Critical reviewArguments for and against movement at the spheno-occipital synostosis: Furthering the debate

BackgroundThe junction between the sphenoid and occipital bones fully ossifies by age 18, forming the spheno-occipital synostosis. William Sutherland and most subsequent craniosacral authors hold that, in adults, cranial motion is, in part, enabled by movement of the synostosis.ObjectivesTo review arguments for and against movement at the synostosis, and the extent to which statements by craniosacral authors regarding the synostosis accord with the mainstream anatomical understanding of their day.MethodA review of relevant literature, and an examination of a number of adult cranial bases, median skull sections and sphenoid bones.ResultsWithin the craniosacral literature, scholarship regarding the junction is poor, with authors often failing to draw upon mainstream anatomical understanding.Three cases have been made regarding movement at the adult junction: (1) it moves because it does not ossify (2) it ossifies but movement, nevertheless, continues and (3) ossification prevents continued movement.150 years of mainstream anatomical understanding refute (1). Proponents of (2) argue that the preponderance of trabecular bone at the synostosis and clivus facilitates movement. However, Cook, who makes the most detailed case for (3), argues that the thickness of the clivus suggests it is “designed” not to move.Proponents of (2) do not consider this point about clivus thickness, but, conversely, proponents of (3) generally do not consider the point that the majority of bone at the clivus is trabecular.ConclusionThe debate over movement at the synostosis and clivus will progress when those involved explicitly address both of these important points.