Monarch Disease Ontology entry MONDO_0019951 (rigid spine syndrome) (RSS) is a slowly progressive childhood-onset congenital muscular dystrophy characterized by contractures of the spinal extensor muscles associated with abnormal posture (limitation of neck and trunk flexure), progressive scoliosis of the spine, early marked cervico-axial muscle weakness with relatively preserved strength and function of the extremities and progressive respiratory insufficiency. Also known as: rigid spine congenital muscular dystrophy.