Relationship between degree of separation of endplate cartilage and severity of intervertebral disc herniation.

Degeneration of intervertebral disc and fissures in the anulus was caused by compression and distraction, which lead to nucleus pulposus herniation. However, controversy remains regarding the exact mechanism behind disc herniation. The aim of this study is to analyze histologically the differences between the three types of disc herniations in an attempt to infer the underlying mechanism. Disc samples extracted from 49 patients who underwent discectomy of the lumbar region were studied by histological analysis. The severity of disc herniation was classified as bulging, protrusion, extrusion, or sequestration based on preoperative magnetic resonance imaging measurements. For comparative analysis of sequestration characteristics, 49 patients were classified into either the sequestration or the non-sequestration group (i.e., protrusion and extrusion) according to disc herniation type. Forty of the 49 patients had cartilage present in their disc samples upon histological analysis. The endplate cartilage-containing samples included two of four (50%) protruded disc patients, 22 of 29 (75.9%) extruded disc patients, and 16 of 16 (100%) sequestrated disc patients and had statistical significance (p = 0.019). There were no significant differences in age, sex, body mass index, length of hospital stays, injection history, surgical methods, and Visual Analog Scale between the sequestration and non-sequestration group (all p > 0.05). Separation of endplate cartilage increased with the severity of disc herniation. Therefore, the mechanism of disc herniation should consider the connection with endplate cartilage as an initiating link in the mechanical failure of intervertebral discs.