Wrist and Forearm Amputations Technique

Transcarpal amputation

At this level, supination and pronation of the forearm, as well as flexion and extension of the wrist, are preserved and can improve the patient's overall function. Furthermore, in comparison with more proximal amputations, the long lever arm provided by transcarpal amputation increases the ease and power with which a prosthesis can be used. However, prosthetic fitting is more difficult and requires a skilled prosthetist.

Ideally, a long full-thickness palmar and shorter dorsal flap should be created in a ratio of 2:1. Finger flexor and extensor tendons should be drawn, divided, and allowed to retract deep into the proximal wound. Conversely, wrist flexor and extensor tendons are identified and released from their distal insertions and reflected proximally out of the way.

Median and ulnar nerves are identified and sectioned well proximal to the amputation site so that the inevitable neuroma formation will occur in a more proximal padded site. At this level, the radial nerve has divided into fine filaments, and each should be sectioned as described above.

After the radial and ulnar arteries are ligated just proximal to the intended level of bone section, the carpus is transected, and all rough edges are rasped to form a smooth rounded contour. The wrist flexors and extensors should be anchored to the remaining carpus in line with their insertions so as to preserve active wrist motion.

Wrist disarticulation

Wrist disarticulation has many of the same advantages as transcarpal amputation with regard to providing a long lever arm and preserved supination and pronation. However, wrist flexion and extension are sacrificed. Because of their length, conventional wrist units are not used, and myoelectric fitting is problematic, as in persons with transcarpal amputations. However, current wrist disarticulation prostheses can be fashioned with thin wrist units that minimize the length discrepancy between upper extremities.

A long full-thickness palmar flap and short dorsal flap at a 2:1 ratio are elevated, with the incision beginning and ending 1.5 cm distal to the radial and ulnar styloid processes, respectively. Identify and ligate arteries and nerves as described above.

Alternatively, Louis et al ^[24] described a technique for minimizing postoperative pain from neuroma formation, which involves extending the incisions proximally between the pronator teres and brachioradialis just distal to the elbow flexion crease and doubly ligating the median, ulnar, and superficial radial nerves at this level. This allows a neuroma-in-continuity to form at this site and away from the prosthetic wall or scar, where it may cause symptoms.

Martini et al ^[25] reported excellent results achieved by freeing the epineural sleeve of the nerve stump approximately 5 mm from the nerve fascicles. The epineurium tube is then filled and sealed with butyl-cyanoacrylate. However, this technique has not been as commonly used in the United States. It is not necessary to ligate the antebrachial cutaneous nerves in the proximal forearm. Electrocautery is used to achieve hemostasis of the anterior and posterior interosseous vessels.

Preserving the triangular fibrocartilage and avoiding damage to the distal radioulnar joint (DRUJ) are imperative. Otherwise, pronation and supination will be reduced, painful, or both. The prominent radial and ulnar styloid processes should be rounded off with a rasp; however, shortening of the radial styloid process should be avoided. Preserving the radial styloid flare improves prosthetic suspension.

Wrist disarticulation is the procedure of choice in children. In general, disarticulations are preferable to transections through bone at a more proximal level because the distal physis is spared and, consequently, the growth of the distal stump continues at a normal rate. In addition, disarticulation prevents terminal overgrowth of the bone.

Distal forearm amputation

Whereas maintaining length remains an important consideration in the upper extremity, the underlying soft tissues in the distal forearm consist of relatively avascular structures, such as fascia and tendon, and may not always offer adequate padding for the bony stump. Furthermore, the skin and subcutaneous tissue in this area are thin and may be predisposed to wound problems.

A good compromise between adequate functional length and adequate wound healing appears to be at the junction of the distal and middle third of the forearm. Despite resection of the DRUJ, some degree of pronation and supination is preserved in persons with forearm amputations. The extent of motion is dependent on the length of residual forearm stump; the longer the stump, the greater the arc of motion.

As with more distal amputations, flaps are fashioned distal to the intended level of bone amputation. However, at this level, anterior and posterior flaps of equal dimension are created and reflected proximally. Vessels, nerves, and tendons or muscle bellies (depending on the level of amputation) are transected similarly to the methods already described.

Proximal forearm amputation

The technique for proximal forearm amputation is similar to that already described for more distal amputations. A short stump having as little as 4 cm of ulna is preferable to an above-elbow amputation. To facilitate prosthetic fitting in these extreme cases, detaching the biceps tendon and reattaching it proximally to the ulna at a position approximating its resting length is advisable. Distal reattachment should be avoided because it may cause a flexion contracture at the elbow.

In individuals with tenuous soft tissue coverage for the stump, rather than resorting to an above-elbow amputation, Jones et al ^[26]  described a salvage technique in which a free latissimus dorsi flap is used. From a functional standpoint, preserving the patient's own elbow is extremely important. Even in persons with very short stumps, improved fitting prosthetic devices such as the Munster device or a split socket with step-up hinges can be used to achieve excellent function.

In the so-called spare parts method sometimes used for large complex defects, tissue for the flap is sourced from the amputated part itself. ^[27]

Krukenberg procedure

More than 80 years ago, Krukenberg described a technique that converts a forearm stump into a pincer that is motorized by the pronator teres. Indications for this procedure have been debated; however, they generally include bilateral upper-extremity amputations, especially in those who are also blind. The procedure also has been used successfully in persons in developing countries who lack the means to obtain expensive prostheses.

This procedure preserves proprioception and stereognosis in the functional stump to allow for effective maneuvering in the dark. It is important to note that this procedure is not recommended as a primary procedure at the time of an amputation, and the procedure must be preceded with appropriate counseling because of cosmetic concerns. Conversely, once this procedure is performed, it does not preclude the use of a functional prosthesis. Therefore, the patient is afforded the option to use either functional strategy.

For this surgical option to be considered, the ulna and radius must extend distal to the majority of the pronator teres (the motor for pinching), and an elbow flexion contracture of less than 70° is required. Swanson et al, ^[28]  Nathan et al, ^[29]  and Garst ^[30]  described several modifications of Krukenberg's original surgical technique, focusing on conservative debulking and flap closure without the need for skin grafts.

The success of this procedure depends directly on the strength of the pronator teres, the sensibility of the skin surrounding both ulna and radius, elbow mobility, and mobility of the ulna and radius at the proximal radioulnar joint (PRUJ). Individual patient expectations and motivations, although more difficult to assess, probably play a major role in outcomes as well.

A soft compressive dressing is applied to the stump. The elastic bandage is applied more tightly distally than proximally to prevent stump edema. Rigid dressings and casts, such as those often used on lower-extremity stumps, are unnecessary in the upper extremity. If a drain is used, it is removed within 24-48 hours. If no contraindications exist for anticoagulation, low-dose subcutaneous heparin (5000 U q12hr) may be administered for deep venous thrombosis (DVT) prophylaxis, especially in patients at high risk. Immediate active range of motion of the shoulder and elbow (and wrist, if applicable) is implemented to prevent joint contractures.

Hematoma

Meticulous hemostasis and, if necessary, use of a drain can minimize the occurrence of postoperative hematomas. If allowed to accumulate, hematomas may provide an attractive medium for bacteria and possibly inhibit proper wound healing. Aspiration of the hematoma under sterile conditions is recommended, followed by a compressive dressing to reduce the recurrence rate. If hematoma accumulation persists, surgical exploration, rather than repeat aspirations, may be required to achieve adequate hemostasis.

Infection

Upper-extremity amputation stump infections are more likely to occur in patients who are immunocompromised, those who have previous vascular diseases, and patients who have grossly contaminated or infected wounds. Like any postoperative infection, superficial infections may be treated with proper wound care, antibiotics, and close observation. However, deep infections with or without an abscess may necessitate further surgical debridement and possibly revision of the amputation to a more proximal level.

A study by Ali et al suggested that delaying formal closure of the amputation for at least 5 days after the procedure can lower the postoperative infection rate. ^[31]

Necrosis

As with infection, superficial areas of skin necrosis may be treated conservatively because healing usually continues under the eschar. However, larger areas of necrosis indicate insufficient vascularization and demand wedge resection or possibly revision of the amputation to a more proximal level.

Contracture

Joint contractures usually are prevented by immediate postoperative active motion. If contractures develop, more aggressive physical therapy may be required, including strengthening the opposing musculature and gentle passive motion. Caution is advised around the elbow because overly forceful passive motion may incite heterotopic ossification.

Neuroma

Regardless of the technique employed to divide peripheral nerves, a neuroma always forms. If the neuroma is compressed against a rigid surface (bone or prosthetic wall) or if the neuroma experiences traction as it remains trapped in the healing scar, then pain is inevitably produced. Efforts to prevent compression or entrapment of neuromas have been described previously.

When a neuroma becomes symptomatic, it usually can be treated by altering the prosthetic socket to avoid pressure or traction on the lesion. When all nonoperative efforts to relieve the pain have failed, the neuroma may be excised successfully and the nerve divided at a more proximal level. In children, neuromas seldom call for surgical intervention.

Phantom sensation

This poorly understood phenomenon is defined as the patient's awareness of the amputated portion of the limb. ^{[32, 33, 34, 35]} The sensations may be disturbing but are rarely painful. Many modalities have been used in an attempt to prevent and minimize the intensity of these sensations. Amitriptyline and gabapentin can be considered first-line agents in the pharmacologic treatment of phantom sensations. Other, less commonly used agents are capsaicin, calcitonin, ^[36] mexiletine, carbamazepine, propranolol, metoprolol, and clonazepam. Many of these drugs have only case report usage and require further investigation.

Promising therapies in the upper extremity have included immediate or early prosthetic fitting. Substantial evidence also exists to support perioperative epidural anesthesia and postoperative intraneural anesthesia applied to transected nerves in amputated lower extremities, which may be effective in the upper extremity. However, such data in the upper extremity are not yet available. Phantom sensations are uncommon in children.

Deep venous thrombosis

Patients who have undergone amputation may be at increased risk for DVT. Although persons with upper-extremity amputations are able to mobilize following their surgery more easily than those with lower-extremity amputations and consequently present with fewer occurrences of DVT, their underlying medical conditions often predispose them to this complication.

Multiple risk factors for DVT, such as age, immobility to some degree, and the amputation itself that involves the ligation of vessels, exist in this population. Furthermore, 25% of patients undergoing vascular surgery have an identifiable hypercoagulable state. Unfortunately, most data pertain to individuals with lower-extremity amputations; therefore, it is difficult to make conclusions about the risks for persons with upper-extremity amputations.

Nevertheless, it would be advisable to administer low-dose subcutaneous heparin to patients while they are in the hospital after amputations, provided that they have no contraindications for anticoagulation. Low-molecular-weight heparins (LMWHs), such as enoxaparin and dalteparin, may increase the risk of bleeding and hematoma formation and may induce more anticoagulation than is necessary in the upper extremity. However, more research is required to assess the risks and benefits of this therapy.

Terminal overgrowth

Although many amputation complications, such as neuroma or phantom pain, are less problematic in children, terminal overgrowth occurs to some degree in all children with amputations; up to 12% of children with amputations require one or more stump revisions.

Forearm amputations are less problematic in the upper extremity than above-elbow amputations are, given that the humerus most commonly is associated with this phenomenon. The radius is the second most likely bone in the upper extremity to demonstrate terminal overgrowth. In individuals with forearm amputations, the most common overgrowth occurs as a pincerlike contour of the radius in relation to the ulna. This deformity occasionally causes the proximal radial epiphysis to tilt. Less commonly, the ulna may overgrow with subcutaneous projection.

The cause of overgrowth is still controversial. Contracture of the soft tissue envelope and disproportionate growth of bone from the proximal physis to the soft tissue have been implicated. However, the current hypothesis, according to Speer, ^[37] is that the established mechanisms of normal fracture healing and local wound healing malfunction and accelerate.

Pediatric patients with disarticulations do not demonstrate terminal overgrowth, because the articular cartilage acts as a natural barrier for this activity. For this reason, as well as to preserve the distal physis and maintain normal stump growth, disarticulations are the treatment of choice in children whenever possible. Most attempts to prevent terminal overgrowth, including capping the bony ends with Silastic or allograft and autograft tissues, have failed. The only treatment for symptomatic terminal overgrowth is revision of the amputation.

Bony spur

Bony spurs occasionally form at the ends of the bones, especially in children. Unlike terminal overgrowth, bony spurs almost never require resection and are well tolerated with prosthetic socket modifications.