As microsurgical expertise has improved, allowing for the safe transfer of smaller and more refined flaps, free tissue transfer has continued to gain popularity for the management of pediatric soft tissue and bony defects. For the past 2 decades pediatric microsurgery has been shown to be technically feasible and reliable. The major advantage of free tissue transfer in children is the ability to reconstruct defects in a single stage, avoiding the historic treatments of skin grafting, tissue expansion, and pedicled flaps. This article reviews the present state-of-the-art in pediatric microsurgery.
Key points
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Pediatric microsurgical procedures have successful outcomes similar to adult reconstructions.
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Free tissue transfer can provide immediate reconstruction of defects without the need for tissue expansion, skin grafting, or muscle sacrifice.
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Dedicated microsurgical centers should perform the bulk of these procedures given the small structures involved and ancillary pediatric expertise which may be required for adequate post-operative care.
Introduction
Early in the evolution of pediatric microsurgery, Gilbert thought that the small vessels in children could pose a technical limitation for free tissue transfer and suggested that a minimum vessel diameter of 0.7 mm was safe for microanastomoses. Vessels smaller than this were initially considered too small for reliable outcomes. As microsurgical expertise has improved, allowing for the safe transfer of smaller and more refined flaps, free tissue transfer has continued to gain popularity for the management of pediatric soft tissue and bony defects. Over the past 2 decades, pediatric microsurgery has been shown to be technically feasible and reliable.
The major advantage of free tissue transfer in children is the ability to reconstruct defects in a single stage. Historically, soft tissue reconstruction in children has required the use of skin grafting, tissue expansion, or pedicled flaps; surgeons would typically follow the reconstructive ladder in choosing a surgical procedure. Split-thickness skin grafting and tissue expansion are techniques that can produce scarring and require several operative procedures or multiple dressing changes to achieve a healed wound. The use of local flaps or pedicled muscle flaps can add further injury and donor site morbidity to an already traumatized extremity. With the advent of free perforator flaps, such as the anterolateral thigh (ALT) flap and superficial circumflex iliac artery perforator (SCIP) flap, donor site morbidity is minimized and no muscle needs to be violated. With present day technology, the authors advocate for using the “reconstructive elevator” and bypass more traditional techniques for the benefits of free tissue transfer in children, allowing for single-stage reconstruction and in many cases primary closure of the donor site. This article reviews the present state-of-the-art in pediatric microsurgery using a global perspective.
Introduction
Early in the evolution of pediatric microsurgery, Gilbert thought that the small vessels in children could pose a technical limitation for free tissue transfer and suggested that a minimum vessel diameter of 0.7 mm was safe for microanastomoses. Vessels smaller than this were initially considered too small for reliable outcomes. As microsurgical expertise has improved, allowing for the safe transfer of smaller and more refined flaps, free tissue transfer has continued to gain popularity for the management of pediatric soft tissue and bony defects. Over the past 2 decades, pediatric microsurgery has been shown to be technically feasible and reliable.
The major advantage of free tissue transfer in children is the ability to reconstruct defects in a single stage. Historically, soft tissue reconstruction in children has required the use of skin grafting, tissue expansion, or pedicled flaps; surgeons would typically follow the reconstructive ladder in choosing a surgical procedure. Split-thickness skin grafting and tissue expansion are techniques that can produce scarring and require several operative procedures or multiple dressing changes to achieve a healed wound. The use of local flaps or pedicled muscle flaps can add further injury and donor site morbidity to an already traumatized extremity. With the advent of free perforator flaps, such as the anterolateral thigh (ALT) flap and superficial circumflex iliac artery perforator (SCIP) flap, donor site morbidity is minimized and no muscle needs to be violated. With present day technology, the authors advocate for using the “reconstructive elevator” and bypass more traditional techniques for the benefits of free tissue transfer in children, allowing for single-stage reconstruction and in many cases primary closure of the donor site. This article reviews the present state-of-the-art in pediatric microsurgery using a global perspective.
Categories of microsurgery in children
Pediatric microsurgery is primarily performed for the reconstruction of congenital defects as well as following trauma and tumor extirpation. Most elective pediatric microsurgery is performed for the reconstruction of congenital facial deformities and congenital hand anomalies. Traumatic defects and tumor reconstructions, while seen less frequently than in the adult population, can pose particular challenges; in these cases, the reconstructive surgeon must allow for ongoing growth and minimize donor site morbidity. Here, the authors provide an overview of the more frequently performed pediatric microvascular procedures within these major categories of congenital deformity, trauma, and tumor.
Congenital Defects
Facial asymmetry
Congenital facial anomalies requiring free tissue transfers include Romberg hemifacial atrophy, hemifacial microsomia, facial clefts, and Treacher Collins syndrome. Many of these patients have some component of facial asymmetry due to a combination of soft tissue and bony hypoplasia. The use of local tissue for the treatment of these deformities is limited and can create further facial morbidity. Free nonvascularized fat or dermal grafts can have unpredictable absorption, and prosthetic implants run the risk of extrusion and infection over time. Adipofascial free flaps have been shown to be an effective alternative for these cases. Shintomi and colleagues used a de-epithelialized groin flap with dermis down for integration into the native fascia with the flap’s fatty side against the facial skin for prevention of skin contracture.
Despite Shintomi’s results, the most commonly used free flap for soft tissue augmentation after Romberg hemifacial atrophy is the scapular and parascapular flaps. These flaps, when combined with their local fascial extension, provide reliable thick tissue that can be safely contoured and secured to the underlying skeleton to avoid migration due to gravity. These flaps provide a large amount of tissue, and the vascular pedicle is long, with a diameter of greater than 1 mm even in young children; however, the donor site is conspicuous and can hypertrophy.
In addition to scapular and parascapular flaps, the use of free omentum to improve facial asymmetry has also been described. The omentum has large donor vessels, and the vascularized fatty tissue can be folded on itself, allowing flexibility in correcting deformities. The disadvantage of using this flap is the need for a laparotomy, the lack of structural support within the flap, and the potential for seroma formation. Laparoscopic omentum harvest makes this a more appealing option in adolescents, but not for infants and toddlers because the omentum is poorly developed in young children.
In Romberg syndrome, the timing of surgery is controversial, and many think that it should only be undertaken after the disease process is quiescent. In comparison, recent studies have shown benefits of the vascularized flap on the native tissue after transfer, even during times of active disease. Earlier placement of free vascularized tissue in theory could necessitate further surgery following the completion of facial growth; however, the authors have found that for smaller contour defects remaining after free tissue transfer, free fat injections from the gluteal, abdominal, or inguinal regions can improve the cosmetic result while avoiding an extended secondary major surgical procedure.
Clefts
Another condition that may benefit from free tissue transfers is the residual wide cleft lip and palate, which have failed primary repair using the local tissue. Futran and Haller originally reported on the use of the free radial forearm flap for the correction of large residual fistulas with good outcomes. Further work by MacLeod and colleagues also reported good results with the use of the free radial forearm flap with and without bone for large palatine defects.
Facial reanimation
The history and nuances of free tissue transfer for facial paralysis are beyond the scope of this review; however, any surgeon embarking on the treatment of this condition needs to have a thorough understanding of the surgical techniques available to treat this heterogeneous condition. In chronic facial nerve palsies, the possibilities of functional return after nerve repair or decompression are minimal due to the deterioration of the motor end plates on the muscle. In such cases, the only option for active motion is the use of functional muscle transfers with either local pedicled flaps or free muscle. Many of the local transfers cannot produce synchronous involuntary facial expressions (particularly smile) to match the contralateral side. The free gracilis functional transfer has become the standard treatment to restore smile in cases of nerve absence or injury.
The 2-staged technique, which classically consists of cross-facial nerve grafting followed by muscle transfer and neurotization, produces minimal donor site morbidity and can allow for synchronous restoration of smile. Recent reports have noted an 11% failure rate with this procedure due to flap complications and the unpredictability of nerve ingrowth from the contralateral side. Bae and colleagues explored the choice of motor nerves to neurotize the transplanted muscle for achieving synchronous and spontaneous function; their results demonstrated that the final outcomes in commissural movement after both cross-facial nerve grafting and neurotization of free functional gracilis using the masseter nerve were similar. In 2009, Terzis and Olivares published Terzis’ lifetime experience with the use of both pectoralis minor muscle and free gracilis in 32 children followed for 5 years or longer. The study noted improvement in smile in all children with the ability of the muscle to grow with the child and provide increasing function over time.
Hand and Upper Limb Anomalies
Congenital hand deformities in children are common, with an incidence of 1.97 per 1000 live births. Although most children with congenital anomalies do well with standard reconstructive procedures, there are 3 groups of children who can benefit from free tissue transfers: (1) children with absent digits; (2) children with radial hypoplasia; and (3) children with pseudoarthrosis of the forearm. Each group will be discussed in further detail.
The causes of congenital absent digits include adactyly, symbrachydactyly, transverse failure of formation, cleft hand, and congenital constriction ring syndrome (or amniotic band syndrome). Great toe or second toe transfer is a means of improving hand function in these children. The primary goal of reconstruction is to establish a useful thumb for opposition. If a thumb is already present, then reconstructive measures should focus on the creation of a stable post to which the child may oppose the thumb. If possible, the creation of a second finger can allow for the utilization of chuck pinch. In addition, a second finger will allow for stabilization of remaining fingers or hypoplastic digits during precision pinch ( Fig. 1 ). A thumb and 2 fingers allow for power grasp, key pinch, and chuck grip and should be considered the goal for reconstruction of the adactylous or congenitally deficient hand.
Jones and Kaplan have described the indications for free toe transfer to the thumb as (1) an absent thumb distal to the carpometacarpal joint with 4 relatively normal fingers ( Fig. 2 ); (2) an absent thumb with only 1 or 2 fingers remaining on the ulnar border of the hand; and (3) complete absence of the thumb and all 4 fingers. Their indications for toe transfers for the reconstruction of congenital absent fingers are (1) absence of all 4 fingers but with a normal thumb remaining and (2) complete absence of all 5 digits. In a study by Kaplan and Jones, the investigators showed good patient outcomes in children with congenital or traumatic missing or hypoplastic digits who underwent reconstruction by microsurgical toe-to-hand transfer. Children regained function, sensation, and ability to perform daily activities. More recent results from Nikkhah and colleagues noted poor active range of motion (ROM) in the transferred digits, but all children were able to perform large object grip and recovery of 2-point discrimination was excellent (5-mm 2-point discrimination). Kay and Wiberg also noted poor active ROM of the toes following transfer; however, even with poor active ROM following surgery, children were still able to grip, which provided an improvement in baseline function. Digit stability appears to be the key factor for function following toe transfer, as digit stability allows force transmission through the transferred toes to the objects that are grasped.
Second toe transfer may also be used in the stabilization of the wrist in cases of radial hypoplasia. Vilkki has described the use of the second metatarsal and proximal phalanx as a means of re-establishing the radial column in cases of Bayne type III and IV radial hypoplasia. The procedure is performed in 2 stages. In the first stage, the wrist and tight radial soft tissues are gradually distracted with and external fixator to establish proper hand alignment before placement of the toe transfer. Once the wrist has straightened, the second toe metatarsal and proximal phalanx are transferred to the radial aspect of the wrist. The metatarsal is stabilized against the ulnar shaft, and the distal end of the proximal phalanx is placed against the remaining base of the scaphoid, trapezium, or second metacarpal. In comparison to centralization and radialization (the standard techniques for wrist stabilization in radial hypoplasia), the Vilkki procedure allows for preservation of wrist flexion and extension, while allowing for ongoing growth of the ulna. Hand alignment as the child develops is dependent on the balanced growth rate of the metatarsal physis and the distal ulnar physis ( Fig. 3 ). This procedure has also recently been shown to be valuable in cases of failed centralization. Using a similar concept, Yang and colleagues in a recent report showed successful long-term outcomes in 4 children with Bayne and Klug type III radial longitudinal deficiency using a vascularized proximal fibular epiphyseal transfer.
Congenital pseudoarthrosis represents the final area where free tissue transfer has been shown to provide substantial improvement over standard treatment methods. Pseudoarthrosis is a rare bone condition that can result in impaired bone development and fracture healing. It is thought to be caused by neurofibromatosis or fibrous dysplasia and leads to persistent nonunions in the radius and/or ulna with associated bony atrophy and deformity. Historic treatment with nonvascularized bone grafting has led to poor outcomes. A literature review showed that bone union was obtained in only 36% of cases treated with casting, nonvascularized bone grafting, and adjunct electrical stimulation. In 1981, Allieu and colleagues reported 2 cases successfully treated with vascularized fibular grafts. The use of a vascularized fibula graft allows for larger resections of all diseased bone and allows for the use of plate and screw fixation, which provides enhanced stability over historic pin or fixator stabilization. In addition, the fibula provides a similar size match for the ulna and radial diaphysis. Recent reports by Bae and colleagues and El Hage and colleagues have noted excellent results with preserved arm growth and bony healing ( Fig. 4 ).
Traumatic Injuries
Lower extremity trauma
Trauma is one of the most common causes for hospital admissions in children. Motor vehicle collisions (MVC) represent a frequent cause of soft tissue trauma in both adults and children. In adults, multiple studies have pointed to the benefits of free tissue coverage for lower-third and middle-third Gustio type IIIb and IIIc injuries following MVC; however, these types of defects occur at a much lower incidence in children secondary to their age-dependent bone plasticity, car-seat restraints, and their placement in the rear passenger compartment. Only 10% of pediatric tibial fractures are open, and only 7% are IIIb injuries. In a decade-long retrospective study, Laine and colleagues only identified 8 cases of Gustilo type IIIb and IIIc injuries in children that required free tissue transfer and bony reconstruction. The low numbers of patients reported in this study emphasizes the infrequency of pediatric trauma requiring free tissue transfer for middle- and upper-third coverage in the lower extremity; however, multiple papers have pointed to the need for free tissue transfer in cases of foot and ankle trauma in children following lawnmower or vehicular injury. Serletti and colleagues reported that 63% of their pediatric free flaps were performed for traumatic injury to the foot or ankle region.
Historically, free muscle, myocutaneous flaps, and radial forearm flaps have been transferred most frequently to cover large defects of the lower extremities in children ; however, the authors think that the ALT is now the best option for lower-extremity coverage in the pediatric patient due to its size and favorable donor site. The flap may be neurotized for sensation and harvested with the tensor fascia lata or iliotibial band for reconstruction of the Achilles tendon or toe extensors. The smooth fasciocutaneous deep surface provided by the ALT is ideal for tendon gliding. In addition, failure rates for this flap in pediatric patients have been reported to be low.
Use of super-microsurgery and perforator-based flaps in pediatric free tissue transfers are becoming more common. Iida and colleagues report on the use of SCIP with a vessel diameter less than 0.7 mm in a 1-year-old child after correction of valgus foot deformity. The SCIP flap represents another perforator flap with an ideal donor site for children producing minimal functional and cosmetic morbidity.
Facial trauma
In a review of 433 pediatric soft issue transfers by Upton and Guo, the greatest number of flaps were performed in the head and neck region; however, only 15 cases were performed for trauma. Most large traumatic defects are the result of burns, which are amenable to free soft tissue transfer. Although the use of free tissue transfer has been clearly established for neck contracture and large scalp burns, the development of newer skin substitutes has allowed many centers to avoid the use of free tissue transfers in situations that were not previously correctable without the use of microsurgical techniques.
Upper extremity trauma
There are 2 major categories of upper limb trauma that consistently benefit from microsurgical intervention in children, and these include digital replantation and free functioning muscle transfers. Although there is no consensus for when pediatric replantation should be performed, an attempt at replant should be made in most cases of pediatric amputation. Early correction of digital amputation may enhance future functional and psychosocial adaptation of these patients. The success rate of large pediatric replantation series ranges from 63% to 97%. Despite these results, pediatric replantation may not be attempted as frequently as it should. In a recent analysis by Berlin and colleagues, examining 455 pediatric patients undergoing replantation, pediatric patients had a lower likelihood of developing a complication requiring an amputation and had a shorter hospital stay than adult patients. Unfortunately, Berlin also noted that the rate of pediatric replantation was relatively low, being only 27% at most in a given year. Berlin’s overall conclusions were that short-term outcomes are better in children than for adults, justifying replantation attempts in this age group.
Success has also been seen in the use of free functioning muscle transfer for restoration of loss of elbow flexion, finger flexor, and finger extensor. Loss of function may be the result of brachial plexus injury or compartment syndrome. The use of gracilis, semitendinosus, pectoralis major, or latissimus dorsi muscles has been described for restoration of function. The first case of pediatric free gracilis transfer was reported by Manktelow in 1984 in a 4-year-old boy suffering from loss of finger flexion following a Volkmann contracture. Since then, numerous reports of gracilis functional transfers have been published for various conditions including polio. Most recently, in a review by Upton and Guo, the authors reported successful outcome after 10 free functional muscle transfers for the treatment of Volkmann contracture using gracilis in 7 patients and latissimus in 3 patients.
Cancer Reconstruction
The quality of life after limb preservation has been shown to be superior to amputation. In children, limb preservation is considered the goal following tumor resection. To provide the patient with an adequate oncologic margin during the tumor resection, large osseous defects can be created that hamper functional limb salvage. Traditionally, structural allografts have been used to fill these defects, providing structural support using cortical bone; however, they are associated with a high complication rate, including fracture and infection. Free vascularized fibular grafts have been shown to provide an osteogenic environment and remain viable even in cases of infection, chemotherapy, and radiotherapy. Although fibular grafts have the ability to undergo hypertrophy and remodel, they lack the structural strength of large cortical allografts. Long bone reconstruction with fibular grafts alone may be prone to fracture, and prolonged times to fibular hypertrophy can limit physical activities. To circumvent the complications associated with allograft or fibular grafts alone, Capanna and colleagues supplemented cortical allografts with intramedullary free fibular grafts. The combination of the osteogenic potential of the vascularized free fibula and the structural support of the cortical allograft makes the use of these grafts particularly attractive in the reconstruction of bony defects in children. Moran and colleagues have noted better than 93% long-term limb salvage rates with this technique in pediatric patients ( Fig. 5 ). This technique has become the gold standard for lower-limb preservation in cases of intercalary bone defects following tumor extirpation.
