CHAPTER 84 THUMB RECONSTRUCTION
WEE-LEON LAM AND FU-CHAN WEI
A functional thumb is critical to overall hand prehension. Efforts to reconstruct the thumb have spanned the history of hand surgery, and thumb reconstruction was one of the first microsurgical free tissue transfers to be attempted in humans.1 A functional thumb must meet the minimum requirements for pulp-to-pulp or tripod pinch to enable fine object manipulation and also hand-digital cylinder grasp for larger objects. Successful thumb reconstruction must therefore result in a construct that has (1) sufficient length to oppose the remaining fingers; (2) mobility of all joints involved in opposition and flexion; (3) adequate sensation for pulp pinch; and finally (4) an acceptable aesthetic appearance.2 Thumb amputation represents one of the few indications where every effort is made for replantation. When replantations fail for whatever reasons, numerous techniques have been described to replace the amputated thumb ranging from simple osteoplastic techniques to complex microsurgical procedures. With increased experience, toe-to-thumb transplantation has become the superior method of reconstruction to achieve all the functional and aesthetic requirements of a thumb in a single-stage procedure. This chapter details the different techniques and their indications and limitations for the wide variety of thumb injuries encountered in clinical practice.
ASSESSMENT AND EVALUATION OF INJURY
A comprehensive history and detailed examination form the basis of decision-making. Salient points in the history include the hand dominance, nature and timing of injury, occupation, hobbies, and patient’s expectations of the final outcome. Lengthy microsurgical procedures may produce a superior functional and aesthetic outcome but are not suitable in every patient. On the other hand, patients must understand the limitations of conventional (non-microsurgical) methods.
A complete hand examination should reveal the important findings of soft tissue deficits, bone or joint injuries, nail bed or tendon lacerations (including zones), neurological damage, and condition of the remaining fingers. Standard investigations should include lateral and anteroposterior radiographs with additional special views for certain injuries, for example, carpometacarpophalangeal (CMC) joint or carpal injuries. Computerized tomography or magnetic resonance imaging is useful to detect certain wrist or ligamentous injuries.
Special considerations for thumb reconstruction from the history, examination, and investigations therefore include:
1. Conditions for opposition:
Thumb opposition depends on an intact basal joint and functional thenar muscles. If these are damaged or deficient, an intact range of movement at the interphalangeal joint may compensate to a certain degree but hand function is impaired. In a thumb with a badly damaged CMC joint, the creation of an immobile post facilitates some degree of functional restoration but the thumb lacks finesse of function. Additional procedures may include addressing any concomitant narrowing or contracture of the first web space to achieve optimum opposition.
2. Condition of the remaining fingers:
An opposable thumb is dependent on its finger counterparts. In the severely mutilated hand, careful positioning of any new thumb or fingers remains critical to ensure adequate pulp-to-pulp or pulp-to-side contact and sufficient grip strength (see below, types IIC and IID metacarpal hand reconstruction).
3. Patient’s motivation and expectations:
For optimum functional recovery, the patients’ cooperation with rehabilitation must follow closely with the reconstructive efforts. It is imperative to obtain this commitment from the patients before subjecting them to any form of surgery, especially if embarking on a lengthy reconstructive procedure. For microsurgical methods, concerns regarding donor foot morbidity must be addressed because this may influence the types of toe flap used for reconstruction.
Thumb deficits can be classified into two broad strategies: defects or amputations. Partial thumb losses result in a variety of missing components and the main goal is to resurface or replace components. Amputations result in complete thumb loss and the goal is to completely restore the length of missing thumb (see Table 84.1). Considerable overlaps exist; for example, an oblique amputation is analogous to a pulp defect. Local options are only suitable for resurfacing of thumb defects, whereas microsurgical options can be used both for resurfacing and replacement of missing components, as well as for amputations (see Table 84.1). For example, the free glabrous skin flap is an excellent option for resurfacing volar pulp defects.
Reconstruction of Thumb Defects
Thumb injuries result in a number of damaged components, including bone, joints, neurovascular bundles, tendons, and soft tissue. Skeletal injuries without missing bony components are managed by accurate anatomic reduction and early mobilization to prevent joint stiffness. In severely damaged joints, arthrodesis remains a valid option for the thumb interphalangeal and even the metacarpophalangeal joint, provided the CMC joint remains mobile. In general, mobility of two out of three joints (including the carpometacarpal joint) should be preserved to achieve effective opposition. Any bony losses should be replaced with bone grafts to maintain length and stability of the thumb. Nerve defects are replaced with nerve grafts whenever possible to restore sensation to the thumb tip. Excellent sources of nerve grafts are the distal posterior interosseous nerve or the medial cutaneous nerve of forearm. For more extensive composite losses including the loss of multiple components, microsurgical reconstructions with composite flaps can be excellent choices to achieve primary, total reconstruction in a single-stage procedure.
More commonly, thumb defects present with skin or soft tissue losses that require resurfacing. A useful classification for coverage of thumb defects is to separately consider the requirements of dorsal and volar defects. Volar pulp defects require pain-free and glabrous (non-slippery) skin with good sensibility, whereas dorsal defects do not require sensate skin to the same degree but have greater cosmetic considerations due to the aesthetic nature of the nail on the thumb tip. Small, superficial volar defects less than 1 cm2 in surface area possess an astonishing ability for healing by secondary intention. The use of wet dressings and antimicrobial cream will promote enough epithelialization within 2 to 3 weeks to cover the raw surfaces. However, deeper defects, or those associated with exposure of the bone, joint, and tendons, especially on the volar aspect, require coverage with local or even microsurgical reconstruction with glabrous skin flaps to achieve optimum results. Local flaps in thumb reconstruction can be homodigital or heterodigital and should ideally meet all the requirements for sensibility and good contour match with minimal donor-site morbidity.
Homodigital Local Flaps. For partial volar pulp defects not crossing the interphalangeal joint, V-Y advancement flaps of the Tranquilli-Leali or Atasoy design are ideal local options to restore pulp and preserve length.3 For defects up to and involving the entire pulp, the Moberg advancement flap can be used effectively, ideally by the incorporation of a V-Y advancement flap proximally to avoid interphalangeal joint flexion as described by O’Brien.4 Based on both neurovascular bundles, this island flap is uniquely suited for thumb reconstruction due to the robust independent dorsal blood supply to the thumb tip. For resurfacing finger tip injuries, this flap design should be used with extreme caution because the lack of independent dorsal blood supply can lead to higher risk of distal flap loss.5The main consideration in dorsal defects is the nail complex, which should be reconstructed whenever possible. More proximal defects not involving the nail can be reconstructed using standard homodigital advancement flaps of the hatchet design, by taking advantage of the skin laxity on the dorsum of the hand. For both volar and dorsal defects, flaps raised from the region of the first web space, either of the dorsal ulnar or radial designs, are useful alternatives although these flaps are not innervated.6 The anatomical basis of these flaps is derived from the constant communication between the dorsal arteries and proper digital arteries that allow the flaps to be raised with a reliable reverse flow through these distal arcades.
Heterodigital Local Flaps. Heterodigital flaps are useful options when the rest of the thumb is injured or where local tissues are inadequate for homodigital options. Choices include the Littler neurovascular flap, first dorsal metacarpal artery flap, innervated lateral middle phalangeal finger flap,7 or the heterodigital arterialized flap from the middle finger.8 Crossed-finger flaps are available as a backup option but should always be used as a last resort as they restrict thumb and donor finger movements and interfere with rehabilitation.
Distant or Regional Flaps. For larger or circumferential defects, regional or distant flaps such as the posterior interosseous flap or reversed radial forearm flap are useful for resurfacing. However, the resultant donor-site morbidity has become less acceptable in today’s practice. The pedicled groin flap remains a reasonable option for the coverage of defects in the dorsum of the hand extending to the thumb, as it avoids further upper limb donor morbidity, offers plenty of redundant skin, and leaves an almost negligible donor scar (Figure 84.1). Despite the disadvantage of having the injured hand in a dependent position, it is also a useful option for the interim coverage of larger thumb defects prior to a toe-to-thumb transplantation without the need to sacrifice any local tissues or recipient vessels.
Microsurgical Free Tissue Transfer. The advent of microsurgery and toe-to-hand transplantation ushered in the possibility of composite tissue replacement as an elegant, one-stage reconstruction without causing further donor morbidity to the rest of the hand. Different flaps have been described, including vascularized osteocutaneous flaps from the groin or vascularized tendon-cutaneous flaps based on the dorsalis pedis region.9 Although these flaps greatly increase the versatility of reconstruction for compound hand and thumb defects, the donor morbidity should be carefully considered and explained to the patient. For resurfacing of volar thumb pulp defects, the free toe pulp or hemi-pulp remains an excellent option in providing a sensate, stable pulp with glabrous skin.
Free Toe Pulp-Flap Design and Elevation. The fibula side of the great toe is selected more often as a donor site than the second toe for the following advantages: it has better two-point discrimination (approximately 7 to 18 mm); more tissue is available; and the possibility for direct closure (avoiding a skin graft) is greater.10 Preoperatively, the skin incisions are outlined according to a template of the defect and extended proximally over the course of the proper digital artery to the first web space. This is where the dissection begins to identify whether the dominant arterial pedicle is the first dorsal or plantar metatarsal arteries (Figure 84.2).11 Once the pedicles (arterial and venous) are identified, efforts are made to meticulously strip off the adventitia to facilitate their tunneling to the recipient vessels during flap inset. The proper digital nerve on the fibula side or terminal branches of the deep peroneal nerve can be included in the flap for subsequent reinnervation with either the proper digital or dorsal digital nerves of the thumb.
FIGURE 84.1. The pedicled groin flap for resurfacing first web space and mutilated hand defects.
FIGURE 84.2. Free toe pulp flap for thumb reconstruction. A. Gangrenous thumb pulp. B. Glabrous skin flap from the fibula side of the great toe. C. Reconstructed thumb pulp. D. Donor site.
RECONSTRUCTION OF THUMB AMPUTATIONS
Amputation of the thumb represents one of the few instances when there is an almost absolute indication for replantation. In the hand with multiple amputations, including the thumb, sacrificing a finger for the thumb as a heterotopic replantation may be a suitable option.12 When replantation fails, various methods (non-microsurgical or microsurgical) are considered to restore the four objectives of length, sensibility, mobility, and aesthetic appearance necessary for a successful thumb reconstruction.
Microsurgical Versus Non-Microsurgical: Which Is Better?
Conventional (non-microsurgical) methods fulfill some but not all of the above four objectives (see Table 84.2). With the advent of microsurgery, toe-to-hand transplantation is an ideal option that facilitates a custom-made, “like-for-like” and single-stage replacement of the amputated thumb at different levels. The foot is a warehouse of flaps in providing tissues of various configurations to “best fit” the missing components. Despite these advantages, one must consider the available expertise and resources for microsurgery, as well as the fitness of patient to tolerate a long microsurgical procedure. Table 84.2 shows the different conventional methods and their comparisons with microsurgical methods with regard to outcomes and also donor morbidity.
Table 84.3 summarizes the different conventional (non-microsurgical) methods recommended for amputations at different levels. The interphalangeal joint is considered the minimum functional level of the thumb and therefore reconstruction of thumb amputations distal to the interphalangeal joint may be less necessary in a patient who has adapted well to a shortened thumb. For more proximal amputations, any accompanying damage to the thenar musculature or the CMC joint may require additional reconstruction with procedures such as opponensplasty or joint reconstruction.
Specific Surgical Techniques
Osteoplastic Thumb Reconstruction. The osteoplastic technique combines an iliac bone graft and pedicled flap from the groin region for restoration of length and bulk. An additional neurovascular sensory flap can be transferred from the ulnar border of the middle finger to resurface the ulnar border of the new thumb for restoration of sensibility. This reconstruction is indicated for amputations distal to the metacarpophalangeal joint for total thumb reconstruction. It can also be used as a first-stage lengthening procedure in conjunction with a second-stage toe-to-thumb transplantation for proximal amputations.13
Pollicization. Pollicization refers to the reconstruction of a thumb by finger substitution. The adjacent finger, usually the index, is transferred as an island on its neurovascular bundle and repositioned in the thumb position. The procedure consists of four key elements:
1. Incisions: Palmar and dorsal incisions are usually required and take into account reconstruction of the new web space.
2. Dissection of the neurovascular bundle: This has to be proximal enough into the palm to allow adequate movement of the index finger into its new position.
3. Re-positioning: This involves three main maneuvers: resection of the finger metacarpal to its shortened length as the new thumb, rotation through 160° into its new position, and finally abduction in order to oppose the remaining fingers effectively.
4. Muscle stabilization: Variations exist among different described techniques but there is usually a predictable sequence as follows (Figure 84.3):
• Extensor indicis—extensor pollicis longus
• Extensor digitorum communis—abductor pollicis longus
• First palmar interosseous—adductor pollicis
• First dorsal interosseous—abductor pollicis.
Pollicization remains an excellent option in congenital thumb hypoplasia or aplasia, where the absence or deficiency of a radial artery precludes microsurgical toe transplantation. In adults, pollicization is a suitable option in proximal defects with a damaged CMC joint. The resected index metacarpal head can be used to replace the trapezium by positioning it on the scaphoid to reconstruct a basal joint that acts in conjunction with the newly reconstructed muscles of opposition. The disadvantages of pollicization in adults include the creation of a three-finger hand, an unnatural looking thumb, and difficulties in retraining for an adult patient.14
The first reported toe-to-thumb transplantation was by Nicolandi in 1891 using a pedicled technique.10 The logic of using toes to replace missing thumbs was not lost and with the advent of microsurgery, toe-to-thumb transplantation took its place as one of the first free tissue transfers attempted.1 To date, toe-to-thumb transplantation has become the undisputed gold standard for thumb reconstruction. Although debates continue over the choices of toe flaps, and whether the greater or lesser toe should be sacrificed for reconstruction, there are certain guidelines that have proved useful in obtaining optimal results for the hand and also for reducing donor morbidity:
1. During selection of toes, it is helpful to remember that the great toe and its variants always provide a better functional and aesthetic outcome than the use of the lesser toes
2. During osteotomy of the great toe, at least 1 cm of the proximal phalanx should be preserved in the foot to ensure better push-off and preservation of foot appearance (this consideration is not necessary when sacrificing a lesser toe). In more proximal amputations, lengthening of the existing thumb metacarpal by additional methods such as preliminary distraction lengthening or interpositional bone grafting can be employed to avoid sacrificing the metatarsophalangeal joint of the great toe
3. For donor foot selection, the left great toe should always be selected due to dominance of the right foot for many important activities, including driving and sports
4. The adequacy of soft tissue and skin and the condition of the first web space are always assessed during the initial injury. If necessary, an interim pedicled groin flap can be used to provide soft tissues coverage, temporary resurfacing, as well as web space reconstruction.
FIGURE 84.3. Pollicization of the second ray. A. Preoperative appearance. B. Postoperative appearance. C. Opposition between the new thumb and the little finger.
With these principles as a foundation, the indications and refinements for the different flaps used in toe-to-thumb transplantations are further summarized in Table 84.4.
Specific Surgical Techniques
Trimmed Great Toe. The trimmed great toe is a variant of the great toe flap that involves reduction of the diameter of the great toe to make it more thumb-like. Patients are warned that there is a resultant loss of 10° to 15° of motion in the interphalangeal joint.10 Preoperatively, the circumference of the normal contralateral thumb is measured at three points: (1) nail eponychium, (2) widest point (the interphalangeal joint), and (3) middle of the proximal phalanx. These measurements are then transposed to the toe for planned excision of these size discrepancies from the medial aspect of the great toe. Elevation begins in the first web space to identify the dominant blood supply followed by a retrograde dissection to free the first dorsal metatarsal artery (80% of cases) or the first plantar metatarsal artery (20% of cases).11 During dissection, the periosteum, medial collateral ligament, and joint capsule are lifted off as a “peri-joint” flap to access the skeletal structure and facilitate a longitudinal osteotomy using an oscillating saw. About 4 to 6 mm of the medial joint prominence along with 2 to 4 mm width of the phalanges is typically removed. Following trimming, it is important to re-drape and repair the peri-joint flap in a tight fashion to prevent joint instability10 (Figure 84.4).
Wraparound Great Toe Flap. Originally described by Morrison and associates,15 the great toe wraparound flap consists of harvesting the nail and soft tissue envelope of the great toe to “wraparound” a nonvascularized iliac crest bone graft. It follows the logic of the trimmed great toe to produce a more aesthetic thumb while preserving the skeletal structure of the donor great toe and thus reducing the donor morbidity of the foot. A more recent modification is our recommendation to include a portion of the distal phalanx for nail support, to avoid swiveling of the wraparound flap and also to decrease the rate of fracture and bone absorption.10 Flap harvest is similar to the trimmed great toe technique, with preoperative markings made but transposed to the lateral (fibula) aspect of the great toe. In further contrast to the trimmed great toe, this size discrepancy is then preserved for donor-site closure by draping it over the remnant stump rather than removing it. An additional cross-toe flap from the second toe is usually required for donor closure. If cross-toe flaps are to be avoided, the skeleton can be shortened down to the proximal phalanx with removal of the interphalangeal joint.
The Metacarpal Hand
The term “metacarpal hand” refers to a devastating hand injury with amputations of all fingers at the level of the metacarpophalangeal joint, with or without injury of the thumb and resulting in a severe loss of hand prehension. If the thumb has been amputated, thumb reconstruction in these patients is especially challenging as concomitant reconstruction of the fingers has to be considered to restore global function of the hand. A classification system for the metacarpal hand10 (Table 84.5) provides several useful reconstructive strategies for various configurations of injuries. Type I refers to injuries with four-finger amputations without thumb or only distal thumb involvement (no reconstruction necessary), whereas type II injuries refer to four-finger proximal amputations with thumb amputations proximal to the interphalangeal joint and further subdivided into four types depending on the severity of thumb injury. If the thenar muscle is intact or possesses adequate function as in types IIA and IIB injury, simultaneous reconstruction of the thumb and two adjacent fingers is recommended to obtain a tripod pinch (Figure 84.5). However, if the thenar muscle (IIC) or if the CMC joint (IID) is damaged, then the thumb reconstruction should be carried out as a staged procedure and delayed until after the finger reconstruction has been completed, with the position of the new thumb first predetermined with the aid of a prosthetic thumb. Once the optimum position has been confirmed, a second-stage thumb reconstruction can be performed, with additional opponensplasty procedures carried out at the time, if necessary.13
FIGURE 84.4. Trimmed great toe to thumb transplantation. A. Traumatic amputation of the thumb at the proximal phalanx. B. Designed trimmed great toe. C. Harvested trimmed great toe. D and E. Appearance and function of the transplanted trimmed great toe (new thumb) and the contralateral thumb.
FIGURE 84.5. Tripod pinch following reconstruction of the thumb and two adjacent fingers. A. Type II metacarpal hand. B. Function and appearance of a reconstructed metacarpal hand after a second toe-to-thumb transplantation and a combined second and third toe to middle and ring finger transplantation. C. Donor sites appearance.
FIGURE 84.6. Reconstruction of useful prehension in bilateral metacarpal hands using toe-to-hand transplantation. A. Preoperative appearance. B. Postoperative appearance.
Although rarer, occasional reconstructions are necessary for bilateral metacarpal hand injuries requiring a careful balance of the injury severity (type I or II), the patient’s needs, and the acceptable level of donor morbidity.10 In the most severe cases (bilateral type II), up to but not exceeding five donor toes can be used to achieve a functional level of prehension. In general, the left great toe can be harvested for dominant thumb reconstruction with an accompanying combined two-toe reconstruction from the opposite foot for achieving a tripod pinch, whereas a lesser toe can be transplanted to reconstruct the nondominant thumb for pulp-to-pulp pinch (Figure 84.6).
Thumb reconstruction is an extremely rewarding aspect of hand surgery, restoring vital prehensions to the hand and greatly improving hand function. With increased experience and sophistication in reconstructive surgery, there is a move toward primary, one-stage, and total reconstruction to meet patients’ expectations for optimal function and superior aesthetic outcome. Future advances in thumb reconstruction are likely to focus on areas such as innovations in microsurgical toe-flap designs, composite tissue allotransplantation for partial hand defects, and also methods of increasing cortical adaptability for a superior sensory recovery.
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