The Effect Of Disc Space Distraction On Adjacent Segment Degeneration After Anterior Cervical Discectomy And Fusion

Part 1 Biomechanical analysis of adjacent level intradiscal pressure bydisc space distraction in an anterior cervical discectomy modelObjective: The incidence of adjacent level intervertebral disc pathology secondary to cervical arthrodesis procedures has been well documented in clinical and laboratory settings. Previousin vitro investigations have reported increases in adjacent level intradiscal pressures(IDPs), intersegmental motion and facet joint stresses following interbody reconstructions. Abnormally elevated intradiscal pressure has been speculated to play a key role in the development of degenerative disc disease. Vertebral distraction is routinely performed during anterior cervical discectomy and fusion(ACDF). The current study was undertaken to compare adjacent level IDPs following an arthrodesis procedure with different vertebral distraction.Methods: A total of 6 male goats C3-7 cervical specimens were used in this investigation. Following intact analysis, all specimens were sequentially four different vertebral distraction models. Testing was performed in displacement control under axial rotation, flexion and extension loading modes. IDPs were recorded at C4-5 and C6-7.Results: With different vertebral distraction, The C4-5 IDPs at both adjacent levels were significantly higher than intact condition(P<0.05). Similar intergroup differences were observed at the C6-7 level(P<0.05). Similar IDPs were recorded between the two and four dentate vertebral distraction by Caspar retractor at both adjacent levels under all loading modes(P>0.05).Conclusion: With the increased vertebral distraction adjacent level IDPs were significantly higher than intact condition under axial rotation, flexion and extension loading modes. No statistical significance on IDPs was found between the two and four dentate vertebral distraction by Caspar retractor at both adjacent levels under all loading modes. Part 2 Adjacent segment degeneration after single-level anterior cervicaldiscectomy and fusion: Disc space distraction and its impact onclinical outcomesObjective: Several risk factors for the development of adjacent segment degeneration(ASD) have been proposed. In addition to these risk factors, we propose that excessive distraction of disc space by cage insertion can be a critical risk factor for ASD after anterior cervical discectomy and fusion(ACDF).The purpose of this study was to find whether the excessive distraction of the disc space by cage insertion was a risk factor would aggravate ASD after ACDF.Methods: One hundred and sixteen consecutive patients who underwent ACDF for single-level cervical disc herniation between June 2006 and November 2008 were retrospectively reviewed Preoperative, postoperative and the final follow-up disc height(DH), sagittal segmental alignment(SSA), and sagittal alignment of the cervical spine(SACS) were measured and compared in adjacent segmental degeneration(ASD) group and non-ASD groupResults: In 116 patients, the radiographic ASD was proven in 29 patients. The clinical outcomes have been significant improved compared to the preoperative scores in both groups. However, the postoperative and final follow-up DH of ASD group were significantly higher than of the Non-ASD group(P<0.05). Multivariate analysis showed that postoperative DH was the most significant risk factor(OR=0.253,95%CI=0.144-0.445).Conclusion: The clinical outcomes of the ACDF for one level degenerative cervical disc disease was satisfactory. Postoperative DH(the distracted distance) had the most impact on the incidence of ASD. Excessive disc space distraction is a considerable risk factor for the development of the radiographic ASD. Part 3 A retrospective study on the clinical outcomes of patients withrevision surgery after 10-year’s anterior cervical discectomy andfusionObjective: The objective of this study was to investigate the clinical outcomes of anterior cervical discectomy and fusion as a revision surgery for adjacent segment disease after primary surgery.Methods: A consecutive case series of 1132 patients underwent anterior cervical discectomy and fusion(ACDF) for cervical spondylotic myelopathy(CSM) from January 1995 to December 2007 in authors’ hospital. A total of 19 patients who underwent one level ACDF for symptomatic recurrent radicular or myelopathic symptoms from adjacent segment disease were included in the study. Patients were evaluated using the Japanese Orthopaedic Association(JOA) Neck Disability Index(NDI) and visual analog scale(VAS) score pre- and postoperatively.Results: In this study, a total of 19 patients with a minimum of 2 years of follow-up data were available for analysis. This series included 10 men and 9 women with a mean age of 61.34±3.87 years. There was significant improvements in JOA, NDI and VAS on neck pain compared to the preoperative means(P<0.05). The postoperative JOA score, RR, and surgical outcome at final followup were comparable between primary and revision surgery(P>0.05). Mean VAS score after revision surgery was significantly lower than that after primary surgery(P<0.05).Conclusion: ASD occurrence rate is high after ACDF. According to our study, the most affected position of CSM requiring revision surgery is C5-6 spinal level, followed by C6-7 level. The patients were more likely to influence superior adjacent levels compared to inferior adjacent level of fusion. The last follow-up results demonstrated that revision fusion surgery on the both superior and inferior adjacent level groups maintains favorable clinical results on patients who underwent one level ACDF for symptomatic new radicular or myelopathic.