Facet joint hypertrophy: the cross-sectional area of the superior articular process of L4 and L5.

With CT imaging, the lumbar facet joints are well visualised and enlargement secondary to degeneration may be noted. We measured the cross-sectional area of the superior articular process of the L5 facet joint in 100 consecutive CT scans and in 71 patients, the L4 process was also measured. We found that the mean cross-sectional area was significantly larger at L5 than at L4. Patient age and sex had no significant effect on the size at either L4 or L5. A review of the radiological reports revealed that the 13 patients with degenerative facet joints and radiologically normal discs did not have significantly larger facet joints than the 35 patients with disc disease and radiologically normal facet joints. In conclusion, the term "facet joint hypertrophy" should not be used when osteoarthritic changes are noted on CT scan, because these joints are not significantly larger than normal facet joints.