Spinal Ligaments

Fig. 1

The 3 spinal columns in traumatology according to Denis [1]: (a) Anterior column, (b) Medium column (with posterior annulus), (c) Posterior column

Certain ligaments have a protective function of the spinal canal and thus of the neurological elements within (posterior longitudinal ligament (PLL), yellow ligament (ligamentum flavum)).

Figure 2 shows the schematic arrangement of the spinal ligaments. Some are longitudinal and extend from the skull to the sacrum: the ventral (anterior) and dorsal (posterior) longitudinal ligaments (ALL and PLL) and the supra-spinous ligament. Others have a segmental arrangement and interconnect adjacent posterior arches: they have the particularity of being in continuity in the horizontal plane. They are from back to the front, the inter-spinous ligament and the yellow ligament, situated between the laminae, extending laterally to the articular capsules. We will see that there are variations according to the spinal level (especially at the level of the cranio-cervical junction) and that there are specific ligaments (stabilizing the roots or peripheral nerves, especially in the lumbar region).

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig2_HTML.png — Fig. 2

Schematic presentation of the spinal ligaments: (1) Anterior longitudinal ligament (ALL); (2) Posterior longitudinal ligament (PLL); (3) Yellow ligament; (4) Inter-spinous ligament; (5) Supra-spinous ligament; (3), (4), and (5) are in continuity in the horizontal plane but they are not in continuity in the vertical plane as (1), (2), and (5)

Ligaments in the Suboccipital Area

A complex ligamentous system around the transverse ligament, which constitues part of the cruciform ligament, with the apical and alar ligaments, stabilizes the odontoid process (peg) behind the anterior arch of C1.

On a strictly sagittal section (Fig. 3), the PLL and ALL ligaments are present: the first inserts on the exocranial aspect of the basilar process of the occiput, the second on the endocranial surface. These two ligaments extend to the sacrum and the first coccygeal vertebra. The PLL has an arrangement which varies according to the spinal levels, as discussed later.

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig3_HTML.jpg — Fig. 3

Sagittal view of the suboccipital region : (1) Transverse ligament, (2) Occipito-transverse ligament; (3) Transverse-axial ligament; (4) Median O–C1 ligament (apex ligament); (5) O–C2 ligament; (6) PLL; (7) Ventral ligament O–C1; (8) C1–C2 ventral ligament; (9) ALL, (1), (2), and (3) = cruciate ligament of C1

The supra-spinous ligament does not exist at this level and is replaced by the posterior cervical ligament or nuchal septum [2] (Fig. 4). This very resistant sagittal septum inserts superiorly on the inion (or external occipital protuberance) and on the external occipital line, and inferiorly on the spinous process of C7. It separates the posterior muscular masses and consists of rather vertical occipital fibers and fibers coming from the spinous processes, oblique in a posteroinferior direction. In a more recent description, Mercer [3] distinguishes two components from this nuchal ligament: a dense dorsal raphe formed by fibers from the upper trapezium, splenius capitis and rhomboideus, and a medial sagittal septum. For this author, it is the dorsal raphe that extends from inion to the spinous process of C7. The medial septum extends from the deep side of the raphe to the inter-spinous ligaments and the atlanto-axial and occipito-axial membranes anteriorly (Fig. 5).

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig4_HTML.png — Fig. 4

Nuchal septum : (1) External occipital protuberance (inion); (2) Occipital fibrous fibers: (3) Spinous fibrous fibers

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig5a_HTML.png — Fig. 5

(a) Nuchal septum (left postero-lateral view) (according to Mercer [3]): (1) Dorsal raphe; (2) Segmental portion of the nuchal ligament; (3) Posterior O–C1 membrane; (4) C1–C2 posterior membrane; (5) Yellow ligament. (b) Nuchal septum dissection: lateral view (A), posterior view (B) (Anatomy Conservatory of Montpellier, Pr F. Bonnel)

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig5b_HTML.png — Fig. 5

(a) Nuchal septum (left postero-lateral view) (according to Mercer [3]): (1) Dorsal raphe; (2) Segmental portion of the nuchal ligament; (3) Posterior O–C1 membrane; (4) C1–C2 posterior membrane; (5) Yellow ligament. (b) Nuchal septum dissection: lateral view (A), posterior view (B) (Anatomy Conservatory of Montpellier, Pr F. Bonnel)

The joint capsule and the yellow ligament only exist at C2–C3. Superiorly, there is a dorsal occipito-atloid membrane or ligament between CO and C1 (as described by Tubbs [4]) and a dorsal atlanto-axial membrane or ligament between C1 and C2, traversed by the nerve of Arnold (a.k.a. the dorsal branch of the second cervical nerve).

Around the odontoid process of C2 and the anterior arch of C1 there are a multitude of small ligaments.

The strictly median formations are from front to back (Fig. 3):

The ventral occipito-atloid ligament (also called the anterior atloido- (or atlanto) occipital membrane) between the basilar process and the anterior arch of C1.
The ventral atloido-axial ligament between the anterior arch of C1 and the anterior surface of the body of C2.
The medial occipito-odontoid ligament or ligament of the apex of the odontoid process.
The occipito-transverse ligament between the basilar process and the transverse ligament which passes behind the odontoid process, which we shall describe in greater detail.
The transverse-axial ligament which is inserted on the lower edge of the transverse ligament and joins the posterior surface of the base of the odontoid process.

These last two ligaments constitute the longitudinal bundle which, together with the transverse ligament, forms a true ligamental cross behind the odontoid process (cruciform ligament of the atlas).

Finally, the median occipito-axial ligament lies between the longitudinal bundle and the PLL.
The membrana tectoria (tectorial membrane) is the most posterior structure, located directly in front of the dura mater [4]. Composed of three layers (superficial, medium, and deep), it has an average height of 6 mm between the clivus and the body of C2, a width of 3 mm and a thickness of 1 mm. This membrana tectoria extends to the lower cervical level to constitute the posterior layer of the PLL (as discussed later).

Figure 6 shows that there are paravertebral structures that are not visible on the strictly sagittal section. Those are:

The lateral occipito-atloid ligaments which reinforce the lateral parts of the O-C1 capsules. Tubbs [5] described 20 anatomic specimens, with consistent findings; for this author, these left and right ligaments reduce lateral flexion and rotation of the O-C1 joint and have an essential role in stabilizing the cranio-cervical junction.
The lateral occipito-odontoid ligaments, which insert on the lateral masses of the occiput, and terminate at the apex of the odontoid process, or somewhat below it, according to Osmotherly [6]: These alar ligaments terminate outside the apex ligament (Fig. 7) [7].
The transverse ligament inserts on the medial side of the articular masses of the atlas; it leaves an imprint on the dorsal surface of the odontoid process and receives the fibers of the longitudinal bundle (occipito-transverse ligament at the top and transverse-axoid at the bottom) to form the cruciform ligament. Its rupture, most often traumatic, in a movement of hyperflexion, can sometimes lead to compression of the spinal cord (Fig. 7). Recently, Tubbs [4] described the transverse occipital ligament which he finds seven times out of ten between the occipital condyles and above the transverse ligament (Fig. 8).

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig6_HTML.png — Fig. 6

Suboccipital ligaments (posterior view). After removal of the posterior arches of C1, C2, and C3, sections a to c from front to back. (a, b) (1) Lateral ligament O–C2; (2) Lateral ligament O–C1; (3) Transverse ligament; (4) Ligament of the apex, (5) Capsule C1–C2; (6) Capsule C2–C3; (7) Occipito-transverse ligament. (c) (1) O–C2 ligament; (2) PLL; (3) Lateral O–C2 ligament

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig7_HTML.png — Fig. 7

Traumatic lesion of the transverse ligament with possible medullary compression in the case of stretching of the alar ligaments and of the apex ligament: (a) Normal top view: (1) Odontoid; (2) Transverse ligament; (3) Ligament of the apex; (4) Alar ligament. (b) Upper view after trauma (direct dislocation C1–C2). (c) Lateral X-Ray: (1) Odontoid; (2) Anterior arch of the atlas

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig8_HTML.png — Fig. 8

Suboccipital ligaments (posterior view) according to Tubbs [4]: (1) Membrana tectoria; (2) Occipital transverse ligament

The Barkow ligament is situated horizontally between the occipital condyles, which passes behind the alar ligaments and the apex of the odontoid process: this ligament reinforces the stabilizing effect of the transverse ligament at the level of the median atloido-axial joint.

The lateral occipito-axial ligaments (Fig. 6c) frame the median occipito-odontoid ligament, already described on the sagittal section.

Ligaments of the Lower Cervical Area

In a severe cervical sprain, all ligaments excluding ALL are ruptured, including the posterior annulus.

Figure 9 includes a lateral view , a sagittal section, and a cranial view. We find from front to back:

The ALL which adheres to the discs and the vertebral bodies.
The intertransverse ligament with close vertebral artery links.
The PLL: Fig. 10 shows that it is made of two bundles: deep, which is thick and fused to the posterior surface of each vertebra, and superficial, which is thin and a prolongation of the tectorial membrane. Between these two bundles circulate the anterior venous plexus. The deep bundle loses its width from C3 to C7 (Fig. 11).
The articular capsules extend posteriorly and medially as the yellow ligament (ligamentum flavum) between the laminae.
The inter-spinous ligament has slightly oblique fibers in an inferior and posterior direction.
The supra-spinous ligament inserts on the tips of the spinous processes; there is still at this level the thick fibrous nuchal septum, separating the posterior right and left muscular masses. Johnson [8], using the plastination technique on eight cadavers, shows that this nuchal septum is formed by aponeurosis of the trapezius, splenius capitis, rhomboideus, and posterior and superior serratus muscles.

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig9_HTML.png — Fig. 9

Ligaments of the lower cervical spine : (a) Lateral view, (b) Sagittal section, (c) Cranial view. (1) ALL; (2) Inter-transversal ligament; (3) Joint capsule; (4) Yellow ligament; (5) Inter-spinous ligament; (6) Supra-spinous ligament; (7) PLL

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig10_HTML.png — Fig. 10

PLL in the cervical region: (1) Deep layer; (2) Superficial layer (membrana tectoria); (3) Venous plexus; (4) Dura mater

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig11_HTML.jpg — Fig. 11

Posterior view of the PLL in the cervical area with its deep and superficial layers. MT = Membrana tectoria; VP = Venous plexus

The transverse line in Fig. 9c separates the ligamentous system from the discocorporeal complex (with PLL and ALL and intertransverse ligaments) and the ligamentous system of the posterior arch comprising all other ligaments. In a hyperflexion mechanism, the rupture of all the described ligamentous elements (posterior annulus included but excluding ALL) characterizes a severe cervical sprain to which we shall return (Fig. 12).

../images/451372_1_En_16_Chapter/451372_1_En_16_Fig12_HTML.jpg — Fig. 12

Ligament lesions in a severe cervical sprain: (1) ALL intact; (2) Rupture of the posterior annulus; (3) PLL rupture; (4) Capsule rupture; (5) Yellow ligament rupture; (6) Inter-spinous ligament rupture; (7) Supra-spinous ligament rupture

There are extra-spinal ligaments in the lower cervical as well as the lumbar level, which tie the spinal nerves to neighboring structures, in particular the transverse processes in the transverse foramina: they have been well described by Kraan [9] with variations depending on root levels.