Letter to the Editor regarding the article "Dynamic cervical myelopathy in young adults" by Hattou L, Morandi X, Le Reste PJ, et al.: Eur Spine J 2014, 23:1515-22.

Abstract

We read with great interest the article by Hattou L et al. [1] published in the European Spine Journal entitled ‘‘Dynamic cervical myelopathy in young adults’’. In this article, the authors state that the aim of the study was to evaluate the efficiency of dynamic MRI to detect six patients with cervical myelopathy without medullary compression on static MRI, and without a medical cause of myelopathy. All the patients had medullary compression on dynamic MRI not shown by static MRI: four in extension and two in flexion. The authors defined the medullary compression on dynamic MRI not shown by static MRI as chronic joint instability. After correlating the manuscript’s content with widely accepted knowledge, expertise and standards of patient care that have already been established for many years, we were not able to confirm the definition of chronic joint instability as dynamic medullary compression (medullary compression on dynamic MRI not shown by static MRI). Numerous classification systems have been proposed to define spine instability. White and Panjabi proposed a checklist point system to assess spinal stability, and this remains one of the best recognised systems to date [2]. Clinical instability refers to a loss of motion stiffness in a particular spinal segment when the application of force to it produces greater displacement than would otherwise be seen in a normal structure. As the authors of the article state, dynamic compressive factors in cervical spondylotic myelopathy are poorly understood: during cervical motions, the spinal cord could be injured by osteophytic bars and discal protrusion; extension movements make the ligamentum flavum bulge inwards, leading to a posterior stenosis [3, 4], and stenosis could compromise venous drainage; also anterior impingement plays a role in compressing the anterior spinal artery [3, 4]. More cases need to be observed to understand and classify this pathology. However, in our opinion, medullary compression at the dynamic MRI is not sufficient evidence to define chronic joint instability. In summary, we agree with the authors’ interpretation that this pathology is a different entity from Hirayama disease or cervical flexion myelopathy. This study suggests that dynamic cervical MRI may be useful for detecting dynamic medullary compression in cases of myelopathy where there is insignificant compression on static MRI, and no evident medical cause. The study also underlines that in most cases the compression was due to an anterior impingement, so anterior cervical interbody fusion appears as an interesting approach in this specific population. However, according to the current literature the definition of chronic joint instability as dynamic medullary compression should be reconsidered.