Transposition of Digits and Soft Tissue Reconstruction in Complex Replantation

TRANSPOSITION OF DIGITS (HETEROTOPIC REPLANTATION)

In the context of devastating upper extremity trauma, extensive damage to amputated parts or the proximal amputation stump frequently renders anatomical restoration of digits impossible. In these severe crush or avulsion injuries, the surgeon must pivot from anatomical replantation to functional salvage via heterotopic replantation—the transposition of digits. By moving viable amputated digits from their original anatomical position to a more functionally critical position, the surgeon can restore a highly functional hand despite the loss of multiple parts.

Biomechanical Priorities in Digit Allocation

The fundamental goal of heterotopic replantation is the restoration of the basic biomechanical functions of the hand: opposition, pinch, and power grip.

• Thumb Reconstruction: The thumb contributes approximately 40% to 50% of overall hand function. Priority must always be given to the restoration of the thumb position. An amputated index or long finger, even if partially damaged, is frequently transposed to the thumb position (pollicization) to restore opposition.
• Pinch Mechanism: Once the thumb is established, the secondary priority is providing a stable post for pinch. This requires a digit in the index or long finger position. The long finger position is often preferred over the index position for single-digit replantation because it centralizes the pinch mechanism and interacts more synergistically with the remaining ulnar digits.
• Power Grip (Cup Restoration): Consideration must subsequently be given to providing digits in the long, ring, and little finger positions to restore the ulnar "cup" of the hand, which is essential for power grip and grasping cylindrical objects.

Bilateral Amputations

In catastrophic bilateral digital amputations, the surgical strategy becomes exponentially more complex. Parts from one hand may be better suited for replantation to the opposite hand to create at least one highly functional extremity.

💡 CLINICAL PEARL:
When digital transposition is considered in bilateral amputations, the dominant hand is strictly given priority. The goal is to consolidate the best available skeletal and soft tissue elements to reconstruct a dominant hand capable of independent activities of daily living (ADLs), even if it leaves the non-dominant hand as a mere assistive post.

PRINCIPLES OF TENDON REPAIR IN REPLANTATION

During replantation, damaged structures are systematically repaired in a serial fashion, progressing from the deep skeletal plane to the more superficial planes. The standard sequence is: bone fixation, extensor tendon repair, flexor tendon repair, arterial anastomosis, nerve repair, and finally venous anastomosis.

However, this sequence is highly adaptable. Tendon repair may intentionally delay the repair of vessels so that deeper structures can be manipulated without placing tension on, or jeopardizing, delicate microvascular anastomoses.

Flexor Tendon Management

The management of flexor tendons in replantation is dictated by the mechanism of injury, the zone of amputation, and the degree of contamination.

Crush and Avulsion Injuries
If the amputating injury involves severe crushing or avulsion, or if the amputation occurs proximal to the flexor digitorum superficialis (FDS) insertion with significant tendon substance loss, primary repair of the flexor tendons is contraindicated.
* Delayed Grafting: In these circumstances, the wound is closed (or covered), and delayed two-stage tendon grafting is planned.
* Silicone Rod Placement: Occasionally, passive silicone rods (Hunter rods) may be inserted at the time of replantation to preserve the retinacular pulley system in anticipation of a second-stage tendon graft.

🚨 SURGICAL WARNING:
The condition of the wound, the extent of contamination, and the potential for deep space infection must be rigorously evaluated before placing a silicone rod. A foreign body in a contaminated, marginally vascularized replant is a nidus for catastrophic infection.

Zone-Specific Repair Techniques
* Distal to FDS Insertion (Zone I): A flexor digitorum profundus (FDP) tendon injured near the distal interphalangeal (DIP) joint is reattached directly to the distal phalanx using a pull-out wire technique or a micro-suture anchor.
* Middle Phalanx Injuries: If the injury is over the middle phalanx and primary repair is impossible, the distal tendon stump is tenodesed to the bone or the remaining tendon sheath to stabilize the DIP joint.
* Proximal Phalanx and Proximal (Zone II and beyond): If the flexor tendons have been sharply severed, both the FDS and FDP are usually repaired primarily.

Advanced Tenorrhaphy Techniques
* The Waikakul Transfer: For Zone II amputations, Waikakul et al. demonstrated that repairing the proximal FDP to the distal FDS stump results in a superior overall arc of motion compared to repairing both tendons. This technique also expedites the replantation process by requiring only one robust repair.
* The Urbaniak Delayed-Tie Technique: Our preferred tenorrhaphy utilizes a modified Kessler technique with 4-0 polyester fiber (Mersilene) sutures. Urbaniak advocates placing the core sutures into each end of the tendon but leaving them untied. This allows the digit to remain extended during the meticulous repair of volar nerves and vessels. Once the microvascular work is complete, the sutures are tied, flexing the finger and protecting the neurovascular bundles.
* Sheath Repair: When technically feasible, the digital flexor sheath is repaired with 5-0 or 6-0 nonabsorbable nylon sutures to prevent bowstringing and minimize adhesions.
* Myotendinous Junction: Injuries at the myotendinous junction in the distal forearm are repaired by reattaching the tendon into the muscle belly using a "fish-mouth" configuration, reinforced with multiple mattress sutures.

Extensor Tendon Management

Extensor tendons are repaired using nonabsorbable 4-0 sutures. Because the extensor mechanism is superficial and prone to adhesion formation, meticulous technique is required.

• Metacarpophalangeal (MCP) Joint to Wrist: Injuries between the MCP joint and the extensor retinaculum are typically repaired with robust mattress sutures or a modified Kessler technique.
• Extensor Retinaculum Level: Extensor tendons injured directly beneath the extensor retinaculum require special attention. A portion of the retinaculum must usually be excised to prevent postoperative tethering and to aid in subsequent tendon gliding. A mattress stitch suffices at this level.
• Myotendinous Level: Similar to flexor tendons, extensor injuries at the myotendinous junction are repaired by inserting the tendon into the muscle belly in a fish-mouth configuration, heavily reinforced with mattress sutures.

PRINCIPLES OF MICROVASCULAR VESSEL REPAIR

The success of any replantation hinges on the patency of the microvascular anastomoses. Identifying the volar digital arteries is generally easier than locating suitable dorsal veins. The digital arteries lie just dorsal to the volar digital nerves.

💡 CLINICAL PEARL:
Anatomical variations are common. Hypoplastic vessels on the radial side of the index finger and the radial side of the thumb are frequently encountered. In thumb replantation, if the palmar digital arteries are unsuitable or avulsed, the princeps pollicis artery can be dissected dorsally to provide robust arterial inflow.

Order of Vessel Repair: Artery First vs. Vein First

Surgeons’ preferences differ regarding the sequence of vessel repair, and the approach must be tailored to the anatomical level of the amputation and the total ischemia time.

Digital Replantation (Artery-First Approach)
In digital amputations, our standard practice is to repair the arteries first.
1. Flow Assessment: This allows immediate assessment of the adequacy of arterial inflow across the anastomosis and through the distal capillary beds.
2. Venous Identification: Restoring arterial flow first causes the dorsal veins to engorge and fill with blood, dramatically aiding in the identification of hard-to-find, collapsed veins.
If veins are repaired first in a digit, the surgeon must wait until the arterial anastomosis is complete to determine if the venous repair is actually functional.

Macro-Amputations: Palm, Wrist, and Forearm (Vein-First Approach)
If the amputation occurs through the palm, wrist, or forearm, the limb contains a large volume of muscle tissue.
* Minimizing Blood Loss: If the limb can be safely revascularized (ischemia time < 6 hours), repairing two or three large veins before the artery minimizes massive exsanguination from the replanted part once arterial flow is restored.

Prolonged Ischemia (> 6 Hours)
If the ischemia time exceeds 6 hours, the paradigm shifts back to an artery-first approach, regardless of the amputation level.
* Mitigating Reperfusion Injury: Repairing the artery first shortens the critical ischemia period, minimizing the risk of revascularizing dying muscle.
* Shunting: Carotid endarterectomy shunts or ventriculoperitoneal shunts can be utilized to establish temporary arterial inflow while the definitive anastomoses are prepared.
* Washout: Prolonged ischemia leads to the accumulation of potassium, lactic acid, and myoglobin in the amputated part. Venous return must be vented (allowed to bleed out) initially to prevent these toxic metabolites from entering the systemic circulation, which could precipitate fatal cardiac arrhythmias or acute renal failure. Once the effluent runs clear, venous repair should follow rapidly to avoid excessive blood loss. A pneumatic tourniquet is invaluable in controlling bleeding during this phase.

Distal Fingertip Replantation (Zone I)

Fingertip amputations present unique microvascular challenges due to the diminutive size of the vessels.
* Central Artery: Identification of a central artery arising from the distal transverse palmar arch (formed by the radial and ulnar digital arteries) is often required. This vessel is located in the midline of the pulp, just volar to the distal phalanx, and measures approximately 0.85 mm in diameter.
* Dorsal Terminal Vein: The corresponding vein is identified in the midline distal to the DIP joint, formed by the confluence of veins from the nail wall. It is approximately 1.0 mm in diameter.
* Delayed Venous Repair (Koshima Technique): Koshima et al. described a highly useful technique for distal replantations where veins are too small or spastic to repair primarily. The surgeon performs the arterial repair, allows the fingertip to engorge with venous blood, and applies medicinal leeches or heparin-soaked pledgets. The patient is returned to the operating room 24 to 48 hours later, at which point the veins are massively dilated and much easier to anastomose.

Perfusion and Vessel Preparation

Both large and small amputated parts benefit from gentle perfusion prior to anastomosis.
* Technique: A small, soft Silastic catheter is introduced into the artery, and the part is gently perfused with heparinized lactated Ringer’s solution.
* Rationale: This clears the microcirculation of microthrombi and thrombogenic material. Crushed small parts and large muscle-containing parts have a significantly higher survival rate when gently dilated and irrigated.

🔪 SURGICAL TECHNIQUE 63-9: Vessel Preparation and Anastomosis

1. Arterial Identification: Under the operating microscope, identify the volar digital arteries. Debride the vessels back to healthy, uninjured intima. Mark the viable arterial ends with a small 9-0 or 10-0 nylon adventitial suture for easy retrieval.
2. Venous Dissection: After the arteries are marked, turn attention to the dorsum of the digit. Carefully dissect the veins from the dorsal skin flap.
3. Venous Mapping:
   • Proximal to Mid-Middle Phalanx: Three or four suitable veins are usually found on the dorsum of the digit between the MCP joint and the midportion of the middle phalanx.
   • Distal to Mid-Middle Phalanx: Distal to this point, only one or two suitable veins may be present.
4. Volar Veins: Although volar veins can occasionally be visualized, they are frequently less reliable, more difficult to mobilize, and prone to compression during postoperative flexion. Rely primarily on the dorsal venous network.
5. Anastomosis: Perform the arterial anastomosis using 10-0 or 11-0 nylon interrupted sutures. Release the clamps and confirm pulsatile flow. Once the dorsal veins engorge, perform the venous anastomoses. Aim for a ratio of two veins repaired for every one artery to ensure adequate venous outflow and prevent congestive failure of the replant.

POSTOPERATIVE PROTOCOLS AND REHABILITATION

The success of a digital transposition and replantation extends far beyond the operating room. Strict adherence to postoperative protocols is mandatory.

• Environment: The patient is kept in a warm, strictly monitored environment. The replanted digits are monitored hourly using clinical observation (color, turgor, capillary refill), surface temperature probes, or implantable Doppler probes. A temperature drop of >2°C or an absolute temperature <30°C is highly indicative of vascular compromise and warrants immediate surgical re-exploration.
• Anticoagulation: Protocols vary, but most centers utilize a combination of intravenous Dextran 40, systemic heparin, or subcutaneous enoxaparin, coupled with oral aspirin (325 mg daily) to prevent microvascular thrombosis.
• Rehabilitation: Early protected motion is critical to prevent tendon adhesions, particularly following complex flexor and extensor repairs. A modified Kleinert or Duran protocol is initiated under the strict guidance of a certified hand therapist within 3 to 5 days postoperatively, provided the vascular status of the replant is stable.

📚 Medical References

• digital replantations, revascularization and toe-transfers, J Hand Surg 6:281, 1981.
• Littler JW: Subtotal reconstruction of thumb, Plast Reconstr Surg 10:215, 1952.
• Littler JW: Principles of reconstructive surgery of the hand. In Converse JM, ed: Reconstructive plastic surgery, vol 4, Philadelphia, 1964, Saunders. Littler JW: Digital transposition. In Adams JP, ed: Current practice in orthopaedic surgery, vol 3, St Louis, 1966, Mosby. Littler JW: On making a thumb: one hundred years of surgical effort, J Hand Surg 1:35, 1976.
• Lobay GW, Moysa GL: Primary neurovascular bundle transfer in the management of avulsed thumbs, J Hand Surg 6:31, 1981.
• Lyall H, Elliot D: Total middle