The thumb is responsible for 40% to 50% of hand function.
The two most important goals of thumb reconstruction are restoration of sensation and opposition.
Thumb reconstruction is approached according to the level of loss.
Preservation of 2 cm of the proximal phalanx is the minimum effective length of the thumb; amputations distal to that level do not require restoration of functional length.
Efforts to reconstruct amputations with adequate length but poor soft tissue coverage concentrate on providing well-padded, durable skin, skeletal stability, and adequate sensibility.
Replantation should be attempted in all cases of thumb amputation proximal to the distal third of the proximal phalanx of the thumb.
The surgical solutions for middle-third amputations fall into one of two categories, used alone or in combination: phalangealization and metacarpal lengthening.
Reconstructive options for proximal-third amputations are osteoplastic reconstruction, toe-to-hand transfer, and pollicization of the index finger or intact adjacent digit.
The traditional approach for loss of thumb and all digits has been to perform phalangealizations of the thumb and small-finger metacarpals; toe-to-hand transfers can also restore hand function after loss of the thumb and all digits.
Careful consideration of the patient’s functional needs is necessary before choosing surgical reconstruction at each level described.
Loss of the thumb can result in functional impairment and an unacceptable appearance to the hand. The thumb is responsible for 40% to 50% of hand function. The following three pinch grips, which are enabled by the function of the thumb, differentiate the human hand from those of other hominids: pad-to-side, three-jaw chuck, and five-jaw cradle/chuck pinch. Kleinman and Strickland realized the great importance of the thumb when they proclaimed “that reconstruction of an opposable thumb should be attempted whenever possible by whatever technical pathways are available to the surgeon.”
Historically, efforts to reconstruct the thumb have focused on phalangealization, osteoplastic reconstruction, and pollicization. Microsurgical techniques have evolved sufficiently to make toe transfer, osteocutaneous composite free or pedicled flaps, and neurovascular pedicle flaps viable options for adding length and preserving sensation. The goals of thumb reconstruction are to recreate thumb function by restoring these important characteristics of the thumb: length; a padded, sensate tip; stability; position; and mobility. Of these goals, the two most important are restoration of sensation and opposition. Furthermore, successful restoration of opposition depends on reestablishing length and carpometacarpal (CMC) joint motion.
Thumb reconstruction begins by stratifying the injury by level of loss ( Fig. 97-1 ). There are three categories of thumb loss: (1) Adequate length, poor soft tissue coverage (distal third of proximal phalanx to thumb tip = distal-third amputation). (2) Subtotal amputation with questionable length (distal third of metacarpal to midproximal phalanx = middle-third amputation). (3) Total amputation with or without CMC joint preservation (amputation proximal to the distal third of the metacarpal = proximal-third amputation).
Thumb position, mobility, and stability are also important considerations for thumb reconstruction. The thumb must be placed in position to contact the other digits. An adduction deformity caused by scar tissue in the first webspace prevents this. Dorsal rotation flaps can be useful in this situation. CMC joint motion is particularly important in allowing rotation in and out of the palm. Fusion of the metacarpophalangeal (MCP) or interphalangeal (IP) joints may be necessary to create a stable post. Adequate thenar musculature provides dynamic stability to the thumb.
Several methods of treatment are available for each level of thumb amputation. Many factors must be considered when planning reconstruction, including the patient’s age, sex, hand dominance, occupation, and presence of other fingers. The patient’s aesthetic expectations, cultural values, and donor site morbidity to both the hand and foot are also important. This chapter reviews the indications for the various procedures available for each level of amputation and provides recent advances and technical pearls for the procedures.
Partial Thumb Amputation with Adequate Length but Poor Soft Tissue Coverage
Patients have minimal functional impairment after amputations of the thumb at the level of the distal third of the proximal phalanx to the thumb tip, also known as distal-third amputations, or the “compensated amputation zone.” Reid has stated that preservation of 2 cm of the proximal phalanx is the minimum effective length of the thumb, and that amputations distal to that level do not require restoration of functional length. Efforts to reconstruct amputations at this level concentrate on providing well-padded, durable skin; skeletal stability; and adequate sensibility. Improved techniques of digital nerve repair have enabled restoration of tactile sensation. More complex procedures, such as neurovascular island pedicle flaps and innervated cross-finger flaps, have expanded the surgeon’s armamentarium when digital nerve repair is not possible.
Amputations that can be revised and closed directly should be done so, with the goal of trimming back the digital nerves proximally enough to prevent development of painful neuromas.
Transverse amputations without exposed bone can be allowed to heal by secondary intention. Studies have shown a mean two-point discrimination of 3.5 mm using this technique. Transverse or dorsal oblique amputations with exposed bone are managed by V-Y advancement flaps ( Fig. 97-2 ), or lateral triangular advancement flaps. Skin grafting does not provide durable or sensate coverage and should not be used for closure of amputations, which cannot be closed primarily. Skin grafts should really only be entertained for defects that would otherwise heal secondarily, but the patient opts for immediate coverage and to forgo dressing changes.
Larger volar soft tissue avulsions that result in defects of up to 2.5 cm of the thumb pad, may be treated with a palmar advancement flap as described by Moberg ( Fig. 97-3 ). This procedure replaces the defect with innervated skin and soft tissue. Midaxial incisions are made on the radial and ulnar sides of the thumb down to the proximal thumb crease. A volar flap that includes both neurovascular bundles is raised. The thumb IP and MCP joints are flexed to allow advancement of the flap, which is sutured to the remaining nail or distal skin edge. The IP joint may be flexed up to 45 degrees without causing a disabling long-term flexion deformity. A variant of this technique with a proximal transverse releasing incision has been described and decreases the need for IP joint flexion. The proximal defect is covered with a full-thickness skin graft.
Defects larger than 2.5 cm require regional flaps for coverage. The heterodigital cross-finger flap from the index finger is one such method that transfers tissue based on the dorsoradial side of the proximal phalanx of the index finger. Incisions are made along the three borders of the flap. A slightly oblique orientation of the incisions facilitates positioning the flap on the volar thumb surface. Special care is taken to include all subcutaneous tissue and veins with the flap and not to violate the paratenon of the extensor mechanism. The flap is sutured in place for 2 to 3 weeks. The dorsal donor defect is covered with a full-thickness skin graft ( Fig. 97-4 ).
Defects associated with digital nerve damage can result in loss of sensibility and function. Innervated cross-finger flaps and neurovascular island pedicle flaps can provide both durable coverage and adequate sensation. The radial innervated cross-finger flap involves mobilization and transfer of a branch of the radial sensory nerve, which is sutured to the ulnar digital nerve of the thumb. When more extensive coverage is required, a neurovascular pedicle flap may be considered. Foucher and Baum first described the “kite flap,” a very mobile flap from the dorsum of the index finger based on the first dorsal metacarpal artery and branches of the radial sensory nerve ( Fig. 97-5 ). This versatile flap can be used to cover volar, dorsal, or circumferential defects in the thumb in one stage. In another technique first described by Littler, an ulnar-based neurovascularly charged soft tissue paddle of skin and soft tissue from the long or ring finger is mobilized and transferred into the defect. An incision connecting the defect in the thumb to the flap facilitates passage of the flap. These methods are technically demanding, have variable results, and may result in considerable donor site morbidity. Special attention to patient needs must be considered before proceeding with these techniques. Keep in mind, that revision amputation at the distal third of the thumb can provide a very functional thumb when the injury has made reconstruction impossible.
Replantation Following Thumb Amputation
Replantation should be attempted in all cases of thumb amputation proximal to the distal third of the proximal phalanx of the thumb. Even thumbs that have poor intraoperative flow or no venous return can survive. Microsurgical techniques and the use of vein grafts have made thumb replantations more successful. Today, even difficult cases, such as crushed or avulsed thumbs, can be successfully reattached.
However, not all amputation replantation attempts have equal success rates. When failure has been analyzed by type of injury, the highest percentage of failures has occurred in broad crush and lawnmower injuries, followed by avulsions, saw injuries, and narrow crush injuries. Inadequate microsurgical training and experience can also result in a high failure rate. The two most important considerations for attempted thumb replantation are restoration of adequate length and sensibility. It has been found that if the length of the thumb is diminished, grip is affected, and if sensibility is diminished, so is the ability for useful fine-motor manipulation.
Technically, surgical replantation begins with bone fixation, followed by reattachment of the flexor pollicis longus, extensor pollicis longus, at least one digital artery, digital nerves, several digital veins, and finally skin closure. With increased experience, there has been a decrease in the incidence of vascular complications, the length of operation, and nursing time, all of which reduce cost. In the long term, medical and economic reasons speak in favor of thumb replantation as the preferred treatment for thumb amputations, particularly those proximal to the IP joint ( Fig. 97-6 ).
Subtotal Amputation (Middle-Third Amputation) with Questionable Length
Sometimes replantation is not possible or unsuccessful for middle-third thumb amputations, for instance, those that occur between the distal third of the metacarpal and the distal third of the proximal phalanx. This zone of injury has unpredictable outcomes because of the potential for unacceptable thumb length. This loss of length decreases hand span, results in difficulty with grasping large objects, and creates problems with dexterous pinch. In addition to this inadequate thumb function, this level of amputation can result in an unacceptable appearance, or insufficient length to allow fitting for a stable prosthesis. The surgical solutions fall into one of two categories, used alone or in combination: phalangealization and metacarpal lengthening.
The first method, called phalangealization, employs different techniques to deepen the first webspace. Increasing the depth of the cleft between the remaining portion of the thumb and the index finger may improve thumb function and facilitate fitting the thumb for a prosthesis. The associated risks include scar sensitivity and weakening of the thumb by release of part or all of the thumb adductor and the first dorsal interosseous muscle. The two main techniques for webspace deepening are Z -plasty and the rotational flap.
The Z -plasty technique rearranges skin flaps along the axis of a skin contracture to increase the length of the web. The surgeon can treat lesser contractures with two-flap Z -plasties and more significant webspace contractures with either four-flap Z -plasties or “walking-man” double-opposing Z -plasties ( Fig. 97-7 ).