Osteomyelitis in limb amputated by amniotic band sequence

Abstract

A preterm (30⁺² week) neonate with below-knee amputation (right lower limb), constriction rings and syndactyly, subsequent to amniotic band sequence, developed pus discharge from the right tibial stump. The neonate did not have clinical features of systemic sepsis. Blood culture was sterile. The pus culture, however, grew methicillin-resistant coagulase-negative Staphylococcus and bone scan was suggestive of osteomyelitis of right proximal tibial stump. Osteomyelitis was likely caused by the contiguous spread of infection from the exposed stump. Neonate was treated with intravenous antibiotics for 4 weeks and discharged on oral feeds.

Background

Amniotic band sequence (ABS) is characterised by one or more congenital anomalies in the neonate, generally attributed to fibrous strings, called amniotic bands, which entangle fetal parts. The estimated incidence varies from 1:1200 to 1:15 000.¹ The anomalies described include limb defects, craniofacial defects and body wall defects.² The limb defects are often multiple and asymmetric and range from constriction rings in limb or digits, clubfoot, joint contractures and syndactyly, to amputation of digits or limbs. The craniofacial abnormalities include facial clefts, anencephaly, encephalocele and asymmetric facial structures. Several internal organ defects, including cardiac, genitourinary and pulmonary defects, have also been described in association with ABS.³

The development of congenital anomalies involves rupture of the amnion at some time during pregnancy, followed by extrusion of amniotic fluid and fetus into the naked chorionic cavity. Fibrous strings called amniotic bands arise from the mesodermic surface of the amnion.⁴ However, some cases of ABS have anomalies, which are not explained by amniotic bands. These include internal visceral defects with the histologically intact amniotic membrane possibly caused by an intrinsic defect in the developing embryo.³ Another explanation is a primary vascular abnormality, unrelated to amniotic bands, causing disruption of blood flow to some fetal parts. Lately, some genetic factors have also been described in the pathogenesis of this disorder.⁵

Amniotic bands may be visualised by antenatal ultrasound (USG) along with characteristic fetal malformations. Thin bands may be seen in relation to fetal parts resulting in restriction of movements, distal oedema, constriction rings or amputation of limbs, along with colour flow Doppler changes.^{6 7} The fibrous bands are seen as T2-hypointense structures on fetal MRI, which in addition provides more detailed visualisation of fetal structures and may therefore be considered if fetal surgery is planned.⁸

Case presentation

A preterm (30⁺² week) male neonate was born to a 37-year-old primigravida mother (non-consanguineous marriage) by caesarean section in view of preterm rupture of membranes for 8 days and severe oligohydramnios. There were no other antenatal complications during pregnancy. Level II USG did not reveal any malformation in fetus. There was no history of maternal smoking, drug abuse, radiation exposure, connective tissue disorders (Raynaud phenomenon, arthralgia, arthritis, etc.), any invasive testing like chorionic villus sampling or any previous uterine surgery in the mother.

Perinatal details

The neonate required initial steps and delivery room CPAP support in view of respiratory distress at birth. The baby was noted to have multiple anomalies in the form of below-knee amputation of the right lower limb with the tibia and fibula bones visible at the stump (figures 1–4). The necrosed amputated part was seen in the amniotic cavity. There were constriction rings in the left foot and syndactyly of second and third digits with amputation of distal phalanx of a fourth digit in the left hand.

Figure 1.

Below-knee amputation of the right lower limb with the tibia and fibula bones visible at the stump.

Figure 2.

Necrosed amputated part in the amniotic cavity.

Figure 3.

Constriction ring in the left foot.

Figure 4.

Defects in the amniotic membrane.

Respiratory distress settled within 12 hours of birth. In view of maternal risk factors with respiratory distress, sepsis screen was done, which was negative (total leucocyte count [TLC]: 7600/mm³; absolute neutrophil count [ANC]: 2965/mm³; erythrocyte sedimentation rate [ESR]: 5 mm; C reactive protein [CRP]: negative; immature to total neutrophil ratio [IT ratio]: 0.10). Neonate remained haemodynamically stable and on room air till day 6 when pus discharge from the amputated stump of the right lower limb with oedema and skin redness around the site was noted. A repeat sepsis screen was done.

Investigations

Repeat sepsis screen was negative (TLC 8800/mm³; ANC: 3520/mm³; ESR: 2 mm; CRP: negative; IT ratio 0.16); however, pus from stump sent for culture/sensitivity grew Staphylococcus hemolyticus (coagulase-negative Staphylococcus) sensitive to vancomycin and amikacin. A plain radiograph revealed proximal stumps of the right tibia and fibula with normal femur but no features of osteomyelitis. However, a bone scan showed increased delayed phase activity in the tibial stump, suggestive of osteomyelitis of the stump. Blood culture was sterile. The neonate did not have any internal visceral organ anomalies on echocardiography, transcranial and abdominal USG.

Differential diagnosis

The initial diagnostic possibilities included local soft tissue infection, osteomyelitis or septic arthritis involving the knee joint. Systemic sepsis was unlikely as the neonate was stable, on room air and tolerating enteral feeds well. Additionally, the sepsis screen was negative twice and blood culture was sterile. The USG did not reveal any evidence of joint involvement. Further, the bone scan was done to differentiate soft tissue infection and osteomyelitis, which revealed osteomyelitis of the amputated tibial stump.

Treatment

Neonate was treated with intravenous antibiotics (vancomycin for 28 days and amikacin for 14 days) along with the daily dressing of bone stump. Strict asepsis was maintained during local care of the amputated stump. The neonate responded well with the disappearance of pus discharge and subsidence of skin oedema and redness. The neonate remained clinically stable during the hospital stay, tolerated feeds well and gained weight adequately. Parents were trained in the local care of amputated stump and maintenance of asepsis.

Outcome and follow-up

The child was subsequently discharged without any antibiotics. At follow-up after 2 weeks, the child was asymptomatic and stump appeared healthy. The child is under our follow-up and is planned for stump closure by the plastic surgery team.

Discussion

In our case, the child presented with right lower limb amputation at birth with constriction bands at several sites in other extremities, making an aetiological diagnosis of amniotic band syndrome clearly evident. This child developed osteomyelitis in the amputated stump during the first week of life. On literature search using the terms ‘amniotic band syndrome’ OR ‘limb amputation’ AND ‘osteomyelitis’ in the MEDLINE database, we found one case of osteomyelitis described in a neonate born at 30 weeks’ gestation with congenital foot amputation, with osteomyelitis developing in the stump. The neonate was managed with intravenous antibiotics and surgical skin graft of the exposed stump.⁹ The ABS may be suspected on antenatal USG or at the time of birth when neonate has characteristic anomalies like asymmetric limb defects, constriction rings and non-midline body wall or craniofacial defects. The placental examination may reveal rupture of the chorion. Treatment of a neonate with ABS includes a multidisciplinary approach including neonatologists, plastic surgeons for the limb defects or facial defects and physiotherapists. With advances in fetoscopic procedures, fetal surgery is now possible which involves lysis of constricting amniotic bands in-utero.¹⁰ Though most cases of ABS are sporadic and the risk of recurrence is low, familial cases have been reported.^{11 12}

Neonatal osteomyelitis is usually a result of bacteraemia and subsequent seeding of metaphysis of long bones; however, spread from contiguous infection is also possible.¹³ ABS with amputation of limbs and digits represents one such situation where bone may be infected because of its exposure to the environment. The most common organism implicated is Staphylococcus aureus followed by coagulase-negative Staphylococcus.¹³ Clinically, osteomyelitis may present with subtle manifestations like local swelling without any signs of systemic infection or may present as severe sepsis and disability. The neonate, in our case, had only local signs of infection but was otherwise stable. The diagnosis of osteomyelitis may be confirmed by various imaging modalities including plain radiograph, USG, bone scan or MRI. In our case, we used a bone scan for confirming the diagnosis. MRI remains the gold-standard investigation with a very high sensitivity for detecting early osteomyelitis.^{13 14} However, MRI may not always be feasible in neonatal practice. Treatment of osteomyelitis usually involves 4–6 week of intravenous antibiotic therapy, which was completed in our patient during the hospital stay.

Patient’s perspective.

It was shocking initially as I was not informed during pregnancy regarding the anomalies of my baby. I was worried about further possible complications like infection in the bone. However, thankfully my child improved with antibiotics. At present, I am hopeful that the constriction bands and syndactyly will be addressed by the plastic surgery team as my child reaches age of 6 months. I am thankful to the hospital and team of doctors and nurses who cared for my baby.

Learning points.

• Contiguous spread, though uncommon in neonates, is an important cause of osteomyelitis, especially in cases of open-exposed bony tissues, like in amputated limbs due to amniotic band syndrome.

• Osteomyelitis is a rare complication in amniotic band syndrome, but should always be kept in mind, particularly in cases of exposed bones. Appropriate care and asepsis during manipulation of amputated limbs can prevent infection, prolonged hospital stay and unnecessary exposure to antibiotics.

• Careful monitoring, suspicion and early detection of osteomyelitis can prevent complications and result in complete resolution of the infection.