Tarsal–carpal coalition syndrome: importance of early diagnosis

Abstract

Tarsal–carpal coalition syndrome is a progressive condition involving synostosis of the wrist, ankle and digits. We describe a mother and her newborn that have this rare inherited condition where the diagnosis was made only after the baby’s birth. The baby’s condition was suspected on antenatal scanning, and he was born with reduced range of motion of his digits, elbows and ankles. The mother’s condition has progressed to involve a fixed flexion deformity of her bilateral elbows, synostoses of her second to fifth digits and extensive coalition of her tarsal and carpal bones. She has required regular osteotomies to improve limb functioning and quality of life.

Background

Tarsal–carpal coalition (TCC) syndrome is a rare autosomal dominant, inherited disorder.^{1 2} It is characterised by progressive synostosis of the tarsals, carpals and phalanges, with shortened first metacarpals, brachydactyly and humeroradial fusion.¹ It is caused by a heterozygous mutation in the NOG gene on chromosome 17q22 which encodes for the noggin protein.² This protein is an antagonist to the transforming growth factor-B family and is vital for proper bone and joint development by inhibiting osteoblast differentiation.²

Given the progression of the synostoses, the ability to detect it on antenatal scanning and by clinical examination in the neonatal period, awareness of this condition is important for timely intervention/s to improve patient outcomes and quality of life. Diagnosis is made clinically and confirmed with identification of a NOG mutation.

Case presentation

A baby boy was born in Western Australia, at 38 weeks gestation with a birth weight of 3250 g and with the appearance of the hands and feet as shown (figure 1). There was no movement at the proximal interphalangeal joints (PIPJs) of the second, third and fourth fingers, and stiff PIPJs were noted on the fifth fingers of both hands. He also had bilateral limitation of wrist and elbow extension and fixed talipes calcaneovarus. Antenatal scans showed wrists and fingers held in extension with paucity of movements and evident foreshortening of bilateral thumbs.

Figure 1.

(A,B) Neonatal brachydactyly involving all fingers and clinodactyly of the second and fourth fingers bilaterally. (C) Neonatal bilateral fixed talipes calcaneovaus.

His mother (primipara) is currently 20 years old and has a fixed flexion deformity of her elbows with synostoses of the PIPJs of the second to fifth fingers bilaterally, brachydactyly, extensive coalition of tarsal and carpal bones (figure 2). She was also born in Western Australia and had no abnormalities on antenatal in-utero scanning. Gross and fine motor delays were detected at 10 months of age, expressed predominantly as an inability to bring food to mouth and persistent talipes equinovarus. Since four years of age, she has had regular bilateral osteotomies approximately every two years, with each foot operated on in separate procedures each time. Initial diagnosis was an unspecified congenital synostosis syndrome. TCC was first suggested as a possible diagnosis when she underwent genetic review during her pregnancy.

Figure 2.

(A) Maternal brachydactyly involving all fingers and clinodactyly of the second and fourth fingers bilaterally, and loss of usual proximal interphalangeal joint skin creases. (B,C) Maternal right and left feet with brachydactyly and evidence of previous corrective osteotomies.

Investigations

After the baby’s birth, the mother and baby underwent genetic testing and both were identified to have a pathogenic single nucleotide variant in the NOG gene resulting in an ‘NM_005450.4:c. [104C>G]’ mutation which is consistent with TCC (OMIM 186570). The baby’s hearing was within normal limits on audiology testing.

The mother underwent a recent CT of her right foot for preoperative planning for a rotational osteotomy which demonstrated profound intertarsal fusion as well as fusion of the first, fourth and fifth tarsometatarsal joints and partial fusion of the third tarsometatarsal joints (figure 3). A previous X-ray of the mother’s right hand taken after a fall showed absent carpal bones and an abnormally shortened and broad-based first metacarpal (figure 4).

Figure 3.

Profound intertarsal fusion as well as fusion of the first, fourth and fifth tarsometatarsal joints and partial fusion of the third tarsometatarsal joints in the mother’s foot.

Figure 4.

Maternal right wrist demonstrating absent carpal bones and an abnormal shortened and broad-based first metacarpal.

Differential diagnosis

Other NOG-related symphalangism spectrum disorders (NOG-SSD)

• Multiple syndrome.

• Proximal symphalangism.

• Stapes ankyloses with broad thumbs.

• Brachydactyly type B2.

Outcome and follow-up

The baby boy was referred to allied health services, orthopaedic surgeons and plastic surgeons for early intervention. He attends physiotherapy on a fortnightly to monthly basis for range of motion stretches and gross motor developmental support. Under the care of the orthopaedic surgeons, he underwent serial casting for his fixed talipes calcaneovarus until four months of age and subsequently was fitted for ankle-foot orthoses at night. No plastic surgery interventions for his hands have been required to date.

The child is now 1 year of age and able to roll front-to-back and back-to-front, sit unassisted and is making attempts at crawling. He is not yet pulling to stand or walking. From a fine motor perspective, he has a raking grasp and can hold objects, but has not demonstrated a pincer grip. He has visual attention for near and far. His language and social skills are appropriate for his age, with the child demonstrating babbling, use of several single words, indicating affection and playing peekaboo.

Discussion

This is a case of a mother and son with TCC, a rare (prevalence <1/1 000 000) inherited condition.¹ This family is the first reported case of TCC in Australia.

The disease course of TCC is a progressive fusion of the PIPJs with variable involvement of the distal interphalangeal joints, elbows and ankles.³ Pain is the most common presenting symptom, followed by deformity and stiffness. Stature, hearing, facial characteristics and intelligence are not affected.³ Coalition ossification may not be apparent on a plain radiograph until 8 years of age, with an MRI being the recommended modality, to assess for non-osseous coalition. The absence of conductive hearing loss distinguishes TCC from other NOG-SSD.³

To date there are seven known mutations that have been identified to cause TCC.^3–6 The NOG mutation identified in the mother, NM_005450.4(NOG):c.[104>G], is known to cause two different synostosis syndromes. It has been previously described in a family with TCC as well as in a sporadic case of proximal symphalangism.^{3 7} This finding suggests that epistatic modifiers in NOG are responsible for the phenotypic differences in these two conditions.³

Management is focused on optimising functioning of limbs and independence through physiotherapy (range of motion and strengthening exercises), occupational therapy (eg, custom-made assistive devices) and repeated orthopaedic and plastic surgeries for optimal functional and cosmetic outcomes. Non-operative treatment is usually the first line, with surgery to follow when conservative management has failed to alleviate symptoms or to correct significant deformity. When coalition involves no more than 30% of the surface area of the subtalar joint, resection has a 77% success rate.⁸ In the case of a failure of resection, triple arthrodesis is generally required.

Learning points.

• Limitation of movements of the proximal interphalangeal joints, wrist, elbows and ankles are highly suspicious for a synostosis syndrome, of which tarsal–carpal coaltion (TCC) is a differential.

• Preservation of hearing distinguishes TCC from other NOG-related symphalangism spectrum disorders.

• Early identification and intervention is critical to optimise outcomes and independence of the individual.