Computed tomographic scanning of L3/4 in suspected disc prolapse: is it necessary?

Computed tomography (CT) scanning is an accepted first line investigation for suspected lumbar prolapsed intervertebral disc disease (PID). However, it does involve ionizing radiation and any possible reduction in the dose is desirable. A questionnaire was sent to a random selection of 60 CT centres in the UK to confirm that a routine scan of the three lower lumbar levels is current practice in a majority of centres, regardless of symptomatic presentation. All orthopaedic CT referrals over 2 years for suspected lumbar disc disease in Sheffield were studied retrospectively. Of 486 cases, 99 (20%) were shown to have disc disease, of which 16 (3.3%) had disease at the L3/4 level. Of these 16 cases, 11 were suspected clinically. Analysis of the long-term outcome of the five unsuspected cases showed that in none did the CT findings make any significant contribution to this outcome. These results have altered our practice. Two-level scanning is now performed routinely and three-level scanning is only performed when specified clinical or radiological indications are present.