A study of the angle of inclination and facet curvature of superior lumbar zygapophyseal facets.

The angle of inclination and depth of curvature of L1-L5 of the superior articular facets of both sexes were measured in 112 lumbar spines. In addition to standard statistical methods data were also analyzed to show various degrees of departure from the "normal." The L3 vertebra showed the least variation and L5 and L1 showed the most. The angle and depth of L1 to L5 showed a small, albeit statistically significant, difference between the two sexes but no laterality differences were apparent. At L1 12.5% of males and 10.4% of females revealed an asymmetry of angle exceeding 20, and at L5 3.1% of males and 1.7% of females showed such tendency. An asymmetry of the depth of curvature of the articular facets exceeding 1.5 mm was recorded in 12.5% of males and 8.3% of females at L1 and 6.5% of males and 2.1% females at L5. The expected values of depth of curvature were lowest at L1 and highest at L3 and L4. It is suggested that a more quantitative approach to the study of the zygapophyseal joint would enhance precision and facilitate meaningful interlaboratory comparisons of published data.