X-ray exposure in odontoid screwing for Anderson type II fracture: comparison between O-arm and C-arm-assisted procedures.

BACKGROUND: Since the odontoid fractures become increasingly common in the aging population, technical improvements are even more needed. The odontoid screwing has been progressively preferred by many surgeons in type II fractures according to the Anderson-D'Alonzo classification system. However, X-ray exposure remains an issue for surgeons and OR staff members. The aim of the present study was to investigate the feasibility of using the O-Arm for odontoid screwing comparing the radiation exposure to the standard C-Arm. METHODS: Patients consequently referred to our center for odontoid type II fractures, from January 2018 to April 2019, eligible for odontoid screwing were enrolled in the present study. They were operated on using either C-Arm or O-Arm-assisted procedures. The surgical duration, number of acquisitions, global X-ray exposure for the OR staff and patients, and screw placement accuracy were evaluated. RESULTS: No differences in terms of patients' demographical characteristics and surgical duration were reported. The number of acquisitions, intraoperative and global X-ray dose, for the OR staff and patients, was lower in O-Arm-assisted procedures (p < 0.05). The screws were all well positioned. CONCLUSIONS: Since the surgical outcomes seem to be similar using the O-Arm for odontoid screwing, the lower X-ray exposure and the possibility for checking the instrumentation positioning with 3D reconstructions before leaving the OR should be considered.

Physics of reshock and mixing in single-mode Richtmyer-Meshkov instability.

The ninth-order weighted essentially nonoscillatory (WENO) shock-capturing method is used to investigate the physics of reshock and mixing in two-dimensional single-mode Richtmyer-Meshkov instability to late times. The initial conditions and computational domain were adapted from the Mach 1.21 air (acetone)/ SF6 shock tube experiment of Collins and Jacobs [J. Fluid Mech. 464, 113 (2002)]: the growth of the bubble and spike amplitudes from fifth- and ninth-order WENO simulations of this experiment were compared to the predictions of linear and nonlinear amplitude growth models, and were shown to be in very good agreement with the experimental data prior to reshock by Latini, Schilling, and Don [Phys. Fluids 19, 024104 (2007)]. In the present investigation, the density, vorticity, baroclinic vorticity production, and simulated density Schlieren fields are first presented to qualitatively describe the reshock process. The baroclinic circulation deposition on the interface is shown to agree with the predictions of the Samtaney-Zabusky model and with linear instability theory. The time evolution of the positive and negative circulation on the interface is considered before and after reshock: it is shown that the magnitudes of the circulations are equal before as well as after reshock, until the interaction of the reflected rarefaction with the layer induces flow symmetry breaking and different evolutions of the magnitude of the positive and negative circulation. The post-reshock mixing layer growth is shown to be in generally good agreement with three models predicting linear growth for a short time following reshock. Next, a comprehensive investigation of local and global mixing properties as a function of time is performed. The distribution and amount of mixed fluid along the shock propagation direction is characterized using averaged mole fraction profiles, a fast kinetic reaction model, and mixing fractions. The modal distribution of energy in the mixing layer is quantified using the spectra of the fluctuating kinetic energy, fluctuating enstrophy, pressure variance, density variance, and baroclinic vorticity production variance. It is shown that a broad range of scales already exists prior to reshock, indicating that the single-mode Richtmyer-Meshkov instability develops nontrivial spectral content from its inception. The comparison of the spectra to the predictions of classical inertial subrange scalings in two-dimensional turbulence shows that the post-reshock spectra may be consistent with many of these scalings over wave number ranges less than a decade. At reshock, fluctuations in all fields (except for the density) are amplified across all scales. Reshock strongly amplifies the circulation, profiles, and mixing fractions, as well as the energy spectra and statistics, leading to enhanced mixing followed by a decay. The mole and mixing fraction profiles become nearly self-similar at late times following reshock; the mixing fraction exhibits an approach toward unity across the layer at the latest time, signifying nearly complete mixing of the gases. To directly quantify the amplification of fluctuations by reshock, the previously considered quantities are compared immediately after and before reshock. Finally, to investigate the decay of fluctuations in the absence of additional waves interacting with the mixing layer following reshock, the boundary condition at the end of the computational domain is changed from reflecting to outflow to allow the reflected rarefaction wave to exit the domain. It is demonstrated that the reflected rarefaction has an important role in breaking symmetry and achieving late-time statistical isotropy of the velocity field.