In vitro evaluation of translating and rotating plates using a robot testing system under follower load.

BACKGROUND CONTEXT: Various modifications to standard "rigid" anterior cervical plate designs (constrained plate) have been developed that allow for some degree of axial translation and/or rotation of the plate (semi-constrained plate)-theoretically promoting proper load sharing with the graft and improved fusion rates. However, previous studies about rigid and dynamic plates have not examined the influence of simulated muscle loading. PURPOSE: The objective of this study was to compare rigid, translating, and rotating plates for single-level corpectomy procedures using a robot testing system with follower load. STUDY DESIGN: In-vitro biomechanical test. METHODS: N = 15 fresh-frozen human (C3-7) cervical specimens were biomechanically tested. The follower load was applied to the specimens at the neutral position from 0 to 100 N. Specimens were randomized into a rigid plate group, a translating plate group and a rotating plate group and then tested in flexion, extension, lateral bending and axial rotation to a pure moment target of 2.0 Nm under 100N of follower load. Range of motion, load sharing, and adjacent level effects were analyzed using a repeated measures analysis of variance (ANOVA). RESULTS: No significant differences were observed between the translating plate and the rigid plate on load sharing at neutral position and C4-6 ROM, but the translating plate was able to maintain load through the graft at a desired level during flexion. The rotating plate shared less load than rigid and translating plates in the neutral position, but cannot maintain the graft load during flexion. CONCLUSIONS: This study demonstrated that, in the presence of simulated muscle loading (follower load), the translating plate demonstrated superior performance for load sharing compared to the rigid and rotating plates.

Effects of secreted factors in culture medium of annulus fibrosus cells on microvascular endothelial cells: elucidating the possible pathomechanisms of matrix degradation and nerve in-growth in disc degeneration.

OBJECTIVE: To test whether the interaction between annulus fibrosus cells (AFCs) and endothelial cells (ECs) disrupts matrix homeostasis and stimulates production of innervation mediators. METHODS: Human microvascular ECs were cultured in the conditioned media of AF cell culture derived from degenerated human surgical specimen. Matrix-metalloproteinases (MMPs) and platelet-derived growth factor (PDGF) of ECs of this culture were analyzed by qRT-PCR, Western, and immunofluorescence. Vascular endothelial growth factor (VEGF), Interleukin-8 (IL-8), and nerve growth factor (NGF) in the media of this cell culture were assayed by ELISA. To determine the effects of ECs on AFCs, qRT-PCR was performed to determine mRNA levels of collagen I, II and aggrecan in AFCs cultured in EC conditioned media. RESULTS: Compared to ECs cultured in naïve media, ECs exposed to AFC conditioned media expressed higher mRNA and protein levels of key biomarkers of invasive EC phenotype, MMP-2 (2×), MMP-13 (4×), and PDGF-B (1.5-2×), and NGF (24.9 ± 15.2 pg/mL vs 0 in naïve media). Treatment of AF cells with EC culture conditioned media decreased collagen type II expression two fold. Considerable quantities of pro-angiogenic factors IL-8 (396.7 ± 302.0 pg/mL) and VEGF (756.2 ± 375.9 pg/mL) were also detected in the conditioned media of untreated AF cell culture. DISCUSSION: AFCs from degenerated discs secreted factors which stimulated EC production of factors known to induce matrix degradation, angiogenesis, and innervation. IL-8 and VEGF maybe the secreted factors from AFCs which mediate a pro-angiogenic stimulus often implicated in the development of disc degeneration.

Histologic signatures of thermal injury: applications in transmyocardial laser revascularization and radiofrequency ablation.

BACKGROUND AND OBJECTIVE: Cardiac treatments such as transmyocardial laser revascularization and radiofrequency ablation cause thermal injury. We sought to provide quantitative histologic methods of assessing such injury by using the inherent birefringence of cardiac muscle and collagen; specifically, to exploit the connection between thermal injury and the loss of birefringence. STUDY DESIGN/MATERIALS AND METHODS: We quantified tissue birefringence changes in vitro for temperatures up to 130 degrees C. This information was used to assess thermal injury associated with myocardial channels made in vitro. We then measured in vivo cardiac injury 30 minutes and 3 days after radiofrequency exposure. RESULTS: Birefringence decreased above 60 degrees C for muscle and above 70 degrees C for collagen. Temperatures above 80 degrees C were associated with collagen fiber straightening and above 95 degrees C with little muscle birefringence. Injury adjacent to laser channels was greatest parallel to cell orientation. In vivo, muscle with reduced birefringence was surrounded by cells exhibiting focal birefringence increases (contraction bands). Early injury assessment marked by birefringence changes corresponded to lesion size at 3 days. CONCLUSION: Polarized light revealed histologic temperature signatures corresponding to irreversible muscle injury and collagen denaturation.

The physics of transmyocardial laser revascularization.

Lasers create channels through the myocardium by ablating the tissue and tissue ablation is achieved by breaking the molecular bonds of the organic constituents of the myocardium. Lasers provide the energy required to dissociate these molecular bonds by the interaction of laser photons with the tissue. However, the energy supplied to the electrons within the bonds must match specific allowed energy levels. Such energy matching is accomplished through different mechanisms by different laser wavelengths. Infrared laser photons are strongly absorbed by water in the tissue and it is the subsequent vaporization of the water that provides the energy necessary to break the bonds. In contrast, ultraviolet laser photons are not absorbed by water and have energies that can match those required for bond dissociation. Thus, ablation by ultraviolet lasers is achieved primarily by direct bond absorption of the photons. Both of these ablation mechanisms produce secondary effects that can cause injury to tissue surrounding the channels. The generation of steam or the gaseous breakdown products of tissue proteins can cause thermal injury in addition to the mechanical injury produced by escape of these gases into the tissue. Furthermore, shock waves generated by ablation are also a possible source of mechanical injury, while free radical molecules capable of cell injury are known to be formed after breaking chemical bonds. The variety of tissue interactions provided by the different lasers should enable the optimal laser treatment to be applied once the optimal channel configuration has been determined.

Rapid orotracheal intubation in the clenched-jaw patient: a modification of the lightwand technique.

Emergency airway management of the patient with a clenched jaw can present a special challenge to the anesthesiologist. We describe four cases in which the patients had a clenched jaw and nasotracheal intubation was either contraindicated or several attempts had failed. All patients were successfully orotracheally intubated by a modification of the lightwand technique.