Radical Scavenging of Poly(Methyl Methacrylate) Bone Cement by Rifampin and Clinically Relevant Properties of the Rifampin-Loaded Cement

Objectives: The objective of this study was to characterize the effect of rifampin incorporation into poly(methyl methacrylate) (pMMA) bone cement. While incompatibilities between the two materials have been previously noted, we sought to identify and quantify the cause of rifampin\u27s effects, including alterations in curing properties, mechanical strength, and residual monomer content. Methods: Four cement groups were prepared using commercial pMMA bone cement: a control; one with 1 g of rifampin; and one each with equimolar amounts of ascorbic acid or hydroquinone relative to the amount of rifampin added. The handling properties, setting time, exothermic output, and monomer loss were measured throughout curing. The mechanical strength of each group was tested over 14 days. A radical scavenging assay was used to assess the scavenging abilities of rifampin and its individual moieties. Results: Compared with control, the rifampin-incorporated cement had a prolonged setting time and a reduction in exothermic output during polymerization. The rifampin cement showed significantly reduced strength and was below the orthopaedic weight-bearing threshold of 70 Mpa. Based on the radical scavenging assay and strength tests, the hydroquinone structure within rifampin was identified as the polymerization inhibitor. Conclusion: The incorporation of rifampin into pMMA bone cement interferes with the cement\u27s radical polymerization. This interference is due to the hydroquinone moiety within rifampin. This combination alters the cement\u27s handling and curing properties, and lowers the strength below the threshold for weight-bearing applications. Additionally, the incomplete polymerization leads to increased toxic monomer output, which discourages its use even in non-weight-bearing applications

Chronic Fibrotic Changes in Experimental Pulmonary Embolization in the Rat Model

Comparative Medicine - OneHealth and Comparative Medicine Poster SessionIntroduction: Fat embolism, a subclinical event, occurs in many clinical settings, such as long bones fractures, liposuction and during cardiopulmonary bypass. Some cases, especially with trauma, result in fat embolism syndrome (FES), a serious manifestation of fat embolism. FES is reported to occur in 5-10% of major trauma cases and can produce profound respiratory problems that may culminate in adult respiratory distress syndrome (ARDS). Embolized fat is hydrolyzed by lipase into free fatty acids which have been shown by previous histological studies to be toxic to the lung. An animal model of fat embolism has been developed utilizing triolein given intravenously (i.v.) to rats. We hypothesized that i.v. triolein will produce histological changes in the lung that are similar to the changes seen in human FES. Methods: Following University animal care approval, unanesthetized Sprague Dawley rats (study n=13, control n=12) were injected with either triolein, 0.2 mL (study) or saline, 0.2 mL (control). Weights were recorded until necropsy at 3 weeks (n=13) and 6 weeks (n=12). Morphometric measurements were made on both H&E and fat-stained tissues from the lungs, heart, kidneys and spleen. All vessels were examined using high magnification fields. Arterial wall thickness (lumen patency) was calculated by vessel luminal and external diameters. The medial-adventitial ratio was calculated from the outer medial diameter divided by the outer adventitial diameter. These values were keyed into statistical software and analysis as a function of time and treatment was calculated using t-tests with significance noted at a p<0.05. Results: Gross pathological changes were seen in lung, heart, kidneys, liver and spleen of the triolein group. Pulmonary histological examination revealed diffuse intra-alveolar hemorrhages and edema with peri-bronchial inflammation. Vasculitis was more prominent in the peri-bronchial areas as well. Pulmonary arteries revealed significant medial thickening as compared with the control groups with lumen patency p=0.004. Adventitia/media ratio, with large variability in the triolein group, was not statistically significant. Conclusions: Our data showed that injected triolein remains in the rat lung after 3 and 6 weeks with associated vascular and septal damage in the lung tissue compared to controls. Discussion: This study is a continuation of our previous study showing an increase of severe pulmonary damage within 3-6 hours following triolein induced fat embolism in the rat, reaching a peak at 96 hrs post injection. Despite unmedicated recovery of general condition and body weight and reopening of the pulmonary arteries and arterioles, collagen and vasculitis persisted up to 6 weeks. Further studies are needed to verify the eventual recovery or the organ evolution toward chronic fibrosis

The effect of starting point placement technique on thoracic transverse process strength: an ex vivo biomechanical study

<p>Abstract</p> <p>Background</p> <p>The use of thoracic pedicle screws in spinal deformity, trauma, and tumor reconstruction is becoming more common. Unsuccessful screw placement may require salvage techniques utilizing transverse process hooks. The effect of different starting point placement techniques on the strength of the transverse process has not previously been reported. The purpose of this paper is to determine the biomechanical properties of the thoracic transverse process following various pedicle screw starting point placement techniques.</p> <p>Methods</p> <p>Forty-seven fresh-frozen human cadaveric thoracic vertebrae from T2 to T9 were disarticulated and matched by bone mineral density (BMD) and transverse process (TP) cross-sectional area. Specimens were randomized to one of four groups: A, control, and three others based on thoracic pedicle screw placement technique; B, straightforward; C, funnel; and D, in-out-in. Initial cortical bone removal for pedicle screw placement was made using a burr at the location on the transverse process or transverse process-laminar junction as published in the original description of each technique. The transverse process was tested measuring load-to-failure simulating a hook in compression mode. Analysis of covariance and Pearson correlation coefficients were used to examine the data.</p> <p>Results</p> <p>Technique was a significant predictor of load-to-failure (<it>P </it>= 0.0007). The least squares mean (LS mean) load-to-failure of group A (control) was 377 N, group B (straightforward) 355 N, group C (funnel) 229 N, and group D (in-out-in) 301 N. Significant differences were noted between groups A and C, A and D, B and C, and C and D. BMD (0.925 g/cm²[range, 0.624-1.301 g/cm²]) was also a significant predictor of load-to-failure, for all specimens grouped together (<it>P </it>< 0.0001) and for each technique (<it>P <</it>0.05). Level and side tested were not found to significantly correlate with load-to-failure.</p> <p>Conclusions</p> <p>The residual coronal plane compressive strength of the thoracic transverse process is dependent upon the screw starting point placement technique. The funnel technique significantly weakens transverse processes as compared to the straightforward technique, which does not significantly weaken the transverse process. It is also dependent upon bone mineral density, and low failure loads even in some control specimens suggest limited usefulness of the transverse process for axial compression loading in the osteoporotic thoracic spine.</p