceration at the distal forearm level.

Clinical Reasoning

The inability to cross fingers indicates loss of interossei muscle function, which is controlled by the ulnar nerve 1, 2. The decreased sensation over the little finger confirms ulnar nerve sensory involvement, as this nerve provides sensation to the ulnar aspect of the hand including the entire little finger 1, 3.

Key Anatomical Considerations

• Motor deficit: Inability to cross fingers demonstrates loss of palmar interossei function (finger adduction) and dorsal interossei function (finger abduction), both innervated exclusively by the ulnar nerve 1
• Sensory deficit: The little finger receives its sensory innervation entirely from the ulnar nerve, making this finding pathognomonic for ulnar nerve injury 1, 2
• Location: A 7cm laceration in the distal forearm places the injury at the level where the ulnar nerve travels alongside the ulnar artery, making it vulnerable to sharp trauma 4, 3

Immediate Management Priorities

Hemostasis

• Apply direct digital pressure and compressive dressings as first-line hemorrhage control 4
• Avoid aggressive surgical exploration solely for hemostasis unless critical bleeding persists 4
• Temporary tourniquet may be applied if direct compression fails, but monitor for ischemic complications 5

Vascular Assessment

• Confirm hand perfusion by checking radial pulse and capillary refill 5, 4
• One intact forearm artery (radial or ulnar) is adequate to sustain hand viability if palmar arch circulation is intact 4
• Critical ischemia would require expeditious surgical restoration, but this is not indicated with adequate perfusion 4

Surgical Planning

This injury requires urgent (not emergent) surgical exploration and nerve repair within 24-48 hours 6, 2.

Rationale for Urgent Repair

• Sharp lacerations from power tools like skill saws create clean nerve transections amenable to primary repair 6, 2
• Microsurgical repair within the first 24-48 hours yields optimal functional outcomes 6, 2
• Delayed repair beyond this window significantly compromises nerve regeneration potential 2

Surgical Approach

• Open reduction and internal fixation of any associated fractures should be performed concurrently 1, 3
• Ulnar nerve exploration requires microsurgical technique for precise reapproximation 2, 3
• Modified surgical approach may be needed to access both the nerve and any vascular structures 3

Critical Pitfalls to Avoid

• Do not delay nerve repair: Unlike closed injuries where neuropraxia may recover spontaneously, sharp lacerations require surgical repair 1, 3
• Do not assume isolated nerve injury: Always assess for concomitant tendon, artery, and bone injuries in forearm lacerations 4, 6
• Do not perform emergent exploration solely for hemostasis: Conservative hemorrhage control is effective for most forearm lacerations 4
• Do not miss associated median nerve injury: A 7cm laceration may involve multiple structures; complete neurological examination is mandatory 6, 2

Expected Recovery

• Neurological recovery is gradual, with complete motor and sensory recovery potentially taking 4 months or longer 1
• Microsurgical repair techniques should lead to reasonable functional outcomes in most patients 2
• Early hand therapy consultation for post-operative rehabilitation is essential to prevent stiffness 7