Treatment for central polydactyly of the foot with nine toes: a rare case report

Abstract

Background

Pediatric polydactyly is a common congenital disorder of the hand and foot that affects the development and psychology of children. It can be classified into postaxial polydactyly, preaxial polydactyly and central polydactyly. Among the three types, central polydactyly is the rarest, resulting in limited literature pertaining to the management of this condition. We present a rare case of central polydactyly of the left foot with nine toes.

Case presentation

A 10-month-old female child was brought to us with left congenital central mirror foot and ill-fitting shoe concerns. The foot had nine toes and eight metatarsals with tarsal duplications. To correct the contour of the foot, the central polydactylous components were excised through a V-shaped incision. After a follow-up period of two years, the outcomes of the operation were satisfactory based on the American Orthopaedic Foot and Ankle Score, and values of the distance between the head of the first metatarsal and fifth metatarsal and the distance between the base of the first metatarsal and fifth metatarsal were improved notably. We successfully treated an extremely rare case of central mirror foot.

Conclusions

There is a unique challenge in treating central polydactyly of the foot, particularly when the tarsal and metatarsal bones are duplicated. Surgeons should identify it preoperatively and take into account the duplicated tarsal bones while planning the surgery.

Clinical trial number

Not applicable.

Background

Polydactyly is one of the most common congenital anomalies of the limbs, characterized by extra digits in the hands or feet, and polydactyly of the foot occurs in approximately 1.7 per 1000 live births [1]. Currently, polydactyly is thought to result from abnormal patterning of the anteroposterior (A-P) axis of the developing appendage, so it can be categorized into three types depending on the location of the duplication: preaxial (first ray), postaxial (fifth ray), and central (middle rays) polydactyly of the foot [2]. Postaxial polydactyly is the most common of the three types, accounting for 80% of duplications, preaxial polydactyly is less common, accounting for 15% of polydactyly of the foot, and central duplication is the rarest, accounting for 5% of cases [3, 4]. The mirror foot, an extremely rare congenital anomaly, refers to duplicated tarsal and metatarsal bones [5]. It consists of seven or more toes and can be described as preaxial or central [6]. Mirror foot can be an isolated condition, but also be associated with other anomalies, such as tibial hypoplasia, fibular dimelia. There is little literature regarding the treatment of central mirror foot with duplication of the metatarsal and tarsal bones. We report the management of a case of central polydactyly with eight metatarsals, nine toes.

Case presentation

A 10-month-old female child with no family history of polydactyly, was brought to the Hand clinic of our hospital, with an abnormal appearance of her left foot with the presence of nine toes. The anteroposterior and oblique radiographs of the foot showed eight metatarsal rays and nine phalangeal rays. The medial toe and the fifth toe had two ossified phalanges and other toes had three ossified phalanges. The fifth toe was hypoplastic, without a stable metatarsophalangeal joint. The clinical examination of child did not reveal any other skeletal abnormalities, and ultrasonic examination of the heart and kidneys did not indicate malformation. Leg anomalies such as tibial hemimelia and fibular dimelia were not found. On the left foot, the distance between the head of the first metatarsal and fifth metatarsal (DHFF) was 39.04 millimeters, the distance between the base of the first metatarsal and fifth metatarsal (DBFF) was 29.03 millimeters, and the ratio of the two distances was approximately 1.34. In contrast, on the right foot, DHFF was 28.36 millimeters, DBFF was 24.22 millimeters, and the ratio of the two distances was approximately 1.17. Between the second and sixth metatarsal rays, there were four duplicated toes with syndactyly (Figs. 1 and 2). The child underwent surgery in May 2022.

Fig. 1

Preoperative X-ray images of the left and right feet

Fig. 2

Intraoperative photographs of the left foot. (A) Dorsal view of incisions and flap design. (B) Plantar view of incisions and flap design

Under general anesthesia and tourniquet control, we designed a dorsal and palmar V-shaped incision in the centre of the left foot for excision of the syndactylized central four toes and the central three metatarsals. At the same time, a dorsal Barsky flap was created to reconstruct a new involved web space. The Barsky flap, initially applied in cleft hand, meant that the skin from either side of the cleft is transferred to widen the first web space. In this case, a curved incision was designed at the fibular wall of the sixth toe to preserve the skin of the sixth web, and a curved incision was designed at the fibular wall of the second toe to remove extra toes, then the skin of the sixth web was inset to cover the defect (Fig. 2).

Incise the skin along the incision marked above and carefully dissect the subcutaneous tissue. The dorsal and palmar V-shaped flaps were sharply elevated, identifying the vessel and nerve of the central four toes and isolating the neurovascular bundles of the second and seventh toes. Continue with the dissection until we identified the common digital vessels and proper digital nerves to second and sixth webs. The arterial bifurcation of the common digital artery was identified, and the branch artery supplying the third toe was ligated to ensure supply to the fibular side of the second toe. Likewise, the branch artery supplying the sixth toe was ligated to ensure supply to the tibial side of the seventh toe. The nerves supplying the central four toes were appropriately cut using cautery. Dissection was then continued until the extensor and flexor tendons were exposed. The tendons were traced distally to their insertions before excision of extra toes. We found the central four toes to be removed all had respectively extensor and flexor tendons (Fig. 3). After confirming that the tendons belonged to the central toes to be removed, they were cut on the proximal side, and the tendons of the preserved toes were retained. And the transverse metatarsal ligaments between second and third toes, and between sixth and seventh toes were cut.

Fig. 3

The tendons were exposed after dissection. (A) The dorsal extensor tendons. (B) The plantar flexor tendons

Bilateral longitudinal periosteal incisions were made along the tibial side of the third metatarsal and fibular side of the fifth metatarsal to remove central three metatarsals. Dissection were continued proximally along above incisions to the base of the metatarsals, and the tarsometatarsal joints (TMT joint) between the third, fourth, fifth metatarsals and tarsals were exposed. The capsule and ligaments of the third, fourth and fifth TMT joint were incised and a wedge osteotomy along the third and fifth metatarsal rays was performed to remove the excess tarsals, avoiding a wide interosseous space between the second and sixth metatarsal rays. The central polydactylous components were then removed, including the soft tissues, phalanxes, metatarsals and tarsals (Fig. 4). After narrowing the intermetatarsal space, two K-wires were drilled transversely through the metatarsals to prevent the enlargement of the newly formed second intermetatarsal angle. Additionally, two additional K-wires were drilled obliquely to stabilize the TMT joints. Subsequently, the incised capsule, along with the dorsal and plantar metatarsal ligaments between the second and sixth metatarsals and the collateral ligaments of the second and sixth TMT joint was reconstructed using 5 − 0 polydioxanone sutures (5 − 0 PDS). The transverse metatarsal ligaments between the second and sixth rays were sutured using 3 − 0 absorbable sutures. The redundant soft tissue between the second and seventh rays was excised, and the subcutaneous tissue was sutured using 5 − 0 absorbable sutures. These can effectively reduce the intermetatarsal space of the second and seventh rays. Following this, the preserved Barsky flap was transferred to cover the lateral wall of the second toe, thereby reconstructing a new second web space. Finally, the dorsal and palmar incisions were closed using 5 − 0 vicryl rapide (Fig. 5). Following the release of the tourniquet, the incisions were covered with erythromycin and subsequently compressed with sterile dressings. The left foot was then immobilized using soft castings. After a period of four weeks, both the castings and K-wires were removed.

Fig. 4

Intraoperative photograph after the central polydactylous components of the left foot were removed

Fig. 5

Postoperative photograph after all the incisions were closed

After a follow-up period of two years, the left foot was observed to be slightly widened (Fig. 6A-B). The child was capable of walking, jumping and running independently without experiencing any pain. We used the American Orthopaedic Foot and Ankle Score (AOFAS) to assessed postoperative outcomes, which focused on range of motion, pain, function and radiographic criteria for ankle-hindfoot, midfoot, hallux and lesser toes [7, 8]. According to AOFAS, the scores were as follow: 100 for the Ankle-Hindfoot, 93 for the Midfoot Scale, 93 for the Hallux and Second Toe Metatarsophalangeal-Interphalangeal Scale, and 100 for the other toes. This clinical rating systems revealed problems that the first intermetatarsal space was widish and the proximal phalanx of the second ray was not in alignment with the metatarsal, existing before surgery. The ratio of DHFF and DBFF was approximately 1.22 on the right foot. On the left foot, the ratio of DHFF and DBFF was corrected from a preoperative value of 1.34 to a postoperative value of 1.24, almost equal to the right foot. Besides, the ratio of DHFF of the left and right feet was corrected from a preoperative value of 1.38 to a postoperative value of 1.13, and DBFF was corrected from a preoperative value of 1.20 to a postoperative value of 1.11 (Fig. 6C). Radiologically, the left foot had improved significantly compared with pre-operation.

Fig. 6

Two-year postoperative images. (A) Dorsal view of the left and right feet. (B) Plantar view of the left and right feet. (C) Postoperative X-ray images of the left and right feet

Discussion

Mirror foot can be classified into preaxial and central mirror foot, and the central type of mirror foot is the rarest type of foot polydactyly [5]. Consequently, it is essential to differentiate central mirror foot from preaxial mirror foot, as treatments for two types of mirror foot are different. Preaxial mirror foot is typically addressed by excising the medial polydactyly, while central mirror foot often involves the removal of hypoplastic central toes. Unlike preaxial mirror foot, the hallux in cases of central polydactyly is situated at the medial side of the foot [9]. And the location of the hallux can be identified based on the distinctive features of only two phalanges and specific skeletal morphology of the first metatarsal. The clinical signs and symptoms of mirror foot are diverse and include spontaneous pain, excruciating walking tenderness, ill-fitting shoe concerns, cosmetic problems and psychosocial difficulties [10]. Surgical treatment aims to restore a normal plantigrade foot with an acceptable aesthetic form that can be easily accommodated in shoes [6].

The optimal timing for the surgical intervention of foot polydactyly remains a subject of debate. Some surgeons advocated for the excision of extra digits prior to the onset of walking, aiming to prevent the expansion of web spaces and to allow for maximum postoperative remodeling of the foot [11, 12]. Conversely, others preferred to perform the excision during childhood after walking age, when ossification, size, soft tissue structures, and the functions of the digits can more accurately assessed [12]. This approach facilitates the development of a more appropriate surgical plan and minimizes the risks associated with anesthesia administration. However, many parents and grandparents often seek surgical intervention shortly after birth, influenced by conventional wisdom and societal perspectives.

In central mirror foot, the plantar and dorsal advancement flaps technique was proposed by Osborn et al. [13] When the second ray is duplicated, laterally based dorsal and plantar flaps are developed, beginning at the medial margin of the forefoot and extending distally along the great toe to the level of the first web space. It was reported that this advancement flap technique narrowed the forefoot and there were minimal functional and shoe wear problems after this procedure. But the incision line at the medial border could be a source of shoe irritation on the scar and the wide mobilization of the flap with the potential for skin necrosis. In addition, Manye Yao used two wavy V-shaped incisions to remove the central polydactylous components in a child with eight-toed central polydactyly on the right foot [14]. Papamerkouriou et al. similarly applied a dorsal and plantar V-shaped incision in the center of the foot to excise the extra skin and polydactylous central rays [15]. These enabled the appropriate management of the extra skin, but there was a potential risk of web creep formation and scar contracture, on account of the incision located in the web [16]. Hence, we used a dorsal and plantar V-shaped incision to excise the central polydactylous components, and the Barsky flap to reconstruct a smooth second web space, preventing web creep formation and scar contracture. This combined flaps was ever reported by Kim et al. to create the first web space in a case of the central mirror foot with seven metatarsals and eight proximal phalanges [17].

Vlahovic et al. previously reported that the excision of supernumerary toes was performed without addressing the excrescent tarsal bone, resulting in a significant gap between the first and second rays and an increased foot width postoperatively [18]. Piette et al. emphasized the reconstruction of the intermetatarsal ligament after excision of the metatarsals and the toes to preserve the transverse arch, and the application of postoperative casting to protect the intermetatarsal ligament reconstruction [10]. Kim et al. excised the second, third and fourth rays and transposed the fifth metatarsal to the base of the amputated second metatarsal, reducing the gap between the metatarsals in another mirror foot [17]. Laliotis et al. used a tight non-absorbable suture to reinforce the approximation of the remaining metatarsals [5, 6].

Verghese at al. reported a series of preaxial mirror foot associated with anomalies of fibula, tibia and leg length discrepancy (LLD) [19]. Deshmukh at al. and Sahoo at al. reported that children had a mirror foot accompanied with hypoplastic tibia [20, 21]. In our case, the child with a central mirror foot was not diagnosed with malformation of other organs and systems. We conducted a wedge resection to excise the central polysyndactyly including the phalanges, metatarsals and tarsals since the most medial ray was the hallux. It’s extremely important for successful treatment of these anomalies to excise supernumerary tarsal bones. For the flap design, we implemented a dorsal and palmar V-shaped incision to remove the central polydactyly, while preserving the original sixth web skin, which was then used to reconstruct a new second web, to prevent web creep formation and scar contracture. Additionally, the new second intermetatarsal space was narrowed by removing the excess soft tissue and reconstructing the transverse metatarsal ligaments and dorsal and plantar metatarsal ligaments between the second and sixth metatarsals. K-wires were also utilized to stabilize the positions of the metatarsal and tarsal bones and restrict the gap between the second and sixth metatarsals.

Conclusion

There is currently little consensus regarding the surgical treatment of central polydactyly due to its rarity. This article focuses on the surgical treatment of central polydactyly with metatarsal and tarsal duplications. Surgeons should distinguish central mirror foot from preaxial mirror foot before deciding on a surgical plan. The limitation of this study is that we could not collect enough cases to make comparison on account of its rarity. But based on reported cases and our clinical experience, we believe that our treatment can help clinicians to correct the central mirror foot.