Allograft Linked to Higher Fusion Rates Over Intervertebral Cages in ACDF

Peer Reviewed

The rate of nonunion in anterior cervical discectomy and fusion (ACDF) was higher in cases using synthetic intervertebral cages than in cases using structural allograft in a retrospective review of data from more than 6,100 patients. Nonunion rates were relatively low regardless of which surgical option was used, researchers reported in the March 15 issue of Spine.
Lateral post-operative ACDF at C5-C6. Lateral post-operative ACDF at C5-C6. Photo Source:“The results from our study suggests that while ACDF has a high fusion rate whether an intervertebral synthetic cage or structural allograft was used,” said senior author Michael J. Lee MD, Professor of Orthopaedic Spine Surgery and Co-Director of Operative Performance Research Institute at the University of Chicago Medical Center. “However, the fusion rate when using a structural allograft was slightly, but statistically significantly greater, than the fusion rate when a synthetic cage was utilized.”

“This large study confirms findings from our study that was recently published in JNS Spine showing a significantly higher rate of pseudoarthrosis and need for revision surgery with use of PEEK devices in 1-level ACDF compared with use of structural allograft,” commented SpineUniverse Editorial Board Member Khoi D. Than, MD.1 “If one of the goals of ACDF is to have separate spinal levels heal into a solid piece of bone, why would you use anything but bone in the disc space?”

However, both experts acknowledged that there may be select situations in which a cage may be preferable to allograft.

Study Design

Dr. Lee and colleagues analyzed outcomes from 6,130 patients who underwent ACDF with structural allograft (n=4,063) or intervertebral cage (n=2,067) and anterior plating between 2007 and 2016 using data from a single nationwide health insurance company. All patients had at least 1-year follow-up data available after their index ACDF procedure. None of the patients had concurrent or delayed posterior arthrodesis, and the two subgroups did not differ significantly in terms of tobacco use, diabetes, and surgical levels.

Low Nonunion Rate Found in Both Groups

The rate of nonunion was 5.32% in the cage group and 1.97% in the allograft group (P<0.0001). The higher rate of nonunion in the cage group remained statistically significant in 25 of 26 analyses that controlled for potentially confounding factors. A higher rate of nonunion also was linked to diabetes, tobacco use, and multiple surgical levels (P<0.0001).

Five previous studies comparing fusion rates in ACDF using cages versus bone graft did not show a statistically significant difference between the two surgical options.2-6 However, Dr. Lee noted that the differences found in the current study may reflect the large size of the study population versus the low sample size used in previous studies.

“The nonunion rate of ACDF is very low at baseline,” Dr. Lee told SpineUniverse. “To compare fusion rates of slightly different techniques would inherently require a large sample population. Prior studies observing no difference between cages versus structural bone graft may not have been adequately powered to statistically conclude that there was no statistically significant difference.”

Dr. Than’s recent study showed a five-fold increased rate of pseudarthrosis with PEEK implants versus structural allografts for ACDF (52% versus 10%; P<0.001), as well as an increased rate of reoperation (24% vs 14%; P=0.01).1 Dr. Than and colleagues found similar outcomes in a multilevel study that is pending publication.

“Surgeons should look at these studies that show the same finding and choose structural allograft when performing ACDF,” Dr. Than said. One barrier to using allograft is that reimbursement for implantation of PEEK devices is per surgical level, while structural allograft can be charged for only once regardless of the number of levels actually performed, Dr. Than noted.

When to Choose ACDF Cages Over Allograft

“There may be anatomic considerations when a cage may be more ideal than a structural allograft,” Dr. Lee said. “This study did not examine fusion rates in the context of corpectomy, only in discectomy. The results of our study are not necessarily applicable to all anterior cervical arthrodesis. In addition, depending on where the surgery is done, structural allograft may not be as readily available as synthetic cages and bone graft extenders.”

Dr. Than agreed that there are specific clinical scenarios in which a cage may be preferable to allograft for ACDF, including traumatic spine injuries or cases involving marked cervical kyphosis.

“One situation that I recently encountered was in the setting of trauma, where the disc space was splayed open and widened,” Dr. Than explained. “Given that allografts top out at a certain size, in this case, I had to place a small corpectomy cage in the disc space.”

“Additionally, some interbody cages offer a greater degree of lordosis,” Dr. Than continued. “Thus, in the setting of significant cervical kyphosis, lordotic ACDF cages may be more advantageous than structural allograft.”

Avenues for Future Research

“This study compared fusion rates of ACDF with structural allograft against ACDF using cages on a very general level,” Dr. Lee said. “It lacks granularity in cage material (titanium, PEEK), bone graft extender, and cage design (expandable, surface porosity). It also lacks granularity in structural bone graft variation (cortico-cancellous, all cortical). Future studies are needed to determine the influence of these factors.”

Dr. Lee has been a consultant for Stryker Spine, DePuy Synthes, and Globus Medical.

Dr. Than is a consultant for Bioventus.

Updated on: 04/10/19
Continue Reading
Pseudarthrosis Found in Half of Patients With PEEK Implants for Anterior Cervical Discectomy and Fusion
Michael J. Lee, MD
Professor of Orthopaedic Spine Surgery
University of Chicago Medicine
Khoi D. Than, MD
Assistant Professor of Neurological Surgery
Oregon Health & Science University

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