Conventional non-microsurgical reconstruction of congenital absent digits usually involves pollicization of the index finger for children born with a hypoplastic or absent thumb (Buck-Gramcko 1971; Manske and McCarroll 1985) and nonvascularized toe phalangeal bone grafting (Entin 1959; Carroll and Green 1975; Goldberg and Watson 1982; Buck-Gramcko and Pereira 1990; Radocha et al. 1993; Cavallo et al. 2003; Jones 2004; Gohla et al. 2005; Unglaub et al. 2006) and distraction lengthening (Matev 1970; Kessler et al. 1977; Seitz and Froimson 1991; Ogino et al. 1994; Pensler et al. 1998; Hülsbergen-Krüger et al. 1998; Dhalla et al. 2001; Miyawaki et al. 2002; Matsuno et al. 2004; Seitz et al. 2010) of hypoplastic digits due to symbrachydactyly, cleft hand, or congenital constriction ring syndrome.

The first microsurgical toe transfer to reconstruct a congenital hand difference was performed by O’Brien et al. (1978) in 1977 who successfully transferred the great toe to reconstruct a hypoplastic thumb in two children. Yoshimura (Yoshimura 1980, 1984) performed 13 toe transfers in 12 children, 10 of whom had sustained traumatic amputations, but 2 had congenital differences – 1 child had an absent thumb, index, and middle fingers, and the second child had congenital constriction ring syndrome involving one finger. May et al. (1981) reported bilateral great toe-to-thumb transfers to reconstruct a 9-year-old boy with bilateral aplasia of his thumb, index, and middle fingers. After other case reports (Nyarady et al. 1983; Meals and Lesavoy 1983), several surgeons have reported larger series of microsurgical toe-to-hand transfers to reconstruct various congenital differences of the hand (Gilbert 1982, 1985; Lister 1988; Eaton and Lister 1991; Shvedovchenko 1993; Vilkki 1995; Kay and Wiberg 1996, Kay and McGuiness 1999; Kay et al. 1996; Van Holder et al. 1999; Foucher et al. 2001; Richardson et al. 2004; Jones et al. 2007; Jones and Kaplan 2013).

Microsurgical toe-to-hand transfers for reconstruction of congenital hand differences have not evolved to a similar extent as toe transfers for reconstruction after trauma and remain controversial. Firstly, surgeons may be reluctant to risk the small but potential loss of a toe transfer in a child who is already missing one or more digits in their hands. Secondly, some pediatric hand surgeons still maintain that children with unilateral absence of one of more digits adapt to their impairment as they grow or can be helped with a static or functional prosthesis. Finally, parents may be reluctant to accept a very complicated reconstructive procedure that carries a small risk of ending up with a missing great or second toe as well as more scars on the hand to show for the failed endeavor.

Rather than just showing pre- and postoperative photographs or videos or fabricating moulages, the author’s practice is to arrange for prospective parents to meet the parents of a child with a similar congenital hand difference who has previously undergone a toe transfer, so that the parents can see for themselves the potential function and appearance of the reconstructed hand, as well as speak with the parents about their concerns (Jones 2013).

Very little has been published on the specific indications for microsurgical reconstruction of congenital absent digits. Most pediatricians and even some hand surgeons do not understand which children should be considered for microsurgical reconstruction. Previous reports of toe transfers for congenital hand differences have all been based primarily on the specific embryological diagnoses, according to the classification of the International Federation of Societies for Surgery of the Hand (Swanson 1976). However, it is the authors’ contention that specific indications for toe transfers are more logically defined by the anatomy of the hand anomaly itself, a concept that is also much more easily understood by referring pediatricians and surgeons (Jones 2012). From an analysis of 235 hands in 204 children born with congenital absent digits over a 15-year period, Jones and Kaplan (Jones 2012) developed a simple documentation system, which allows hand surgeons to describe the morphological or radiographic appearance or the functional status of a child’s hand with congenital absent digits, based on which digits are missing and their level of absence. Each hand can be described by three letters R (radial), C (central), and U (ulnar) as well as five numbers. The first letter and number designate which rays are missing, and the second and third letters and numbers designate which rays are present. Consequently, an absent thumb would be designated as R1U4, a hand with a thumb but absent fingers would be designated as U4R1, and complete absence of all five digits would be designated as R5. The spectrum of radial deficiencies includes R1U4, R2U3, R3U2, and R4U1. There are 15 morphological phenotypes of congenital absent digits – the three most common phenotypes being U4R1 (thumb but absence of all four fingers corresponding to the monodactylous type III symbrachydactyly), R1U4 (absent thumb), and R5 (aplastic hand). Unlike most other classifications, this documentation system not only facilitates communication between hand surgeons but also incorporates all the previous subclassification systems that have attempted to describe congenital absent digits in radial, central, and ulnar deficiencies, symbrachydactyly, and congenital constriction ring syndrome. However, most importantly, it has allowed the development of an algorithm that predicts whether conventional or microsurgical reconstruction is indicated for each specific phenotype. Of the 15 phenotypes, only 7 phenotypes are potential indications for microsurgical reconstruction with toe-to-hand transfers: R1U4, R2U3, R3U2, R4U1, R5, U4R1, and occasionally C3R1U1. For a child missing a thumb but with four relatively normal fingers (R1U4), it is intuitive to reconstruct a thumb to oppose to these fingers, either by pollicization of the index finger or by a toe-to-thumb transfer. Similarly for a child missing all four fingers (U4R1), it is logical to reconstruct one or two fingers to allow pinch and grasp to the normal thumb, either by distraction lengthening or by toe-to-hand transfers.

There appear to be four indications for considering microsurgical reconstruction of an absent thumb (Jones 2013; Fig. 10):

There appear to be two indications for considering toe transfers to reconstruct absent fingers (Jones and Kaplan 2013; Fig. 10):

The optimal age for performing a toe transfer to reconstruct a congenital hand difference has not been defined. Generally, the earlier that a toe transfer is performed, the better the chance of cortical integration. Children with a unilateral congenital hand anomaly should probably be reconstructed at an earlier age, before the use of the contralateral normal hand dominates. However, the real limiting factor in pediatric toe transfers is the size of the donor and recipient vessels, which must be of adequate size to facilitate the microsurgical anastomoses. Gilbert (1982, 1985) and Lister (Lister 1988) have performed toe transfers in children as young as 6–12 months of age, but toe transfers have also been successful in older children between 11 and 17 years of age (Spokevicius 1997). The senior author usually performs toe transfers between 2 and 3 years of age.

After a traumatic injury to a child’s hand, there is always some blame, either attached to or accepted by one of the parents. The parental response to a child born with a congenital hand difference resembles the bereavement response. Each parent must deal with their own sense of loss, as well as the obligation to direct the treatment of their child. Listening to the child’s parents and allowing them to express their understanding of their child’s condition and their hopes and expectations for reconstruction are vitally important. Some surgeons have recommended that the parents and child meet with a clinical psychologist prior to considering a toe-to-hand transfer, and it has been documented that psychological counseling may play an integral role in decision-making in pediatric hand surgery (Bradbury et al. 1994). The parents should be prepared psychologically for the substantial amount of time and energy that will be required during the pre- and postoperative period. In addition, they must understand and accept the fact that a toe transfer can fail, leaving the child with the same deficit in the hand but also now missing a toe in the foot. If the parents and/or child cannot accept the time commitment and the potential risk of failure, this surgery should not be considered.

Usually with congenital hand differences, the child will have been examined by a pediatrician for other congenital anomalies and possibly even by a geneticist to exclude any syndrome. A detailed examination of the involved upper extremity should be performed or if the child is very young, observed while playing. More proximal shoulder or elbow abnormalities should be excluded such as Poland’s syndrome or radial-ulnar synostosis. The presence or absence of a radiocarpal joint as well as the number and length of any metacarpal bones should be determined. The presence or absence of a thumb and whether there is a thumb carpometacarpal joint are important if a toe-to-thumb transfer is being considered. Dimpling of the skin in symbrachydactyly may indicate the presence of flexor tendons in the vicinity of the nubbins.

One or other of the child’s feet may be positioned close enough to the affected hand, so that the parents and/or child can visualize what the transferred toe might look like. Occasionally, congenital anomalies of the lower extremities may coexist with upper extremity anomalies and especially with bilateral congenital hand differences; the availability of donor toes may be limited because of associated foot anomalies.

Plain radiographs of both hands and both feet should be obtained to determine the presence of metacarpals and whether a carpometacarpal joint of the thumb is present or absent. In children where the carpal or metacarpal bones have not yet ossified, an MRI scan may be considered.

The necessity for preoperative angiography of either the upper or lower extremity remains controversial. Greenberg and May (1988) found a preoperative lateral angiogram of the foot to be helpful in identifying the location and size of the first dorsal metatarsal (FDMA) and first plantar metatarsal arteries (FPMA). The author no longer obtains angiograms but listens to the dorsalis pedis and first dorsal metatarsal artery in both feet with a handheld Doppler probe. The dorsalis pedis artery can be traced distally into the first dorsal metatarsal artery lying between the great toe and second toe metatarsals using an 8 MHz pencil Doppler ultrasound probe. The dominance of the FDMA can be assessed from the presence or absence of a Doppler signal and the potential depth of the FDMA from the intensity of the signal (superficial, within, or deep to the interosseous muscles).

A final preoperative evaluation should always be performed by the child’s pediatrician a few days prior to any toe-to-hand transfer to exclude any viral infection, which might compromise postoperative respiratory function after a multi-hour operation.

The arterial anatomy of both the great toe and the second toe is based on either the first dorsal metatarsal artery (FDMA), a continuation of the dorsalis pedis artery, or the first plantar metatarsal artery (FPMA) (Villen and Julve 2002). Superficial veins drain to the medial side of the dorsum of the foot and then into the greater saphenous vein. Sensibility to the plantar surface of the great toe or second toe is provided by the tibial (medial) and fibular (lateral) digital nerves and to the dorsal surface by the deep peroneal nerve.

The child is positioned supine with the arm and hand on a hand table and the donor foot at the end of the operating table. General anesthesia is occasionally supplemented with an axillary block or continuous brachial plexus infusion. A Foley catheter is used to monitor urine output and fluid status, but central venous catheters are not used routinely. A regular tourniquet is applied to the upper arm, and a sterile tourniquet is applied to the thigh, since a skin graft may need to be harvested later from the thigh or groin.