Joints and ligaments of the vertebral column
The vertebral column is composed of the vertebrae and the fibrocartilaginous intervertebral (IV) discs between them. It forms the main skeleton of the neck and back, extending from the base of the skull to the tip of the coccyx. The vertebral column consists of several joints that permit various movements of the column. These joints are typically organized into the joints of the vertebral bodies, joints of the vertebral arches, craniovertebral joints, costovertebral joints, and the sacroiliac joints.
Similar to most typical joints, the vertebral column is associated with various ligaments. These ligaments serve to strengthen and stabilize the articulating bones and structures that form the joints of the vertebrae, as well as resist excessive movements of the vertebral column. The major ligaments of the vertebral column include: the anterior and posterior longitudinal ligaments, ligamenta flava, supraspinatus ligament, ligamentum nuchae and the interspinous ligaments.
This article will discuss the anatomy and function of the joints and ligaments of the vertebral column.
- Joints of the vertebral bodies
- Ligaments of the vertebral bodies
- Joints of the vertebral arches
- Ligaments of the vertebral arches
- Craniovertebral joints
- Craniovertebral ligaments
- Costovertebral joints
- Costovertebral ligaments
- Sacroiliac joints
- Sacroiliac ligaments
- Clinical relations
Joints of the vertebral bodies
The main joints of the vertebral bodies from C2 to S1 are secondary cartilaginous joints (symphyses, singular: symphysis) called intervertebral (IV) discs. The articular surfaces of adjacent vertebral bodies are lined by sheets of hyaline cartilage (vertebral end-plates) and linked together by the fibrocartilaginous IV discs.
The IV discs are designed for weight-bearing and strength and increase in thickness as the vertebral column descends. Each IV disc consists of a thick outer ring of fibrous cartilage called the annulus fibrosus which surrounds an inner, central gelatinous core called the nucleus pulposus. The annulus fibrosus is composed of concentric layers of fibrocartilage surrounded by an outer ring of collagen. The gelatinous nature of the nucleus pulposus promotes flexibility of the vertebral column and acts as a shock absorber, absorbing compression forces between vertebrae.
In addition to the intervertebral discs, the vertebral bodies of the typical cervical vertebrae (C3-C7) bear small synovial joints called uncovertebral joints (of Luschka). These joints are formed between the uncinate processes (unci), which are crests on the superolateral regions of the vertebral bodies, and the inferolateral surfaces of the vertebral bodies which lie superior to them. These joints play a role in the control of cervical spine movements and also stabilize the neck.
Some authors consider the Luschka’s joints to be degenerative spaces in the discs occupied by extracellular fluid. Other authors believe they are synovial joints. The uncovertebral joints frequently undergo arthritic changes resulting in bone spur formation, which may cause neck pain.
Ligaments of the vertebral bodies
The joints of the vertebral bodies are supported and stabilized by ligaments which also serve to resist movements such as hyperextension of the vertebral column which may cause injury. These ligaments include the anterior and posterior longitudinal ligaments.
Anterior longitudinal ligament
The anterolateral surfaces of the vertebral bodies and IV discs are covered and connected by a strong and broad band of fibrous tissue called the anterior longitudinal ligament. This ligament attaches superiorly to the occipital bone, anterior to the foramen magnum, and to the anterior tubercle of vertebra C1 (atlas). It then extends caudally to the anterior (pelvic) surface of the upper sacrum.
The anterior longitudinal ligament has several layers and in addition to supporting the joints between the vertebral bodies, it is the only ligament that prevents hyperextension of the spine.
Posterior longitudinal ligament
The posterior longitudinal ligament runs along the posterior surfaces of the vertebral bodies within the vertebral canal. It is attached to the vertebral bodies and mainly the intervertebral discs along its length from the body of C2 (axis) to the sacrum. From its superior attachment, the posterior longitudinal ligament extends into the intracranial aspect of the base of the skull as the tectorial membrane. Compared to the anterior longitudinal ligament, this ligament is much narrower, relatively weaker. It resists hyperflexion of the vertebral column and helps prevent posterior herniation of the nucleus pulposus of an IV disc.
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Joints of the vertebral arches
The joints of the vertebral arches are plane synovial joints known as the zygapophyseal joints, often called facet joints. These joints are formed between the superior and the inferior articular processes (zygapophyses) of adjoining vertebrae. The articular surface of each facet joint is lined by hyaline cartilage and each joint is enclosed by a thin, loose joint capsule (articular capsule).
The zygapophyseal joints permit gliding movements, however, the type of movements permitted depend on the region of the vertebral column and the shape and orientation of the articular surfaces. The facet joints of the cervical region slope inferiorly from anterior to posterior. This disposition of the joints, along with the large size of the IV disc relative to the cervical vertebral bodies, allows for a wide range of movements including flexion, extension, lateral flexion and rotation. In the thoracic region, these joints are vertically placed, limiting flexion and extension but mainly permitting rotational movements. The lumbar facet joints are oriented in the sagittal plane with adjacent processes interlocked, however, limited flexion, extension and lateral flexion are still possible.
Ligaments of the vertebral arches
The joints of the vertebral arches are reinforced and supported by several accessory ligaments which unite the laminae, transverse processes, and spinous processes. These joints include the ligamenta flava, interspinous ligaments, supraspinous ligament, nuchal ligament and the intertransverse ligaments.
The ligamenta flava (singular: ligamentum flavum) are thin, broad ligaments that connect the laminae of adjacent vertebral arches on each side. They are mainly composed of yellow elastic tissue and form part of the posterior surface of the vertebral canal. Each ligament runs almost vertically from the anterior surface of the lamina above to the posterior surface of the lamina below. The ligaments on opposite sides typically converge and blend in the midline. The main function of the ligamenta flava are to resist separation of the laminae during flexion and to aid in the extension of the vertebral column back to its erect anatomical posture.
The interspinous ligaments connect adjacent vertebral spinous processes. This thin ligament attaches from the base to the apex of each spinous process, blending with the ligamenta flava ventrally and supraspinous ligament dorsally.
The supraspinous ligament is a cord-like band that runs along and connects the tips of the spinous processes from vertebra C7 to the sacrum. It is continuous superiorly with the nuchal ligament of the cervical region. This ligament prevents separation of spinous processes during flexion and resists hyperflexion.
Nuchal ligament (ligamentum nuchae)
The nuchal ligament is a thick, triangular, fibroelastic band at the back of the neck that extends between the base of the skull and C7 in the midline. Specifically, it attaches from the external occipital protuberance to the posterior border of the foramen magnum, the posterior tubercle of vertebra C1 and the apices of the remaining cervical spinous processes. The apex of the triangular nuchal ligament attaches to the tip of the spinous process of C7 where it merges inferiorly with the supraspinous ligament. The function of the nuchal ligament is to support the head. It resists flexion and restores the head to its anatomical position. Additionally, this ligament serves as a surface for attachment of muscles of the posterior neck and shoulder.
The intertransverse ligaments are sheets of connective tissue that connect the transverse processes of adjoining vertebrae. They extend from the upper border of the transverse process of one vertebra to the lower border of the transverse process above. Unlike other ligaments, the intertransverse ligaments do not have distinct medial and lateral borders and are often blended with adjacent muscles. The main function of these ligaments is to limit lateral flexion of the vertebral column.
The craniovertebral joints, as the name suggests, form the skeletal connections between the cranium and vertebral column. They consist of two sets of joints; the atlanto-occipital joints (‘yes’ or nodding movement joint), formed between the atlas (C1 vertebra) and the occipital bone of the cranium, and the atlanto-axial joints (‘no’ or rotational movement joints) formed between the atlas and the axis (C2 vertebra). These joints are synovial joints that have no IV discs. Their specialized design allows for a wider range of movement than in the rest of the vertebral column.
The atlanto-occipital joints are a pair of condyloid type synovial joints formed between the superior articular surfaces of the atlas and the condyles of the occipital bone. The main movements at these joints are flexion and extension, which enables nodding of the head, on the vertebral column. However, they also permit slight lateral flexion and rotation.
The atlanto-axial joints consist of three synovial joints, two lateral joints and one median joint. The two lateral atlanto-axial joints (right and left) are formed by articulations between the inferior facets of the lateral masses of C1 vertebra and the superior articular facets of C2 vertebra. These joints are gliding synovial joints. The median atlanto-axial joint, on the other hand, is a synovial pivot joint between the dens of the axis and the anterior arch of the atlas.
Working together, the atlanto-axial joints permit rotation of the atlas together with the cranium, around the dens of axis, allowing the head to be turned from side to side.
The craniovertebral ligaments consist of several ligaments that support the connection of the skull to the vertebral column. These ligaments include the anterior and posterior atlanto-occipital membranes which are related to the atlanto-occipital joints along with various other ligaments associated with the atlanto-axial joints. These atlanto-axial ligaments include the transverse ligament of the atlas, cruciform ligament of the atlas, alar ligaments, apical ligament of the dens, anterior and posterior atlanto-axial membrane, and finally, the tectorial membrane.
There are two atlanto-occipital ligaments that connect the cranium to C1 and thus support and resist excessive movement of the atlanto-occipital joints.
- The anterior atlanto-occipital membrane extends from the anterior arch of the atlas to the anterior margin of the foramen magnum. It is composed of broad, dense fibers and is continuous with the anterior longitudinal ligament inferiorly.
- The posterior atlanto-occipital membrane is a relatively thin sheet of tissue that runs between the posterior margin of the foramen magnum and the upper border of the posterior arch of the atlas.
There are several atlanto-axial ligaments that stabilize the atlanto-axial joint and allow rotation of the head.
- The transverse ligament of the atlas is a strong, broad band extending between the tubercles on the medial aspects of the lateral masses of the atlas that holds the dens in position. It arches across the posterior aspect of the dens and bears a thin layer of articular cartilage anteriorly, which articulates with the posterior articular facet of the dens. A strong median longitudinal band arises from the superior margin of the transverse ligament of the atlas to the occipital bone. A similar but much weaker longitudinal band also passes from the lower margin of the transverse ligament of the atlas to the posterior surface of the axis. The transverse ligament of the atlas together with both the superior and inferior longitudinal bands form the cruciform (cruciate) ligament of the atlas, which is so named due to its resemblance to a cross.
- The alar ligaments are short, rounded cords that resist excessive rotation of the head. They extend from posterolateral sides of the apex of the dens to to the lateral margins of the foramen magnum.
- The apical ligament of the dens is a weak, narrow band located between the alar ligaments. It runs from the tip of the dens to the anterior margin of the foramen magnum and is the fibrous remnant of the notochord and its sheath. This ligament plays a minor role in stabilizing the atlanto-axial ligament.
- The anterior atlanto-axial membrane is a strong band that runs between the anterior arch of the atlas to the body of the axis. The posterior atlanto-axial membrane, on the other hand, is a thin membrane that extends between the posterior arch of the atlas to the laminae of the axis.
- The tectorial membrane (membrana tectoria) is a broad, strong superior continuation of the posterior longitudinal ligament. From the body of C2, it runs across the median atlanto-axial joint and its ligaments (alar and cruciform), and through the foramen magnum to attach to the central floor of the cranial cavity, where it blends with the cranial dura mater.
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So far, we have looked at the joints and ligaments of the vertebrae with either other vertebrae or with the skull. Now, we will describe another category of joints of the vertebral column called the costovertebral joints. These consist of two groups of plane synovial joints that join the proximal ends of the ribs to their corresponding vertebrae. For typical ribs, these joints are the costocorporeal joints (joints of heads of ribs) between the heads of ribs and the adjacent vertebral bodies and the costotransverse joints in which the tubercle of the rib articulates with the transverse process of its related vertebra. These joints permit elevation and depression of the rib cage on the vertebral column and are thus important in adjusting the volume of the thoracic cage during breathing.
Joints of heads of ribs (costocorporeal joints)
The heads of typical ribs have two convex articular facets: a superior facet that articulates with the body of the vertebra above and an inferior facet which articulates with its related (same-numbered) vertebra. Each costocorporeal joint is composed of two synovial compartments separated by an intra-articular ligament which connects the crest of the head of the rib to the adjacent intervertebral disc. The heads of atypical ribs (ribs 1, 11, 12 and sometimes10) bear a single articular facet and only articulate with their corresponding vertebral body. Accordingly, these ribs lack an intra-articular ligament.
The costotransverse joints are synovial joints between the articular facet on the tubercle of the rib and the transverse costal facet on the transverse process of the vertebra of the same number. These joints are present in only ribs 1 - 10. Ribs 11 and 12 lack tubercles and do not articulate with transverse processes of their related vertebrae.
These are ligaments associated with the costovertebral joints that are responsible for maintaining appropriate alignment between the ribs and the thoracic vertebrae. The costovertebral ligaments include the intra-articular ligament of head of rib, radiate ligament of head of rib and the costotransverse ligaments.
- The intra-articular ligament of head of rib is a short band located within the joints of heads of typical ribs. It arises from the crest of the head of the rib and attaches directly to the adjacent IV disc, separating the two articular surfaces on the head of the rib.
- The radiate ligaments of head of rib connects the anterior margin of the head of the rib to the sides of the bodies of two vertebrae and the IV disc between them.
- There are three main costotransverse ligaments that function to stabilize the costotransverse joints. The first, the costotransverse ligament attaches the neck of the rib to the transverse process, filling the costotransverse foramen between the neck of the rib and its adjacent transverse process. The superior costotransverse ligament is a broad band that extends from the superior surface of the neck of the rib to the transverse process of the vertebra above. Finally, there is the short, thick lateral costotransverse ligament which lies lateral to the joint. It runs from the tip of the transverse process to the roughened non-articular part of the tubercle of the rib to strengthen the posterior aspect of the joint.
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The sacroiliac joints are compound joints that occur between the articular surfaces of the sacrum and the iliac parts of the hip bones. Each joint is composed of an anterior synovial part between the ear-shaped articular facets of the sacrum and ilium which are covered by hyaline articular cartilage, and a posterior syndesmosis between the tuberosities of the same bones.
These joints have great strength and are specialized to bear the weight of the axial skeleton and transmit it to the hip bones and the lower limbs. Unlike most synovial joints, the sacroiliac joints have limited mobility partly because of their irregular, interlocking articular surfaces and also because of associated stabilizing ligaments.
As a consequence of the weight-bearing nature of the sacroiliac joints, their associated ligaments firmly attach the sacrum to the iliac bones by strengthening and stabilizing the joint. The sacroiliac ligaments consist of three main ligaments which are the anterior, interosseous and posterior sacroiliac ligaments, as well as two main accessory ligaments: sacrotuberous ligament and sacrospinous ligament. The main function of these accessory ligaments is to prevent forward tilting of the sacral promontory.
- The anterior sacroiliac ligament is largely formed by a thickening of the anterior portion of the fibrous capsule of the synovial part of the sacroiliac joint. The fibers of this ligament course anteroinferiorly to the joint.
- The interosseous sacroiliac ligament is located deep between the tuberosities of the sacrum and ilium and forms the main bond between the bones. It is the largest and strongest of the main ligaments.
- The posterior sacroiliac ligament overlies the interosseous sacroiliac ligament and its fibers run upward and outward in an oblique manner, similar to the interosseous ligament. The posterior sacroiliac ligament is joined inferiorly by the accessory ligaments.
- The sacrotuberous ligament is a triangular ligament with a broad attachment that extends from the posterior ilium and lateral sacrum and coccyx to the ischial tuberosity. It transforms the greater sciatic notch of the hip bone into a foramen through which serevral structures exit the pelvis into the gluteal region.
- The sacrospinous ligament is the smaller of the two accessory ligaments and is located deep to the sacrotuberus ligament. It is also triangular in shape and extends from the lateral sacrum and coccyx to the ischial spine. This ligament transforms the lesser sciatic notch into a foramen.
Spondylolysis and spondylolisthesis
Spondylolysis is a condition characterised by a defect in a portion of the spine called the pars interarticularis (a small segment of bone joining the inferior and superior articular processes of a zygapophyseal joint). This pars interarticularis defect may be on one side of the spine only (unilateral) or both sides (bilateral). The condition commonly occurs at L5-S1, but may occur at L4-5 and rarely at a higher level. Spondylolysis is the most common cause of spondylolisthesis, in which one vertebral body slides forward over another and may compress spinal nerves, causing low back or lower limb pain.
Rupture of the transverse ligament of the atlas
Rupture of transverse ligament is a destabilizing injury that can occur in isolation or with atlanto-axial subluxation or an atlas fracture. In this condition, the transverse ligament is disrupted and may cause anterior translation of the atlas in relation to the lower cervical spine. The condition is results in neck pain and is sometimes associated with head injury. Diffuse motor neuron loss may occur if the pyramidal tract is affected.
Fracture of the dens (odontoid process fracture)
Fracture of the dens or odontoid process of C2 (axis) is more common in the elderly and may present after minimal trauma and with minimal neck pain. Some people suffering from dens fracture also present with neurologic symptoms and minimal neck pain.
Facet joint sprain
Facet joint sprain can also be referred to as zygapophyseal joint sprain, or facet joint dysfunction. It is a common condition characterized by damage or tearing of the connective tissue (ligaments, cartilage and joint capsule) of one of the facet/zygapophyseal joints of the upper back. Facet joint sprains typically occur during excessive bending ( flexion, extension, or lateral flexion), lifting or twisting movements. They may occur traumatically or due to repetitive or prolonged forces. They may also occur as a result of prolonged poor posture (e.g. sitting slouched or sleeping in the fetal position) and mainly leads to back pain.
Sacroiliitis refers to inflammation of one or both sacroiliac joints, and is one cause of unilateral low back pain. Individuals with this condition may experience pain in the lower back, buttock or thigh, depending on the degree of inflammation.
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