Prenatal diagnosis and postnatal outcome of fetal congenital knee dislocation: systematic review of literature

OBJECTIVES

Congenital knee dislocation (CKD) is a rare condition, affecting 1 in 100 000 newborns. Its prenatal diagnosis is challenging and not well described in the literature, especially when it appears isolated and not as part of a complex malformation or syndromic pattern. The purpose of this study was to provide a comprehensive review of the available literature on the prenatal diagnosis and postnatal outcome of CKD and to summarize the current evidence on this topic.

METHODS

A systematic review of the literature on the prenatal diagnosis of CKD was performed in PubMed, Scopus and EMBASE. A predefined combination of specific keywords was used, focusing on intrauterine manifestations, diagnostic methods, prenatal behavior, postnatal treatment and neonatal outcome as well as long-term outcome in terms of ambulation, motion and joint stability. The quality of studies was assessed using the National Institutes of Health tool for quality assessment of case series. A summary of results was carried out providing proportions and rates of diagnostic and prognostic features associated with this rare condition.

RESULTS

In total, 20 cases were retrieved for analysis, of which 19 were obtained from the identified eligible studies (n = 16) and one was an unpublished case from our center. The median gestational age at prenatal diagnosis, which was made using ultrasound in most cases, was 20 weeks (range, 14-38 weeks). Bilaterality was observed in 11/20 (55%) cases. The condition was isolated in 7/20 (35%) cases and associated with other anomalies in 13/20 (65%) cases. An association was observed with oligohydramnios (4/20 (20%)), and an invasive procedure was performed in 13/20 (65%) cases, including 11 cases with an invasive procedure performed for diagnostic purposes. Genetic testing was normal in all isolated cases for which information was available (4/7), while a genetic syndrome was present in 10/13 (77%) non-isolated cases (Larsen, Noonan, Grebe, Desbuquois or Escobar syndrome). There were seven terminations of pregnancy, of which six were performed in cases with associated anomalies and one in an isolated case, 11 cases of postnatal survival, one case of intrauterine death and one of neonatal death. The fetal and neonatal deaths occurred in cases with associated anomalies or abnormal genetic findings. Postnatal treatment was mostly conservative, with only two reports (18% of the 11 surviving neonates) of surgical intervention, both in cases with associated anomalies. Postnatal follow-up was up to 1 year in most cases, and motor outlook appeared normal in all isolated cases.

CONCLUSIONS

CKD is a rare fetal anomaly with a prenatal diagnosis achievable from the early second trimester, for which a favorable outcome can be expected when no associated anomalies are present. Prenatal diagnosis should include detailed ultrasound assessment and amniocentesis for extensive genetic studies, particularly in non-isolated cases. Early postnatal treatment achieves success in most cases without surgical intervention and leads to a normal motor outlook. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Novel in-frame FLNB deletion causes Larsen syndrome in a three-generation pedigree

A 4-yr-old female with congenital knee dislocations and joint laxity was noted to have a strong maternal family history comprising multiple individuals with knee problems and clubfeet. As the knee issues were the predominant clinical features, clinical testing included sequencing of LMX1B, TBX2, and TBX4, which identified no significant variants. Research genome sequencing was performed in the proband, parents, and maternal grandfather. A heterozygous in-frame deletion in FLNB c. 5468_5470delAGG, which predicts p.(Glu1823del), segregated with the disease. The variant is rare in the gnomAD database, removes a residue that is evolutionarily conserved, and is predicted to alter protein length. Larsen syndrome may present with pathology that primarily involves one joint and thus may be difficult to differentiate clinically from other skeletal dysplasias or arthrogryposis syndromes. The p.(Glu1823del) variant maps to a filamin repeat domain where other disease-causing variants are clustered, consistent with a probable gain-of-function mechanism. It has reportedly been observed in two individuals in the gnomAD database, suggesting that mild presentations of Larsen syndrome, like the individual reported here, may be underdiagnosed in the general population.