A 2.5 cm Volar Thumb Defect With Exposed Flexor Tendon in a Smoker
A 29-year-old right-handed machinist sustains a crush-avulsion injury to the volar right thumb. After debridement there is a 2.5 by 2 cm full-thickness defect extending from the interphalangeal flexion crease to 5 mm proximal to the nail fold. The flexor pollicis longus tendon and bare distal phalanx are exposed; there is no bone loss, the nail bed is intact, and the interphalangeal and metacarpophalangeal joints are supple. The wound edges are clean. He smokes one pack per day and has no other medical problems. He works with high-vibration tools and needs to return to that job.
1. Rank your reconstructive options for this defect and justify your choice, taking his smoking into account.
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The defect requires durable, sensate, glabrous skin; a graft will not survive over bare bone and tendon, and healing by secondary intention would contract and stiffen the thumb.
- First dorsal metacarpal artery (kite) flap. Axial-pattern skin from the dorsum of the index metacarpophalangeal and proximal phalangeal region, single stage, reliably reaches the volar thumb, covers 2.5 to 3 cm, and can be raised with a dorsal sensory branch of the radial nerve for some sensibility. Best fit for his defect.
- Moberg volar advancement. Ideal sensate glabrous skin, but reliable advancement is about 1 to 1.5 cm; a 2.5 cm defect would demand extreme interphalangeal flexion and risks a fixed flexion contracture.
- Thenar flap. Two-stage, good color match, sensate, but requires prolonged proximal interphalangeal flexion and risks stiffness; better suited to distal tip defects, particularly in children.
- Free toe pulp transfer. The best sensibility and tissue quality, but requires microsurgery and a longer recovery; reserve for failures or patients with very high sensibility demands.
- Skin graft. Contraindicated over exposed tendon and bone.
Smoking is the modifier: counsel cessation at least four weeks before and after surgery, keep the pedicle wide and untwisted, avoid tension and pressure on the inset, and warn him that tip necrosis and cold intolerance are more likely. If he will not stop, a staged thenar flap or a graft after granulation over the tendon may be the safer compromise.
2. What are the sensibility requirements for thumb pulp reconstruction, and how do you counsel him about final two-point discrimination, cold intolerance, and grip?
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The normal thumb pulp achieves static two-point discrimination of 6 mm or better, and the thumb accounts for a disproportionate share of pinch and fine manipulation. For a working hand, protective sensibility in the range of 10 to 15 mm is the realistic minimum; anything worse turns the thumb into a liability around sharp and hot objects.
An innervated first dorsal metacarpal artery flap, coapted to a divided branch of the radial digital nerve, typically lands in the 10 to 15 mm range rather than at normal values. It will not match a Moberg advancement for quality of sensation, but it will be adequate for most grasp and pinch tasks. Nonsensate coverage in a machinist would be a poor result regardless of how well the skin matches.
Counsel him that cold intolerance and hypersensitivity at the flap margin are common and often improve over 12 to 24 months, that it is worse in smokers, and that grip and pinch strength typically return to about 80 to 90 percent of the contralateral side with therapy. If the radial digital nerve was also divided, primary epineurial repair under magnification, or grafting for a gap, is performed at the same setting, and the flap nerve is coapted to the distal stump so that the reconstructed pulp has some afferent input. Set expectations now rather than at the six-month visit.
3. Outline the postoperative protocol, including monitoring, therapy, and his return to high-vibration machining work.
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Monitoring: hourly flap checks for the first 24 to 48 hours, then every four hours, looking at color, capillary refill, temperature, and turgor. Keep the hand elevated and warm, avoid caffeine and nicotine, and avoid any constrictive dressing or circumferential bandage. A congested flap is salvaged by releasing the inset and, if needed, leech therapy; an arterial problem needs re-exploration rather than watchful waiting.
Therapy: splint the thumb in a safe position for 10 to 14 days, then begin gentle active motion of the interphalangeal and metacarpophalangeal joints with a hand therapist. Tendon gliding matters because the flexor pollicis longus was exposed and the flap is adherent to the bed. Address the index donor site, which has been skin grafted, with early motion to prevent first web tightness.
Return to work: machining requires protective sensibility, a healed stable wound, and adequate grip. Realistically this is 8 to 12 weeks, with a period of light duty before full vibration exposure. Prescribe a protective glove, discuss cold-weather limitation, and warn that prolonged vibration may produce symptoms in a flap-covered digit. Document the counseling about smoking cessation, which remains the single most modifiable factor in his outcome.