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

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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° (kyphosis) to postoperative 14.5°. 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° at upper and 10.2° 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.

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The Authors have no financial interest in the instrumentation and methodology advanced in this manuscript. The paper complies with the current laws of our country, with a consent was taken from all the patients underwent the study.

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Correspondence to Ahmed Elsawaf.

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Hiroshi Nakagawa, Nagoya, Japan

This is an excellent paper on effect of cervical dynamics on ASD following anterior cervical cage fusion.

The authors proved that the compensatory increase in the ROM of the adjacent segments had a direct impact on the pathogenesis of ASD, especially at the levels with preexisting asymptomatic degenerative disease.

We have had an experience of more than 400 cases with cervical discogenic disease and OPLL which were treated by anterior microsurgical decompression and fixation with cylindrical titanium cages with similar results. As pointed out by the authors, the natural history of cervical spondylosis seems to have an important factor for development of ASD which is most likely accelerated by anterior cervical fixation especially at the lower cervical levels.

The surgical intervention to the asymptomatic adjacent levels remains controversial as well as surgical indication of an artificial disc in relatively aged patients with cervical spondylosis.

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Elsawaf, A., Mastronardi, L., Roperto, R. et al. Effect of cervical dynamics on adjacent segment degeneration after anterior cervical fusion with cages. Neurosurg Rev 32, 215–224 (2009).

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