Digit and Hand Replantation

Replantation is the surgical reattachment of a body part that has been completely amputated; revascularisation is the restoration of blood flow to a part that remains partially attached but is critically ischaemic. Both are managed by the same microsurgical team using the same principles of bone fixation, tendon repair, microvascular anastomosis and nerve coaptation.

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History. The world's first arm replantation was reported by Malt and McKhann, in a 12-year-old boy, in 1962; the first successful thumb replantation was by Komatsu and Tamai in Japan in 1968. Digital replantation became clinically routine once the operating microscope, fine monofilament nylon sutures (10-0, 11-0) and structured post-operative monitoring and salvage protocols were in place.

The decision. The decision to replant is not automatic. It is a calculated judgement, and a viva on replantation starts with the first two items on this list before anyone mentions a microscope:

• The mechanism of injury (sharp, crush, avulsion) - the most important predictor of success
• The ischaemia time, warm and cold - dictates muscle viability and the risk of reperfusion injury
• The level of amputation (zone, digit, hand, more proximal)
• The patient: age, vocation, hand dominance, comorbidities, expectations and choice
• The resources: microsurgical team, theatre time, monitoring capability

Indications. The BSSH/ASSH consensus list:

• Thumb amputation at any level - an absolute indication, because the thumb is approximately 40% of hand function
• Multiple digit amputation - replant at least one or two to restore tripod pinch
• Single digit amputation in a child - excellent functional recovery and nerve regeneration
• Single digit in selected adults - musicians and professionals with unique hand requirements
• Hand, wrist, forearm or arm amputation - survival and function are both reasonable in specialist units
• Bilateral digital or hand amputation - at least one side must be restored

Contraindications. The absolute list is shorter than trainees believe; the relative list is the one that tests judgement.

Absolute. Any one of these settles it:

• A part that is destroyed, severely crushed or degloved beyond surgical reconstruction
• Multiple-level amputation in the same digit
• Prolonged warm ischaemia beyond tissue tolerance - the limits by level are set out under ischaemia time below
• A patient medically unfit to tolerate 6-12 hours of anaesthesia, whether from polytrauma or severe medical comorbidity
• Self-inflicted amputation in a psychiatrically unstable patient

Relative. These are weighed against the patient in front of you:

• Single finger amputation at zone II in an adult - the most debated indication
• Avulsion injury with extensive vessel and nerve damage
• Severe contamination (farmyard, marine, sewerage)
• Prolonged ischaemia in a part containing significant muscle
• A fingertip distal to the DIP joint in an adult, where supermicrosurgery may be required (in a child, consider a composite graft)
• A patient unable or unwilling to commit to prolonged rehabilitation - the very elderly with no rehabilitation potential, the patient who expects to be "back to normal", or drug-seeking behaviour
• A surgeon or centre without microsurgical capability and no safe transfer pathway

Arteries. Each digit is supplied by two proper digital arteries, one radial and one ulnar, running on the volar surface just deep to the volar skin and superficial to the flexor tendon sheath. The radial digital artery is usually dominant in the index, middle and ring fingers; the ulnar digital artery is dominant in the thumb and little finger, and the "all-ulnar" thumb is a well-recognised variant. At each phalanx the arteries give off dorsal branches to the dorsal skin, nail bed and distal phalanx.

Veins. Drainage is predominantly by the dorsal veins, which lie in the subcutaneous tissue on the dorsum of the digit; volar veins exist but are smaller and less reliable. The dorsal veins are the target for venous anastomosis because they are larger, more numerous and easier to work with under the microscope.

Nerves. The proper digital nerves run alongside the proper digital arteries on the radial and ulnar sides of the volar digit. They are pure sensory nerves to the pulp, volar skin, dorsal distal skin and nail bed; the dorsum of the proximal and middle phalanges is supplied by the dorsal sensory branch of the radial or ulnar nerve. Coaptation must restore both volar and dorsal sensibility, to prevent painful neuroma and to allow fine touch discrimination.

Tendons. The insertions decide what each repair restores:

• Flexor digitorum profundus inserts on the volar base of the distal phalanx and flexes the DIP joint
• Flexor digitorum superficialis inserts on the volar shaft of the middle phalanx and flexes the PIP joint
• The flexor tendon sheath, zone II of Verdan's classification, overlies the tendons from the distal palmar crease to the middle of the middle phalanx
• The extensor is a single extensor digitorum communis tendon over the proximal phalanx, with a central slip inserting on the base of the middle phalanx and lateral bands joining to insert on the base of the distal phalanx

Bone. The distal, middle and proximal phalanges are short tubular bones with good cortical purchase for K-wires. The head of each phalanx flares slightly, which makes rigid plate fixation less common in the digit, so K-wires (axial, crossed or longitudinal) are the workhorse. In the hand (metacarpals) and forearm (radius, ulna) plate fixation is feasible, more rigid, and allows early mobilisation.

Ischaemia time. The principle first, because it generates every number: skeletal muscle is the tissue that dies, and a digit contains none. Skin, tendon, bone and nerve tolerate ischaemia for many hours; muscle begins irreversible injury at around 4 to 6 hours of warm ischaemia and, on reperfusion, releases potassium and myoglobin into the circulation. So the further proximal the amputation, the shorter the clock - not because the vessels are harder, but because of what lies between them.

• Digits (no muscle): warm ischaemia up to about 12 hours, cold up to about 24 hours, with successful replants reported at 30 hours and beyond
• Hand at the carpus or transmetacarpal level (intrinsic muscle present): warm about 6 hours, cold about 12 hours
• Forearm and arm (large muscle bulk): warm about 6 hours and preferably less, cold about 12 hours - and here the clock is genuinely hard, because the muscle is the limiting factor, through myonecrosis and the reperfusion injury described below

Do not turn down a digit on time alone. A well-cooled digit presenting at 10 hours is still a candidate, and the commonest error here is refusing a salvageable part using major-limb figures.

Cooling is what buys the difference, and it must be done correctly. Wrap the part in saline-moistened gauze, seal it in a plastic bag, and place the bag in iced water or on ice; the part travels with the patient. Never place the part directly against ice, never use dry ice, and never freeze it - freezing forms intracellular crystals and destroys the tissue, converting a replantable part into a specimen. Do not immerse it in antiseptic or alcohol.

Bone shortening relaxes every repair. Shortening the bone by 5-10 mm converts a high-tension vessel, nerve and tendon repair into a low-tension one. It is the single most important technical decision, and it is made first: do not attempt a primary repair under tension; shorten the bone, then repair everything else. A digital replant with 5 mm of shortening is functionally indistinguishable from one with none; a digital replant whose arterial anastomosis failed from tension is functionally a dead digit.

There is no internervous plane in a replantation, and looking for one misses the point: the wound has already made the exposure. The dissection follows the traumatic wound edges and extends them, exposing the cut structures serially so that each can be identified and tagged before any repair begins. Hunting for a second digital artery after the bone is fixed and the flexor repaired is far harder than finding it at the start.

Mid-digit (zones I, II and III). The volar and dorsal approaches are used together, the volar for the arteries and nerves and the dorsal for the veins and the bone fixation. The volar side is opened through mid-lateral or Bruner-style zig-zag incisions, identifying the flexor sheath, the proper digital neurovascular bundles, and the distal cut ends of the digital arteries and nerves.

Hand level (palm, metacarpal). Extend the volar wound proximally into the palm with a Bruner or mid-lateral incision to identify and tag the common digital arteries and nerves and the flexor tendons, and expose the metacarpal fractures for fixation. A separate dorsal incision over the metacarpals finds the dorsal veins and extensor tendons.

Wrist level and more proximal. The volar incision is extended proximally to expose the median nerve, ulnar nerve, radial and ulnar arteries and the flexor tendons; a separate dorsal incision exposes the extensor tendons, dorsal veins, and the radius and ulna for fixation. The two approaches are linked by the circumferential skin at the level of injury, which is usually debrided and used to expose all structures.

Tag everything first. On both sides of the cut, identify and tag:

• Both proper digital arteries (or the common digital arteries in the palm)
• Both proper digital nerves
• The flexor digitorum profundus and, where present, superficialis tendons
• The extensor tendon
• The dorsal veins, usually 2-4 per digit
• The bone ends
• The digital skin edges, for orientation and length

Position and teams. Supine on a radiolucent operating table with the arm extended on a hand table, positioned so that two surgical teams can work at once: one prepares the stump, the other prepares the amputated part on a separate instrument table. As soon as the part arrives in theatre it is inspected, photographed, radiographed if bony injury is suspected, and its vessels, nerves and tendons are identified under the microscope and tagged. It stays cooled, as described above, and is only taken out of cooling when the team is ready for the anastomosis.

Anaesthesia and tourniquet. General anaesthesia is the standard for adults. Some centres use regional anaesthesia (an axillary brachial plexus block), which may provide intra-operative vasodilation, post-operative analgesia and sympathetic blockade. An upper-arm or forearm tourniquet is used for the initial wound debridement and vessel identification and then released; avoid prolonged tourniquet use once the anastomosis is being performed.

Magnification and instruments. An operating microscope at 10x to 25x is mandatory for all vessel and nerve work; some surgeons use 4x-6x loupes for vein harvesting and nerve preparation. The microsurgical set holds micro-forceps, micro-scissors, a micro-needle holder, jeweller's forceps, vessel dilators, and single and double micro-clamps.

Sutures and irrigation. Monofilament nylon (Ethilon or similar) on a fine taper needle, sized to the vessel: 9-0 for larger proximal vessels, 10-0 for digital vessels, 11-0 for supermicrosurgical distal vessels. The vessel ends and lumens are irrigated with heparinised saline, 1000 units of heparin in 100 mL of normal saline.

Anticoagulation. Prophylactic systemic heparin during the anastomosis (low-dose, 5000 units subcutaneously or 1000 units intravenously per hour) is used by many centres, but practice varies, and aspirin and dextran are used by some units. Topical heparin irrigation of the vessel ends is universal.

Survival in modern series is 80-90% for digits and 60-80% for hand and forearm amputations, but function and patient satisfaction are not guaranteed by survival. The complication profile is both technical and functional.

Vascular. Arterial thrombosis is most common in the first 24-72 hours; venous congestion is more common than arterial occlusion, particularly in fingertip replants, and is managed by leech therapy for the first 24-48 hours, nail plate removal to allow bleeding, or re-exploration with revision of the venous anastomosis. Recognition of each and the take-back are set out under post-operative care.

No-reflow. Despite a patent anastomosis the microcirculation fails to reperfuse and the digit stays mottled and cool, the result of prolonged ischaemia, reperfusion injury and microthrombi. It is difficult to manage; hyperbaric oxygen, intravenous iloprost and sympathectomy are the options considered.

Reperfusion injury after a proximal replant. Compartment syndrome of the forearm or hand needs urgent fasciotomy; myoglobinuria and acute kidney injury need aggressive intravenous fluid resuscitation, urinary alkalinisation and dialysis if required; hyperkalaemia and acidosis are monitored and corrected in real time. The physiology is under ischaemia time above.

Nerve. A neuroma at the repair site, particularly where the nerve was repaired under tension, may need later excision and grafting. Stiffness and dysaesthesia are the particular problems of the zone II replant with poor flexor recovery. Cold intolerance, the subject of the pearl below, is managed by warming, gloves and reassurance.

Tendon. Adhesions after a zone II flexor repair in the digital sheath are a common cause of poor active flexion and are managed by tenolysis at 3-6 months. Rupture of the flexor or extensor repair, early or delayed, is managed by re-repair or tendon grafting; disruption of the central slip leads to lateral band migration and a boutonniere deformity.

Bone and infection. Nonunion or malunion at the osteotomy site is rare with K-wire fixation. Pin-track infection with externalised K-wires is managed by pin care, oral antibiotics and early wire removal, and joint stiffness after prolonged immobilisation by hand therapy and dynamic splinting. Superficial wound infection is common and managed with oral antibiotics and wound care; deep infection or osteomyelitis is rare but devastating and may lead to loss of the replant.

Systemic. Venous thromboembolism is uncommon in upper limb surgery but reported; fat embolism is rare but reported in major limb replants; and the long operation with its blood loss brings drug reactions and transfusion complications.

Function. Stiffness is the commonest long-term problem, and zone II replants have the worst prognosis. Chronic pain affects a minority, and intrinsic muscle function may fail after prolonged ischaemia.

There is no single universal guideline for replantation, but international consensus exists through the major hand surgery societies on the core indications, sequence of repair and post-operative care.