There are many potential sources of spine related symptoms. To have any understanding of these symptoms, a basic knowledge of spinal structure and function is necessary.
Spinal Intervertebral Disc
An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together. Their role as shock absorbers in the spine is crucial.
Intervertebral discs consist of an outer fibrous ring, the anulus fibrosus disci intervertebralis, which surrounds an inner gel-like center, the nucleus pulposus. The anulus fibrosus consists of several layers (laminae) of fibrocartilage made up of both type I and type II collagen. Type I is concentrated toward the edge of the ring, where it provides greater strength. The stiff laminae can withstand compressive forces. The fibrous intervertebral disc contains the nucleus pulposus and this helps to distribute pressure evenly across the disc. This prevents the development of stress concentrations which could cause damage to the underlying vertebrae or to their endplates. The nucleus pulposus contains loose fibers suspended in a mucoprotein gel. The nucleus of the disc acts as a shock absorber, absorbing the impact of the body’s activities and keeping the two vertebrae separated. It is the remnant of the notochord.
The annulus fibrosus is the tough circular exterior of the intervertebral disc that surrounds the soft inner core, the nucleus pulposus. This outer portion is composed of a ring of ligament fibers that encases the inner core of the disc and securely connects the spinal vertebrae above and below the disc.
Nucleus pulposus is the inner core of the vertebral disc. The core is composed of a jelly-like material that consists of mainly water, as well as a loose network of collagen fibers.
The elastic inner structure allows the vertebral disc to withstand forces of compression and torsion. With age, the body’s discs dehydrate and become stiffer, causing the disc to be less able to adjust to compression. The nucleus pulposus can herniate through the protective layer of annulus fibrosus, leaking out of the disc space and inflaming the nerve roots next to the disc.
The annular fibers prevent the nucleus pulposus, which is comprised of a gelatinous material, from herniating or leaking out of the disc by hydraulically sealing the nucleus and evenly distributing any pressure and force imposed on the intervertebral disc.
There is one disc between each pair of vertebrae, except for the first cervical segment, the atlas. The atlas is a ring around the roughly cone-shaped extension of the axis (second cervical segment). The axis acts as a post around which the atlas can rotate, allowing the neck to swivel. There are 23 discs in the human spine: 6 in the neck (cervical region), 12 in the middle back (thoracic region), and 5 in the lower back (lumbar region). For example, the disc between the fifth and sixth cervical vertebrae is designated “C5-6”.
The intervertebral disc functions to separate the vertebrae from each other and provides the surface for the shock-absorbing gel of the nucleus pulposus. The nucleus pulposus of the disc functions to distribute hydraulic pressure in all directions within each intervertebral disc under compressive loads. The nucleus pulposus consists of large vacuolated notochord cells, small chondrocyte-like cells, collagen fibrils, and aggrecan, a proteoglycan that aggregates by binding to hyaluronan. Attached to each aggrecan molecule are glycosaminoglycan (GAG) chains of chondroitin sulfate and keratan sulfate. Aggrecan is highly negatively charged, allowing the nucleus pulposus to swell by imbibing water. The amount of glycosaminoglycans (and hence water) decreases with age and degeneration.
The facet joints are the joints in your spine that make your back flexible and enable you to bend and twist. Nerves exit your spinal cord through these joints on their way to other parts of your body. Healthy facet joints have cartilage, which allows your vertebrae to move smoothly against each other without grinding.
Common Intervertebral Joint Conditions
The facet joints are the joints in your spine that make your back flexible and enable you to bend and twist. Nerves exit your spinal cord through these joints on their way to other parts of your body. Healthy facet joints have cartilage, which allows your vertebrae to move smoothly against each other without grinding.Facet joints are synovial joints. This means each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing joints to move or glide smoothly (articulate) against each other.These joints allow flexion (bend forward), extension (bend backward), and twisting motion. Certain types of movement are restricted. The spine is made more stable due to the interlocking nature to adjacent vertebrae.
Common Facet Joint Conditions
- facet joint Synovitis
- facet joint strain
- facet syndrome
- facet joint osteoarthritis
- autoimmune arthritis / rheumatoid / lupus
Spinal Cord and Canal
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone where it passes through the foramen magnum, and meets and enters the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) in men and around 43 cm (17 in) long in women. Also, the spinal cord has a varying width, ranging from 13 mm (1⁄2 in) thick in the cervical and lumbar regions to 6.4 mm (1⁄4 in) thick in the thoracic area.
The spinal cord functions primarily in the transmission of nerve signals from the motor cortex to the body, and from the afferent fibers of the sensory neurons to the sensory cortex. It is also a center for coordinating many reflexes and contains reflex arcs that can independently control reflexes and central pattern generators.
The spinal canal (or vertebral canal or spinal cavity) is the space in the vertebral column formed by the vertebrae through which the spinal cord passes. It is a process of the dorsal body cavity. This canal is enclosed within the vertebral foramen of the vertebrae. In the intervertebral spaces, the canal is protected by the ligamentum flavum posteriorly and the posterior longitudinal ligament anteriorly.
The outermost layer of the meninges, the dura mater, is closely associated with the arachnoid mater which in turn is loosely connected to the innermost layer, the pia mater. The meninges divide the spinal canal into the epidural space and the subarachnoid space. The pia mater is closely attached to the spinal cord. A subdural space is generally only present due to trauma and/or pathological situations. The subarachnoid space is filled with cerebrospinal fluid and contains the vessels that supply the spinal cord, namely the anterior spinal artery and the paired posterior spinal arteries, accompanied by corresponding spinal veins. The anterior and posterior spinal arteries form anastomoses known as the vasocorona of the spinal cord and these supply nutrients to the canal. The epidural space contains loose fatty tissue, and a network of large, thin-walled blood vessels called the internal vertebral venous plexuses.
Spinal stenosis is a narrowing of the canal which can occur in any region of the spine and can be caused by a number of factors.
Common Spinal Canal and Cord Conditions
- Spinal canal stenosis
- Cauda equina syndrome
Ligaments are fibrous bands or sheets of connective tissue linking two or more bones, cartilages, or structures together. One or more ligaments provide stability to a joint during rest and movement. Excessive movements such as hyper–extension or hyper–flexion, may be restricted by ligaments. Further, some ligaments prevent movement in certain directions.
Three of the more important ligaments in the spine are the Ligamentum Flavum, Anterior Longitudinal Ligament and the Posterior Longitudinal Ligament.
The Ligamentum Flavum forms a cover over the dura mater: a layer of tissue that protects the spinal cord. This ligament connects under the facet joints to create a small curtain over the posterior openings between the vertebrae.
The Anterior Longitudinal Ligament attaches to the front (anterior) of each vertebra. This ligament runs up and down the spine (vertical or longitudinal).
The Posterior Longitudinal Ligament runs up and down behind (posterior) the spine and inside the spinal canal.
Common Spinal ligament Conditions
- Ligament flavum hypertrophy
- Atlanto-occipital ligament
- Sacro-iliac ligament strain
Muscles are named according to their shape, location, or a combination. They are further categorized according function such as flexion, extension, or rotation. Muscles and ligaments work together to support the spine, hold it upright, and control movement during rest and activity.
Common Spinal Muscle Conditions
- Muscle strains
- Spinal deconditioning / core strength weakness
- Piriformis Syndrome
- Myofascial Pain Syndrome
Vertebrae are the 33 individual, interlocking bones that form the spinal column. Each vertebra has three main functional components: the vertebral body for load-bearing, the vertebral arch to protect the spinal cord, and transverse processes for ligament attachment. The spinal column consists of seven cervical, twelve thoracic, and five lumbar vertebrae in addition to five fused vertebrae of the sacral region and four fused vertebrae forming the coccyx. The vertebrae in each region have unique features that help them perform their main functions. Vertebrae are interconnected by facet joints that allow mobility in the spine. Intervertebral discs separate the individual bones providing additional weight-bearing support.
Common Vertebrae Conditions
- Pars stress fracture