Surgical Reconstruction of Type IV Hypoplasia of the Thumb (Floating Thumb) in Infants: A Retrospective Analysis of Functional Outcomes and Radiographic Alignment

Introduction

Thumb hypoplasia or absence in pediatric patients poses a complex challenge in reconstructive surgery, demanding inventive approaches to restore both form and function [1,2]. The classification of thumb hypoplasia, as proposed by previous studies, encompasses 5 distinct types: type I to type V [3,4]. Various surgical techniques have been used for reconstruction of the hypoplastic thumb. The techniques include first web space reconstruction using local flaps, ulnar collateral ligament imbrication or reconstruction using flexor digitorum superficialis tendon slip for uniaxial MP joint instability, and opposition transfer using either abductor digiti minimi or flexor digitorum superficialis tendon, which is tailored to the degree of hypoplasia [5]. For instance, Schneider et al described using a free transfer of metatarsal bone to correct hypoplastic thumbs, one of the earlier techniques for this condition [6]. Tong et al later reported using a reversed vascularized second metatarsal flap for more severe cases of Manske type IIIB and IV thumb hypoplasia, which reduced donor site morbidity [7].

Among congenital anomalies, the “floating thumb” stands out, characterized by the absence of skeletal support, presenting unique challenges in the reconstructive process [8,9]. This floating variant constitutes approximately 0.9% to 15% of all instances of thumb polydactyly, which is caused by genetic predispositions, environmental influences, and developmental anomalies [10,11]. The thumb’s pivotal role in manual dexterity and precision grip underscores the need for comprehensive interventions addressing skeletal deficits and functional complexities.

The floating thumb anomaly manifests across a spectrum of deformities, ranging from mild dysplasia to severe dissociation of the thumb from the hand [12]. Beyond the evident aesthetic concerns, these anomalies significantly impact hand function and overall limb dexterity. Conventional reconstructive methods have centered around metacarpal augmentation, tendon transfers, and soft tissue reconstruction [13,14]. In a previous study, Liu et al focused specifically on surgical reconstruction for the more severe type IIIB and IV cases using a non-vascularized fourth metatarsal bone graft, which achieved reasonable hand function and cosmesis in 16 patients with 17 type IIIB and IV hypoplastic thumbs over 46 months, despite 2 nonunions [15]. However, these approaches can be limited in cases with severe deficiency, demanding alternative strategies to achieve optimal outcomes. For instance, Takagi et al reported that pollicization of the index finger offers a solution for severely floating thumbs, allowing retention of 5 digits while improving function under the presence of the available fingers in the donor area [13]. Furthermore, proper care, planning, technique selection, adjunct procedures, and rehabilitation are essential for optimal functional results [16].

Polydactylous hallux, a congenital anomaly characterized by the presence of supernumerary digits on the foot, present in various forms [17]. Hallux polydactyly involves the presence of extra toes adjacent to or at the tip of the big toe [18]. Non-hallux polydactyly, on the other hand, encompasses extra digits on toes other than the big toe, which could include additional second, third, fourth, or fifth toes, or even extra connecting tissue between these toes [19]. These diverse manifestations of polydactylous toes can impact walking and footwear choices, often requiring surgical intervention to improve function and appearance. Patients with floating thumb can benefit from polydactylous hallux transfer, which offers a tailored and new approach to reconstructing the absent metacarpal and digit structures of the affected thumb.

Therefore, this retrospective study describes 11 infants with congenital hypoplasia of the thumb type IV (floating thumb) who underwent surgical reconstruction using a modified vascularized polydactylous hallux flap. Our surgical technique involves the concurrent transfer of polydactylous hallux elements to reconstruct the absent metacarpal and digit structures of the affected thumb. The rationale underpinning this approach is the exploitation of the inherent osteogenic and soft tissue qualities of the hallux to address the intricate anatomical deficits associated with floating thumbs. Notably absent from existing literature, this technique represents a unique and unexplored avenue, with our preliminary study documenting the initial experiences of 11 pediatric patients who underwent this groundbreaking reconstructive procedure.

Material and Methods

INCLUSION CRITERIA:

Pediatric patients (6–24 months) diagnosed with floating thumb deformities, characterized by the absence of skeletal support, were eligible for inclusion in this study. Furthermore, patients were required to exhibit polydactylous toes involving the hallux (Figure 1A–1C). All patients underwent thorough clinical and radiographic evaluations to confirm the diagnosis.

EXCLUSION CRITERIA:

Patients with contraindications for surgery, pre-existing neurological disorders affecting hand function, or other systemic conditions affecting surgical outcomes were excluded. Additionally, those with inadequate follow-up compliance were not considered for inclusion.

GENERAL INFORMATION:

In the present study, a cohort of 11 pediatric patients (age range: 6–24 months) meeting the inclusion criteria were included, while 5 pediatric patients were excluded. Demographic information, including age, sex, and preoperative clinical assessments, was recorded for each patient.

SURGERY:

In the initial procedure, we chose patients with the floating thumb and took X-rays to confirm the structure of the hand and foot (Figure 2A–2F). Then, we performed an S-shaped incision on the dorsal side of the floating thumb of the hand (Figure 3A). Under a microscope, we dissected 1 vein, 1 artery, and 1 radial cutaneous nerve on the dorsal side of the wrist, labeling them for later use. The stump of the first metacarpal head was dissected and repaired for preservation. Double V-shaped incisions were made on the left dorsal and plantar aspects of the polydactylous hallux (Figure 3B). We dissected 1 dorsal toe vein, 1 plantar-base artery, and 1 multi-toe nerve under a microscope. The polydactylous hallux were completely freed, retaining the corresponding length of blood vessels needed for vascular transplantation in the recipient area (Figure 3C, 3D). We performed a lateral wedge osteotomy proximal to the first metatarsal, removing the remaining metatarsal bone in the proximal part of the polydactylous hallux. The toe was separated at the junction of its dorsal and plantar aspects on one side and placed in the affected area of the right hand. The distal phalanges of multiple digits were fixed to the stump of the head of the first metacarpal, and the proximal phalanges were fixed to the base of the second metacarpal. The toe vein was anastomosed with the hand vein, the toe nerve with the radial dorsal cutaneous nerve, and the toe artery with the dorsal carpal artery (Figure 3E, 3F). Internal fixation devices were removed after confirming complete bone union on radiographs at 2 months. The patients underwent a second operation 3 months later, involving the reconstruction of the thumb extension function using the extensor intrinsic tendon of the index finger and thumb flexion function using the superficial tendon of the ring finger (Figure 3G–3I). This established the function of an opposable thumb with the metacarpal longus tendon. We successfully reconstructed the interphalangeal joint as a carpometacarpal joint, grafted the proximal phalangeal bone as carpal bone, and grafted the distal phalangeal bone as the first metacarpal bone.

POSTOPERATIVE TREATMENT:

Postoperatively, patients received a standardized rehabilitation protocol, including physical therapy and occupational therapy. Regular follow-up appointments were scheduled to monitor progress and address any concerns.

EVALUATION METHODS AND OBSERVATION INDICATORS:

Clinical assessments included measurements of thumb opposition, grasp strength, and overall hand function. Objective evaluation criteria were established for functional improvements. Radiographic assessments were conducted to analyze skeletal alignment and integrity.

IMAGING EVALUATION:

Standard radiographic imaging, including X-rays and, where applicable, advanced imaging modalities, such as magnetic resonance imaging (MRI), was employed for the thorough evaluation of skeletal reconstruction and the integrity of vascular and neural connections.

COMPLICATIONS:

Intraoperative and postoperative complications were systematically documented. Complications encompass vascular and nerve-related issues, wound healing problems, and any unforeseen challenges encountered during the surgical process.

STATISTICAL ANALYSIS:

Descriptive statistical analyses were performed to summarize demographic data and clinical outcomes. Continuous variables were expressed as means with standard deviations, and categorical variables were presented as frequencies and percentages.

Results

CLINICAL AND IMAGING RESULTS:

The cohort of 11 pediatric patients underwent the complete 2-stage surgical protocol (Table 1). Early clinical results revealed that the total active motion was 128.91°±12.15°, and the grasp strength, lateral pinch strength, and tip pinch strength were 88.27±3.98%, 71.91±8.20%, 68.27±8.29%, respectively, when comparted with the normal side (Figure 4, Table 2). Radiographic assessments demonstrated satisfactory skeletal alignment and integrity of vascular and neural connections postoperatively.

INTRAOPERATIVE AND POSTOPERATIVE COMPLICATIONS:

No major intraoperative complications were encountered. Postoperatively, minor complications, including transient edema and delayed wound healing, were observed in 2 patients. These complications were managed conservatively, and no long-term adverse effects were noted.

Discussion

This retrospective study describes the surgical technique utilizing a modified vascularized polydactylous hallux flap transfer to reconstruct congenital floating thumb deformities in 11 pediatric patients. The polydactylous hallux elements were transferred to reconstruct the absent metacarpal and digit structures of the affected thumb. Early results showed satisfactory total active motion and grasp strength and confirmed skeletal alignment and vascular/neural integrity on imaging. Minor complications, including edema and delayed healing, were observed in 2 patients but were managed conservatively. Overall, this approach exploiting the osteogenic and soft tissue qualities of the polydactylous hallux offers a promising reconstruction for intricate floating thumb deficits.

The initial surgical procedure, including an S-shaped incision and meticulous dissection, serves as a critical foundation. Simultaneous polydactylous toe transfer, focusing on maintaining vascular and nerve integrity, combines skeletal support with intrinsic connectivity. This holistic approach aims to provide a comprehensive solution to the multifaceted problem posed by the floating thumb. The second operation, refining thumb functions through intrinsic and extrinsic tendon grafts, marks a pivotal step in achieving optimal functional outcomes. Tendon grafting complexities in pediatric patients demand a nuanced understanding of growth patterns and the delicate balance between stability and flexibility [20]. Early assessments revealed promising improvements in thumb opposition, grasp strength, and overall hand function, which are similar to those of a previous study [21]. Therefore, the new approach indicates potentially enhanced quality of life for these pediatric patients. Radiographic evidence of satisfactory alignment postoperatively adds credibility to the viability of our approach.

The advantage of simultaneous polydactylous hallux transfer for treating floating thumbs lies in its tailored and new approach to addressing complex hand anomalies. By utilizing the hallux (big toe) from the foot to reconstruct the absent metacarpal and digit structures of the affected thumb, this technique offers several distinct advantages. First, the hallux provides an anatomical match in terms of size and functionality, ensuring a more natural appearance and improved functional outcomes for the reconstructed thumb. Additionally, the hallux possesses robust skeletal support and ample soft tissue coverage, facilitating the creation of a stable and functional thumb. Furthermore, by utilizing the hallux as a donor digit, the procedure minimizes donor site morbidity and avoids the need for additional surgeries on other digits, thereby streamlining the reconstructive process.

However, the study’s limitations, including a small sample size and limited postoperative data, underscore the need for caution in generalizing these results. Further investigations with larger cohorts and extended follow-up periods are imperative to validate the durability and efficacy of our approach.

Conclusions

In conclusion, this retrospective study of 11 pediatric cases demonstrates the efficacy and safety of using a modified vascularized polydactylous hallux flap for surgical reconstruction of congenital hypoplasia of thumb type IV (floating thumb) deformities, which offers an effective solution to restore thumb opposition, grasp capabilities, and overall hand dexterity in patients with congenital floating thumb deformities. As we navigate the intricate path of pediatric hand reconstruction, new techniques such as the one presented contribute to expanding the repertoire of surgical options, offering hope for improved outcomes in challenging cases of thumb deformities.