The eponym Lasègue sign has been applied to the increase in sciatic pain caused by flexing the extended lower extremity on the abdomen. The sign was never put into writing by Lasègue but by his pupils. He did not describe the test in the usual reference, "Considerations on Sciatica," in 1864. That article has to do with his analysis of then-current theories of sciatica and his own clinical observations. Sciatica was divided into a benign and a serious form, and two examples of each were described. Emphasis was laid on the constant, fixed sciatic pain, as contrasted with the irregular, largely nocturnal, episodes of lancinating pain. Atrophy of leg muscles was not to be explained on the basis of disuse but by a disorder of the nerve, which also was responsible for the typical neuralgia, unlike that of any other part of the body except possibly neuralgia of the brachial plexus. Treatments currently available (cupping, vesicants, and injections of atropine solution) were unavailing. The steps are unknown by which Lasègue came to modify his 1864 views that any sort of flexion or extension of the lower extremity did not exacerbate the pain; in the 1881 thesis of his pupil, Forst, that straight-leg raising sign is described and illustrated and ascribed to his teacher, Professor Lasègue.
Sugar O. Charles Lasègue and His 'Considerations on Sciatica'. JAMA. 1985;253(12):1767-1768. doi:10.1001/jama.1985.03350360093026