The potential of proximal junctional kyphosis prevention using a novel tether pedicle screw construct: an in silico study comparing the influence of standard and dynamic techniques on adjacent-level range of motion and load pattern.

OBJECTIVE: A tether pedicle screw (TPS) enables individual stepless pretensioning and is placed at one or two levels above the upper instrumented vertebra (UIV+1 and UIV+2, respectively). This study aimed to evaluate a novel customized TPS for the prevention of proximal junctional kyphosis (PJK) and to investigate the potential to generate a smoother force transition from cranial to long fusion during trunk flexion, instead of an abrupt change at the UIV, following adult spinal deformity surgery. METHODS: A finite element model was designed based on an adult patient with spinal deformity instrumented from T10 to S1. Five different sagittal balance types and implant configurations were tested. The proximal range of motion (ROM) and intervertebral stress were examined, with a special focus on their respective discontinuities. RESULTS: Tension shielding at UIV/UIV+1 by the TPS was consistent irrespective of sagittal profiles. The use of TPSs at UIV+1 and UIV+2 increased the efficacy in reducing spinal ROM discontinuity at UIV/UIV+1, as compared with the use of TPSs at UIV+1 only. Through the use of two pairs of TPSs cranial to the UIV, the optimal tension configuration could be defined to avoid a reduction effect at UIV+1. Neither the addition of transition rods to the TPSs nor the use of transition rods in combination with standard pedicle screws improved the junctional mechanics when compared with TPSs at UIV+1/UIV+2. CONCLUSIONS: A smoother motion discontinuity at the UIV can be achieved via implementation of a TPS strategy. This new technology shows favorable in silico mechanics for reducing the risk of PJK.

Recommendations for design and conduct of preclinical in vivo studies of orthopedic device-related infection.

Orthopedic device-related infection (ODRI), including both fracture-related infection (FRI) and periprosthetic joint infection (PJI), remain among the most challenging complications in orthopedic and musculoskeletal trauma surgery. ODRI has been convincingly shown to delay healing, worsen functional outcome and incur significant socio-economic costs. To address this clinical problem, ever more sophisticated technologies targeting the prevention and/or treatment of ODRI are being developed and tested in vitro and in vivo. Among the most commonly described innovations are antimicrobial-coated orthopedic devices, antimicrobial-loaded bone cements and void fillers, and dual osteo-inductive/antimicrobial biomaterials. Unfortunately, translation of these technologies to the clinic has been limited, at least partially due to the challenging and still evolving regulatory environment for antimicrobial drug-device combination products, and a lack of clarity in the burden of proof required in preclinical studies. Preclinical in vivo testing (i.e. animal studies) represents a critical phase of the multidisciplinary effort to design, produce and reliably test both safety and efficacy of any new antimicrobial device. Nonetheless, current in vivo testing protocols, procedures, models, and assessments are highly disparate, irregularly conducted and reported, and without standardization and validation. The purpose of the present opinion piece is to discuss best practices in preclinical in vivo testing of antimicrobial interventions targeting ODRI. By sharing these experience-driven views, we aim to aid others in conducting such studies both for fundamental biomedical research, but also for regulatory and clinical evaluation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:271-287, 2019.

NMP-modified PMMA bone cement with adapted mechanical and hardening properties for the use in cancellous bone augmentation.

The use of polymethylmethacrylate (PMMA) to reinforce vertebral bodies (Vertebroplasty) leads to an increase in the Young's modulus of the augmented vertebral body. Fractures in the adjacent vertebrae may be the consequence thereof. Hence, PMMA with a reduced Young's modulus may be suitable for vertebroplasty. The goal of this study was to produce and characterize stiffness-adapted PMMA cements. Modified PMMA bone cements were produced by adding N-methyl-pyrrolidone (NMP). Young's modulus, yield strength, polymerization temperature, setting time, and hardening behavior of different cements were analyzed. Focus was on the mechanical properties of the material after different storage conditions (in air at room temperature and in PBS at 37 degrees C). The Young's modulus decreased from 2670 MPa (air)/2384 MPa (PBS) for the regular cement to 76 MPa (air)/320 MPa (PBS) for a material composition with 60% of the MMA substituted by NMP. Yield strength decreased from 85 MPa (air)/78 MPa (PBS) to 2 MPa (air)/24 MPa (PBS) between the regular cement and the 60% composition. Polymerization temperature decreased from 70 degrees C (regular cement) to 48 degrees C for the 30% composition. The hardening behavior exhibited an extension in handling time up to 200% by the modification presented. Modification of PMMA cement using NMP seems to be a promising method to make the PMMA cement more compliant for the use in cancellous bone augmentation in osteoporotic patients: adjustment of its mechanical properties close to those of cancellous bone, lower polymerization temperature, and extended handling time.

Antibacterial coating systems.

The local application of antibiotics is a well-known procedure that has been in successful clinical use for more than 20 years. The most frequently used carrier substance for the antibiotic or other antibacterial substances is polymethylmethacrylate (PMMA). However, because PMMA is not resorbable, as much as 70% of the antibiotic dose is permanently sequestered in the PMMA cement and therefore not available to combat bacterial colonization. Antibacterial coatings of metal implants represent an attractive solution to simplify the local application of an antibacterial substance in fracture care. Several coating technologies have been investigated, involving different carrier materials as well as different antibacterial substances. A fully resorbable coating containing gentamicin sulphate has yielded promising results in animal studies and intramedullary tibial nails with this coating have already been implanted successfully in a few patients. In the future, the main developmental focus for antibacterial coatings for implants will lie in tailoring the release characteristics and the antibacterial substance to minimize the risk of breeding resistant bacterial strains while maximizing the efficacy of the coating.