Joints and Ligaments of the Vertebral Column
The joints of the vertebral column, like other typical joints, involve the union of two or more bones. However, those of the vertebral column involve the vertebral bodies, and between the vertebrae and surrounding bones and cartilages e.g. the costovertebral joints. The joints of the vertebral column, therefore, include the:
- Joints of the vertebral bodies
- Joints of the vertebral arches
- Craniovertebral joints (atlantoaxial and atlanto-occipital joints)
- Costovertebral joints
- Sacroiliac joints
Also typical of most somatic joints are ligaments which serve to strengthen and stabilize such joints. Ligaments found in the joints of the vertebral column are ligaments of the vertebral column and they function to support/hold together articulating bones and structures forming the vertebral joints as well as resist hyperflexion and hyperextension of the vertebral column, e.g. the anterior longitudinal ligament, ligamenta flava.
Joints And Ligaments
Joints of the vertebral bodies
The joints of the vertebral bodies are secondary cartilaginous joints (symphyses, singular: symphysis) designed for weight bearing and strength. The articulating surfaces of adjacent vertebrae are connected by intervertebral (IV) discs and ligaments.
The IV discs provide strong attachment between the vertebral bodies, uniting them into a continuous semi rigid column and forming the inferior half of the anterior border of the IV foramen (fig.1). In total, the discs (IV discs) account for 20-25% of the length (height) of the vertebral column. The IV discs also permit movement between adjacent vertebrae, and their resilient deformability allows them to serve as shock absorbers. Each IV disc consists of an annulus fibrosus (an outer fibrous part) and a nucleus pulposus (a gelatinous central mass or central core).
The uncovertebral joints (of Luschka) are located between the unci of the bodies of C3-C6 vertebrae and the beveled inferolateral surfaces of the vertebral bodies lying superior to them. The articulating surfaces of the joint like structures are covered with cartilage moistened by fluid contained within an interposed potential space or “capsule”.
Some authors consider the Luschka’s joints to be degenerative spaces (fissures) in the discs occupied by extracellular fluid. Other authors believe they are synovial joints. The uncovertebral joints are frequent sites of spur formation, which may cause neck pain.
The joints of the vertebral bodies are richly supported and stabilized by ligaments which also serve to prevent damaging movement, e.g. hyperextension of the vertebral column. Those ligaments include:
- The anterior longitudinal ligament: This ligament is a strong, broad fibrous band that covers and connects the anterolateral aspects of the vertebral bodies and IV discs. The ligament extends from the pelvic surface of the sacrum to the anterior tubercle of vertebra C1 (atlas) and the occipital bone anterior to the foramen magnum. It prevents hyperflexion of the vertebral column, maintaining stability of the joints between the vertebral bodies. The anterior longitudinal ligament is the only ligament that limits extension; all other ligaments of the vertebral column, like the IV ligaments, limit forms of flexion.
- The posterior longitudinal ligament: This ligament is a much narrower, somewhat weaker band than the anterior longitudinal ligament. The posterior longitudinal ligament runs within the vertebral canal along the posterior aspect of the vertebral bodies. It is attached mainly to the IV discs and less so to the posterior aspects of the vertebral bodies from C2 (axis) to the sacrum, often bridging fat and vessels between the ligament and the bony surface.
The posterior longitudinal ligament weakly resists hyperflexion of the vertebral column and helps prevent or redirect posterior herniation of the nucleus pulposus of an IV disc. It is well provided with nociceptive (pain) nerve endings.
Joints of the Vertebral Arches
The joints of the vertebral arches are the zygapophysial joints (often called facet joints). These articulations are plane synovial joints between the superior and the inferior articular processes (zygapophyses) of adjacent vertebrae (fig.4). Each facet joint is surrounded by a thin, loose joint capsule (articular capsule). Those in the cervical region are especially thin and loose, reflecting the wide range of movement.
Accessory ligaments unite the laminae (of the IV discs), transverse processes, and spinous processes and help stabilize the joints. The range (amount) of movement of the zygapophysial joints is determined by the size of the IV disc relative to that of the vertebral body, and the joints permit gliding movements between the articular processes.
The zygapophysial joints are innervated by articular branches that arise from the medial branches of the posterior rami of special nerves.
The craniovertebral joints, like the name suggests, form the skeletal connections between the cranium and vertebral column. The joints are synovial joints that have no IV discs. Their design gives a wider range of movement than in the rest of the vertebral column. It is composed of two sets of joints, the atlanto-occipital joints (‘the Yes or nodding movement joints’) formed between the atlas (C1 vertebra) and the occipital bone of the cranium, and the atlantoaxial joints (‘the no or rotational movement joints’) formed between the atlas and the axis (C2 vertebra).
The articulations of the craniovertebral joints involve the occipital condyles, atlas, and the axis.
- Atlanto-occipital joints: these joints, between the superior articular surfaces of the atlas and the occipital condyles, permit nodding of the head, such as the neck flexion and extension occurring when indicating approval (the “yes” movement). The atlanto-occipital joints also permit side-ways tilting of the head. The main movement is flexion, with a little lateral bending (lateral flexion) and rotation.
The anterior and posterior atlanto-occipital membranes, which extend from the anterior and posterior arches of C1 to the anterior and posterior margins of the foramen magnum, connect the cranium and atlas. The anterior atlanto-occipital membranes are continuous with the anterior longitudinal ligament and they also function to prevent excessive movement of the atlanto-occipital joints.
- Atlantoaxial Joints: There are three atlantoaxial joints, two lateral (right and left atlantoaxial joints, lying between the inferior facets of the lateral masses of C1 and the superior facets of C2), and one median atlantoaxial joint (between the dens of the axis and the anterior arch of the atlas).
The lateral atlantoaxial joints are gliding type of synovial joints, whereas the median atlantoaxial joint is a pivot joint. Movement at all three atlantoaxial joint types permit the head to be turned from side to side, as occurs when rotating the head to indicate disapproval (the “no” movement).
Posteriorly, the atlantoaxial joint is held together by the transverse ligament of the atlas. The alar ligaments extend from the sides of the dens to the lateral margins of the foramen magnum. These short, rounded cords, approximately 0.5cm in diameter, attach the cranium to vertebra C1 and serve as check ligaments, preventing excessive rotation at the joints.
The tectorial membrane, a strong superior continuation of the posterior longitudinal ligament, crosses the median atlantoaxial joint through the foramen magnum to the central floor of the cranial cavity. It runs from the body of C2 to the internal surface of the occipital bone and also covers the alar and transverse ligaments.
The articular bones of the costovertebral joints are the ribs (head of ribs) and the adjacent vertebral bodies. The joint is traversed by intervertebral disc. There is also a costotransverse joint in which the tubercle of the rib articulates with the transverse process of a vertebra. Movements at the costovertebral joints include elevation and depression of the rib cage, e.g. as in inspiration and expiration.
The costovertebral joints are strengthened by an intra-articular ligament found within the joints, as well as a radiate sternocostal ligament that fans out from the anterior margin of the head of the rib to the sides of the bodies of two vertebrae and the IV disc between them.
The sacroiliac joints, formed by the sacrum and the iliac bones (pubic bones), are specialized compound synovial and syndesmotic joints. They are strong, weight-bearing compound joints, consisting of an anterior synovial joint (between the ear-shaped auricular surfaces of the sacrum and ilium, covered with articular cartilage) and a posterior syndesmosis (between the tuberosities of the same bones).
The sacroiliac joint differs from most other synovial joints in that limited mobility is allowed, a consequence of their role in transmitting the weight of most of the body to the hip bones. As long as tight apposition is maintained between the articular surfaces, the sacroiliac joints remain stable.
The sacrum is actually suspended between the iliac bones and is firmly attached to them by posterior and interosseous sacroiliac ligaments. The thin anterior sacroiliac ligaments are merely the anterior part of the fibrous capsule of the synovial part of the joint. The abundant interosseous sacroiliac ligaments (lying deep in the tuberosities of the sacrum and ilium and occupying an area of approximately 10cm2) are the primary structures involved in transferring the weight of the upper body from the axial skeleton to the two ilia of the appendicular skeleton.
The posterior sacroiliac ligaments are the posterior external continuation of the same mass of fibrous tissue. The sacroiliac joints are also strengthened by the sacrotuberous ligament posteriorly and the sacrospinous ligament which passes from the lateral sacrum and coccyx to the ischial spine.
Movement at the sacroiliac joint is limited by the interlocking of the articulating bones and the sacroiliac ligaments to slight gliding and rotation movements. Rotation at this joint is also counterbalanced by the strong sacrotuberous and sacrospinous ligaments.
Accessory Ligaments of the Intervertebral Joints
The laminae of the adjacent vertebral arches are joined by broad, pale yellow elastic tissue called the ligamenta flava (coined from the Latin word “flavus”).
Ligamenta flava extend almost vertically from the lamina above to the lamina below, those of the opposite sides meeting and blending in the midline. These ligaments bind the lamina of the adjoining vertebrae together, forming alternating sections of the posterior wall of the vertebral canal.
The adjoining spinous processes are united by weak, almost membranous interspinous ligaments and the strong supraspinous ligaments. The cord-like supra-spinous processes from C7 to the sacrum, and merges superiorly with the nuchal ligament (Latin: ligamentum nuchae) – the strong, broad, median band at the back of the neck. Connecting the adjacent transverse processes of the vertebrae is another group of ligaments called the intertransverse ligaments.