INTRODUCTION
Polydactyly of the foot is among the most common congenital anomalies of the foot. It is characterized by six toes, with or without duplication of the corresponding metatarsals or phalanges [
1]. The manifestations of polydactyly of the foot may range from vestigial soft-tissue masses to an additional fully formed digit. Depending on the position of the extra toe, polydactyly of the foot can be classified as preaxial, central, or postaxial. Among these, the postaxial type is the most frequently encountered [
2]. Watanabe et al. [
3] proposed a dichotomization of these abnormalities based on their appearance on radiography as fifth or sixth ray duplications (with phalangeal or metatarsal bifurcation, respectively). When the condition involves syndactyly of the fourth and fifth toes, it is referred to as polysyndactyly, which is characterized by a dominant fifth toe and a hypoplastic sixth toe.
Simple excision of the extra toes does not yield satisfactory results due to the diverse and complicated shapes of polysyndactyly of the foot. The choice of which toe to excise has a significant effect on the postoperative outcome and cosmesis, and remains a controversial issue. The commonly described treatment for postaxial type polysyndactyly involves resection of the fifth toe to preserve the neurovascular bundles of the fourth and sixth toes [
4,
5]. However, the sixth toe is occasionally noticeably short of reaching the arcade of toes, with disfigurement of the toenail. The sixth toe also has a variable degree of lateral axis deviation, which requires wedge osteotomy of the proximal phalanx to achieve better alignment with the remaining toes. The traumatic process of wedge osteotomy can lead to shortening of the phalanx with circulatory compromise, and this procedure does not consistently yield satisfactory outcomes.
The literature contains insufficient information regarding the management of polysyndactyly of the foot. This study aimed to introduce an individualized method for treating patients with postaxial polysyndactyly of the foot by sparing the fifth toe and removing the short and deviated sixth toe. We also compared the surgical results to those of the previous method, which involved saving the sixth toe instead of the fifth, to verify the advantages of this individualized method.
RESULTS
The demographic information and clinical features of the patients are shown in
Table 1. No significant differences were found between the two groups regarding sex distribution, the average age at the time of surgery, and follow-up duration. There were no S0-type cases in either group, given that all patients had some degree of syndactylism with the adjacent toe. All cases were M0 with no metatarsal involvement of the extra digit.
Table 2 shows the forefoot width, angle difference, and toe length before and after surgery in both groups. The postoperative ratio of the affected to unaffected side was calculated for each category. The closer the ratio was to 1, the greater the similarity between the affected and unaffected sides. No significant difference was found between the two groups regarding the forefoot width ratio. However, the angle difference ratio significantly differed between fifth toe-spared group and sixth toe-spared group (1.23 vs. 1.59, P<0.05). The toe length ratio also significantly differed between the two groups (0.99 vs. 0.74, P<0.01).
Satisfaction with the results showed a significant difference between the two groups (P<0.05) (
Table 3). In the fifth toe-spared group, guardians were satisfied with the overall appearance of the foot and the spared toe, without residual deformity Bor lateral deviation (
Figs. 3,
4).
There were no postoperative complications such as wound dehiscence, wound infection, bone growth delay, or bone malunion in either group until the final follow-up visit. However, in the fifth toe-spared group, there were two cases of hypertrophic scarring, which were not sufficiently severe to necessitate additional surgery, and one case of callus formation, which required reoperation. In the sixth toe-spared group, there was one case of hypertrophic scarring, one case that resulted in total loss of the toenail (
Fig. 5), and three cases of valgus deformity, of which one required reoperation of wedge osteotomy 2 years after initial surgery.
DISCUSSION
Polydactyly of the foot is among the most commonly encountered anomalies of the limbs, and accounts for 45% of congenital foot abnormalities [
8-
10]. This condition results from established genetic syndromes in some cases, but most frequently occurs as an isolated trait with an autosomal dominant pattern of inheritance and variable expressivity (gene penetrance) [
11]. Polysyndactyly of the feet primarily affects the fifth toes, while polysyndactyly of the hand most commonly affects the third and fourth fingers of the hands, with partial or complete digital duplication within the affected web [
12,
13]. This condition involves a dominant mutation with variable expression in the
HOXD13 gene, which encodes a transcription factor that plays an essential role in the development of the limbs [
14]. Altered
HOXD13 expression affects the embryonic development of the foot, resulting in polysyndactyly [
12].
Numerous suggestions have been made regarding the classification of polydactyly of the foot. Conventional classifications are based on only morphology and do not reflect surgical planning or predict postoperative outcomes. In this study, the SAM system [
6] was used for classification. This system can be used to customize surgical methods and preoperatively predict outcomes such as residual deformities. The category of syndactylism (S) reflects the requirement for skin grafts during surgery. In this study, all patients received skin grafts. The category of axis deviation (A) measures the axis deviation of the toe to be preserved and indicates the need for wedge osteotomy. The average axis deviation of the toe to be preserved was 21.3° in the fifth toe-spared group and 30.5° in the sixth toe-spared group. In the fifth toe-spared group, no cases required wedge osteotomy, whereas 85% of cases needed wedge osteotomy in the sixth toe-spared group. The category of metatarsal extension (M) describes the extent of metatarsal duplication. All of our cases were classified as M0, indicating no involvement of the metatarsal bone. Therefore, the primary purpose of reconstruction in this study was to achieve aesthetic improvement, rather than functional improvement.
Decisions regarding which toe to excise and the method by which this is achieved are regularly encountered clinical issues in polydactyly surgery because these aspects have a significant effect on the postoperative results and appearance [
7,
15,
16]. Usami et al. [
1] described four cases of on-top plasty to lengthen the toe in short-type postaxial polydactyly of the foot. The procedure involved separating and elevating the fifth toe with the neurovascular bundle in the metatarsophalangeal joint (distal component), followed by transferring the elevated toe ray to the top of the remaining proximal phalanx (proximal component) of the neighboring sixth toe after osteotomy. The results showed improvement in the total bone length and correction of the valgus deformity. Iba et al. [
17] determined the toe to be excised depending on the appearance, alignment, and radiographic findings and focused on reconstructing the collateral ligament. The repair was performed with a proximally-based ligament or periosteal sleeve from the excised toe, and there were no cases of varus or valgus deformities.
An advantage of sparing the fifth toe is that excising the lateral sixth toe is an easier approach than excising the medial fifth toe. Furthermore, it is markedly less complicated than on-top plasty, but still yields highly satisfactory results. Although dividing the fourth web space and excising the sixth toe puts the fifth toe at risk of damaging the neurovascular bundles on both sides, there was no circulatory compromise, wound problems, or toe loss in this study. The preserved fifth toe exhibited no axis deviation and did not require wedge osteotomy, and the toe length was comparable to that of the unaffected side. Therefore, we recommend sparing the fifth toe if the sixth toe is too short or laterally deviated (A1 and A2 in the SAM classification).
In previous reviews, it was pointed out that excision of the lateral toe can lead to two common complications: valgus deformity and postoperative pain due to callus formation [
7,
18,
19]. In this study, one case in the fifth toe-spared group experienced painful postoperative callus formation, which required removal 2 years after the primary surgery. However, there were no cases of valgus deformities. During the procedure of preserving the fifth toe, a small component of the proximal phalanx of the sixth toe was preserved to support the middle phalanx of the fifth toe. The disadvantage of this procedure is a relatively thick fifth toe after surgery due to the presence of two bones in the proximal phalanx. However, the thickness was not unpleasant enough to reduce cosmetic satisfaction or induce any discomfort while wearing shoes.
In this study, the angle difference was used as a measurement to reflect both the length and lateral deviation of the most lateral toe. This parameter indicated the degree of order in the arcade of the toes. If the most lateral toe is either very short or laterally deviated, the angle difference is larger, reflecting a disturbance of the orderly arcade of the toes. In sixth toe-spared group, the angle difference on the affected side did not always improve postoperatively. The preserved sixth toe was short and became shorter after wedge osteotomy, which led to a greater angle difference.
The limitations of this study include the relatively short follow-up period for confirming the postoperative results. The A-P foot X-rays used for measurements were not consistently acquired vertically above the foot with full extension of all toes due to difficulties in the cooperation of the children. Additionally, the children’s guardians assessed subjective satisfaction, instead of the children themselves. However, the results were compared between two similar demographic groups of patients. In each group, values were compared in ratios to overcome the varying rate of growth in children. This study also provided exact numbers for critical lengths and angles, which reflect aesthetic aspects of the foot. Nonetheless, further research is needed to assess the vascular structure of the fifth toe accurately. Subsequently, assessments of the tendon, ligament, and movement of the toe should be conducted using magnetic resonance imaging and ultrasonography to reinforce the final decision.
In cases of postaxial polysyndactyly in which simultaneous web reconstruction is required, the medial toe tends to be excised. However, in cases with short sixth toes with axis deviation, sparing the fifth toe reduces the need for wedge osteotomy, yielding a safe and effective treatment with high cosmetic satisfaction.