In a soon to be published Spine Journal study of 181 subjects (1), Rajasekaran found that Lumbar Disc Herniation (LDH) due to End Plate Junction Failure (EPJF) was more common (65%) than annulus fibrosis rupture. The EPJF presented radiographically as a vertebral corner defect in 30 patients, rim avulsion in 46, frank bony avulsion in 24 and avulsion at both upper and lower end plates in 4. Thirteen discs with radiographically normal end plates demonstrated cartilage or bone avulsion intraoperatively. Post contrast MRI in 20 patients showed dye leak at the end plate junction proving EPJF as main cause of lumbar disc herniation.
Under compressive loading, the bulging of the cartilaginous end plates into the vertebral bodies causes stress capable of producing fracture. These fractures may allow the liquid nucleus to squirt through the end plate into the vertebral body (McGill, 1997). This process may be associated with an audible “pop”. Sometimes a local area of bone collapses under the end plate to create a pit or crater (aka Schmorls Node). With the loss of nuclear material into the vertebra, the disc will inevitably loose height- often radiographically misdiagnosed as DDD.
As a means of differentiation, end plate fractures will generally not tolerate compressive loading, while true herniation will tolerate compressive loads so long as the disc is not flexed.
The heel drop test is another means of differentiating endplate fractures. This test is performed by having a standing patient raise up on their toes, then abruptly drop onto their heels. Pain is consistent with an endplate fracture.
Clinical Pearls from this paper:
- Most disc herniations are through the endplate—not the annulus
- Vertebral corner defect indicates a possible endplate fracture
- Compressive loading and the heel drop test may help differentiate EPJF from annular failure as a cause of disc herniation.
1. S Rajasekaran ISSLS Prize Winner: The Anatomy of Failure in Lumbar Disc Herniation An in-vivo, multi-modal, prospective study of 181 subjects. Spine. Publish Ahead of Print
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