Lumbosacral nerve root anomalies have been docu- Reports based on both diagnostic methods are mented in the literature for over 30 years (Zagnoni 1949). biased since only those patients with low back symptoms Little significance has, however, been attributed to these are normally investigated (Bernini, Wiesel and Rothman anomalies because of the paucity of studies and the low 1980; Postacchini et a!. 1982). incidences reported, ranging from 0.34% to 2.7% (Ethel- Another method of diagnosing lumbosacral root berg and Riishede 1952; Bonola and Bedeschi 1956; entrapment advocated by Scarf et a!. (198 1) is the use of Postacchini, Urso and Ferro 1982). Niedre and Macnab dermatomal somatosensory evoked responses. This, (1983) have stated that anomalous nerve roots should be however, presupposes a reliable knowledge of the suspected in all failed operations for disc lesions ; this could be very significant for, in the USA, 200 000 patients every year have operations for herniated discs and of these as many as 33% may result in failure (Scarf et a!. 1981). It is clearly imperative to know the true incidence of nerve root anomalies and the various types ; this might improve the success rate of spinal operations consider- ably. A redefinition of the anatomy of the lumbosacral spine seems to be indicated in the hope of improving diagnosis.

see http://www.boneandjoint.org.uk/highwire/filestream/13126/field_highwire_article_pdf/0/411.full-text.pdf