Endplate junction failure determined the cause of lumbar disc herniation

Issue: October 2013

In an award-winning study, researchers from India concluded that the endplate junction — rather than the anulus fibrosis — is the most common point of failure in patients with lumbar disc herniation.

“If the disc herniates, the classic teaching is that it is the rupture of anulus fibrosus,” Prof.S. Rajasekaran, MS, MCh, FRCS (Ed), FRCS (London), FACS, PhD, of Ganga Hospital, Tamil Nadu, India, said during his presentation at the International Society for the Study of the Lumbar Spine Annual Meeting. “We were able to identify it [in the anulus] in only 35% [of patients]. We observed in our study that this failure, where there is an avulsion in the endplate along with the anulus, is found in the majority (65%) of patients,” he said.

Rajasekaran and colleagues performed an in vivo, multimodal, prospective study of 181 patients who underwent single-level discectomy. They analyzed 905 lumbar discs and included 724 uninvolved discs as the control group and 181 operated discs as the study group. Overall, 9% of patients were younger than 20 years old. The rest were aged between 21 years and 60 years. The investigators found 90% of patients had herniations in the lower two lumbar levels.

They examined the endplate junction and anulus fibrosis in patients using plain radiographs, thin slice CT at the level of the endplate, serial post-contrast MRI, intraoperative observations and histopathological study.

Classification of disc herniations

The researchers created a classification system to identify disc herniations. A type 1 disc herniation was classified as a patient with endplate junction failure (EPJF), and a type 2 disc herniation was classified as a patient with no evidence of EPJF. Rajasekaran and colleagues ultimately classified 65% of patients as having type 1 disc herniation and 35% of patients as having type 2 disc herniation.

Thin section CT images demonstrate endplate avulsion in type 1 herniation (yellow arrows). Shown are (A) type 1A with a vertebral corner; (B) type B1 with a rim avulsion of the endplate; (C) type 1C with a large bony avulsion of the endplate; (D) type 1D with proximal and distal endplate avulsion; (E) L5-S1 disc prolapse on sagittal MRI, and (F) type 2 herniation where endplate avulsion is absent.

Of the patients with no EPJF or type 2, 11 patients had anular high-intensity zones.

On CT images, EPJF presented as vertebral corner defects in 30 patients (type 1A), rim avulsion in 46 patients (type 1B), bony frank avulsion in 24 patients (type 1C) and avulsion of the upper or lower endplates in four patients (type 1D).

Preoperative CT images indicated that EPJF caused lumbar disc herniation in 58% of patients. However, based on the discs that the investigators excised, 13 those discs, which showed no evidence of EPJF radiologically, were observed to have cartilaginous or small bony endplates intraoperatively. The addition of these discs to the 104 radiological type 1 herniations increased the incidence of type 1 herniation to 65%. Anulus fibrosus rupture caused lumbar disc herniation in 35% of patients.

Study limitations

Serial post-contrast MRI with gadodamide was performed in 20 patients (10 each with type 1 and type 2 discs).

“On post-contrast MRI, the [dye] leak starts at the endplate junction, which means this is the site where the anatomical failure has happened,” Rajasekaran said. Eight type 1 discs and five type 2 discs showed evidence of dye leakage at the endplate junction.

Rajasekaran said he and colleagues only included patients who underwent surgery, which limited the study. The natural history in variations between type 1 and 2 disc herniations was not identified and the significance of Modic changes was not explored.

“The endplate junction failure is the more common pathway than the anulus failure,” Rajasekaran said. “This provides new insights in understanding and planning prevention for this common problem.” – by Renee Blisard Buddle

Reference:
Rajasekaran S. Paper #053. Presented at: International Society for the Study of the Lumbar Spine Meeting; May 13-17, 2013; Scottsdale, Ariz., USA.

For more information:

S. Rajasekaran, MS, MCh, FRCS (Ed), FRCS (London), FACS, PhD, can be reached at 313 Mettupalayam Rd., Coimbatore, 641043 India; email: rajasekaran.orth@gmail.com.

Disclosure: Rajasekaran has no relevant financial disclosures.