Thoracolumbar mortice joint: radiological and histological observations.

The superior articular processes and mammillary processes of T11 and T12 and L1 often form a 'mortice-like' enclosure for the inferior articular processes of the vertebra above. From 630 thoracolumbar junction CT investigations, 297 individuals demonstrated one or more mortice joints. The frequency and variety of mortice joints from T10-11 to T12-L1 were classified into three main types, according to segmental level and orientation of their zygapophysial joints. The T11-12 level accounted for 77% of all mortice joints, with 20% at T12-L1 and 3% at T10-11. In 27% of cases a unilateral mortice joint was demonstrated, often in association with marked zygapophysial joint tropism. Radiographic features of 43 cadaveric mortice joints were compared with their histological characteristics.