Hand, Wrist, and Microsurgery
What this domain tests
Flexor and extensor tendon zones, nerve injury classification and repair, carpal instability, replantation, and microvascular principles.
Core rules
- Flexor tendon zones: zone I is distal to the flexor digitorum superficialis insertion (jersey finger), zone II spans the fibro-osseous sheath, zone III the palm, zone IV the carpal tunnel, zone V proximal to the canal.
- Zone II repairs use a multistrand core suture, generally four strands, plus a running epitendinous suture, followed by early controlled mobilization to limit adhesions.
- Nerve injury: Seddon's neurapraxia, axonotmesis, and neurotmesis, refined by Sunderland's five degrees. Sharp transections are repaired primarily with tension-free epineurial or grouped fascicular technique.
- Replantation requires sharp amputation, limited warm ischemia, and enough healthy vessel to debride to; two arteries and at least three veins are the aim. Vein grafts are used for arterial gaps, and vein repairs are often coupled.
- Scaphoid fractures: tenderness in the anatomic snuffbox with negative radiographs is treated as a fracture until proven otherwise.
Worked example
A 28-year-old with a volar laceration at the proximal phalanx of the index finger: no active distal interphalangeal flexion, intact sensation. Diagnosis: zone II flexor digitorum profundus laceration. Answer: explore, repair the profundus with a four-strand core and epitendinous suture, keep the sheath and pulley system as intact as possible, and start early protected mobilization with a hand therapist.
Traps that cost marks
- Labeling a scaphoid fracture a "wrist sprain" and producing a nonunion.
- Examining tendon function after infiltrating local anesthetic.
- Ignoring a taut, painful hand as early compartment syndrome.