Figure. Sagittal magnetic resonance imaging of the lower back.
A 34-year-old man presents with lower back pain that has persisted for 3 months. The patient is not experiencing any pain that radiates down the leg and has not had any changes in his bowel or bladder function. He describes a few severe attacks of lower back pain when reaching for something while seated. Physical examination reveals palpable spasm over the paraspinous muscles of the lumbar spine. Motor function and sensation in the legs are normal. Sagittal magnetic resonance imaging (MRI) is obtained (Figure) and shows darkened discs at the L4-L5 and L5-SI levels.
Submit your diagnosis to see full explanation.
The lumbar intervertebral disc consists of a jelly-like core, the nucleus pulposus, and is surrounded by a tough outer ring called the annulus fibrosis. The nucleus pulposus is made up of approximately 88% water.1 Lumbar discs function as shock absorbers and allow motion and stability of the spine. When combined, the vertebral discs provide 25% of the length of the spine.2
The most precise diagnostic imaging used to evaluate the overall health of vertebral discs is MRI. A darkened disc on MRI indicates a decrease in hydration and degeneration of the disc material. Adequate disc hydration allows the disc to resist axial compression in the spine; as the disc loses hydration (disc desiccation), the vertebral end plates start to degenerate due to the increased compressive forces. The degenerative cascade starts with disc desiccation, followed by disc collapse, and finally vertebral endplate degeneration. Degeneration of the endplates can result in lower back pain.1-3
Lumbar spine fusion may be considered in the presence of vertebral endplate degenerative changes and lower back pain. Isolated lower back pain is often called discogenic or axial back pain, and surgical treatment is controversial due to multifactorial causes of pain and unpredictable surgical outcomes.1-3
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
1. Moore D. Lumbar disc herniation. OrthoBullets website. Updated September 13, 2020. Accessed November 11, 2020. https://www.orthobullets.com/spine/2035/lumbar-disc-herniation.
2. Waxenbaum JA, Reddy V, Futterman B. Anatomy, back, intervertebral discs. StatPearls [Internet]; Treasure Island (FL): StatPearls Publishing: 2020.
2. Setton LA, Chen J. Mechanics and biology of the intervertebral disc and relevance to disc degeneration. J Bone Joint Surg Am. 2006;88(2):52-57.