Application of Manual Traction Forces on the Cervical Discs With Degenerative Annular Fibers: A Finite Element Model Analysis

Degeneration in intervertebral discs is a complex multifactorial process. Studies have speculated the biomechanical and biochemical reasons factoring the degenerative disc pathology. Disc degeneration begins in inner nucleus pulposus (NP) that has high fluid content. As degeneration advances over time, the load is shifted from inner NP to outer annulus fibrosus (AF) that is more fibrous in nature. In addition to morphological changes in the discs that occur with degeneration in the form of tears and delamination, tissue compositional variations are also noted. These degenerative changes have not only been seen in the disc tissue matrix, but they are also quite apparent in the fibers of AF in the form of incompleteness and laxity [1]. These tensile fibers in AF have a critical functionality in maintaining the mechanical strength of the disc segments, and any form of degenerative impairment in these fibers may lead to abnormal physiology, both in the AF and NP. Despite past research have reported the annular and nucleus stresses in degenerative discs, area that still unclear is the relative contributions of degenerative properties in annular fibers — incompleteness and slackness — to the overall degenerative disc response. Typically, degeneration related neck pain that involve abnormal disc pressures has been shown to be temporarily relieved by the therapeutical application of manual traction forces. The objective of the present study is to understand the pattern of stresses in the AF and NP due to degenerative AF fibers when the manual traction forces are applied on the degenerated discs.