Comparative Description of In Vitro and In Vivo MRSA Biofilms on Titanium Surfaces: Why Animal Models Still Matter

NASS 32nd Annual Meeting Proceedings / The Spine Journal 17 (2017) S111–S165 196. The Influence of Single-Level vs Multilevel Decompression on the Outcome in Multisegmental Lumbar Spinal Stenosis: Analysis of the Lumbar Spinal Outcome Study (LSOS) Data — A Swiss Prospective Multicenter Cohort Study Nils H. Ulrich, MD1, Jakob M. Burgstaller, MD, DDS, PhD2, Ulrike Held, PhD, MSc2, Sebastian Winklhofer, MD3, Mazda Farshad, MD, MPH4, Giuseppe Pichierri, PhD5, Johann Steurer, MD6, Francois Porchet, MD, PhD1; 1Schulthess Clinic Zürich, Zurich, ZH, Switzerland; 2Zurich University, Horten Centre for Patient Oriented Research and Knowledge Transfer, Zurich, Zurich, Switzerland; 3University Hospital Zurich, Zurich, Switzerland; 4Balgrist University Hospital, Zürich, Switzerland; 5Horten Centre, Zurich, Switzerland; 6Horten Centre for Patient Oriented Research and Knowledge Transfer, University of Zurich, Zurich, Switzerland BACKGROUND CONTEXT: In multisegmental lumbar spinal stenotic cases, the decision as to how many levels of stenosis need to be operated to achieve the best possible clinical outcome is still unknown and remains a controversy between spine surgeons. PURPOSE: To assess whether patients with confirmed multisegmental lumbar spinal stenosis (LSS) benefit more from a single- or a multilevel decompression. STUDY DESIGN/SETTING: Prospective multicenter cohort study. PATIENT SAMPLE: Patients of the Swiss Lumbar Stenosis Outcome Study (LSOS) with confirmed multi-segmental LSS undergoing first-time decompression without fusion were enrolled in this study. OUTCOME MEASURES: The main outcomes of this study were Spinal Stenosis Measure (SSM) symptoms and function over time, measured at baseline, 6, 12, and 24 months follow-up. Further outcomes of interest were changes in SSM, Numeric Rating Scale (NRS), Feeling Thermometer (FT), the EQ-5D-EL, and the Roland and Morris Disability Questionnaire (RMDQ) from baseline to 6, 12, and 24 months. METHODS: In order to quantify the effect of number of decompressed levels, we used mixed effects models and accounted for the repeated observations in main outcomes (SSM symptoms and SSM function) over time. RESULTS: After 12 months, a total of 141 patients met the inclusion criteria; of these, 33 (23%) underwent a single-level and 108 (77%) a multilevel decompression. Multilevel decompression was associated with a significantly less favorable SSM symptoms and function score, respectively, as compared to single-level decompression. In all further outcomes of interest, single-level as well as multilevel patients improved over time. CONCLUSIONS: Our study showed that in multisegmental stenotic cases, a single-level decompression was associated with a significantly more favorable SSM symptoms and function score, respectively, as compared to multilevel decompression. This study provides evidence that in multisegmental stenotic cases, a single-level decompression might be sufficient to improve patient’s symptoms and function. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. https://doi.org/10.1016/j.spinee.2017.07.244

197. Decompression Surgery Alone vs Decompression Plus Fusion in Symptomatic Lumbar Spinal Stenosis: A Swiss Prospective Multicenter Cohort Study with Three Years of Follow-Up Nils H. Ulrich, MD1, Jakob M. Burgstaller, MD, DDS, PhD2, Giuseppe Pichierri, PhD3, Maria Wertli, MD, PhD2,4, Mazda Farshad, MD, MPH5, Johann Steurer, MD6, Ulrike Held, PhD, MSc2, Francois Porchet, MD, PhD1; 1Schulthess Clinic Zürich, Zurich, ZH, Switzerland; 2Zurich University, Horten Centre for Patient Oriented Research and Knowledge Transfer, Zurich, Zurich, Switzerland; 3Horten Centre, Zurich, Switzerland; 4Department of General Internal Medicine, Bern University Hospital, University of Bern, Bern, Switzerland; 5Balgrist University Hospital, Zürich, Switzerland; 6 Horten Centre for Patient Oriented Research and Knowledge Transfer, University of Zurich, Zurich, Switzerland

S139

BACKGROUND CONTEXT: To estimate the added effect of surgical fusion as compared to decompression surgery alone in symptomatic lumbar spinal stenosis patients with spondylolisthesis. PURPOSE: The optimal surgical management of lumbar spinal stenosis patients with spondylolisthesis remains controversial. STUDY DESIGN/SETTING: Retrospective analysis of a prospective, multicenter cohort study. PATIENT SAMPLE: Patients of the Swiss Lumbar Stenosis Outcome Study (LSOS) with confirmed DLSS and spondylolisthesis were enrolled in this study. OUTCOME MEASURES: Patients of the LSOS with confirmed DLSS and spondylolisthesis were enrolled in this study. The outcomes of this study were Spinal Stenosis Measure (SSM) symptoms (score range 1–5, bestworst) and function (1–4) over time, measured at baseline, 6, 12, 24 and 36 months of follow-up. METHODS: To quantify the effect of fusion surgery as compared to decompression alone and number of decompressed levels, we used mixed effects models and accounted for the repeated observations in main outcomes (SSM symptoms and SSM function) over time. In addition to individual patients’ random effects, we also fitted random slopes for follow-up time points and compared these two approaches with Akaike’s Information Criterion (AIC) and the chi-squared test. Confounders were adjusted with fixed effects for age, gender, BMI, diabetes, CIRS musculoskeletal disorders and duration of symptoms. RESULTS: One hundred and thirty-one patients undergoing decompression surgery alone (n=85) or decompression plus fusion surgery (n=46) were included in this study. In the multiple mixed effects model, the adjusted effect of fusion vs decompression alone surgery on SSM symptoms was 0.06 (95% confidence interval, CI: −0.16 to 0.27) and −0.07 (95% CI: −0.25 to 0.10) on SSM function, respectively. CONCLUSIONS: Among the patients with degenerative lumbar spinal stenosis and spondylolisthesis, our study confirms that in the two groups, decompression alone and decompression plus fusion, patients distinctively benefited from surgical treatment. When adjusted for confounders, fusion surgery was not associated with a more favorable outcome in both SSM scores as compared to decompression alone surgery. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. https://doi.org/10.1016/j.spinee.2017.07.245

Friday, October 27, 2017 1:15 PM–2:45 PM Infection 198. Comparative Description of In Vitro and In Vivo MRSA Biofilms on Titanium Surfaces: Why Animal Models Still Matter Houssam Bouloussa, MD, MSc1, Vincent Humblot, PhD2, Charles Court, MD, PhD2; 1Hôpital Armand Trousseau, Paris, France; 2 France BACKGROUND CONTEXT: In vitro biofilm studies on controlled surfaces demonstrate the advantages of facilitating imaging studies and allowing extensive bacteriological studies while being easily accessible and cheap. However, the in vivo role of the environment is completely occulted. An in vitro and in vivo (rabbit prosthetic joint infection [PJI] model) assessment of a quaternary ammonium polymer (QAP) antibacterial coating was performed on titanium against methicillin-resistant Staphylococcus aureus (MRSA). In addition, in vitro and in vivo characteristics of biofilm growth patterns and organization were described. PURPOSE: To evaluate the antibacterial and anti-biofilm activity of a new antibacterial polymer as a coating on titanium and compare the outcomes in vitro and in vivo. STUDY DESIGN/SETTING: In vitro and in vivo bacteriologic studies.

S140

NASS 32nd Annual Meeting Proceedings / The Spine Journal 17 (2017) S111–S165

PATIENT SAMPLE: Animal study: 42 rabbits. OUTCOME MEASURES: Bacterial counting on surfaces, including bone bacterial density. Scanning-electron microscopy qualitative biofilm assessment. METHODS: In vitro antibacterial activity: a MRSA strain isolated from a patient with a PJI was cultured in Brain Heart Infusion (BHI) at 37°C overnight. A 107 CFU/mL 20 µL bacterial suspension in BHI was simultaneously applied on 1 cm2 titanium plates (control vs coated with a QAP) at 37°C. Cultures were sequentially stopped after 1 hour and 24 hours, diluted in 0.9% saline and vortexed for detachment of live bacteria and bacterial counting. In vivo: forty-two New-Zealand White female rabbits (2.8 kg) underwent a unipolar knee joint replacement (TiAl6V4 tibial implant, 24 controls vs 18 grafted). A 7×106 inoculum was injected following wound closure. Implants were removed at day 14, rinsed with PBS, vortexed for adherent bacterial count. Proximal-third tibias were resected, crushed and cultured. Implants for 6 rabbits (3 controls, 3 treated) were fixed at day 3, 7, and 14 (SEM-FEG). Biofilm morphological comparison in vitro vs in vivo: a 106 CFU/mL bacterial suspension in 500 µL BHI was simultaneously deposited on 10 plates (control vs coated). Cultures at 37°C were sequentially stopped after 6 h, 12 h, 24 h, 72 h, and 7 days (medium was replaced every 24 h). Plates were rinsed with PBS 5% and fixed in PBS/ 2.5% glutaraldehyde. In vivo control implants were removed, fixed and compared with in vitro control plates. SEM-FEG (Scanning ElectronMicroscopy with Field Emission Gun) biofilm images were obtained in all controls. RESULTS: A 1.6 log10 reduction of bacteria occurred on coated surfaces vs control in 1 hour, respectively 6.96 log10 UFC/mL vs 8.56 log10 UFC/mL, and 1.1 log10 in 24 hours, respectively 9.20 log10 UFC/mL vs 10.17 log10 UFC/mL, p<.0001. In vitro anti-biofilm activity against controls was significant up to 7 days. In vivo, bone bacterial density did not differ between treated and control rabbits (4.5±1.5log10 vs 5.2±1.4 log10, p=.07); neither did bacterial adherence (respectively 3.6±1.9 log10 vs 3.8±1.8 log10, p=.36). While in vitro MRSA on controls showed a high bacterial proliferation with a rare biofilm matrix, in vivo MRSA on controls produced profuse polysaccharide complex filaments faster with rare bacteria. CONCLUSIONS: In vitro anti-biofilm activity of QAP-coated surfaces did not predict in vivo outcome. Animal models are crucial as biofilm morphology and growth considerably differed from in vitro. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. https://doi.org/10.1016/j.spinee.2017.07.247

199. “Smart” Polymer Coating Prevents Spinal Implant Infection in a Mouse Model of Spine Surgery Howard Y. Park, MD1, Weixian Xi, PhD2, Suwei Zhu, PhD3, Vishal Hegde, MD4, Stephen Zoller, MD1, Tatiana Segura, PhD2, Nicholas Bernthal, MD5; 1Department of Orthopaedic Surgery, UCLA Medical Center, Los Angeles, CA, USA; 2University of California Los Angeles, Los Angeles, CA, USA; 3Pabst Patent Group, Atlanta, GA, USA; 4 Department of Orthopaedic Surgery, UCLA, Los Angeles, CA, USA; 5 UCLA, Santa Monica, CA, USA BACKGROUND CONTEXT: Spine implant infections are devastating conditions that occur at a rate of 2%–8% of all elective spine surgeries which necessitate extended antibiotic treatment. Definitive explantation of the implants is often a last resort as it can destabilize the spine, especially in cases prior to fusion. In an attempt to reduce infection, antibiotic eluting implant coatings may reduce infection rates, and in turn, improve resistance to biofilm formation. PURPOSE: This study aims to elucidate the role of a novel poly (ethylene glycol)-propylene sulfide (PEG-PPS) polymer coating loaded with antibiotics in the treatment of spinal implant biofilm infections. STUDY DESIGN/SETTING: Randomized controlled experiment utilizing a mouse model of spine implant infection to test a novel coating technology loaded with varying antibiotics. PATIENT SAMPLE: N/A.

OUTCOME MEASURES: Bioluminescence representative of bacterial burden. METHODS: A novel, biodegradable coating using branched poly(ethylene glycol)-propylene sulfide (PEG-PPS) polymer was designed to deliver antibiotics both passively and actively. The in vivo efficacy of PEG-PPS coating delivering vancomycin and tigecycline was tested using a well-established mouse model of spinal implant infection in which biolumenscent Xen 36 (PerkinElmer, Hopkinton, MA) Staphycoccus aureus were inoculated on implants surgically inserted into the L4 spinous processes. Three groups were compared: PEGPPS coating alone, PEG-PPS coating with Vancomycin, and PEG-PPS with tigecycline. The primary outcome was the quantity of bioluminescence produced by bacteria for four weeks following inoculation. RESULTS: A total of 10 mice were tested in each treatment group. Bioluminescence was highest at all time points with the PEG-PPS coating alone followed by the tigecycline and vancomycin groups. The tigecycline loaded PEG-PPS coating group exhibited bioluminescence levels lower than PEG-PPS alone until 14 days postoperatively at which time it plateaued at levels within error of the PEG-PPS coated implants. Mice treated with vancomycin loaded PEG-PPS exhibited lower bioluminescence at all time points. CONCLUSIONS: PEG-PPS polymer coating in conjunction with vancomycin effectively reduced bacterial burden throughout a 28-day postop course at all time points, whereas PEG-PPS with tigecycline reduced infection until postop day 14. In contrast to PEG-PPS alone and PEG-PPS loaded with tigecycline, PEG-PPS coating loaded with vancomycin exhibited a fourweek bacterial bioluminescence level near the postop day 0 level suggestive of no overall increase in bacterial burden. Based on these data, PEG-PPS polymer loaded with vancomycin provides sustained suppression of bacterial infection. As such, this coating may become part of the armamentarium of surgeon tools to effectively eradicate the devastating complication of implant infection. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. https://doi.org/10.1016/j.spinee.2017.07.248

200. An Assessment of the Inherent Antimicrobial Resistance of Biomaterials Utilized in Spinal Fusion Surgery Craig A. Kuhns, MD1, Bryan J. McEntire, PhD, MBA2, Ryan M. Bock, PhD2, Giuseppe Pezzotti, PhD3,4,5,6, Bhajanjit Bal, MD2,7; 1 Austin Spine Specialists, Austin, TX, USA; 2Amedica Corporation, Salt Lake City, UT, USA; 3Ceramic Physics Laboratory, Kyoto Institute of Technology, Kyoto, Japan; 4Department of Orthopedic Surgery, Tokyo Medical University, Tokyo, Japan; 5Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan; 6The Center for Advanced Medical Engineering and Informatics, Osaka University, Osaka, Japan; 7 Department of Orthopaedic Surgery, University of Missouri, Columbia, MO, USA BACKGROUND CONTEXT: Perioperative and latent infections are leading causes of revision surgery for orthopedic devices resulting in significant increased patient care, comorbidities and costs. This is a growing problem due to the rising antibiotic resistance of nosocomial bacteria to germicidal therapies. Considerable research has targeted the selection and development of biomaterials that may inherently reduce or eliminate implant-related infections. PURPOSE: In this in vitro study, we compared biofilm formation on biomaterials commonly used in spinal fusion surgery—silicon nitride (Si3N4), polyetheretherketone (PEEK), and titanium alloy (Ti6Al4V)—using one grampositive and one gram-negative bacterial species. STUDY DESIGN/SETTING: Not applicable. PATIENT SAMPLE: Not applicable. OUTCOME MEASURES: Not applicable. METHODS: Several variations of surface treated silicon nitride (Si3N4, MC2®, Amedica Corporation, Salt Lake City, UT) along with polyetheretherketone (PEEK, ASTM D6262), and medical grade titanium alloy (Ti6Al4V, ASTM F136) were prepared or acquired as Ø12.7×1 mm discs for use in this well-