InFill Lumbar Fusion Systems Increase Bone Graft Volume Over Standard Prepacked Cages in Lumbar Interbody Fusion

Peer Review by Joshua M. Ammerman, MD

The InFill® Graft Delivery System allows for in situ delivery of bone graft material during lumbar interbody fusion surgery, with an up to 94% increase in bone graft volume compared with use of standard prepacked cages, according to a pilot study using Pinnacle Spine Group’s InFill Lateral system by Burak M. Ozgur, MD and Erin Gleckman PA-C. Pinnacle’s family of InFill lumbar implants, and the InFill Graft Delivery System were designed to overcome the biologic void that exists with traditional fusion systems, which limits bone growth.

“In traditional fusion procedures, the surgeon or the surgeon’s assistant packs bone graft material into the inner cavity of the spinal implant by hand, and then hammers the implant into position within the spine,” explained Zach Sowell, President of Pinnacle Spine Group. During this implantation process, some graft material may fall out and there may be gaps of space between the graft material and the endplate, as was demonstrated using CT-scans in the pilot study.

“Unfortunately, this leaves a biologic void between the implant, its biologics, and a well-prepared endplate,” Mr. Sowell told SpineUniverse. Osteoblasts and osteoclasts are climbers, not jumpers, and need a scaffolding to grow on, he noted.

The InFill Graft Delivery System can be used to “bulk up” a prepacked implant, or for a complete fill of the implant and disc space in-situ to maximize contact with the vertebral endplates, according to Mr. Sowell. The delivery system is used with proprietary interbody fusion devices designed with anterior vents that are angled to direct growth of bone graft material into the anterior space and to optimize endplate surface contact.

Pilot Study Shows 94% Greater Bone Graft Volume With InFill System
In the pilot study, researchers compared the volume of bone graft material in Pinnacle Spine PEEK cage spacers when prepacked and implanted into a cadaver versus when additional bone graft material was injected into prepacked cages following implantation.

All cages were prepacked with calcium phosphate biomaterial mixed with a contrast agent to allow for visualization on CT scan. According to the device manufacturer, the volume within each cage is 3.4 cc, which increases to 3.67 cc when the space in the anterior vent holes is included in the calculation.

The prepacked cages were then implanted at every level between T12-S1, and CT scans were used to measure bone graft volume. Next, the same mixture of calcium phosphate/contrast agent was injected into each cage using InFill Graft Delivery System and CT imaging was repeated.

The increase in volume following injection with the InFill delivery system ranged from 35% to 94%, depending on the level (Table). The Figure shows 3D CT scans taken pre- and post-InFill injection, illustrating the biological void between the biomaterial and endplate before the injection as well as the improved superior and inferior endplate opposition of the graft following injection, according to the study investigators. In addition, the investigators observed that a significant amount of the graft material fell out when a traditionally pre-packed cage was inserted.

graph volume chartThe investigators observed that a significant amount of the graft material fell out when a traditionally pre-packed cage was inserted.“This pilot study demonstrates definitively that this InFill technology can aid in improving graft filling and attaining better space filling with endplate coverage and surface area contact,” Drs. Ozgur and Gleckman concluded. “Additional work may demonstrate that this finding will then yield better fusion results and perhaps more efficiency in interbody space packing and cost effective use of graft materials, bone void fillers, and recombinant DNA technologies.”

3D CT scan image of pre-InFill injection of graft materials. Image Courtesy of Pinnacle Spine Group.3D CT scan image of pre-InFill injection of graft materials. Image Courtesy of Pinnacle Spine Group.

3D CT scan image of post-InFill injection of graft materials. Image Courtesy of Pinnacle Spine Group.3D CT scan image of post-InFill injection of graft materials. Image Courtesy of Pinnacle Spine Group.A large variety of graft materials are compatible with the InFill delivery systems, according to Mr. Sowell. Products that are not compatible include those with larger particulate sizes, such as bone chunk type products and autografts that are not milled down to a fine particulate level.

“The trend in biologics these days is heavily geared toward flowable materials, so more and more biologics are compatible with our systems, including the newest technologies such as stem cell-type products,” Mr. Sowell told SpineUniverse. “There are a large variety of products already on the market that have preclinical results suggesting that they will flow through our delivery system adequately.”

Peer Commentary

Joshua M. Ammerman, MD
Assistant Professor
Department of Neurological Surgery
George Washington University School of Medicine
Washington, DC

Dr. Burak Ozgur et al, has examined the InFill Lateral system from Pinnacle Spine Group as a potential solution to a common and rather frustrating operative challenge—that is, how to keep graft material within the cage during impaction. 

As an experienced interbody surgeon, I have personally experienced the frequent frustration of losing graft material during cage insertion, not only in the lateral space but during TLIF and ALIF procedures.  A number of devices (eg, sleds, cage covers) and techniques (eg, tying sutures around cages) have been described to try to address this issue, but none that I have tried seems as effective as the results reported by Dr. Ozgur on the InFill system, which eliminated this issue by delivering the draft material post-impaction, maximizing bony endplate contact with the graft material.

Clinical studies will be needed to supplement this cadaveric study to determine whether Infill results in improved fusion rates over standard existing techniques; none the less, the concept studied is appealing.

Updated on: 02/08/18
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