ABSTRACT
Lumbar fusion surgery has grown in popularity as a solution to lower back pain. Surgical site infection (SSI) is a serious complication of spinal surgery, affecting as high as 8.5% of the patient population. If the SSI cannot be eradicated with intravenous antibiotics, the next step is second surgery, which increases the cost imposed on the patient and extends recovery time. An implantable ultrasound-triggered polyether ether ketone device for the dispersal of antibiotics has been developed as a potential solution. In this study, the device was constructed of bioabsorbable medical grade polymer, enabling gradual degradation, and manufactured via fused filament fabrication (FFF). A novel bioabsorbable filament was manufactured and validated with gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The filament was consistent in molecular weight and thermal properties (p = 0.348 and p = 0.487, respectively). The filament was utilized for FFF of the device. Dimensional accuracy of the device was assessed with µCT analysis. Dimensional differences between the printed device and intended design were minimal. Degradation of raw material, filament, and the device was performed in accordance to ASTM F1635-16 for a month to determine how melting the material impacted the degradation properties. The degradation rate was found to be similar among the samples weeks one through three however, the raw material degraded at a slower rate by the final week (p = 0.039). This study demonstrated the feasibility of utilizing medical grade bioabsorbable polymers in FFF.
ABSTRACT
BACKGROUND: In order to improve oxidation resistance, antioxidants such as vitamin-E are added to polyethylene used in the bearing surfaces of orthopedic components. Currently, little is known about the efficacy of this treatment in vivo. This study therefore reports on the reasons for revision, surface damage mechanisms, and oxidation of retrieved vitamin E-stabilized highly crosslinked polyethylene (HXLPE) for total knee arthroplasty. METHODS: We examined 103 retrieved knee inserts fabricated from vitamin E (VE)-stabilized HXLPE and 67 fabricated from remelted HXLPE as a control. The implantation times were 1.2 ± 1.3 and 1.5 ± 1.3 years for the VE and control cohorts, respectively. The inserts were evaluated for 7 surface damage mechanisms using a semiquantitative scoring method and analyzed for oxidation using Fourier-transform infrared spectroscopy. Reasons for revision were also assessed using operative notes created at time of retrieval. RESULTS: Both groups were revised primarily for instability, infection, and loosening. Burnishing, pitting, and scratching were the most common damage mechanisms observed, with the VE cohort demonstrating less surface damage than the control. Measured oxidation for the cohort was low, with a median oxidation index of 0.09 ± .05 for the articulating surface, 0.05 ± 0.06 for the backside, 0.08 ± 0.06 for the anterior/posterior surfaces, and 0.08 ± 0.05 for the stabilizing post. As compared to the control cohort, oxidation tended to be less for the VE group at the articulating (P < .001) and backside (P = .003) surfaces, although the median differences were minimal and may not be clinically significant. CONCLUSION: The results indicate positive fatigue damage resistance and oxidation resistance for the retrieved VE-stabilized total knee arthroplasty inserts.
