Ligaments of the Lumbar Spine
(Redirected from Mamillo-accessory Ligament)
There are three parts to the interspinous ligaments. Ventrally there are fibres that run posterocranially from the dorsal aspect of the ligamentum flavum to the anterior half of the lower border of the upper spinous process. Dorsally there are fibres that run from the posterior half of the upper border of the lower spinous process and pass behind the posterior border of the upper spinous process. Viewed anteriorly but not posteriorly, there are two interspinous ligaments that are separated by fat. The interspinous ligaments provide little resistance to spinous process separation with forward flexion.
The supraspinous ligament is not a true ligament, but rather largely consists of tendinous fibres from the back muscles, and is only well developed at the upper lumbar levels. It terminates at L3 in 22%, L4 in 73%, bridges L4-5 in 5%, and is routinely absent at L5-S1.
The superficial layer is collagenous and thought to represent superficial fascial condensation, and anchors the skin to the thoracolumbar fascia. It provides little resistance to spinous process separation. The middle layer consists of intertwining fibres of the thoracolumbar fascia and the aponeurosis of longissimus thoracis. The deep layer consists of strong tendinous fibres from the aponeurosis of longissimus thoracis. The tendons aggregate in a parallel manner towards the spinous processes, creating the impression of a ligament.
At the caudal levels of L4 and L5 there are only oblique fibres of the thoracolumbar fascia that intersect over the spinous processes and fuse with the aponeurosis of the longissimus thoracic that attach to the spinous processes.
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 to supply the facet joint and multifidus. 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.
The lumbar mamillo-accessory ligaments. Transverse process (tp), superior articular process (sap), mamillary process (mp), accessory process (sp), mamillo-accessory ligament (mal). 
Dorsal aspect of the third lumbar vertebra showing a probed MAF on the left. mamillary process (MP), accessory process (AP), mamillo-accessory foramen (MAF), mamillo-accessory ligament (MAL).
- Bogduk. The lumbar mamillo--accessory ligament. Its anatomical and neurosurgical significance. Spine 1981. 6:162-7. PMID: 6456553. DOI.
- Mahato. Mamillo-accessory notch and foramen: distribution patterns and correlation with superior lumbar facet structure. Morphologie : bulletin de l'Association des anatomistes 2014. 98:176-81. PMID: 24889272. DOI.