Radiographic series depicting natural history of an evolving slip, surgical treatment and remodelling. A) Radiographic appearances of a ‘pre-slip’ on the left in a 13-year-old boy with thigh pain. There is widening of the growth plate and metaphyseal blanch. B) Twelve months later continuing symptoms. Trewthowan’s sign is present (see text). C) After a further 2 months there are signs of advanced chronic slip with remodelling on the left and possible displacement on the right (Klein’s line, see text). D, E) Appearances post screw stabilization. Note the differing screw entry points (anterior on the left) necessary to engage the epiphysis. F) Eleven months postoperation there is evidence of remodelling.