Do stand-alone interbody spacers with integrated screws provide adequate segmental stability for multilevel cervical arthrodesis?
BACKGROUND
Some postoperative complications after anterior cervical fusions have been attributed to anterior cervical plate (ACP) profiles and the necessary wide operative exposure for their insertion. Consequently, low-profile stand-alone interbody spacers with integrated screws (SIS) have been developed. Although SIS constructs have demonstrated similar biomechanical stability to the ACP in single-level fusions, their role as a stand-alone device in multilevel reconstructions has not been thoroughly evaluated.


OBJECTIVE
To evaluate the acute segmental stability afforded by an SIS device compared with the traditional ACP in the setting of a multilevel cervical arthrodesis.


METHODS
In vitro human cadaveric biomechanical analysis.


METHODS
Thirteen human cadaveric cervical spines (C2-T1) were nondestructively tested with a custom 6 df spine simulator under axial rotation, flexion-extension, and lateral bending loading. After intact analysis, eight single-levels (C4-C5/C6-C7) from four specimens were instrumented and tested with ACP and SIS. Nine specimens were tested with C5-C7 SIS, C5-C7 ACP, C4-C7 ACP, C4-C7 ACP+posterior fixation, C4-C7 SIS, and C4-C7 SIS+posterior fixation. Testing order was randomized with each additional level instrumented. Full range of motion (ROM) data were obtained and analyzed by each loading modality, using mean comparisons with repeated measures analysis of variance. Paired t tests were used for post hoc analysis with Sidak correction for multiple comparisons.


RESULTS
No significant difference in ROM was noted between the ACP and SIS for single-level fixation (p>.05). For multisegment reconstructions (two and three levels), the ACP proved superior to SIS and intact condition, with significantly lower ROM in all planes (p<.05). When either the three-level SIS or ACP constructs were supplemented with posterior lateral mass fixation, there was a greater than 80% reduction in ROM under all testing modalities (p<.05), with no significant difference between the ACP and SIS constructs (p>.05).


CONCLUSIONS
The SIS device may be a reasonable option as a stand-alone device for single-level fixation. However, SIS devices should be used with careful consideration in the setting of multilevel cervical fusion. However, when supplemented with posterior fixation, SIS devices are a sound biomechanical alternative to ACP for multilevel fusion constructs.
Department of Orthopaedic Surgery, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bethesda, MD 20889, USA.
Haines
H
Paik
Department of Orthopaedic Surgery, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bethesda, MD 20889, USA.
Daniel G
DG
Kang
Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO 63110, USA. Electronic address: armyspine@yahoo.com.
Ronald A
RA
Lehman
Division of Orthopaedics, Department of Surgery, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.
Mario J
MJ
Cardoso
Department of Orthopaedic Surgery, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bethesda, MD 20889, USA.
Rachel E
RE
Gaume
Department of Orthopaedic Surgery, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bethesda, MD 20889, USA.
Divya V
DV
Ambati
Department of Orthopaedic Surgery, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bethesda, MD 20889, USA; Department of Neurosurgery, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bethesda, MD 20889, USA.
Anton E
AE
Dmitriev
D001696:Biomechanical Phenomena / Q000502:physiology; D001860:Bone Plates; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000601:surgery*; D006801:Humans; D016059:Range of Motion, Articular / Q000502:physiology; D019651:Plastic Surgery Procedures / Q000295:instrumentation*; D012399:Rotation; D013123:Spinal Fusion / Q000295:instrumentation*
Anchored interbody spacer; Biomechanical stability; Cervical; Integrated screws; Multilevel cervical arthrodesis; Stand-alone cervical interbody spacer