Abstract
Fetal kicking and movements generate biomechanical stimulation in the fetal skeleton, which is important for prenatal musculoskeletal development, particularly joint shape. Developmental dysplasia of the hip (DDH) is the most common joint shape abnormality at birth, with many risk factors for the condition being associated with restricted fetal movement. In this study, we investigate the biomechanics of fetal movements in such situations, namely fetal breech position, oligohydramnios and primiparity (firstborn pregnancy). We also investigate twin pregnancies, which are not at greater risk of DDH incidence, despite the more restricted intra-uterine environment. We track fetal movements for each of these situations using cine-MRI technology, quantify the kick and muscle forces, and characterise the resulting stress and strain in the hip joint, testing the hypothesis that altered biomechanical stimuli may explain the link between certain intra-uterine conditions and risk of DDH. Kick force, stress and strain were found to be significantly lower in cases of breech position and oligohydramnios. Similarly, firstborn fetuses were found to generate significantly lower kick forces than non-firstborns. Interestingly, no significant difference was observed in twins compared to singletons. This research represents the first evidence of a link between the biomechanics of fetal movements and the risk of DDH, potentially informing the development of future preventative measures and enhanced diagnosis. Our results emphasise the importance of ultrasound screening for breech position and oligohydramnios, particularly later in pregnancy, and suggest that earlier intervention to correct breech position through external cephalic version could reduce the risk of hip dysplasia.
Highlights
Fetal movements during pregnancy are a natural part of the development process, and are detectable from 10 gestational weeks using ultrasound (de Vries and Fong, 2006)
This study presents the first quantification of stress and strain as biomechanical stimuli in the fetal hip joint for a range of fetal positions and intra-uterine conditions, and is the first to establish a relationship between altered stress and strain magnitudes and known risk factors for developmental dysplasia of the hip (DDH)
In cases of fetal breech position and oligohydramnios, fetal kick force and stress and strain stimulation were significantly lower than in healthy cephalic conditions. Both of these conditions represent more restricted mechanical environments, with reduced range of movement and space for fetal leg movements, and are linked to an increased risk of DDH (Hinderaker et al, 1994; Muller and Seddon, 1953). By quantifying these movements and the resulting stress and strain for the first time, our results suggest that mechanobiology may explain the link between these conditions and risk of DDH
Summary
Fetal movements during pregnancy are a natural part of the development process, and are detectable from 10 gestational weeks using ultrasound (de Vries and Fong, 2006). Fetal movements are known to play a significant role in normal development of the musculoskeletal system (reviewed in Nowlan, 2015). In cases of neuromuscular disorders with severely reduced or absent fetal movement, patients present with skeletal malformations such as joint fusions, craniofacial abnormalities and hypo-mineralised bones (Aronsson et al, 1994; Rodríguez et al, 1988a; Rodríguez et al, 1988b). Clinical evidence for the importance of fetal movements for skeletal development has been reinforced by studies of animal models, with abnormal joint conditions arising in both immobilised chick embryos and mutant mouse embryos with reduced or absent muscle activity (Kahn et al, 2009; Nowlan et al, 2010a, 2010b, 2014; Roddy et al, 2011).
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