The ligamentum mamillo-accessorium is a fibrous band of the lumbar spine that connects the processus mamillaris to the processus accessorius of the same lumbar vertebra. It spans the intervening groove and forms a fibro-osseous tunnel for the medial branch of the dorsal ramus of the spinal nerve[^1].
Anatomy
The ligamentum mamillo-accessorium is typically found at lumbar vertebrae L1 through L5. It runs between:
Processus mamillaris (at the dorsal margin of the superior articular process)
Processus accessorius (at the dorsal aspect of the base of the transverse process)
The medial branch of the dorsal ramus runs below the ligament and innervates, among other structures, the facet joints (articulationes zygapophysiales). The ligament thereby serves as an anatomical guide structure for the nerve.
Figure
Clinical relevance
Ossification of the ligament can lead to compression or irritation of the medial branch. Because this branch provides sensory innervation to the facet joints, an association with chronic low back pain has been discussed.