Kinetic analysis of anterior cervical discectomy and fusion supplemented with transarticular facet screws

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>The clinical success rates of anterior cervical discectomy and fusion (ACDF) procedures are substantially reduced as more cervical levels are included in the fusion procedure. One method that has been proposed as an adjunctive technique for multilevel ACDF is the placement of screws across the facet joints (“transfacet screws”). However, the biomechanical stability imparted by transfacet screw placement (either unilaterally or bilaterally) has not been reported. Therefore, the purpose of this study was to determine the acute stability conferred by implementation of unilateral and bilateral transfacet screws to an ACDF construct.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Eight C2–T1 fresh-frozen human cadaveric spines (3 female and 5 male; mean age 50 years) were tested. Three different instrumentation variants were performed on cadaveric cervical spines across C4–7: 1) ACDF with an intervertebral spacer and standard plate/screw instrumentation; 2) ACDF with an intervertebral spacer and standard plate/screw instrumentation with unilateral facet screw placement; and 3) ACDF with an intervertebral spacer and standard plate/screw instrumentation with bilateral facet screw placement. Kinetic ranges of motion in flexion-extension, lateral bending, and axial rotation at 1.5 Nm were captured after each of these procedures and were statistically analyzed for significance.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>All 3 fixation scenarios produced statistically significant reductions (p &lt; 0.05) in all 3 bending planes compared with the intact condition. The addition of a unilateral facet screw to the ACDF construct produced significant reductions at the C4–5 and C6–7 levels in lateral bending and axial rotation but not in flexion-extension motion. Bilateral facet screw fixation did not produce any statistically significant decreases in flexion-extension motion compared with unilateral facet screw fixation. However, in lateral bending, significant reductions at the C4–5 and C5–6 levels were observed with the addition of a second facet screw. The untreated, adjacent levels (C2–3, C3–4, and C7–1) did not demonstrate significant differences in range of motion.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>The data demonstrated that adjunctive unilateral facet screw fixation to an ACDF construct provides significant gains in stability and should be considered a potential option for increasing the likelihood for obtaining a successful arthrodesis for multilevel ACDF procedures.</jats:p></jats:sec>

Biomechanical evaluation of DTRAX^&reg; posterior cervical cage stabilization with and without lateral mass fixation

“…Previous studies report favorable clinical and radiographic outcomes in patients with single-level cervical radiculopathy secondary to spondylosis treated with posterior cervical spacers or cages placed between the facet joints 5,11. The current study demonstrated that both lateral mass constructs and bilateral posterior cervical cages offer comparable postoperative segmental stability; both techniques significantly decreased cervical ROM in FE, LB, and AR.…”

Biomechanical Analysis of an Anterior Cervical Discectomy and Fusion Pseudarthrosis Model Revised With Machined Interfacet Allograft Spacers

“…30,31 The placement of facet screws have shown biomechanical and clinical promise, but placement above C5 may be limited due to occipital prominence. 10 Corollary issues may arise with placement of interfacet spacers at the lower cervical segments due to inadequate imaging and prominence of the shoulders. Further investigation is needed to determine the feasibility of minimal access placement at all cervical levels.…”

“…Controlling segmental motion of the facet joints by blocking with bone graft or interfacet allograft spacers may stabilize the spine and result in spine fusion and indirect foraminal decompression. 10,[12][13][14][15][16][17] Machined interfacet allograft spacers are placed directly into the facet joint and they have a relatively large surface area that stiffens the spinal segment, and potentially increases foraminal height and area to indirectly decompress the neuroforamina. 11,17,18 Interfacet allograft spacers are machined cortical allografts sized 2 to 4 mm in height and contain ridges that provide stability to resist retropulsion.…”

Comparison of Intervertebral ROM in Multi-Level Cadaveric Lumbar Spines Using Distinct Pure Moment Loading Approaches

“…4,[10][11][12][13][14][15] Mechanistically, the pure moment is applied to the end vertebrae ensuring equal loading to all segments of the spinal column, 1 even as the spine deforms during testing. This has been accomplished in multiple forms with varying complexity and ease of use, including cable and pulley systems, 2,11,13 in which load application is assisted with static weights or load frame actuation, motor-actuated robotic arms, [15][16][17] and hydraulicallyor pneumatically-actuated gimbal systems 10,12,18 that can be configured to apply pure moments at one or both ends of the spinal segment. Stepwise moment application using cable and pulley systems has been the predominant method of flexibility testing 19,20 and is still prevalent in the current literature.…”

“…Stepwise moment application using cable and pulley systems has been the predominant method of flexibility testing 19,20 and is still prevalent in the current literature. 14,[21][22][23] More recently, continuous loading of cadaveric spine specimens has been introduced, 10,12,15,18 representing a more physiologic laboratory technique with which to evaluate spine flexibility, with the major advantage that it permits the analysis of the spine's behavior in the neutral zone. 24 Despite the perceived notion that the kinematic response of the test constructs under pure moments applied with the varying approaches are similar, few studies have quantified the differences, if they exist, in intervertebral range of motion (ROM) resulting from laboratory-specific loading apparatuses.…”