Computed Tomography and Magnetic Resonance Imaging Features of Pedal Ectrodactyly with Lateral Hindfoot Syndrome: A Case Report

Hong Kong J Radiol 2024 Sep;27(3):e176-82 | Epub 2 September 2024

 

 

¹ Department of Radiology, Pamela Youde Nethersole Eastern Hospital, Hong Kong SAR, China

² Department of Orthopaedics and Traumatology, Pamela Youde Nethersole Eastern Hospital, Hong Kong SAR, China

 

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Ectrodactyly, also known as split hand and foot deformity, is a rare congenital skeletal deformity characterised by deficiency or absence of the central digital rays. The central cleft simulates the appearance of a lobster claw.[1] It can present as an isolated deformity or part of a syndrome—usually with autosomal dominance inheritance—such as the ectrodactyly-ectodermal dysplasia-clefting syndrome or limb-mammary syndrome.[2] [3]

 

We present a case with non-syndromic pedal ectrodactyly. The patient presented with chronic pain over the lateral ankle. To the best of our knowledge, this is the first report of imaging findings, highlighting consequent soft tissue findings in an adult with split foot deformity.

 

A 31-year-old female with known left foot deformity since birth presented with a 2-year history of increasing pain over the lateral ankle. The pain was worse on movement and weight-bearing. There was no preceding injury. She was born full term by normal spontaneous delivery. She enjoyed good past health and had no other known congenital anomalies. Physical examination revealed clefting deformity and abnormal configuration of the left foot. The lateral ankle joint was tender with mild local swelling.

 

Radiographs and reconstructed three-dimensional computed tomography of the left foot and ankle revealed the presence of two complete rays and a singular tarsal bone articulating with the first ray. An incomplete ray was seen in between, comprised of two phalanges and a metatarsal head. The base of the proximal phalanx and the metatarsal head formed anomalous articulation with the first metatarsal head (Figure 1).

 

Figure 1. (a) Dorsopalmar oblique view of X-ray of the left foot. An incomplete ray and a single metatarsal articulating with the first ray are demonstrated. Synostosis of the talus and calcaneum is evident. (b) Frontal view of X-ray of the bilateral ankle joints shows abnormal configuration of the left calcaneum (notched arrow) and shortened and widened left distal fibula (arrow). Osteoarthritic changes of the left calcaneofibular neo-facet are evident. (c) Reformatted computed tomography in bone window of the left foot. The proximal phalanx (PP) and metatarsal head (MT) of the incomplete ray articulate with the first metatarsal head.

 

The left hindfoot was formed by a single bony structure with anterior bifid appearance, simulating non-segmentation of the talus and calcaneus (hereby termed the talocalcaneal complex) [Figures 1 and 2]. A calcaneofibular neo-facet was demonstrated. The distal fibula was shortened while the lateral malleolus appeared widened (Figures 1 and 2).

 

Figure 2. Reconstructed three-dimensional computed tomography of the left foot and the ankle, demonstrating the bony anatomy in lateral oblique (a) and frontal (b) projections, as well as the soft tissue components in the lateral (c) and frontal (d) projections.

 

Pes planar deformity was evident with loss of both medial and lateral longitudinal arches. The talus-first metatarsal angle (Meary’s angle) measured 15° while the calcaneal inclination angle approached 0°, signifying loss of the medial and lateral arches, respectively (Figure 3a). There was widening of the talocalcaneal angle, suggestive of hindfoot valgus deformity (Figure 3b). Osteophytes and subchondral sclerosis were seen around the first tarsalmetatarsal joint, suggestive of midfoot arthrosis (Figure 3b).

 

Figure 3. (a) Lateral view of X-ray of the left foot showing pes planar deformity and a talus-first metatarsal angle of 15˚ convex downwards (Meary’s angle in normal individuals is normally 0˚) [black dotted lines]. The calcaneal inclination angle, measured between the calcaneal inclination axis and the supporting horizontal surface, approaches 0˚ (normal, 20-30˚) [white dotted line]. (b) Dorsopalmar view of X-ray of the bilateral feet. Widened talocalcaneal angle (38˚) [black solid lines] is compared with normal right side (20˚) [white solid lines] (Kite’s angle in normal individuals is normally 25-40˚). It also shows arthrosis of the first tarsal-metatarsal joint (white arrow).

 

Computed tomography of the left ankle joint revealed bony remodelling with flat neo-facets at the calcaneofibular articulation. Secondary osteoarthritic changes and osteophytes were observed (Figure 4a). Magnetic resonance imaging showed associated marrow oedema, moderate synovial thickening, and interposed soft tissue oedema. Mild thickening of the adjacent peroneus brevis and longus tendon sheaths was observed (Figures 4b to 4e). Overall features were suggestive of lateral hindfoot impingement syndrome.

 

Figure 4. (a) Computed tomography and (b-e) magnetic resonance imaging of the left ankle joint. (a) Reformatted coronal projection showing osteophytosis (black arrows) and osteoarthritic changes of the calcaneofibular neo-facet. (b) Sagittal proton density (PD)–weighted short tau inversion recovery image. Increased marrow signals (hollow notched arrows) over distal fibula (DF) and talocalcaneal complex are suggestive of oedema. (c) Coronal PD-weighted fat-saturation image showing moderate soft tissue oedema and thickened sheath of the peroneus longus tendon (solid notched arrow). (d, e) Sequential PD-weighted axial slides through the talofibular joint showing moderate synovial thickening and interposed soft tissue oedema (black arrows).

 

Normal anterior talofibular ligament and calcaneofibular ligament were not well delineated, possibly due to either congenital absence or secondary to chronic impingement-related tearing (Figure 5a and 5b). The posterior talofibular ligament and anterior inferior tibiofibular ligament were small in calibre. Moderate thickening and high heterogeneous short tau inversion recovery signals of the peroneus longus tendon was seen, suggestive of tendinosis and interstitial tear (Figure 5c and 5d). It was possibly a sequala of the altered hindfoot biomechanics.

 

Figure 5. (a) Proton density (PD)–weighted axial view through the right distal calf for comparison. (b) PD-weighted axial view through the left distal calf. Normal anterior talofibular ligament (white arrow) is not well demonstrated. All muscles in the anterior, lateral, and posterior compartments are atrophic. (c) PD-weighted reformatted sagittal image and (d) PD-weighted fat-saturated sequence axial image showing thickening of the plantar portion of the peroneus longus tendon (notched arrows), with high heterogeneous signals suggestive of tendinosis and interstitial tear.

 

The left peroneus longus and brevis muscles were atrophic compared with the right side. Normal infra-malleolar portion of the peroneus brevis tendon was not demonstrated (Figure 6). Other calf muscles had smaller bulk than the right side, most evident at the lateral and posterior compartments (Figure 5b). The plantar portions of the tendons in the anterior and posterior compartment were attenuated.

 

Figure 6. Proton density–weighted axial magnetic resonance images through the right (a) and left (b) distal calves, with the anterior, posterior, and lateral compartments highlighted in green, blue, and yellow, respectively. The left peroneal brevis (PB) and peroneal longus (PL) muscles are atrophic. Muscles in the posterior compartment (tibialis posterior [PT], flexor digitorum longus [FDL], and flexor hallucis longus [FHL]) are also atrophic. Muscle bulks in the anterior compartment (left extensor hallucis longus [EHL] and extensor digitorum longus [EDL]) are preserved. The plantar portion of the anterior and posterior compartment tendons are mostly attenuated (not shown).

 

Ectrodactyly derives from the Greek words ‘ektromo’ and ‘daktylos’, meaning abortion and fingers, respectively. It is nonetheless not limited to the digits or upper limbs. Reportedly it represents a spectrum of limbic deformity, from aphalangia, adactylia and acheiria, to hemimelia or amelia. Most cases of sporadic ectrodactyly are unilateral.[4] The pathogenesis involves failure of initiation of apical ectodermal ridge, or subsequent signalling pathways, that contributes to truncation of all skeletal elements over the distal developing limb bud.[3]

 

Although ectrodactyly commonly presents as an isolated finding, it may form part of a syndrome. Ectrodactyly-ectodermal dysplasia-clefting syndrome is the most reported. It is an autosomal dominant condition, affecting structures derived from the ectoderm such as hair, skin, nails, and teeth, with such presentations as skin hypopigmentation, sparse hair, and dental defects. Genitourinary and lacrimal duct anomalies are also common. Limb-mammary syndrome is also well studied. It is characterised by mammary gland and nipple hypoplasia.[5] Other less common syndromes associated with ectrodactyly include Karsch–Neugebauer-syndrome (congenital nystagmus), Patterson-Stevenson- Fontaine syndrome (mandibulofacial dysostosis), and Adams-Oliver syndrome (scalp defect).[5] [6] Despite the characteristic features, marked phenotypic variability is reported, possibly related to variable expression and incomplete penetrance.

 

Blauth and Borisch[7] proposed a radiological classification for cleft foot that describes a spectrum of metatarsal defects ranging from types I to VI. The characteristics and possible associated features are shown in the Table.[7] With an incomplete metatarsus and two absent rays, our patient fell between type IV and V. In line with the findings, our patient demonstrates possible synostosis of the talus and calcaneum. From the case series, the authors suggested that cleft formation begins at the second or third ray, then proceeds in a distal to proximal fashion.[7] The fifth ray is usually the last affected (Table). Synostosis is commonly seen at the margin of the cleft. Associated features such as syndactyly, polydactyly and cross-bone deformities may be observed, yet appear widely variable.

 

Table. Radiological classification for cleft foot[7]

 

The presence of an incomplete ray caught our attention. According to the known pattern of deformation, the distal portion of the ray should be first affected. For the incomplete ray, provided the absence of a proximal metatarsal, the development of the distal metatarsal and phalanges are not to be expected. In split-hand deformities, syndactyly of the remaining digits is reportedly common. There are also rare cases of triphalangeal thumbs.[5] In the case series by Blauth and Borisch,[7] a few cases displaying central polydactylous element were also reported. Two of the cases showed duplicated phalanges of the second digit.[7] We remain open to the possibility that the incomplete metatarsal head in our patient might arise from the first ray as a polydactylous deformity.

 

The Bluman-Myerson classification stages adult acquired flatfoot deformity (AAFD) based on severity and rigidity of the flatfoot deformity.[8] The bony deformities in our patient caused severe and irreversible hindfoot valgus and rigid flatfoot deformity, classified as stage III AAFD. The altered bony configuration leads to lateral hindfoot (or subfibular) impingement with associated soft tissue fibrosis, midfoot arthrosis, peroneal tendinopathy, and calcaneofibular ligament entrapment.[9] Stage III AAFD is also not uncommonly present in patients with congenital tarsal coalition due to arch flattening and associated rigid hindfoot valgus.[10] The principles of treating stage III AAFD include correcting hindfoot valgus, realigning the midfoot from abduction deformity, and relieving the lateral compartment. In normal individuals, arthrodesis of the talonavicular and subtalar joints is usually performed, where most deformities are found. The calcaneocuboid joint may also be fused, after balancing against the risks of ankle valgus, failure of the deltoid ligament and worsened foot rigidity.[11] In our case, the aim of surgical treatment will be to relieve lateral compartment pressure and the associated pain. A bony procedure is needed as the primary pathology is bone anomaly. Treatment options are limited by a deformed talocalcaneal complex, the absence of few mid- and hind-foot bony structures and hence such joints as the subtalar and calcaneocuboid joints. Medialising calcaneal (talocalcaneal complex, in our case) osteotomy is the most feasible option. In view of the osteoarthritis of the calcaneofibular neo-facet, this procedure may not completely relieve the pain. Ankle fusion would be the last resort to treat the arthritic pain since severe functional disability would result.

 

Common features of ectrodactyly, including absent metatarsals and tarsal synostosis, are present in this case. The presence of an incomplete distal ray around the cleft is nonetheless discordant with current knowledge; we propose that it may arise from the first ray as a polydactylous deformity. Pes planus deformity and associated lateral hindfoot impingement syndrome were well demonstrated across different imaging modalities and consistent with the clinical presentation. Future case series directed at associated soft tissue injuries may be helpful in planning rehabilitation programmes and surgical interventions.