Ligaments of the Lumbar Spine
There is a notch between the mamillary process and accessory process on each side of every lumbar vertebra. This notch is converted into a foramen by the mamillo-accessory ligament, through which the medial branch of the dorsal ramus passes through. The ligament at any segment is related to the nerve of the next caudal segment (e.g. the L5 ligament is related to the L4 medial branch).
It is not a true ligament because it connects two points on the same bone. Its structure resembles a tendon more than a ligament and it has been interpreted as being a tendon of the semispinalis musculature in the lumbar spine. It is about 1-2mm thick.
The ligament can be ossified which converts the notch into a bony foramen, which is a normal phenomenon in a minority of people.
The structure has no biomechanical significance.
