Hand Surgery and Upper Extremity
What this domain tests
Zonal anatomy, tendon and nerve repair principles, recognition of the emergency (compartment syndrome, high-pressure injection, tenosynovitis) and replantation selection.
Anatomy and zones
- Flexor zones: I (FDS insertion to FDP insertion - profundus only, jersey finger); II (A1 pulley to FDS insertion, historically "no man's land"); III (A1 to carpal tunnel, lumbricals); IV (carpal tunnel); V (forearm).
- Extensor zones I–VIII alternate over joints and bones; zone I is mallet, zone III is boutonnière.
- Nerve examination: median - thumb abduction, opposition, OK sign; ulnar - finger abduction/adduction, Froment's sign, clawing of ring and small; radial - wrist drop, first web sensation.
- Static two-point discrimination is normal at 6 mm or less; moving at 4 mm or less.
Core rules
- Flexor tendon repair: 4-strand core suture with epitendinous running suture, gapping under 2 mm, preserving A2 and A4 pulleys, with early controlled mobilisation.
- Nerve repair within 3 weeks where possible; gaps over 2–3 cm need grafting; conduits for short gaps only.
- Tendon transfers require supple joints, an expendable donor, a straight line of pull, and one tendon for one function.
- Kanavel's four signs of flexor tenosynovitis: flexed posture, fusiform swelling, sheath tenderness, pain on passive extension - surgical emergency with intravenous antibiotics and drainage.
- Scaphoid fractures can be radiographically occult with retrograde blood supply, so proximal pole avascular necrosis is the risk; immobilise and repeat imaging or CT/MRI.
Worked example
A painter sustains a high-pressure paint-gun injection to the index finger pulp, with only mild pain and a small puncture. Reasoning: this is a surgical emergency. The material tracks along tendon sheaths and neurovascular bundles, and initial benign appearance is deceptive. Treat with broad-spectrum antibiotics and tetanus prophylaxis, urgent extensive debridement of all involved planes through volar and dorsal incisions, splinting and admission; amputation rates remain high, especially with oil-based compounds.
Traps
- Reassuring a patient whose scaphoid X-ray is normal.
- Splinting a mallet finger at the metacarpophalangeal joint instead of holding the distal joint in extension for 6–8 weeks.
- Dividing the entire flexor sheath rather than releasing only A1 for a trigger finger.
- Failing to measure compartment pressures in an anxious, tense forearm with pain on passive stretch.
- Placing an amputated digit directly on ice.