Three-dimensional motion analysis of the cervical spine for comparison of anterior cervical decompression and fusion versus artificial disc replacement in 17 patients

Abstract

Object Cervical arthroplasty with an artificial disc (AD) has emerged as an alternative to anterior cervical discectomy and fusion (ACDF) for the management of cervical spondylosis. This study aims to provide 3D motion analysis data comparing patients after ACDF and AD replacement. Methods Ten patients who underwent C5–6 ACDF and 7 who underwent C5–6 AD replacement were enrolled. Using biplanar fluoroscopy and a model-based track technique (accurate up to 0.6 mm and 0.6°), motion analysis of axial rotation and flexion-extension of the neck was performed. Three nonoperative segments (C3–4, C4–5, and C6–7) were assessed for both intervertebral rotation (coronal, sagittal, and axial planes) and facet shear (anteroposterior and mediolateral). Results There was no difference in total neck motion comparing ACDF and AD replacement for neck extension (43.3° ± 10.2° vs 44.3° ± 12.6°, p = 0.866) and rotation (36.0° ± 6.5° vs 38.2° ± 9.3°, p = 0.576). For extension, when measured as a percentage of total neck motion, there was a greater amount of rotation at the nonoperated segments in the ACDF group than in the AD group (p = 0.003). When comparing specific motion segments, greater normalized rotation was seen in the ACDF group at C3–4 (33.2% ± 4.9% vs 26.8% ± 6.6%, p = 0.036) and C6–7 (28.5% ± 6.7% vs 20.5% ± 5.5%, p = 0.009) but not at C4–5 (33.5% ± 6.4% vs 31.8% ± 4.0%, p = 0.562). For neck rotation, greater rotation was observed at the nonoperative segments in the ACDF group than in the AD group (p = 0.024), but the differences between individual segments did not reach significance (p ≥ 0.146). Increased mediolateral facet shear was seen on neck extension with ACDF versus AD replacement (p = 0.008). Comparing each segment, C3–4 (0.9 ± 0.5 mm vs 0.4 ± 0.1 mm, p = 0.039) and C4–5 (1.0 ± 0.4 mm vs 0.5 ± 0.2 mm, p = 0.022) showed increased shear while C6–7 (1.0 ± 0.4 mm vs 1.0 ± 0.5 mm, p = 0.767) did not. Conclusions This study illustrates increased motion at nonoperative segments in patients who have undergone ACDF compared with those who have undergone AD replacement. Further studies will be required to examine whether these changes contribute to adjacent-segment disease.

Narrative review of the in vivo mechanics of the cervical spine after anterior arthrodesis as revealed by dynamic biplane radiography

“…In agreement with ROM and ICR results, it does not appear that single‐level cervical arthrodesis affects the pattern of cervical motion segment contributions to flexion/extension . Studies that report that adjacent segment contributions are increased after arthrodesis in comparison to after arthroplasty must be interpreted carefully . Due to the arthrodesis, motion will be lost at the operated motion segment, reducing the total cervical spine ROM.…”

“…These limitations were initially addressed individually, by using MRI images to track three‐dimensional spine kinematics in static supine positions, and by using single‐plane fluoroscopic imaging in combination with computer software to automatically track two‐dimensional dynamic vertebral body movement . More recently, imaging systems have been developed to collect synchronized biplane radiographs during functional three‐dimensional movements . Several groups have demonstrated that vertebral motion can be tracked with an accuracy of better than 1 mm and one degree during dynamic multi‐planar movements using this technology .…”

“…). This novel imaging and tracking technology has recently been combined with custom computational algorithms to characterize cervical spine mechanics in young healthy adults, in middle‐aged asymptomatic adults and arthrodesis patients, and in arthrodesis and arthroplasty patients …”

Postoperative segmental hypermobility after cervical arthroplasty: A possible pathomechanism for outcome failure

“…McDonald et al reported that there may be some degree of hypermobility at non-operative segments subsequent to an ACDF procedure, which has been suggested to result in increased compressive axial stress between the articulating surfaces, thereby facilitating cartilage degeneration [15]. According to Kim et al the postoperative ROM might even be underestimated because it might temporarily decrease due to persisting axial neck pain during the early postoperative period [16].…”

In Cervical Arthroplasty Only Prostheses With Flexible Biomechanical Properties Should Be Used for Achieving a Near-physiological Motion Pattern

“…A great variety of biomechanical studies have been published about cervical arthroplasty. Most studies focus on the ROM or on changes in disc height and facet translation compared with normal individuals and with patients after ACDF, or on clinical results [9][10][11][12][13][14][15][16][17][18][19][20][21]. Several studies also investigate qualitative motion of disc prostheses [1][2][3][4][5][6][7][8]22], but we did not nd studies investigating how the COR after insertion of a prosthesis compares with healthy individuals, which is important because our data shows that the COR in patients with disc herniations is not at a physiological position anymore and therefore the prae-op COR cannot be used as reference:…”