Presentation and multidisciplinary management of a unique case of lower limb dysmelia resulting from amniotic band syndrome

Abstract

A neonate was born with a unique congenital lower limb dysmelia due to an abnormal presentation of amniotic band syndrome. An anomalous soft tissue tether from the plantar surface of the right foot to the right buttock caused extreme knee flexion, tibial rotation and malformation of the developing foot. This complex malformation required a multidisciplinary team (MDT) approach to decide between reconstruction and amputation. The band of tissue was released operatively at 73 days postdelivery, improving knee extension, and the tissue was banked on the thigh as a tube pedicle for future reconstruction. The patient underwent rehabilitation, which has been shown to be vital for synovial joint formation. At 18 months old, the decision was made to proceed with through-knee amputation and a prosthesis. The literature discussed shows the importance of an MDT approach in complex lower limb cases to give the best functional outcome for the patient.

Background

Amniotic band syndrome (ABS), also termed constriction ring or ring constriction sequence, compromises a collection of intrauterine malformations.¹ The classical presentation in the literature describes constriction rings (restrictive bands of tissue) around the limb.² However, to raise awareness about the life-changing impact ABS can have, we present the case of a rare form of ABS, which formed a soft tissue tether between the right foot and right buttock; leading to a unique and complex lower limb malformation which poses a complicated multidisciplinary challenge.

Case presentation

A neonate was born to a mother and father in their 30s, both without significant medical history. The 20-week scan identified an abnormal right knee and foot position. Subsequently, a 21-week foetal abnormality scan showed detached amniotic membranes throughout, with the right foot entangled within, and foot anatomy disrupted. A skull vertex deficiency was also demonstrated, likely due to amniotic rupture. The obstetric plan was to bring the mother to full term, however, due to a raised pulsatility index on the umbilical artery Doppler, labour was induced at 34+3 weeks. The neonate was born at a tertiary centre via normal vaginal delivery.

Neonatal examination found the right knee in fixed flexion at 120° with external rotation of the tibia and foot (figure 1). Anatomical development appeared to have been disrupted by a congenital band that traversed the right lower limb and right buttock (figure 2), holding the developing knee in extreme flexion with consequent development of a popliteal pterygium. The band from foot to buttock was approximately 10 mm in diameter and no structures were palpable within. The plantar surface of the foot had a protuberance suggesting polydactyly. The skull vertex abnormality was diagnosed as a dermoid cyst. The patient also had a single palmar crease bilaterally, tongue tie (which did not cause any issues with feeding, so was managed conservatively), hypoplastic left thumb, chest wall asymmetry and a left foot third webspace syndactyly.

Figure 1.

The right foot externally rotated and dorsiflexed.

Figure 2.

The right lower limb, showing the congenital band traversing up to the right buttock, and the extra-axial digit on the plantar surface of the foot.

Investigations

Histological placental analysis demonstrated amnion disruption-like changes, and a nuclear squamous-like material, in keeping with ABS. Microarray showed no significant abnormalities. A 332 Kb duplication on chromosome 20 was identified in both the neonate and mother, however, clinical geneticists concluded this was of uncertain significance. Hip ultrasound imaging showed normal anatomy. Right lower limb X-rays demonstrated a fully formed femur, tibia and fibula. However, the tibia was externally rotated, and the right foot showed a partially developed phalanx in the pre-axial extra digit.

Postoperatively, ultrasound confirmed that the patella and extensor mechanism of the lower leg were subluxed laterally, with the foot in calcaneovalgus position.

Treatment

At 73 days old, the patient underwent congenital band and preaxial extra digit release. This procedure permitted partial extension of the knee joint, enabling physical rehabilitation, and introducing the possibility of further reconstruction or below-knee prosthesis. The nail plate and several stumps of amniotic band-like tissue were removed from the extra digit, and both the congenital band on the thigh and extra digit were left in situ as ‘spare parts’ in case of future reconstruction (figure 3).

Figure 3.

The right lower limb after release of the congenital band.

Postoperatively, the position of the knee improved from approximately 150° to 90°. The patient received input from physiotherapists, prosthetists and neonatal teams, and was reviewed in a joint orthoplastic appointment. At 15 months, it was noted that despite the congenital band release there was no active quadriceps function and a significant flexion deformity remained at the knee. At this point, the patient was achieving all developmental motor milestones except walking. An MDT decision was made according to the principles of shared decision-making, along with the patient’s parents, to proceed with amputation and subsequent prosthesis fitting, as it was felt that this would give the best functional outcome and enable the child to walk.

At 17 months old, the dermoid cyst on the scalp was excised. At 18 months old, the patient underwent a right through-knee amputation (figure 4). Within 2 weeks of the operation, the child was kneeling and attempting to stand on the amputated stump.

Figure 4.

The right lower limb after through-knee amputation.

Outcome and follow-up

The patient has now been fitted for a prosthetic leg, has started to walk with the aid of the prosthesis and is meeting all other developmental milestones. Looking forward, the child will require acrosyndactyly release for the left toes, and is still under investigation for a chest wall asymmetry and Blauth grade 1 hypoplastic thumb. However, the child should achieve a good functional outcome and enjoy a relatively normal life.

Discussion

Although each case of ABS is unique, the deformities can be grouped into constriction rings, limb defects, body wall defects and craniofacial defects (table 1).² The classical presentation encompasses limb constriction rings and amputation. In a study of 71 ABS cases, 18% involved only lower limbs.¹ This is equivalent to 0.17 per 10 000 births, demonstrating how rare our patient’s lower limb deformity is. Additionally, there are only two cases in the literature which demonstrate a similar ABS-linked skin pedicle.^{3 4} However, these also show the classical constriction rings, which our patient was missing, and unfortunately neither case progressed to the stage of considering reconstructive options.

Table 1.

Classification of amniotic band syndrome defects, adapted from Lowry et al²

1	Amniotic bands/constriction rings with or without limb defects
2	Body wall defect with or without limb defect, with or without amniotic bands/constriction rings
3	Amniotic bands/constriction rings with craniofacial defects
4	Amniotic bands/constriction rings with limb and craniofacial defects
5	Amniotic bands/constriction rings, craniofacial defects and body wall defects

Two theories of aetiology have been hypothesised. The now discredited intrinsic model describes anomalies secondary to vascular injury. This was rebuked by Bamforth,⁵ who found that anomalies occurred prior to embryonic circulation establishment. The more widely accepted extrinsic model theorises that amnion rupture in early pregnancy causes loose amniotic strands to entrap or affix to the fetus.¹ As the ring is inflexible but the fetus continues to grow, it results in a tourniquet effect with amputation of a limb or digit. This is reflected in our case by the malformation pattern and lack of vascular insufficiency to the distal lower limb. However, neither theory explains all the defects that can be associated with ABS.

The malformations in the literature are polymorphic and do not follow any syndromic patterns, therefore, each patient is managed uniquely to give the best functional outcome. In a 35-year study⁶ focusing on management of ABS in upper limbs, 16 different procedures were carried out, most commonly excision of constriction band with Z-plasty. The average number of procedures per patient was 6.7, however, the maximum was 19 procedures.⁶ The potential need for multiple reconstructive surgeries throughout the patient’s childhood was taken in to consideration in this MDT decision, and it emphasises the need for counselling and strong communication with the patient’s family with respect to long-term management.

An MDT approach for the management of ABS is imperative. Alongside this, counselling in the perinatal period is vital for the parents, to explain the potential range of malformations and quality of life. For limb malformations which are complex to reconstruct, such as this case, an MDT approach is effective at giving a good functional outcome in 93% of cases.⁷ The main reason MDT plans are not implemented is patients opting for a more conservative approach, therefore patient preference must be considered. Kotsougiani-Fischer et al⁷ showed that when an MDT recommended limb salvage in adult patients it was achieved in 91% of cases. To manage future complex congenital conditions, we would advocate for a multidisciplinary clinic with plastic surgery, orthopaedic surgery and prosthetists in the perinatal period.

In this patient, it was hoped that release of the congenital band would improve the function of the knee. Animal models have shown that immobilisation in utero significantly affects chondrocyte proliferation, endochondral ossification and joint formation, leading to loss of function of synovial joints. This is due to loss of gene expression and signalling proteins, including Fibroblast Growth Factor 2 and Bone Morphogenetic Protein 2, which are responsible for the differentiation of tissues at joints. In humans, this has been described as Foetal Akinesia Deformation Sequence. Inhibition of foetal movement causes contractures, hypomineralisation and joint dysplasia. The treatment for this condition is mechanical stimulation. It is hypothesised that, in cases like ours, physiotherapy could recreate the signalling pathways and improve the malformations caused by immobilisation of joints.⁸

When it became clear that the knee was not functional, the decision was made for a through-knee amputation and prosthetic lower limb. A through-knee amputation, as opposed to above-knee, allowed for preservation of femoral length and maximal potential for femoral growth. The distal femoral physis accounts for 70% of the femoral longitudinal growth and is the quickest growing growth plate in the body. A met-analysis looking at paediatric distal femoral fractures showed 52% of patients developed significant growth disturbances.⁹ Therefore, a through-knee amputation would minimise the need for multiple future surgeries and allow our patient the best functional outcome.

This unique case demonstrates an atypical presentation of ABS involving extreme knee flexion, tibial rotation, lateral subluxation of the patella and extensor mechanism and malformation of the developing foot, presenting a complex reconstructive challenge. We highlight the need for a combination of physiotherapy to encourage development of synovial joints; an MDT approach to complex congenital limb malformations; and adequate parental counselling, to ensure the best functional outcome for the patient.

Learning points.

• Amniotic band syndrome (ABS) does not only cause the classical constriction rings; it can lead to complex and life-changing limb malformations.

• Adequate parent counselling is needed in the perinatal period to prepare the parents for the implications and long-term management of ABS.

• In complex limb malformations, such as this case, an multidisciplinary team approach is vital, and effective at giving a good functional outcome in 93% of cases.

• In some cases, the best functional outcome for the patient may be achieved by amputation rather than complex reconstruction.

Ethics statements

Patient consent for publication

Consent obtained from parent(s)/guardian(s).