Spine anatomy terms can feel overwhelming when you are navigating chronic back pain. This glossary defines the most important concepts — from individual disc structures to regenerative treatment approaches — so you can engage more confidently in conversations with your care team. Outcomes from any spine treatment vary by individual; this resource is educational, not a substitute for a clinical evaluation.

Annulus Fibrosus

The annulus fibrosus is the tough, fibrous outer ring of each intervertebral disc. Composed of multiple concentric layers of collagen fibers, it encases the softer, gel-like nucleus pulposus within. This robust structure provides stability to the spine and helps resist compressive forces during daily movement. Tears or fissures in the annulus fibrosus are a common source of chronic low back pain, because they can allow inflammatory chemicals from the disc’s interior to leak out and irritate nearby nerves. These tears often struggle to heal on their own due to the limited blood supply within the disc — making them a primary target for advanced biologic disc repair approaches.

Nucleus Pulposus

The nucleus pulposus is the soft, gelatinous center of an intervertebral disc. Rich in water and proteoglycans, it serves as the disc’s primary shock absorber, distributing pressure evenly across adjacent vertebrae. When the annulus fibrosus develops a tear, the nucleus pulposus may begin to bulge or herniate through the opening, potentially compressing nearby spinal nerves. This compression can produce symptoms such as pain, numbness, or weakness that radiate into the arms or legs, depending on the level affected. Preserving the integrity of the nucleus pulposus is considered central to long-term spinal comfort.

Intervertebral Disc

An intervertebral disc is a specialized cushioning structure located between each vertebra in the spinal column. These discs act as shock absorbers during movement and allow the spine to flex, extend, and rotate. Each disc consists of two main components: the annulus fibrosus (tough outer ring) and the nucleus pulposus (soft inner core). Over time, or following injury, discs may degenerate, bulge, or herniate, potentially irritating or compressing spinal nerves. Understanding disc anatomy is foundational to interpreting imaging findings and evaluating treatment options for many spine-related conditions.

Vertebra

A vertebra is one of the 33 individual bones that make up the spinal column, extending from the base of the skull to the pelvis. Stacked in sequence, these bones form a protective canal for the spinal cord. Each vertebra typically consists of a load-bearing body and a posterior arch that contributes to the neural canal. Between most vertebrae sit the intervertebral discs, providing cushioning and enabling flexible movement. Problems affecting the vertebral bodies or the discs between them can significantly influence spinal health and contribute to various pain conditions.

Foramen

A foramen (plural: foramina) is a natural opening in the spinal column through which spinal nerve roots exit the spinal canal and branch out to the rest of the body. Neural foramina are present between each pair of vertebrae on both sides of the spine. When these openings narrow — often due to disc bulging, herniation, bone spurs, or thickened ligaments — the exiting nerve root may become compressed. This compression can produce pain, numbness, tingling, or weakness in the region supplied by the affected nerve, a presentation known as radiculopathy.

Facet Joint

Facet joints are small, paired joints located at the back of each vertebra, connecting adjacent vertebral segments. They provide stability while permitting controlled movements such as bending, twisting, and extension. Like other synovial joints in the body, facet joints have cartilage and a joint capsule, making them susceptible to arthritic changes, inflammation, and wear over time. When facet joints become inflamed or damaged, they can become a notable source of localized back or neck pain — one that may feel distinct from disc-related pain and often worsens with certain positions or movements.

Annular Tear

An annular tear is a rip or fissure in the annulus fibrosus, the disc’s tough outer layer. These tears can develop from acute injury, repetitive mechanical stress, or age-related degeneration. When the annulus tears, it compromises the structural integrity of the disc and may allow inflammatory chemicals from the nucleus pulposus to escape and irritate adjacent nerves — contributing to significant pain. Because the disc’s blood supply is limited, annular tears often fail to heal adequately on their own. Addressing these tears is a central focus of biologic disc repair and annular tear repair approaches.

Expert Take

Annular tears are frequently identified as a root cause of chronic discogenic pain. In patients where conservative care has not produced adequate relief, a structural repair strategy — rather than symptom management alone — may offer a more durable path forward. Candidacy is evaluated individually.

Degenerative Disc Disease (DDD)

Despite its name, Degenerative Disc Disease (DDD) is not a discrete disease but rather a condition describing the progressive breakdown of one or more intervertebral discs over time. This process — common with aging — can cause discs to lose hydration, height, and elasticity, diminishing their shock-absorbing function. In some individuals, disc degeneration may contribute to chronic back or neck pain, stiffness, or related conditions such as herniated discs or spinal stenosis. Many patients with DDD pursue therapies aimed at supporting disc health rather than simply masking symptoms. Learn more about DDD and spinal fusion alternatives.

Herniated Disc

A herniated disc occurs when the nucleus pulposus pushes through a tear in the annulus fibrosus, extending beyond the disc’s normal boundary. This protrusion can press directly on nearby spinal nerves or, in severe cases, the spinal cord itself. Commonly referred to as a “ruptured disc” or “slipped disc,” a herniation may produce sharp, radiating pain into the arms or legs (radiculopathy or sciatica), along with numbness, tingling, and muscle weakness. Identifying the precise level and direction of herniation guides targeted evaluation and treatment planning. See our comparison of bulging disc vs. herniated disc for further detail.

Bulging Disc

A bulging disc occurs when the intervertebral disc extends beyond its normal perimeter while the annulus fibrosus remains structurally intact — containing the nucleus pulposus within. Unlike a herniation, where the nucleus breaks through the outer ring, a bulging disc involves a more generalized outward protrusion. While often considered less severe than a true herniation, a bulging disc can still produce significant pain if it presses on adjacent spinal nerves or other structures within the spinal canal. Symptoms may include localized back pain and, when nerves are involved, radiating pain, numbness, or tingling in the limbs.

Sciatica

Sciatica describes a pattern of symptoms — rather than a standalone diagnosis — characterized by pain that travels along the path of the sciatic nerve. This nerve, the longest in the body, extends from the lower spine through the buttocks and down the back of each leg. Sciatica commonly arises from compression or irritation of nerve roots in the lower lumbar spine, most often due to a herniated disc, spinal stenosis, or bone spurs. Many patients report sharp, shooting pain, numbness, tingling, or leg weakness, frequently aggravated by prolonged sitting or certain movements. Explore common myths about sciatica and non-surgical relief options.

Radiculopathy

Radiculopathy refers to symptoms arising from the compression or irritation of a spinal nerve root, producing pain, numbness, tingling, or weakness that travels along the nerve’s distribution. The location of symptoms depends on which level is affected: cervical radiculopathy involves the neck and arms, while lumbar radiculopathy affects the lower back and legs. Common underlying causes include herniated discs, bone spurs, and spinal stenosis. Effective management typically requires addressing the root cause of nerve root impingement rather than symptoms alone.

Discogenic Pain

Discogenic pain is a form of chronic back pain that originates directly from a damaged or degenerated intervertebral disc — from the disc’s internal structures rather than from nerve root compression. It is typically felt in the central lower back and tends to worsen with activities that increase intradiscal pressure, such as sitting for long periods, bending, lifting, or coughing. Discogenic pain is commonly associated with annular tears or advanced disc degeneration. Accurate identification of this pain source is important for selecting appropriate non-surgical strategies, including annular tear repair.

Fibrin

Fibrin is a natural protein produced during the body’s clotting response. It forms the structural meshwork of a blood clot and serves as a scaffold that supports tissue repair. In the context of regenerative spine care, fibrin is carefully prepared and precisely injected into damaged intervertebral discs. When used in intra-annular fibrin injection, it may help seal annular tears, stabilize the disc, and limit the leakage of inflammatory materials — supporting the disc’s natural healing process. Outcomes vary by patient; candidacy for the fibrin procedure is evaluated on an individual basis. For a broader overview, visit our regenerative spine treatment glossary.

Expert Take

Fibrin’s role as a natural biological scaffold makes it a compelling candidate for intradiscal repair. When applied through intra-annular fibrin injection, it targets the structural defect at the source of discogenic pain. Because disc pathology varies considerably across patients, thorough diagnostic imaging and clinical evaluation are essential before determining whether this approach is appropriate.

Intradiscal Injection

An intradiscal injection is a procedure in which therapeutic substances are delivered directly into the interior of an intervertebral disc. This differs from epidural steroid injections, which target the space surrounding the nerves, or facet joint injections, which address the posterior joints. Intradiscal injections require precise placement — typically guided by fluoroscopy (real-time X-ray imaging) — to ensure accurate delivery within the disc’s nucleus or annular regions. This targeted approach is central to intra-annular fibrin injection, allowing the biologic agent to act directly at the site of disc damage.

Regenerative Medicine

Regenerative medicine is a field focused on therapies that aim to activate the body’s natural healing mechanisms to repair or restore damaged tissues. In spine care, regenerative approaches seek to address the underlying cause of disc-related pain rather than simply managing symptoms or removing disc tissue through surgery. Techniques such as intra-annular fibrin injection represent this philosophy — attempting to seal annular tears, stabilize disc structure, and reduce inflammation. Patients considering regenerative spine care are evaluated individually to determine whether this approach aligns with their specific diagnosis, imaging findings, and clinical history. Explore non-surgical disc treatments for chronic back pain for additional context.

For a deeper dive into disc condition terminology, visit our companion resource: Glossary of Key Terms in Spine Anatomy and Disc Conditions. For diagnostic imaging terms, see our Diagnostic Imaging and Evaluation Glossary.