Nine toes; Mirror Foot Deformity.

Mirror foot is a very rare congenital anomaly, with only a few papers presenting definitive treatment for this entity. There are limited management recommendations. Most cases are treated before walking age. In our case, there were no associated developmental defects of the leg. The child underwent complex rays resection with medial foot reconstruction. After 7.5 years of followup, definitive surgical treatment was performed with satisfactory cosmetic and functional outcome.

INTRODUCTION

Polydactyly is a relatively common anomaly of the foot.1 It is characterized by the presence of supernumerary digits involving the hands, feet or both.12 The overall incidence of polydactyly is 1.7/1000 births with significantly higher incidence among African-American population.13 Polydactyly occurs as an isolated deformity or as a part of an established genetic syndrome.1345 Temtamy and McKusick described polydactyly based on the location of the extra digits: Preaxial (medial ray), central and postaxial (lateral ray).236 There is no strict definition of foot polydactyly and the condition is often compared with hand anomalies.5 There are several classification systems for foot polydactyly, based upon metatarsal morphology, ray involvement and levels of duplication.12 Preaxial mirror polydactyly of the foot, also called mirror foot, is a distinctly rare anomaly with less than 30 cases reported in literature to date and with even less documentation of definitive treatment.57 Although some authors consider mirror foot as any foot with mirror image polydactyly, others believe that mirror duplication of all the skeletal elements of the foot on the tibial aspect must be present to fulfill the criteria for diagnosing a mirror foot.78 The primary treatment for preaxial mirror polydactyly is surgical and is more complex compared to postaxial polydactyly.2 There are limited management recommendations in literature for this anomaly and various complications such as hallux varus, splaying of the first ray and short first metatarsal, should be anticipated when planning the reconstruction.367

CASE REPORT

A 14 month old female patient was referred to our out-patient clinic with a congenital malformation of the right foot. Both pregnancy and delivery was unremarkable. There was no family history of congenital malformations. Clinical examination showed that the trunk, upper limbs and the left lower limb were normal. There was no limb-length discrepancy. Normal range of motion of the knee, subtalar and ankle joints on the right lower limb was noted. Motion of the metatarsophalangeal (MTP) joints appeared normal. There were obvious supernumerary digits on the medial aspect of the right foot. Between the hallux and four normal toes, there were four duplicated toes with syndactyly between the first and the second. The lateral four digits appeared normal [Figure 1a]. Radiographs of the lower extremities revealed normal findings other than the right foot. On radiographs of the foot, there were eight fully developed digits with metatarsal bones, small rudimentary digit without metatarsal bone and with first metatarsal being hypoplastic [Figure 1b]. Based on the clinical and radiographic findings, a diagnosis of mirror foot was made. Corrective surgical procedure was performed under general anesthesia and tourniquet control. A wedge resection of the four duplicated rays was performed followed by complete release of the first MTP joint. Release of the tight abductor hallucis tendon was performed. The first ray was brought laterally to close the wedge and was held in place with a Kirschner wire [Figure 1c]. The postoperative course was uneventful. A long leg cast was applied. After extraction of Kirschner wire, we lost contact with patient for 7.5 years. The patient reviewed back at the age of 9 years with her mother. She had difficulties walking and shoe wearing. A cutaneous scar was noted over the medial aspect of the right foot as a result of the previous surgical intervention. The right foot was wide; with abduction of the first MTP joint [Figure 2a]. Radiographs revealed a wide space between the first and second rays. Angulation of first MTP joint (near 130°), with a supernumerary tarsal bone was noticed between the medial and intermediate cuneiform bones [Figure 2b]. All metatarsals were in adducted position. During the second surgical procedure excision of supernumerary tarsal bone was performed. Reposition of the first metatarsal bone was performed and held in place with a 2 mm Kirschner wire. Correction of hallux varus was held in place with 1, 8 mm Kirschner wire. Reinsertion of the tight abductor halluces tendon was performed. A long leg cast was applied for two weeks. After this period the sutures were removed and short leg cast was applied for following four weeks. After six weeks full weight bearing was allowed. The final result was satisfactory functionally and aesthetically [Figure 2c].

Figure 1

(a) Clinical photograph showing mirror foot appearance of the right foot at the time of first admission (b) Anteroposterior x-ray of the right foot showing eight metatarsal and nine toes (c) Postoperative clinical photograph showing resection of four rays

Figure 2

(a) Clinical appearance of the foot after 7½ year (b) Anteroposterior x-ray of the foot showing wide space between 1st and 2nd ray, supernumerary tarsal bone and hallux varus (c) clinical photograph of the foot showing appearance after the second surgical procedure

DISCUSSION

The formation of the limbs is regulated by a complex series of molecular signals.19 Three signaling centers that control limb development have been discovered: The apical ectodermal ridge (AER), the “zone of polarizing activity” and the wingless-type (Wnt) signaling center.9 The limb buds form deep to a thick band of ectoderm. At the apex of each limb bud, the ectoderm thickens to form an AER. The AER exerts an influence on the limb mesenchyme that initiates growth and development of the limbs in a proximo-distal axis. Mesenchymal cells aggregate at the posterior margin of the limb bud to form the “zone of polarizing activity” which regulates limb growth and development on an antero-posterior axis.69 Wnt signaling center secretes factors that induce the underlying mesoderm to adopt the dorsal characteristics.9 During the 7th week, condensations of mesenchyme form digital rays and toes in the footplates.1

The exact etiology of polydactyly is not fully understood.3 It can occur as an isolated deformity with different forms of polydactyly representing distinct genetic entities or in association with other congenital anomalies such as hand polydactyly and/or syndactyly, anorectal anomalies, tibial deficiencies, cleft of the lip and palate, cardiac defects.12 Polydactyly have been associated with several syndromes: Pallister-Hall, Lawrence-Moon-Bardet-Biedl, Ellis Van Creveld, Rubinstein-Taybi, facio digital, cephalo-polysyndactyly, Holt-Oram and Down syndrome.17 Polydactyly of the foot is a relatively common anomaly.3 Several classifications of foot polydactyly are available in the literature. Temtamy and McKusick based their classification on the location of extra digits and the syndrome involved.2 Venn Watson introduced a morphologic classification based upon the anatomic configuration of the metatarsals and duplicated bony parts.10 Fukazawa et al. made an analogy with the mirror hand classification.5 Watanabe et al. classified polydactyly into medial, central and lateral ray groups, further subdivided into tarsal, metatarsal, proximal phalangeal and distal phalangeal groups.1 This classification was found most useful by several authors.1411

Mirror foot represents extreme form of foot polydactyly. Some authors stated that mirror foot and diplopodia are descriptive terms for the same condition.812 Diplopodia simply suggests that the foot is duplicated and the supernumerary toes do not have to be in the mirror duplication.8 Khan et al. stated that diplopodia has to be differentiated from polydacyly, where accessory tarsal or metatarsal bones are not seen.13 Etiology of mirror foot is connected to aberrant positioning of the “zone of polarizing activity”.6 The true definition of mirror foot is author dependent and classification of this anomaly is based on sporadic cases.25 Sudesh et al. stated that mirror foot should be differentiated from polydactyly by presence of accessory tarsal bones.7 Watanabe et al. have added mirror duplication of the foot to the spectrum of preaxial polydactyly.111 Belthur et al. suggested that the mirror foot represents an extreme form of preaxial polydactyly and they have added this deformity as additional type of preaxial polydactyly.1 Verghese et al. proposed the term “preaxial mirror polydactyly” which includes feet with supernumerary rays situated medial to the first ray (preaxially) with characteristics of postaxial toes. They have not included tarsal duplication because of its variability.8 Preaxial mirror polydactyly (mirror foot) is an extremely rare condition. It can be associated with tibial and fibular abnormalities, with anomalies of hindfoot, midfoot and forefoot, variably expressed.128 Fukazawa et al. in their study have reported that until 2009 only 28 cases of mirror feet have been reported in English literature with only seven cases documented for their treatment.5678 Our patient has been treated 10 years ago and at that time there were even fewer reports on mirror foot. Treatment of this anomaly is complex because it has both functional and a esthetic implications.67 McCarthy et al. and Galois et al. stated that the surgical treatment of preaxial polydactyly is complex with poor long term result.34 Most cases are treated during childhood, before or after walking age with individualized approach for every patient.35 At the time of the first treatment our patient was 14-month-old. Some authors have advocated that the surgery should be delayed until ossification and hence the accurate anatomic assessment is possible.14 Our patient had mirror foot with eight metatarsals and nine toes. 10 toes are the highest number reported in literature.5 Karchinov stated that excision of supernumerary tarsal bones is very important for successful treatment of these anomalies.15 In our case during first surgical treatment supernumerary tarsal bone was not excised. After 7.5 years gap, it was obvious that excision of supernumerary rays without excision of supernumerary tarsal bone was not sufficient. Clinical and aesthetical outcome after the second surgical treatment and excision of the supernumerary tarsal bone was significantly better.

To conclude, a case of nine toes mirror foot is presented. At first operation a supernumerary tarsal bone was not excised. After a 7.5 year gap in followup the patient was presented with varus deformity of the first ray. After excision of the supernumerary tarsal bone and realignment of the first ray the result was significantly better. The rarity of the condition and the scarcity of literature regarding its management contributed to failure of the first operation and this report might therefore help others avoid a similar outcome.