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Injured Disc Takes the Path of Least Resistance

Low back pain from disc problems is a common problem. Most disc herniations occur at the L4-L5 and L5-S1 levels. Less than 10 percent occur in the upper lumbar spine at L3-4. In this study two groups of patients were compared. The study group had a L3-L4 disc herniation. The control group had L4-5 or L5-S1 herniation.

The disc is like a cushion located between two vertebrae. If damaged, torn, or worn, disc material can get pushed out of the disc space in any direction. Disc herniations are labeled according to their anatomic location. For example, if it pushes straight back it's called posterior. If it moves to one side or the other, it's classified as lateral. A disc that protrudes to the back and side at the same time is posterolateral.

The authors used CT scans and MRIs to see where herniations occur at the L3-L4 level. They compared this to herniations at lower levels. Most lower disc problems are posterolateral. The authors assumed disc problems in the upper lumbar spine would be more lateral.

They were right. The herniation occurs where there is the least resistance. A ligament behind the vertebrae at L3-L4 called the posterior longitudinal ligament (PLL) keeps the disc from pushing back. The path of least resistance at this level is to the side (lateral).

They also found that L3-L4 herniations are most likely to occur in older adults. These patients report thigh pain. On exam there is weakness in the quadriceps muscle. This is the muscle used to extend the knee. The knee reflexes are also decreased.

The authors say this information is helpful. When an older patient presents with these symptoms, the doctor will know to look for a disc problem in the upper lumbar spine. Knowing where the disc is likely to protrude will help doctors use imaging studies to trace the path of the herniated disc.


Eran Tamir, MD, et al. Clinical Presentation and Anatomic Position of L3-L4 Disc Herniation. In Journal of Spinal Disorders. December 2004. Vol. 17. No. 6. Pp. 467-469.

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