Configuration of the connective tissue in the posterior atlanto-occipital interspace : A sheet plastination and confocal microscopy study

The connective tissue structures in the posterior atlanto-occipital region were investigated using E12 sheet plastinations and confocal microscopy. To define the relationship between rectus capitis posterior minor (RCPm), posterior atlanto-occipital (PAO) membrane, nuchal ligament, and the spinal dura in the PAO interspace. It has been speculated that connections between the dura and muscles and/or ligaments in the PAO interspace may transmit forces from the cervical spine joint complexes to the pain-sensitive dura, generating cervicogenic headaches. Anatomic structures involved in these connections include the RCPm, PAO membrane, and nuchal ligament. However, there is little information about the nature of these connections and the relationships between these anatomic structures. The study used a combined approach, consisting of the gross anatomic dissection of nine cadavers and the E12 sheet plastination method for thirteen adult human cadavers, five of which were further examined using confocal microscopy. The study demonstrates that (1) the tendinous fibers from the medial and deep part of the RCPm muscle are continuous antero-inferiorly with the spinal dura; (2) the PAO membrane is part of the RCPm fascia and tendon and the perivascular sheathes; (3) antero-inferiorly the PAO membrane fuses with the spinal dura rather than the atlas; and (4) the nuchal ligament does not exist in the PAO interspace. The connective tissue structures that connect the spinal dura to the RCPm muscle in the PAO interspace are the RCPm fascia and tendinous fibers and perivascular sheathes.