Case presentation

A 38-year-old man, a worker in building companies, was admitted in our clinic because of low back pain with radiation to the right leg, which was lasting for about two months before his admission, followed by leg weakness. The patient in the physical examination showed only limitation of straight leg raising test on the affected side. The symptoms were these of L5 nerve root involvement. The patient related the onset of his symptoms to a specific episode of trauma caused by lifting of a heavy object. The initial symptom was hip pain.

Lumbar MRI revealed L4-L5 intervertebral disc herniation (Figure 1, 2). Plain x-rays and myelography were not performed.

Figure 1

Fig.1:Axial T2 MRI image showing disc herniation

Figure 2

Fig 2: Sagittal T2 MRI image depicting disc herniation. Attention should be paid in the different coloration of disc and lesion

During the operation hypertrophic ligamentum flavum was found and excised. Further exploration of the intervertebral disc space and the neighbouring lumbar spinal canal revealed no disc herniation, fragmentation or sequestration. Postoperatively the patient was markedly improved.

Discussion

Although intervertebral disc herniation accounts mostly for a cause of low back pain and sciatica it is nowadays generally accepted that posterior structures play also an important role in this pathology¹. In cases of posterior spinal elements symptomatology the pain is referred pain originating from the posterior ramous of the spinal nerve.

Various explanations have been proposed to account for radicular symptoms in the absence of a protruded disc. Most explanations have blamed structures which might narrow the nerve root foramen such as thickened ligamentum flavum^2,3, subluxation of the facet joints^4,5, retropulsion of one vertebral body on its neighbouring⁶, adhesions between the nerve root and the posterior ligaments⁷, general bulging of the whole edge of the disc⁸ and protrusion of the posterior longitudinal ligament ⁹.

In the literature there are a few reports concerning ligamentum flavum hypertrophy simulating lumbar disc protrusion^10,11. It was shown that degeneration of lumbar ligamentum flavum can cause lumbar stenosis and root pain and that resection of it can relieve the symptoms¹¹.

Fibrosis is believed to be the main cause of ligamentum flavum hypertrophy, which is caused by the accumulation of mechanical stress, with or without the aging process, especially along the dorsal aspect of the ligamentum flavum^12,13. Our patient was a worker in house building companies and heavy mechanical stress was an everyday situation for him.

MR images in the sagittal plane are important in demonstrating hypertrophy of the ligamentum flavum and can provide accurate measurements of its thickness¹⁴. In our case it was not easy to recognise from MR images hypertrophy of the ligamentum flavum. May be acquisition of thin slices MR images of the affected area could pose the diagnosis in such a case.