Porous PEEK May Have Better Impact Durability Over Titanium-Coated Device

Peer Reviewed

Simulated cervical impaction testing showed fundamental differences in the response of porous versus titanium-coated polyether-ether-ketone (PEEK) devices, according to a study published online ahead of print in The Spine Journal.

Results of the study revealed that, “The titanium-coated PEEK cages experienced extensive delamination of the titanium coating from the underlying PEEK,” said senior author David L. Safranski, PhD, Director of Basic Research at MedShape, Atlanta, GA. “In contrast, the porous PEEK cages remained intact and experienced minimal deformation of the porous structure.”

“Porous PEEK devices will survive insertion and maintain a high degree of porosity,” Dr. Safranski told SpineUniverse. “Titanium-coated devices may be at risk for delamination, which would produce metallic particulate debris that may induce a negative immune response.”
Healthy bone versus bone with osteoporosisPorous PEEK structure have been linked to improved osseointegration.Why Is Impact Durability a Concern?
While rough plasma-sprayed titanium coating and porous PEEK structure have been linked to improved osseointegration, concerns have been raised over reports of titanium-coating delamination and wear particle generation as well as the lack of impact durability data on porous PEEK structure beyond that obtained for FDA clearance, the study authors explained.

Wearing away of the titanium coating and collapse of a porous surface may lead to a smooth surface similar to that found on conventional devices, which have poor osseointegration, the researchers explained. In addition, particle debris caused by titanium degradation from surface abrasion could lead to inflammation in surrounding tissue, aseptic loosening, bone resorption, and ultimately negative fusion outcome, they noted.

Simulated Cervical Impaction Test
The following cervical interbody fusion devices were evaluated in this study (6 per device): smooth PEEK device with ridges (Spinal Elements, Crystal®, 11×14×12mm, 7°), a plasma-sprayed titanium-coated PEEK device with ridges (X-spine, Calix PC™, 11×14×12mm, 7°), and a porous PEEK device without ridges (NuVasive, Cohere®, 12×14×10mm, 0°). The devices were placed between two polyurethane blocks (vertebral body surrogates) and a 1-lb guided weight was repeatedly dropped onto the anterior face of the device at a maximum speed of 2.6 m/s under a 200-N axial preload until the device was fully impacted between the polyurethane blocks.

“These conditions are meant to replicate a severe case of impaction during surgical delivery of the cervical cage,” Dr. Safranski explained.

Microcomputed tomography was used to measure the porous architecture of the leading edge of porous PEEK devices before and after impaction. Scanning electron microscopy (SEM) was used to image the surfaces of smooth PEEK and titanium-coated devices before and after impaction, and energy-dispersive x-ray spectroscopy was used to confirm SEM titanium-coating coverage. A laser confocal microscope was used to measure surface roughness before and after impaction testing for the smooth PEEK and titanium-coated devices.

Outcomes
The porous PEEK devices maintained a high porosity (>65%) and showed minimal changes to pore size and depth following impaction. The leading edge of porous PEEK devices showed a mean decrease in porosity of 1.0%, a mean decrease in poor depth of 54.3 µm, and a mean decrease in pore size of 12.4 µm (P<.05).

Titanium-coated PEEK devices showed a mean decrease in titanium-coated coverage area of 27.8% following impaction. In contrast, smooth devices showed a lack of damage and minor scratching near the ridges. In addition, the average surface roughness decreased by 1.82±0.19 µm for titanium-coated devices and 0.77±0.06 µm for smooth PEEK devices following the impaction test (P<.05).

The findings “suggest that more functional testing may need to be considered during the design of interbody fusion devices,” the study authors concluded.

Commentary

Khoi D. Than, MD
Assistant Professor, Department of Neurological Surgery
Oregon Health & Science University
Portland, OR

This study has several limitations, as noted by the study authors. First, wear was assessed differently for each of the three cage types evaluated in the study; thus, this is not a scientifically sound comparison. Second, the titanium-coated PEEK device was the biggest device evaluated in this study. A larger device pushed into a tight space would be expected to show more wear than smaller devices. Also, while the researchers noted that the titanium coating showed more wear on the lateral aspect of the device, we would be more concerned with wear on the top and bottom of the device as those are the sides that impact on bone.

A third limitation is that the porous PEEK devices took only one strike to fully impact between the polyurethane blocks, which is not a realistic expectation in clinical practice. It never takes one strike to implant a cage in a patient; if it does, then the cage is too loose and will not be properly implanted.

Finally, the titanium device mass loss was greater than porous or smooth PEEK, which is to be expected given that the titanium implant was likely heavier at baseline. Thus, it might be more helpful to compare the percent mass loss for each device was rather than change in weight.

Disclosures
Dr. Safranski is an employee of and owns stock/stock options in MedShape, Inc. He also owns stock/stock options in Vertera Spine, Inc.

Dr. Than has no relevant disclosures.

Updated on: 06/07/18
Continue Reading
Facilitating Greater Osseointegration Properties with a Deeply Porous Titanium Scaffold on PEEK
Khoi D. Than, MD
Assistant Professor
Department of Neurological Surgery
Oregon Health & Science University
Portland, Oregon
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