Cortical bone facet spacers for cervical spine decompression: effects on intervertebral kinetics and foraminal area

Abstract

<jats:sec> <jats:title>OBJECT</jats:title> <jats:p>Nerve root decompression to relieve pain and radiculopathy remains one of the main goals of fusion-promoting procedures in the subaxial cervical spine. The use of allograft facet spacers has been suggested as a potential alternative for performing foraminotomies to increase the space available for the cervical nerve roots while providing segmental stiffening. Therefore, the goal of this cadaveric biomechanical study was to determine the acute changes in kinetics and foraminal area after the insertion of cortical bone facet spacers into the subaxial cervical spine.</jats:p></jats:sec> <jats:sec> <jats:title>METHODS</jats:title> <jats:p>Allograft spacers (2 mm in height) were placed bilaterally into cadaveric cervical spine specimens (C2-T1, age of donors 57.5 ± 9.5 years, n = 7) at 1 (C4–5) and 3 (C3–6) levels with and without laminectomies and posterior lateral mass screw fixation. Standard stereophotogrammetry under pure moment loading was used to assess spinal kinetics. In addition, the authors performed 3D principal component analysis of CT scans to determine changes in foraminal cross-sectional area (FCSA) available for the spinal nerve roots.</jats:p></jats:sec> <jats:sec> <jats:title>RESULTS</jats:title> <jats:p>Generally, the introduction of 2-mm-height facet spacers to the cervical spine produced mild, statistically insignificant reductions in motion with particular exceptions at the levels of implantation. No significant adjacent-level motion effects in any bending plane were observed. The addition of the posterior instrumentation (PI) to the intact spines resulted in statistically significant reductions in motion at all cervical levels and bending planes. The same kinetic results were obtained when PI was added to spines that also had facet spacers at 3 levels and spines that had been destabilized by en bloc laminectomy. The addition of 2-mm facet spacers at C3–4, C4–5, and C5–6 did produce statistically significant increases in FCSA at those levels.</jats:p></jats:sec> <jats:sec> <jats:title>CONCLUSIONS</jats:title> <jats:p>The addition of allograft cervical facet spacers should be considered a potential option to accomplish indirect foraminal decompression as measured in this cadaveric biomechanical study. However, 2-mm spacers without supplemental instrumentation do not provide significantly increased spinal segmental stability.</jats:p></jats:sec>

Lumbar canal stenosis: analyzing the role of stabilization and the futility of decompression as treatment

“…Other authors have recently presented their results of successful treatment by facet distraction techniques. 16,18,22 Similar forms of treatment by distraction performed using spinous process and laminar distraction devices are currently gaining popularity. 1,2,17,20 As our understanding of spinal degeneration matured further, we realized that it was not neural compression or deformation that was the cause of symptoms in chronic or longstanding and progressive degenerative disease, but subtle instability-related microinjury to the neural structures that was the cause of neurological symptoms and deficits.…”

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

“…Maulucci et al investigated the effect of a 2 mm cortical facet spacer on foraminal area and segmental stability in conjunction with LMS and bilateral rods 7. Bilateral spacers in both single- and three-level constructs increased foraminal height and provided increased segmental stability, although the kinematic results were not statistically significant.…”

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

“…9 Posterior lateral mass fixation is the most commonly utilized technique although other fixation methods such as interfacet screws and interfacet allograft spacers may provide sufficient stability to allow healing of the motion segment. 10,11 The facet joints align the spinal column and aid in control of motions in all axes. The facet orientation changes from coronal in the cervical and thoracic spines to more sagittal in the lumbar spine, which correspondingly changes direction of movements at those levels.…”

“…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. In a cadaveric kinematic study, Tan et al reported the interfacet spacer grafts increased foraminal height by 1.4 mm and cross-sectional area by 18%.…”