“Comparison of Adjacent Segment Degeneration After Non-Rigid Fixation System and Posterior Lumbar Interbody Fusion for Single-Level Lumbar Disc Herniation: A New Method of MRI Analysis of Lumbar Nucleus Pulposus Volumen”

This article refers to:

In Vitro Biomechanical Study of Epidural Pressure during the Z-shape Elevating-Pulling Reduction Technique for Cervical Unilateral Locked Facets

The authors present an interesting point of view of a very difficult sometimes to diagnose injury, which is the unilateral facet disclocation of the subaxial cervical spine.

A model is created using cadaver head-neck-torso model after Ivancic´s model.¹

Classically the reduction of unilateral facets needs ventral flexion plus lateral bending toward the injured side to unlock the injured facet to apply then a rotation toward the affected side and then lateral bending toward the unaffected side,² in real life the muscle spasm makes this manoeuver difficult and uncomfortable for the patient, thus the high percentage of failure, as cited by the authors.

In this sense, the value of a device-controlled reduction manoeuver might be of interest. Although nevertheless the proposed reduction manoeuver is reversing the one that was previously created, in actual fact, this is not really a snag, as reduction manoeuvers are almost always devised as reversing the injuring mechanisms.

My personal choice when confronted with a patient with a unilateral facet dislocation with radiculopathy and a reasonably healthy disc is a direct unilateral posterior approach with drilling of the facet to avoid any distractive force,³ anterior distractive forces are not always capable of reducing unilaterally locked facets.

However, the main objective of this paper is to address the pressure changes within the canal at different relative positions of the C5 and C6 vertebrae and in this issue the results are quite clear and conclusive: the unilateral locked facet position creates the highest intracanal pressure⁴ while the perched facet situation does not cause a very different situation from both the reduction and physiological curvature measurements.⁴

Just for the sake of an order of magnitude, pressure should be below 70 Hg mm,⁵ which is the cord perfusion average pressure, and this level was surpassed in several situations with this model, and not only with locked facets.

It can be discussed whether pressure measurements in this kind of model are similar to real-life environment (no cerebrospinal fluid) but, so long as it is a comparison between situations and not absolute values, I think they are representative.

Then, after this increase in pressure is taken into account, the issue arises that unilateral facet dislocations in a locked position should have to be reduced as soon as possible, in order to lower these high values at the injured level.

Some discussion can be raised from the level (C5–C6), regarding whether this situation would be reproducible at other levels, but the statistical significance and common sense are so clear about that I believe this rise in pressure can be easily expected also at other levels.

Although the pressure measurements derived from this study may not be entirely equivalent to a physiologic environment, and the data do not mandate a change in current clinical practice, this study emphasizes concerns about the pressure within the canal of an injured spine, and, moving a step forward, during reduction manoeuvres; substantiating the need for care and attention to this issue.

DECLARATION OF INTEREST

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.