Discography: can pain in a morphologically normal disc be due to an adjacent abnormal disc?

Biomechanical effect of C5-C6 intervertebral disc degeneration on the human lower cervical spine (C3-C7): a finite element study

The biomechanical effects of intervertebral discs and facet joints degeneration on the cervical spine are essential to understanding the mechanisms of spinal disorders to improve pathological and clinical treatment. In this study, the biomechanical effects of a progressively degenerated C5-C6 segment on the human lower cervical spine are determined by a detailed simulation of intervertebral disc degeneration. A detailed asymmetric three-dimension intact finite element model was developed using computed tomography scan data of the human lower cervical spine (C3-C7). The intact finite element model was then modified at the C5-C6 segment to build three degenerated models, such as mild, moderate, and severe degeneration. The physiological compressive load 73.6 N, and moment 1 Nm were applied at the superior endplate of the vertebra C3, and the inferior endplate of the C7 vertebra was a constraint for all degrees of freedom. Range of motion, maximum von Mises stress in the annulus, intradiscal pressure, and facet joint force of the degenerated models were computed. With progressive degeneration in the C5-C6 segment, the range of motion of degenerated and normal segments decreases in all postures. Intradiscal pressure of the degenerated segment decreases but increases in normal segments of degenerated segment C5-C6, and facet joint forces increase at both degenerated and normal segments. This study emphasizes that the degenerated disc alters the degenerated and normal segments' motion and loading patterns. The abnormal increase in facet joint force in the degenerated models threatened to accelerate the degeneration in the normal segments.

The transfer of disc pressure to adjacent discs in discography: a specificity problem?

STUDY DESIGN

In vivo experimental study.

OBJECTIVE

The primary objective of the study was to investigate pressure transmission to adjacent discs during discography. A secondary objective was to quantify the transmitted pressure, both in contrast injected and noninjected porcine intervertebral discs.

SUMMARY OF BACKGROUND DATA

Discography is used to before surgery identify painful discs. A pain response during discography that is concordant with the patient's experienced back pain is regarded as an indication that the injected disc is the source of pain. However, the sensitivity and specificity of discography are matters of debate. Pressure-controlled discographies have been reported to reduce the number of false-positive discs using low pressure criteria. Preliminary data indicated a transfer of pressure from an injected to an adjacent disc during discography. Pressure transmission in vivo during lumbar discography, not reported before might, if clinically present, contribute to a false-positive diagnosis.

METHODS

Thirty-six lumbar discs in 9 adolescent pigs were investigated. Intradiscal pressure was recorded during contrast injection, using a 0.36/0.25 mm fiber-optic pressure transducer inserted into the nucleus pulposus via a 22 G needle. The pressure was measured simultaneously in 2 adjacent discs during contrast injection into 1 of the discs at pressures up to 8 bar. Transmitted pressure was recorded both in noninjected discs and in discs that were prefilled with contrast.

RESULTS

Thirty-three discs were successfully examined. During contrast injection, there was an intradiscal pressure rise in the adjacent disc with a median value of 16.0% (range, 3.2-37.0) over baseline pressure. There was no significant difference in pressure increase between the noninjected and prefilled discs (P < 0.68).

CONCLUSION

Discography of porcine discs induces a pressure increase in adjacent discs. A similar pressure transfer during human clinical discography might elicit false-positive pain reactions.

Motion changes in adjacent segments due to moderate and severe degeneration in C5-C6 disc: a poroelastic C3-T1 finite element model study

STUDY DESIGN

Biomechanics of normal vertebral segments adjacent to a degenerated segment in the cervical spine.

OBJECTIVE

To test the hypothesis of higher motion changes in the segment immediately inferior to a degenerated segment.

SUMMARY OF BACKGROUND DATA

Past research has shown how disc degeneration (DD) affects adjacent segments; however, these studies are conducted only on the lumbar spine or the experimental protocols used are characterized by the presence of degeneration in adjacent segments. The question arises as to how much of the degenerative effect in a particular segment is internal to degeneration at that segment and how much is caused by degeneration at adjacent segments. It would be clinically relevant to analyze biomechanical changes in adjacent segments in the cervical spine by considering DD at only one segment, where adjacent segments remain normal.

METHODS

A poroelastic, 3-dimensional finite element model of a normal C3-T1 segment was validated and then used for the degenerative study. Two additional C3-T1 models were developed with moderate and severe degenerative C5-C6 disc grades. Disc geometry and tissue material properties were modified to simulate C5-C6 DD. Intersegmental rotational motions (C4-C5, C5-C6, and C6-C7) for the 3 C3-T1 models were computed under moment loads.

RESULTS

With progressive C5-C6 DD, motion decreased at that segment. At adjacent segments, higher motion changes were observed mainly in flexion/extension. Inferior C6-C7 motion changes were higher than superior C4-C5 motion changes. The inferior C6-C7 motion was affected even when C5-C6 DD was moderate, and it was further affected by severe C5-C6 DD. The superior C4-C7 motion, however, was mostly affected by severe C5-C6 DD.

CONCLUSION

The hypothesis of higher motion changes in the normal C6-C7 segment immediately inferior to a degenerated C5-C6 segment was found to be true. Future experiments on multisegmental cervical spines are recommended to verify the current data.