Congenital absence of lumbosacral articular process: report of three cases.

Defective anomaly of the articular process of the lumbosacral region in three young women is reported. One had a bilateral defect at the lower facet of L1 with defect at L5 right lower and S1 right upper facets. Another had bilateral defects at L5 lower facets, and the third had a defect at the left lower facet of L5 with other anomalies of the lamina. Based on classification of 37 anomalies including those previously reported in the literature, it is concluded that unilateral defect at the lumbosacral apophyseal joint involving both upper and lower facets is the most common anomaly. The pathogenesis of all anomalies is apparently complex. The intervertebral instability caused by these defects may provoke occasional low-back pain, especially in younger persons with a unilateral L5/S1 anomaly.