High Ulnar Nerve Laceration in a Carpenter
A 34-year-old right-hand-dominant man sustained a glass laceration at the mid-humerus 10 days ago. The ulnar nerve was repaired primarily. He now has clawing of the ring and small fingers, weak finger abduction, a positive Froment sign, and reduced sensation in the small finger. He works as a carpenter and asks whether he will regain grip strength. Examination shows full passive motion, no intrinsic muscle wasting yet, and the repair was under modest tension. He wants to know whether a nerve transfer should have been done and whether tendon transfers can help now.
1. Explain the expected recovery after a high ulnar nerve repair and the rationale for considering nerve transfer at the time of repair or early thereafter.
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A high ulnar nerve laceration at the mid-humerus requires axons to regenerate a long distance to the intrinsic muscles. Regeneration proceeds at roughly 1 mm per day, so intrinsic reinnervation may not begin for many months, and the intrinsic muscles can become fibrotic before axons arrive. Sensory recovery is generally better than motor recovery because sensory end organs tolerate denervation longer. This is why high ulnar nerve injuries have a poor prognosis for intrinsic hand function despite a technically satisfactory repair. Distal nerve transfers, such as transferring the anterior interosseous nerve branch to the ulnar motor branch, can shorten the regeneration distance and are best performed before irreversible muscle fibrosis, often within 6–12 months of injury. In an acute clean laceration, primary repair remains standard, but the surgeon should consider whether a concomitant distal transfer is appropriate if the repair is under tension or the gap is long.
2. If intrinsic function does not recover, what tendon transfers would you plan for clawing and pinch, and when would you perform them?
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For ulnar clawing, I would consider a Zancolli lasso procedure using the flexor digitorum superficialis of the ring and small fingers, or a Stiles–Littler transfer, to restore metacarpophalangeal flexion and correct the intrinsic minus posture. For pinch, I would consider transferring the extensor carpi radialis brevis or a flexor digitorum superficialis tendon to the adductor pollicis, and an opponensplasty for thumb opposition if needed. The timing depends on the nerve repair: I would wait at least 12–18 months for signs of reinnervation before declaring failure, but if a distal nerve transfer was performed, the window may be shorter. Tendon transfers should not be done too early, because they can destroy a chance of spontaneous reinnervation. I would also address thumb web contracture and provide therapy to maintain passive motion while waiting.
3. How does the level of injury affect sensory and motor prognosis, and what would you tell him about returning to carpentry?
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The more proximal the ulnar nerve injury, the longer the regeneration distance and the worse the intrinsic motor prognosis. A mid-humerus injury is high enough that intrinsic recovery is uncertain, while a wrist-level injury has a much better chance of intrinsic recovery. Sensation in the small finger may recover earlier and more completely than intrinsic strength. For a carpenter, grip and pinch strength, endurance, and protective sensation are critical. I would tell him that he may regain useful sensation and wrist/finger flexion, but that intrinsic wasting and clawing may persist, and that tendon transfers can improve pinch and grip if recovery fails. He should be counseled about cold intolerance, neuroma risk, and the need for protective gloves. Return to heavy carpentry would depend on pain control, sensation, and strength after reconstruction.