Several human conditions have a tendency to affect one side of the body over the other. Do lumbar disc prolapses have such a tendency? We sought to answer this question by an analysis of operated cases.

Primary lumbar microdiscectomy cases were identified using the coding system. 1286 cases were identified and in 764 the laterality was not recorded. Electronic records were then examined to establish, where possible, the side of the procedure from the clinic letter or discharge summary. 22 cases were eliminated due to miscoding (laminectomy, instrumentation, revision) and in 24 the side of the operation could not be established. In the remaining 1240 cases (96.4%) the laterality was determined.

Patients who underwent primary lumbar microdiscectomy in a single neurosurgical unit over a 5-year period (2002-2007).

Procedures were bilateral, left or right.

126 cases were bilateral. There were 1114 defined lateral cases. 618 (55.5%) were on the left compared to 496 (44.5%) on the right. The ratio of left to right is close to 5:4. The null hypothesis was that the number of left and right sided operations would be equal. The findings of this study were statistically highly significant (p value < 0.001, binomial test) and the null hypothesis could be rejected.

There is a small but definite preponderance of left sided over right sided cases at a ratio of 5:4. This finding may have implications regarding our understanding of both the epidemiology and biomechanics of lumbar disc prolapse.