Causes of Spinal Pain

There are six major categories for the causes of spinal pain (degenerative, deformity, trauma, infection, tumor, inflammatory). However, the most common by far is degenerative conditions of the spine. 80 percent of the adult population will have an episode of low back pain in their lifetime. Fortunately, 90 percent will obtain relief of pain within six to eight weeks and ninety five percent will be free of pain within six months. However, 70 to 90 percent will have a recurrence of their pain. Five percent of this population will go on to chronic pain and disability. Low back pain is the second most common reason for a physician visit. The common cold is first.

The best model to explain the changes responsible for spinal pain is called the degenerative cascade. It is based on the concept of the spinal motion segment. The spinal motion segment consists of the intervertebral disc, the vertebrae above and below the disc, the paired facet joints behind the disc, and the nerves within the spinal canal. The motion segment is highly resistant to loading forces during the first two decades of life. However, beginning in the third decade (twenties), the spine begins to age (degenerate) and continues to age progressively until death. As the spine degenerates, it is less able to resist loads (normal and abnormal) and is more susceptible to injury. Aging (degeneration), single injury, or multiple injuries lead to changes in the structural integrity of the disc, facet joints, and vertebral end plate cartilage.

The degenerative cascade is divided into three stages depending on the amount of damage to the disc and facet joints at any point in time. Stage I (dysfunction) starts at an early age (20-30) and is a reflection of the first changes of degeneration. Stage II (instability) follows dysfunction as degeneration progresses or abnormal loading is not corrected or treated. It represents more severe tissue damage and usually occurs later in life (late 30s- early 50s). Stage III (stabilization) is the end stage of the degenerative cascade. It reflects the most severe tissue damage and attempts at physiologic repair of the tissue. This stage occurs in the 60s and beyond.

Stage I Dysfunction

Stage II Instability

Stage III Stabilization

Clinical Manifestations

Stage I Dysfunction
      This stage usually presents as acute mechanical low back pain. It is typically the patient's first episode of pain and is usually short lived, self-limited, and improves with minimal intervention. Extension and/or rotation usually produce pain from the facet joints at this stage. Pain from the annulus/disc is usually limited to back pain worsened by flexion or torsional movement, sitting, and bending.

Stage II Instability
      This stage also presents as predominantly low back pain. However, it is usually more severe and is not short lived, self-limited, and requires significant intervention. It is often the patients repeated episode of back pain. It is during this phase that recurrent annular tears can lead to a disc rupture or herniation. The pain from a disc herniation is more predominantly leg pain secondary to nerve root compression. Because of the more severe tissue damage and incomplete healing of the tissues, the episodes of back pain are more frequent, severe, and disabling.

Stage III Stabilization
     This stage can also present as back pain; however, now leg pain is more prevalent. The hypertrophy and bone spurs of the facet joint combined with the loss of disc height and bone spurs formed around the rim of the disc produces spinal stenosis (narrowing of the spinal canal). This can produce lateral recess and foraminal stenosis, which causes nerve root pain. It can also cause central stenosis producing claudication (leg pain worsened by walking relieved by sitting down in a flexed position).

The degenerative cascade is a very useful model. It describes the physiologic (normal) changes of aging in the spine. These changes may or may not be painful (which explains the high incidence of abnormal findings on imaging studies in asymptomatic or pain free individuals). It gives us an anatomic and physiologic basis for understanding where spine pain originates. When a patient presents with spine pain, we can identify what stage of the cascade their injury represents and what tissue is injured. We can then recommend treatment on a rational basis and predict the outcome of that treatment. We can also educate patients to recognize that their initial back pain is a warning sign of the negative potential of the degenerative cascade. With emphasis on education, life style changes, exercise, and body mechanics we can alter the long-term consequences.