Replantation 

Replantation of completely amputated digits has been a medical reality since 1968, when Komatsu and Tamai first reported successful replantation of a completely amputated thumb.^[1] Amputation of digits is common. Approximately 100,000 digital amputations occur per year in the US. Of these, an estimated 30% are suitable for replantation. The exact number of replantations performed yearly is unknown. However, the number appears to be decreasing, secondary to more rigid selection criteria, improved workplace safety procedures, and better-designed protection devices on power tools.

An image depicting digital amputation can be seen below.

Carrel performed experimental replantation of a canine hind limb in 1906.^[2] Malt successfully replanted a completely amputated arm in 1964,^[3] and Meredith performed replantation after a distal radius/wrist injury in 1965.^[4] Chinese surgeons at the Sixth People's Hospital performed successful replantations in the 1960s. However, the first digital replantation occurred in 1968, with Komatsu and Tamai's report of a successful thumb reattachment.

A complete amputation occurs when the injured part is no longer attached to the patient. If any portion of the digit remains attached, a partial or near amputation has occurred, and the repair process is a revascularization, not a replantation.^[5]

Frequency

As stated above, approximately 100,000 digital amputations occur per year in the US, and about 30% of these are suitable for replantation. The exact number of replantations performed yearly is unknown, but the number appears to be decreasing due to more rigid selection criteria,^[6] improved workplace safety procedures, and better designed protection devices on power tools.

Amputations of digits occur secondary to laceration, crush, avulsion, and combination injuries. They may occur at any location but frequently occur at work or at home. Amputations have been reported in children secondary to injuries from exercise equipment, car doors, and home doors. In adults, injuries occur from saws, knives, hydraulic wood splitters, and a variety of industrial machines.

Home injuries frequently involve table or circular saws. Work injuries are multifactorial, and demographics are changing constantly because safety equipment is added and equipment is adapted following mishaps to prevent similar occurrences.

Following amputation, cell death is irreversible if ischemia produces critical cell lysis. Prior to irreversible cell death, reperfusion is possible. Time from injury to reperfusion and salvage depends upon the type of tissue involved and the temperature of the injured part.^[7] Muscle at room temperature is irreversibly damaged in 6-8 hours; if cooled, it can withstand a maximum of 8-12 hours of ischemia. However, if digits are cooled without freezing, they may survive longer than 100 hours.

The clinical presentation of a completely amputated digit is obvious. The important considerations are the level of the injury, the mechanism of the trauma, and the general health of the patient. In general, diagnostic testing is not indicated, with the exception of plain radiographs to evaluate bony integrity. Routine preoperative evaluation of the patient is critical. It may not be possible to determine replantation potential without exploration in the operating room.

Indications for surgical replantation have evolved over the last 20 years. The major indications for replantation in the absence of prolonged ischemia, segmental damage, and diffuse crush or severe avulsion injuries are amputations of the thumb, multiple digits, a digit in a child, and a digit distal to the flexor digitorum superficialis insertion.

The important anatomic consideration is the size of the injured vessel. In children older than 2 years, vessels proximal to the middle portion of the middle phalanx are more than 0.4 mm. In adults, digital arteries are more than 0.4 mm proximal to the lunula of the nail. The radial digital arteries to the thumb and the index finger, and the ulnar digital artery to the little finger are, in general, significantly smaller than the parallel vessels.

Relative contraindications to surgery are complete amputation of a digit proximal to the flexor digitorum superficialis insertion, severe crush or avulsion injuries, segmented injuries, and/or severe bony comminution with loss of bone and joint integrity.

Major contraindications to surgery are prolonged warm ischemia, crush or avulsion injuries with diffuse arterial damage, and/or inability to obtain reconstruction that would allow a functional digit.