Final answer:
The lumbar facets are primarily oriented in a sagittal plane, allowing flexion and extension of the vertebral column.
Step-by-step explanation:
The lumbar facets are the synovial joints formed between the articular processes of the lumbar vertebrae. These facets are responsible for allowing movement between the vertebrae. With the exception of the L5/S1 lumbar facets, the rest of the lumbar facets are oriented in a more sagittal plane than the frontal plane. This means that they primarily allow movement in the sagittal plane, which includes flexion (forward bending) and extension (backward bending) of the vertebral column.