• To document in vivo, the anatomical site of failure in lumbar disc herniation (LDH)

Conventional wisdom states that the mode of failure and cause of disc herniation is secondary to a rupture of nucleus material through the annulus fibrosis.

In this paper, the senior author prospectively defined the nature of intraoperatively identified disc herniations in 181 consecutive patients qualified for inclusion. Inclusion criteria included requiring a single level lumbar microdiscectomy, age less than 60, no canal stenosis, no prior lumbar spinal surgery and normal bone mineral density.

Intraoperative findings were recorded. Discs with clear evidence of endplate junction failure were considered a type I herniation. Disc herniations secondary to annular failure were defined as a type II herniation. A validation process was used to check the intra-and inter observer reliability.

Prior to surgical microdiscectomy, each patient had radiologic studies including plain radiographs, thin slices CT scans at the level of the end plates, and 1.5 Tesla MRI imaging.

One surgeon performed all the operations, at one facility.

724 nonoperated disc herniations identified from other patients were also evaluated as a control. Comparison of findings was made.

Histology was also used to identify endplate or bony fragments attached to the surgically removed herniated disc fragments.

The surgically treated patients had a 104/181 (57.4%) ratio of type I herniations. This was a significant contrast to the 84/724 ratio of type I herniations identified in the non-surgically treated patients. The difference was statistically significant.

For the surgically treated population, the location of endplate failure was to the inferior endplate of the disc level.

Review of CT scan results identifying obvious endplate junction failure for the operatively treated patient population also indicated a 58% identification of endplate avulsion. This was consistent to the intraoperative findings.

This was an excellent study, and for the first time examined a control of population who had microdiscectomy surgery for mode of failure. For the surgically treated population, there is an indication that endplate junction failure may be the more common cause of HNP in this population.

Several conclusions were drawn from this study. Surprisingly, they did not discuss the possibility that endplate junction failure related disc herniations may not clinically resolve with nonsurgical treatment, compared to annular failure related disc herniations. Nevertheless, this is an excellent prospective evaluation of the mode of failure for lumbar disc herniation in a very narrowly defined population.