COMPARISON OF RADIOGRAPHIC CHANGES AFTER ACDF VERSUS BRYAN DISC ARTHROPLASTY IN SINGLE AND BI-LEVEL CASES

Abstract

Background: Cervical myelopathy and radiculopathy has been treated commonly with anterior cervical decompression and fusion with autologous bone graft and anterior cervical plating. Long term results have shown excellent pain relief and 73%–90% fusion rates. However, the development of late adjacent-level disease has been reported following anterior cervical arthrodesis which recently have been correlated to clinical findings. The Bryan disc arthroplasty device was developed to preserve the kinematics of the functional spine unit thus preventing adjacent level disease. There have been few studies comparing the incidence of adjacent level changes in patients undergoing ACDF compared to implantation of a Bryan disc arthroplasty device.

Objectives: The object of this study is to compare the clinical results and radiographic outcomes of anterior cervical decompression and fusion versus cervical disc replacement using the Bryan Cervical Disc Prosthesis (Medtronic Sofamor Danek, Memphis, TN) in terms of overall range of motion (ROM) of the cervical spine; ROM, anterior intervertebral height (AIH), posterior intervertebral height (PIH) and radiographic changes at the implanted and adjacent levels.

Methods: The study consisted of 105 patients with symptomatic single or two-level cervical disc disease. Fifty-one received the Bryan Cervical Artificial Disc Prosthesis (Medtronic Sofamor Danek, Memphis, TN). A total of 63 Bryan disc were placed in these 51 patients. A single-level procedure was performed in 39 patients and a two-level procedure in the other twelve. The patient group who underwent ACDF totaled 54 patients which consisted of 26 single level cases and 28 double level cases. The Bryan group had a mean follow-up 19 months (12–38). The mean follow-up for the ACDF group was 20 months (12–40 months). All patients were evaluated using static and dynamic cervical spine radiographs as well as MR imaging.

All patients underwent anterior cervical discectomy followed by anterior cervical plating or implantation of the Bryan artificial disc prosthesis, done by one surgeon. Clinical evaluation included the visual analogue scale (VAS), and neck disability index (NDI). Radiographic evaluation included static and dynamic flexion-extension radiographs in an upright position using the computer software (Infinitt PiviewSTAR 5051) program. Range of motion/disc space angle and inter vertebral height were measured at the operative site and adjacent levels. Functional spinal unit (FSU) and overall sagittal alignment (C2–C7) were also measured pre-operatively, postoperatively and at final follow-up. ROM was calculated for all 3 areas and data collected were compared from pre operative to last follow-up as well as between the two groups. Radiographic assessment for adjacent level changes was also done. Radiologic change was analyzed using chi square test (95% confidence interval). Other data were analyzed using the mixed model. (SAS enterprise guide 4.1 version)

Results: There was clinical improvement within each group in terms of VAS and NDI scores from pre-op to final follow-up for both single (VAS: p=0.8371, NDI: p=0.2872) and double (VAS: p=0.2938, NDI: p=0.6753) level surgeries but not significantly between the two groups. Overall, ROM and intervertebral height was relatively well maintained during the follow-up in the Bryan group compared to ACDF. Comparing the pattern of ROM measurements from pre-op to final follow-up between the two arms regardless of the number of levels operated on; significant differences were noted for overall ROM of the cervical spine (p< .0001) and all other levels except at the upper level for single level surgeries (p=0.2872). In terms of inter vertebral height measurements from pre-op to final follow-up, statistically significant (p< 0.0001 and p=0.0172) differences in the pattern between the two groups were noted at all levels except for the AIH of single level surgeries at the upper (p=0.1264) and lower (p=0.7598) levels as well as PIH for double level surgeries at the upper (p=0.8363) level. Radiologic change was 3.5 times more observed for the ACDF group compared to the Bryan group.

Conclusion: Clinical status of both groups, regardless of the number of levels, showed improvement. Although clinical outcomes between the two groups were not significantly different at final follow-up, radiographic parameters, namely ROM and intervertebral heights at the operated site, some adjacent levels as well as FSU and overall sagittal alignment of the cervical spine were relatively well maintained in our Bryan group compared to our ACDF group. We surmise that to a certain degree, the maintenance of these parameters could contribute to reduce development of adjacent level change. Noteworthy is that radiographic change was 3.5 times more observed for ACDF surgeries. A longer period of evaluation is needed, to see if all these radiographic changes will translate to symptomatic adjacent level disease.