Society of Bone and

Several locomotor disorders in children that come to the attention of orthopaedic surgeons have their origin in fetal life and present as congenital anomalies. These include cerebral palsy (which may be considered as a congenital anomaly as, in the majority of cases, the impairment is prepartum in timing), club foot and arthrogryposis. Alternatively, conditions that present as locomotor disorders may arise from impairments that have occurred intra-partum or in early childhood. Cerebral palsy also features strongly in this group. This anno-tation will consider the role of twinning in the pathogenesis of locomotor disorders and will focus on cerebral palsy, but will also consider the possible role of twinning in other congeni-tal anomalies. Pathogenic mechanisms of impairment in twins Crucial to the pathogenesis of many abnormal-ities in twins is the zygosity and chorionicity of the conception. The fertilisation of two ova produces dizygous twins which are dichorionic and have separate placental circulations. Divi-sion of a single fertilised ovum leads to mono-zygotic (identical) twins and the timing of the division determines chorionicity. Early division leads to dichorionic twins, later division to monochorionic twins and very late division to incomplete separation or conjoined twins. Concerns arise with monochorionic twinning owing to placental vascular anastomoses that are present. Chronic haemodynamic instability between fetuses results in the feto-fetal trans-fusion syndromes. These anastomoses are also a channel for other mechanisms which may damage the fetus. A proposed hypothesis is that thrombo-emboli or thromboplastin, released from the dead fetus, produce ischaemic damage in the co-twin