Anterior cervical discectomy and fusion (ACDF) is a common type of neck surgery that involves the removal of a damaged disc to relieve pressure on the spinal cord or nerve root and thereby relieve pain, numbness, weakness or associated tingling. The damaged disc is removed between two vertebral bones with simultaneous fusion surgery. Fusion involves placing a bone graft or “cage” and/or implants where the disc was originally to stabilize and strengthen the area.
The use of cages for the ACDF is important postoperatively for alignment of the cervical spine and to maintain the height of the intervertebral disc. Few studies, however, have examined the impact of underlying spongy or “spongy” bone contact with regard to handling large loads from the cage. Additionally, it is still unclear whether a cage with or without screws will be the best choice for long-term fusion because micro-movement or sliding distance and sagging or cage penetration still occur at several occasions.
Researchers from Florida Atlantic University’s College of Engineering and Computer Science, in collaboration with Frank Vrionis, MD, lead study author and director of the Marcus Neuroscience Institute, part of Baptist Health; and professor of surgery, Schmidt College of Medicine at FAU, are the first to assess the effect of range of motion, cage migration, and collapse using variable-angle screws. The Marcus Neuroscience Institute has its center on the Boca Raton Regional Hospital campus and satellite locations at Bethesda Hospital in Boynton Beach and Deerfield Beach.
For the study, the researchers developed five finite element models from a cervical spine model. The first model was an intact spine model and the second model was a modified model with cage insertion and a 2-level static plate. The other three models were modified models with the same cage insert and a 2-level dynamic plate. They compared ACDF cages with and without screws on the biomechanical characteristics of the human spine, the implanted cage, and associated hardware by comparing micromotion and sag.
The results of the study, published in The Spine Diary, the newspaper Global Neurosurgery and Asian Spine Journalshowed that the combination cage-screw and anterior plating model has promising potential to reduce the risk of micromovement and collapse of cages implanted in ACDFs at two or more levels. This method may increase construct stiffness and reduce the incidence of clinical and fusion failure after ACDF, which, in turn, may reduce the need for revision surgeries or additional posterior realignment.
“Anterior cervical discectomy and fusion are widely used to treat patients with spinal disorders, where the cage is an essential component in achieving satisfactory fusion results. Risk factors for cage migration are multifactorial and include factors related to the patient, radiological features, surgical techniques and postoperative factors,” Vrionis said. “Our results showed that the plate used in our study provided directional stability and achieved excellent fusion, indicating promising clinical outcomes for patients with degenerative disease of the cervical spine.”
Vrionis further explains that due to the biomechanical stability of the current construct, there was no need for a rigid cervical collar, which is typically used by other surgeons.
“Furthermore, with more than 100 clinical cases, there was no evidence of nonunion or lack of fusion, which is a treated complication of anterior cervical disc surgery,” Vrionis said.
Lower screw rotation angle resulted in higher biomechanical performance and lower incidence of migration and collapse compared to higher rotation angle in multi-level applications, regardless of load. The researchers believe the underlying mechanism may be due to the screw-cage sticking to the bone and the constrained bottom of the C5 vertebra, making it more rigid.
“Our research aims to develop a platform for next-generation patient-specific spine surgery by combining intelligent image processing, AI/machine learning technology, finite element simulation and 3D printing to help surgeons design a surgery plan for each patient,” Chi-Tay Tsai, Ph.D., study co-author and professor in FAU’s Department of Oceanic and Mechanical Engineering, and director of the FAU Spine Biomechanics Laboratory.
The researchers demonstrated that the screw cage was able to prevent sagging under all loading scenarios better than the screwless cage.
“Our clinical and biomechanical data showed that the results with the rigid static plate are very good. The main reason may be due to a larger contact surface between cortical bone and cancellous bone in the cage-screw than in unanchored cage constructions,” Tsai said.
ACDF is one of the most performed spine surgeries in the United States with an average of 137,000 procedures performed each year.
“The new methodology developed by our researchers in collaboration with Drs. Vrionis and O’Connor of the Marcus Neuroscience Institute holds great promise for improving anterior cervical discectomy and fusion and ultimately helping to relieve pain and discomfort. that patients experience from various disorders of the spine and neck,” said Stella Batalama, Ph.D., Dean, FAU College of Engineering and Computer Science.
Other co-authors on the study are Erik Engeberg, Ph.D., professor in the Department of Oceanic and Mechanical Engineering at FAU; Maohua Lin, Ph.D., Research Scientist, Department of Oceanic and Mechanical Engineering, FAU; Stephen Z. Shapiro, MD, neurosurgical resident at Louisiana State University; and James Doulgeris, Ph.D., both in the Department of Neurosurgery, Marcus Neuroscience Institute, Boca Raton Regional Hospital, part of Baptist Health; Rudy Paul, Ph.D., Department of Oceanic and Mechanical Engineering at FAU; and Timothy E. O’Connor, Ph.D., Department of Neurosurgery, Marcus Neuroscience Institute.
The research was funded by the Boca Raton Regional Hospital Foundation attributed to Tsai, principal investigator.