Thumb reconstruction: Microsurgical techniques

Decision-making for the thumb

The functional thumb depends on adequate length, sensibility, stability, and the function of the thenar muscle group to perform opposition. Microvascular toe-to-thumb transplantations can achieve the first three objectives in a single stage with a superior aesthetic result; however, opposition depends on the function of the thenar muscles and could benefit from additional procedures when compromised. The function of the thumb decreases by 50% once the amputation level is proximal to the interphalangeal joint and reaches 100% once it crosses the metacarpophalangeal joint. Amputations distal to the interphalangeal joint are generally well tolerated but, in certain patients, the additional length, stability, and sensibility from a transplanted distal toe transfer is desired and can be proposed as an option.

Various classifications and reconstructive algorithms exist for thumb defects, although the underlying principles relate mainly to the types of tissue and the length of thumb missing. Toe-to-thumb transplantations can be successfully performed with various modifications of the great toe, including whole great toe, trimmed great toe, great-toe wraparound flaps, pulp flaps, and the second toe. The decision to use which toe or its variation should be individualized not only to the thumb defect and the patient's needs, but also with careful consideration of the donor site. In general, thumb reconstruction using the great toe or its variants provides better functional outcomes in terms of tripod pinch, side-to-side and pulp-to-side pinch, as well as appearance than the lesser toes do, although augmentation procedures for second toes to improve bulk have been described. If the great toe is used, at least 1 cm of the proximal phalanx should be preserved in the foot to ensure better push-off and preservation of foot appearance; the great toe is therefore an ideal option for thumb amputation levels distal to the mid-metacarpal shaft. In a more proximal amputation, additional challenges are inadequate bone stump length and thenar muscle function. The first can be overcome by a transmetatarsal transfer of the second toe or preliminary distraction lengthening of the existing metacarpal ray or interpositional bone grafting between the transferred toe and the metacarpal without sacrificing the base of proximal phalanx or the metatarsophalangeal joint of the great toe. The destruction of the thenar musculature and the subsequent loss of opposition, however, may necessitate pronation osteosynthesis, but is better corrected by primary opposition transfer in the authors' experience.

Decision-making for fingers

Classification of finger defects is similar to the thumb and pertains to the type of tissue and length of finger missing, with the additional consideration of which finger is involved and whether there are single or multiple amputations. The definition of proximal or distal amputations is determined by its relation to the insertion of the flexor digitorum superficialis tendon. Toe transplantation to more distal finger amputations can be achieved by a wide variety of options, including the use of vascularized nail grafts, pulp flaps, wraparound flaps, and partial second toes, depending on what tissues are missing. These operations are rewarding due to the restoration of high-density pulp sensation, fine pinch, and cosmetic appearance of the nail. A partial second-toe flap which includes the distal interphalangeal joint or both the proximal and distal interphalangeal joints is indicated in amputations distal to the flexor digitorum superficialis insertion. In contrast, a whole second-toe flap is indicated in carefully selected patients with more proximal amputations; the ideal level, however, is distal to the middle of the proximal phalanx as reconstructions for more proximal amputations usually result in a slightly shorter finger.

Decision-making for patients with multiple finger amputations is largely guided by the specific occupational and cosmetic needs of the patient. In general, two adjacent fingers should be reconstructed wherever possible to allow a stable tripod pinch or hook grip. Preferential reconstruction of the radial two fingers should be recommended for patients who require fine pinch and the ulnar two digits for manual workers who require a strong grip. However, multiple finger amputation could be too complicated to be addressed with toe transfer alone, and additional procedures such as lengthening and ray amputation could be necessary, as well.

Decision-making for the metacarpal hand

The term “metacarpal hand” refers to a hand injury with multiple finger amputations at the level of the metacarpophalangeal (MCP) joint, or immediately proximal or distal to it. Delitala was perhaps the first to coin this term and, since then, various classification systems have been proposed, with varying levels of clinical usefulness. A classification system based on reconstructive options and different stages of injury has proved useful in our experience ( Tables 14.1 & 14.2 ). This takes into account the level of finger amputations and thumb involvement, and provides guidelines for the reconstructive technique as well as prediction of the functional outcome after reconstruction. Type I refers to four-finger proximal amputations without the thumb or only distal-thumb involvement (no thumb reconstruction necessary). In type IA where the amputation level is distal to the MCP joint, the focus is on the selection of two separate toes or combined second–third-, or third–fourth-toe transplantations depending on the presence of webspace ( Fig. 14.3 ). To ensure that the different digits curve around an object more evenly in grasp prehension, the length of the remaining amputation stumps should not be longer than that of a normal little finger when considering a combined second- and third-toe transfer. For type IB, where the amputation level is through the joints with intact articular surfaces, combined second and third toes are harvested as composite joint transfers. For type (IC) where the amputation level is proximal to the MCP joints, combined second and third toes as transmetatarsal transfers is indicated. Reconstruction of two adjacent fingers allows for a stable tripod pinch, although reconstruction of all four fingers is possible in certain selected patients with acceptable donor site morbidity ( Fig. 14.4 ).

Type II injuries refer similarly to four-finger proximal amputations but with various levels of thumb involvement proximal to the base of the proximal phalanx. The reconstruction of fingers with toe transplantations follows a similar decision-making process as for type I defects, but reconstruction of the thumb is determined by the presence or absence of a functional thenar musculature. If the thenar muscles are intact or possess adequate function (types IIA and IIB), a one-stage procedure to reconstruct the thumb and two adjacent fingers is recommended. If the thenar muscles are missing or have inadequate function (IIC), the thumb reconstruction should follow finger reconstructions in a second stage and only after the thumb position is determined by the aid of prosthesis while the fingers assume their final positions ( Fig. 14.5 ). Either pronation osteosynthesis or an opposition transfer can be performed to provide better pinch.

Decision-making in bilateral metacarpal hand injuries requires a careful balance of the severity of injury (type I or II), patient's needs, and donor site morbidity. Other options should also be discussed with the patient. Type II injuries are much more difficult than type I, requiring up to but not exceeding five toes to achieve a functional level of prehension. In general, the use of a great toe, usually from the left foot, is sacrificed for dominant thumb reconstruction together with a combined two-toe reconstruction from the opposite foot to achieve a tripod pinch. In the non-dominant hand, single-digit pulp-to-pulp pinch is considered adequate with the use of a lesser toe for thumb reconstruction. Although the option of sacrificing both great toes or more lesser toes for hand reconstruction may seem attractive, we have found that the donor morbidity reaches a level that is incompatible with activities of daily living. In instances where multiple toes are needed, the patient needs to participate fully in the decision-making with regard to the foot morbidity, especially in certain populations where patients are far less tolerant of sacrificing their toes to reconstruct their hands ( Fig. 14.6 ).

For the metacarpal hand, the same strategies and tactics described above apply. In the type I metacarpal hand (thumb and one finger preserved beyond the functional length), multiple-toe transplantation may be warranted and may yield significant correction of hand function. Toe transfer would add more fingers, improving finger length, form and function, and the hand cascade. The reconstructed fingers do not have to be adjacent to each other.

In type II metacarpal hand (one or two fingers are preserved beyond functional length), the timing of thumb reconstruction depends on the status of the basal joint and thenar muscles. When these are adequate, simultaneous toe transfer for the thumb and the fingers can be performed. Otherwise, finger reconstruction is performed first. In type II, the goal of toe transfer is to reconstruct both the thumb and adjacent two fingers if the hand lacks one or two radial fingers. If a radial finger is present, improved grip and overall hand cascade may still be improved by ulnar and central placement of additional toes.