Digit Replantation

Anatomy and Physiology

The level of amputation is related to the zone of flexor tendon injury. Labeling the different zones of flexor tendon injury is relative to the insertion of the flexor digitorum profundus, the level of the digital pulley system, and the location of the carpal tunnel. Zone 1 injuries comprise those injuries in which the transection occurs distal to the origin of the flexor digitorum superficialis tendon. Zone 2 injuries lie between the distal insertion of the flexor digitorum superficialis and the A1 pulley, located just proximal to the metacarpophalangeal joint. Zone 3 flexor tendon injuries and amputations occur between the A1 pulley and the distal edge of the carpal tunnel. Injuries through the carpal tunnel qualify as zone 4 injuries. Zone 5 amputations and flexor tendon injuries occur proximal to the carpal tunnel.

Zone I amputations involve only the flexor digitorum profundus tendon, leaving motion intact at the proximal interphalangeal joint (PIP). Amputations at this level portend a favorable outcome; however, if the amputation occurs at the distal aspect of the middle phalanx or past the distal interphalangeal joint (DIP), the small diameter of the digital vessels may preclude replant. Amputations at this level have classically had a very poor outcome due to the inability of the repair to pass between the complex digital pulley system. However, zone 2 amputations are not absolute contraindications to replantation and should still merit consideration with properly selected patients. In general, the outcomes of replantation in zones 3 to 5 depend on other patient and injury factors, such as ischemia time, mechanism of amputation, and patient comorbidities, then on the level of amputation.[5][6][7]

Indications

General indications for upper extremity replantation are thumb amputation, multiple-digit amputation, mid-palm (trans-metacarpal) amputation, single-digit amputations distal to the insertion of the flexor digitorum superficialis tendon (zone 1), sharp amputations at the hand, forearm, or elbow level, and any amputation in a child. Any patient transferred to a Level 1 trauma center or replant-capable facility should be done after consultation with the hand surgeon to ensure the transfer is appropriate.[5]

Contraindications

General contraindications are severe crush or avulsion injuries, multiple-level injuries, single-finger amputation proximal to the insertion of the flexor digitorum superficialis tendon (proximal to zone 1), prolonged ischemia time, and mentally or physically unstable patients. Patients with absolute contraindications to replantation do not need emergent transfer to a replant-capable facility if their wounds are otherwise manageable at the facility of initial presentation.

Equipment

Digit replantation requires the use of an operating microscope as well as appropriate microsurgical instruments and sutures. If this equipment is not readily available at the treating facility, the patient may require a transfer to a facility with the proper resources.

Personnel

Any surgeon trained in microsurgical technique and hand replantation may perform digit replantation. This training typically would include any attending orthopedic or plastic surgeon. However,  this procedure requires specialized equipment and personnel who are familiar with that equipment. These resources may not be available at all institutions. Orthopedic, plastic, or general surgeons with the Certificate of Added Qualifications (CAQ) in hand surgery are the best resources for performing replantation or referring to facilities where replantation is possible. 

Preparation

Handling of Amputated Extremity Parts

Transportation of the amputated part is paramount in preserving viability. The most widely utilized and effective preservation method is wrapping the amputated extremity in gauze moistened with a physiologic solution (normal saline or lactated ringers), placing the wrapped amputated part in a plastic bag, then putting this plastic bag on ice. Alternatively, the part may be immersed in a physiologic solution in 1 bag and then placed on ice. Amputated extremity parts should never be placed directly on ice, as this may result in frostbite or other soft tissue injuries to the amputated part. Such damage may preclude replantation altogether or compromise the achievable functional result of replantation.

Ischemia Time 

Timing is critical in replantation surgery. The amount of muscle in the amputated part determines the amount of ischemia time each part tolerates. Digits contain no muscle, and the bone and soft tissue present in each digit have a relatively low metabolic rate and formation of toxic byproducts of ischemia. Therefore, digits amputated in zone 1 and zone 2 may tolerate up to 12 hours of warm ischemia time and up to 24 hours of cold ischemia time. Muscle makes up a substantial portion of the soft tissue in zone 3 to 5 amputations. Extremities amputated at this level tolerate no more than 6 hours of warm ischemia time or 12 hours of cold ischemia time. Because of this, vascular shunting to the amputated part may be necessary for forearm or elbow amputations before initiating the surgical repair.

Technique or Treatment

Sequence of Repair

When possible, the amputated part should be taken to the operating room before the patient for thorough debridement and examination under the microscope. The quality of the tissue, specifically the nerves and blood vessels, is examined before committing to replantation. Identifiable structures should be tagged with sutures or microchips. The first step in replantation is bone shortening and fixation. The bone should be shortened enough to remove all tension from subsequent soft tissue repairs. In the pediatric population, any bony shortening should not sacrifice the physis. Bony fixation is followed by extensor tendon, then flexor tendon repair. The surgeon should then initiate arterial repair. No matter the level of amputation, anastomosing intact and healthy arterial intima on each side of the repair is paramount to success. If this requires excessive debridement, vein grafts are necessary. Ample vein grafts are typically available from the ipsilateral extremity in the cephalic or basilic vein. However, lower extremity vein grafts may be necessary. Nerve repair is the next step, followed by vein repair. Lastly, the surgeon completes soft tissue coverage of the repair.[2][8][9][10]

In short, the sequence of repair is as follows:

1. Bone
2. Extensor tendon
3. Flexor tendon
4. Artery
5. Nerve
6. Vein
7. Soft tissue

Complications

Complications of flexor tendon injuries can include bleeding, infection, replant failure, and finger stiffness. Venous congestion of the finger is a common problem as anastomosis of damaged dorsal veins is often difficult. Various strategies to prevent or treat venous congestion exist, including removing the nail plate, fishmouth incisions over the fingertip with heparin pledget application, or the application of leeches. Any patient begun on leech therapy should also be placed on ciprofloxacin therapy to prevent infection from Aeromonas hydrophilia.

Clinical Significance

If performed by an experienced hand and microsurgeon, replant viability rates should be at least 80% following replantation. Motion at the affected joints depends on the level of amputation, mechanism of amputation, and compliance with postoperative therapy. Patients should receive counsel before surgery that the motion in replanted digits averages only approximately 50% of normal. Furthermore, patients undergoing replantation average ten days in the hospital and approximately 7 months of time off. The best results generally come from replantation of the thumb, hand, distal forearm, and fingers distal to insert the flexor digitorum superficialis (zone 1).

Enhancing Healthcare Team Outcomes

Digit reimplantation requires an interprofessional team. Once the digit is reimplanted, close monitoring is required to ensure that no ischemia or infection occurs. Following the surgery, patients require prolonged physical therapy to regain joint function and strength. While digit reimplantation does have success, the procedure does not work for everyone.[11][12][13]