Effect of cervical dynamics on adjacent segment degeneration after anterior cervical fusion with cages

Abstract

The objective of this study is to evaluate the effect of anterior cervical discectomy and fusion (ACDF) on the motion of the cervical spine and dynamic stress (tendency to kyphosis) on adjacent segments and on the overall spinal alignment which may predispose to symptomatic disc diseases at other levels. Twenty consecutive patients underwent ACDF with a mean follow-up of 28 months (range 13-38). Preoperative and postoperative clinical assessments were done by using the neck disability index (NDI) and the Japanese Orthopedic Association (JOA) score. In all cases, at the last follow-up control, a neuro-radiographic assessment [cervical spine static and dynamic X-ray and magnetic resonance imaging (MRI)] was done. The angle of the operated disc space, the disc space angle of contiguous segments, and their range of motion (ROM) and the kyphotic Cobb angle (C2-7) were measured by computer software. The study was done at Sant'Andrea Hospital, Rome, Italy in the period from November 2003 to November 2005. We observed that: the mean Cobb angle improved significantly (p < 0.001) from 3.4 degrees (kyphosis) to postoperative 14.5 degrees. This normalization of angle showed a direct effect on improvement of myelopathic patients, but it had a statistically nonsignificant effect on adjacent segments degeneration (ASD). The mean segmental ROM of adjacent segments did not show significant instability. The mean was 11.1 degrees at upper and 10.2 degrees at lower levels (close to normal). In six cases, the ROM was higher than normal: five of these patients demonstrated symptomatic adjacent segment pathology. Postoperative improvement of mean JOA and NDI scores was statistically significant (p < 0.001). Anyway, symptomatic ASD was observed in five patients (20%): in four of them, the higher disc spaces and in one, the lower disc spaces were involved. In four cases, the preoperative MRI showed slight and asymptomatic disc degeneration at the same levels involved subsequently. This ASD was significantly related to the increased ROM at the segments involved. Follow-up X-rays showed solid fusion with absence of movement in all but one case (at 13-month follow-up), who showed slight movement in the operated level in spite of clinical improvement. The follow-up MRI showed, in all cases, good decompression in the treated levels. Compensatory increase in ROM of the contiguous motion segments in patients subjected to ACDF may lead to ASD especially in those cases with asymptomatic adjacent subclinical degenerative disease. If these preliminary results will be confirmed by larger series, it could be reasonable in young selected patients with soft disc herniation to adopt total disc arthroplasty instead of fusion after cervical micro-discectomy.

The effect of multilevel anterior cervical fusion on neck motion

“…This may play a major role in cervical ROM following multilevel anterior cervical fusion. Although compensatory motion always developed at the adjacent level [8,[18][19][20], the compensation may not be enough for the loss of motion of 3 or 4 segments.…”

Long-term Evaluation of Cervical Disc Arthroplasty with the Mobi-C© Cervical Disc: A Randomized, Prospective, Multicenter Clinical Trial with Seven-Year Follow-up

“…As motion in treated segments is eliminated through fusion, adjacent segments become hypermobile and adjacent discs experience increased loads and stresses. [4][5][6][7] In turn, these kinematic changes have the potential to initiate or accelerate pathologies in intact segments. Unfortunately, the immobility of treated segments is the very nature of the fusion procedure, required for stabilization after discectomy.…”

Subsequent surgery rates after cervical total disc replacement using a Mobi-C Cervical Disc Prosthesis versus anterior cervical discectomy and fusion: a prospective randomized clinical trial with 5-year follow-up

“…26 However, investigators have also reported an increase in motion, shear strain, and intradiscal pressure in adjacent vertebrae after treatment. 10,21 The displacement of motion and mechanical stress to adjacent segments is a major concern because force and motion translocation are believed to lead to increased rates of adjacent-segment degeneration in patients treated with ACDF. 6,10,16,17,21 It is also hypothesized that adjacent-segment degeneration is further heightened in multilevel ACDF treatment.…”