Digit Amputation

Etiology

In traumatic injuries, one should assess the patient in accordance with the advanced trauma life support approach (airway, breathing, circulation, etc.) for a systematic assessment of the patient and to rule out any life-threatening injuries before referring or transferring patients for further specialist management of their finger injuries. Determining the mechanism of injury is crucial, as it could affect decisions regarding management and outcome for the patient. Sharp injuries may provide a clear amputation level, whereas blunt trauma may correlate with crush injuries at the level of the amputation, and avulsion injuries can cause distant trauma away from the level of visible injury.

Epidemiology

Amputation injuries represent approximately 1% of all trauma-related injuries presenting to the emergency department, with finger and thumb amputations being the most common.[1] Fingertip and partial digit amputation are the most frequent presentations, complete digit and multiple digit amputations are less common, with most injuries occurring at home.[2] Its incidence is higher in adults (men greater than women, approximately 4 to 1) than children (approximately 3 to 1 adult to child ratio). Working with power tools is the most common cause of injury in adults.

Pathophysiology

Typically, once a finger amputation has occurred, ischemic tolerance times are 12 hours if warm and up to 24 hours if cold. For more proximal amputations, these times are halved. The amputated part should be covered in a normal saline-soaked gauze, sealed in a plastic bag and submerged in icy water with no direct contact with ice. If there is direct contact with ice, it could result in tissue damage and render the amputated part non-viable. More proximal amputations are less tolerant of ischemia due to the presence of muscle tissue, which can undergo irreversible changes after 6 hours of ischemia.[3][4]

History and Physical

History:

The important aspects to be noted in history are hand dominance, occupation, time of injury, mechanism of injury, other associated injuries, comorbidities, and NPO status.

Physical Exam:

Level of amputation, structures involved, neurovascular status, function, and degree of contamination (if relevant). It is vital to assess the amputated part and ultimately determine its suitability for replanting respective to the mechanism of injury (e.g., crush, guillotine-style, avulsion).

Finger amputations classification is generally according to the level of amputation. The Sebastian and Chung classification is outlined below[5]:

• Zone 1 distal amputations 
  • Zone 1A - distal to lunula, through the sterile matrix
  • Zone 1B - between lunula and nailbed
• Zone 1 proximal amputations
  • Zone 1C - between flexor digitorum profundus insertion and neck of the middle phalanx
  • Zone 1D - between the neck of the middle phalanx and insertion of the flexor digitorum superficialis

Evaluation

Laboratory:(optional depending on the clinical scenario)

CBC (complete blood count) to assess for blood loss

Coagulation studies (only if the patient is known to be on anticoagulants)

Imaging:

Plain radiograph of the affected finger/hand and amputated part; this allows assessment of bony injuries, bone quality, and guide decisions regarding bony fixation methods. Angiograms are normally not requested unless it forms part of investigations for other injuries.

Treatment / Management

Initial management - first aid, ATLS approach to the patient, preserve amputated part, tetanus vaccination, and antibiotics as per local hospital guidelines.

In the traumatic setting, the ideal candidate for replantation should be young, healthy, sharp mechanism of injury (giving a clear amputation level), minimal tissue destruction, and contamination.[3]

Indications for replantation[1][3]:

• Thumb amputation - loss of thumb represent approximately 40 to 50% loss of hand function
• Multiple finger amputations
• Amputations at or proximal to palm
• Pediatric patients with finger amputation(s) at any level
• Single finger amputation distal to the insertion of the flexor digitorum superficialis (zone I) (studies have shown that replantation distal to this insertion point had better outcomes than those proximal)
• Patient consideration - specialist requirement, e.g., occupation or pre-morbid compromised hand function

Contraindications and relative contraindications[3]:

• Single-digit injury through flexor tendon zone II
• Smoking
• Severe crush
• Mangled limb
• Heavy contamination
• Segmental injuries
• Prolonged warm ischaemic time
• Medically unfit
• Improperly preserved amputated part.
• Avulsion injuries 
• Other life-threatening injuries
• Mentally unstable
• Previous surgery to the affected finger 
• 'Redline' or 'red ribbon' sign (seen in vessels during surgery), which predicts the level of intimal damage in the vessel

Once the patient arrives in the operating theater, the amputated part should undergo a careful assessment for suitability for replanting. All structures should be dissected and identified, especially the neurovascular bundle. If no suitable vessels are identified, then replantation should not proceed. Usually, there is an order for repair of structures:

1. Bone fixation with or without bone shortening to allow repair of soft tissue
2. Tendon repair - extensor and flexor tendons
3. Nerve repair
4. Arterial anastomosis
5. Venous anastomosis (if suitable veins are present)

Bone fixation should be simple and quick to perform, but it also depends on the configuration of bony injuries. Usually, two Kirschner wires are an option, but other fixation methods may also be used (i.e., plate fixation). Occasionally, bone shortening is required before fixation to allow for soft tissue closure and repair of neurovascular structures without excessive tension. 

In case the restoration is not possible, and the clinician decides to opt for amputating or forming a stump, then provide a mobile, stable, painless stump with the least interference from the remaining tendon and joint function to ensure the most useful result. Whenever possible, use volar skin for the stump coverage because it provides skin that is thicker and more sensate than dorsal skin. The options for rearrangement of volar tissue to cover the stump include:

• Fillet flaps
• Volar V-Y flaps
• Bilateral V-Y flaps
• Homodigital island flaps

In an acute setting, the "dog ears" should be left to decrease the tension and the likelihood of ischemia to the remaining flaps, and these dog ears disappear over time. Regarding the treatment of the bone in a digital amputation/stump formation, the bone under the stump end must be smooth. The remaining bone chips and devitalized bone should be removed. The articular cartilage can be preserved when the amputation occurs at the level of the interphalangeal (IP) joint. This can provide a shock pad for trauma and potentially causes less pain under than skin than the bone edges.

While addressing the nerve at the stump end, it is vital to avoid neuroma formation in this location. The nerve end should be in a position away from the stump end or an anticipated point-of-contact pressure. To decrease the likelihood of neuroma formation at the stump end, traction neurectomy of the digital nerve should be performed bilaterally for each digital amputation. Tendon insertions should be preserved where possible as the preservation of a tendon insertion enhances the active mobility and function of an amputation stump. Adhesions can result, and so early mobilization of the digit is recommended.

Differential Diagnosis

Digit amputations tend to be a straight forward presentation, but infectious processes can mimic amputation leading to loss of fingers/toes.

Prognosis

Previous studies have found these factors to have a substantial effect on functional outcome[6]:

1. Level of the amputation
2. Number of fingers injured
3. Circumstance and mechanism surround the injury
4. Time from injury

Survival rates following replantation have been reported between 80 to 90%, although these figures have come from specialist institutions. It is also worth noting that venous repair improves survival regardless of the level of amputation. This fact is important, as the venous repair is not always possible, and as a result, it could lead to venous congestion.  One solution would be to make a small distal incision to allow venous drainage or the use of leeches.

Complications

Complications classify according to the time of onset[1]

• Early complications
  • Arterial insufficiency
    • Arterial thrombosis presents typically as a pale, cool and pulseless digit
    • It is vital during the post-operative period to maximize blood flow through the anastomoses and prevent thrombosis
  • Venous insufficiency
    • Venous congestion typically presents as a purple digit with brisk capillary refill and swelling
    • Concerns of possible anastomosis failure or thrombosis should prompt urgent return to theatre for salvage - in cases of venous congestion, leech therapy or anticoagulation may be considered to improve venous return
  • Infection
• Late complications
  • Cold intolerance
  • Tendon adhesions
  • Stiffness
  • Bony malunion
  • Altered sensation