Direct Current Electrical Stimulation Increases the Fusion Rate of Spinal Fusion Cages

Study Design. A randomized experimental evaluation of direct current stimulation in a validated animal model with an experimental control group, using blinded radiographic, biomechanical, histologic, and statistical measures. Objectives. To evaluate the efficacy of the adjunctive use of direct current stimulation on the fusion rate and speed of healing of titanium interbody fusion cages packed with autograft in a sheep lumbar interbody fusion model. Summary of Background Data. Titanium lumbar interbody spinal fusion cages have been reported to be 90% effective for single-level lumbar interbody fusion. However, fusion rates are reported to be between 70% and 80% in patients with multilevel fusions or with risk factors such as obesity, tobacco use, or metabolic disorders. The authors hypothesized that direct current stimulation would increase the fusion rate of titanium interbody fusion cages packed with autograft in a sheep lumbar interbody fusion model. Methods. Twenty-two sheep underwent lumbar discectomy and fusion at L4–L5 with an 11- × 20-mm Bagby and Kuslich (BAK) cage packed with autograft. Seven sheep received a BAK cage and no current. Seven sheep had a cage and a 40-μA current applied with a direct current stimulator. Eight sheep had a BAK cage and a 100-μA current applied. All sheep were killed 4 months after surgery. The efficacy of electrical stimulation in promoting interbody fusion was assessed by performing radiographic, biomechanical, and histologic analyses in a blinded fashion. Results. The histologic fusion rate increased as the direct current dose increased from 0 μA to 40 μA to 100 μA (P \u3c 0.009). Histologically, all animals in the 100-μA group had fusions in both the right and left sides of the cage. Direct current stimulation had a significant effect on increasing the stiffness of the treated motion segment in right lateral bending (P \u3c 0.120), left lateral bending (P \u3c 0.017), right axial rotation (P \u3c 0.004), left axial rotation (P \u3c 0.073), extension (P \u3c 0.078), and flexion (P \u3c 0.029) over nonstimulated levels. Conclusion. Direct current stimulation increased the histologic and biomechanical fusion rate and the speed of healing of lumbar interbody spinal fusion cages in an ovine model at 4 months

Influence of airway structure on gas expirograms

Bioengineering research has been conducted in the area of respiratory gas transport to determine the effects of emphysema, a chronic obstructive pulmonary disease (COPD), on the shape of the CO\sb2 expirogram and to develop a reliable noninvasive pulmonary function test sensitive to this disorder that afflicts 14 million Americans and is attributable to over 100,000 deaths annually. This work has also contributed to the basic science of pulmonary physiology in healthy lungs, since details of the interactions of gas transport, pulmonary circulation, and airway anatomy are not completely understood. A single-path theory of respiratory gas transport has been developed into a computer model that simulates the movement of gases from the alveolar-blood interface to the mouth during tidal air flow in a single-path model (SPM) of the entire bronchial tree, with a small number of adjustable input parameters representing physical, physiological, and anatomical features of real lungs. SPM simulations were compared to steady state gas expirograms measured on healthy subjects and patients with COPD. Instrumentation consisted of hardware and software developed for a computerized fast-response quadrapole mass spectrometer system that is capable of simultaneously measuring CO\sb2 and infused inert gas expirograms. After extensive experimental and simulation studies on data from healthy subjects and patients with COPD, an optimization algorithm was developed to find the structural SPM input parameters necessary to fit simulated gas washout results to experimental data from any particular subject. Through the interaction of laboratory experiments and numerical modeling, the basis for a pulmonary function test has evolved that quantifies the gas transport limitation and the alveolar tissue obliteration of emphysema, and is corroborated by conventional pulmonary function test data. This is the first time that acinar airway information has been recovered from gas expirograms that is seen to distinguish between health and disease

Evaluation of a synthetic vertebral body augmentation model for rapid and reliable cyclic compression life testing of materials for balloon kyphoplasty

Screening of augmentation materials for use in balloon kyphoplasty (BKP) may be carried out using vertebral bodies (VBs) prepared from fresh cadaveric or animal model spines, but this approach has many drawbacks. Alternatively, a validated synthetic VB augmentation model may be used. In the present work, such a model - a cube (26 mm sides) of low-density polyurethane foam with a centrally located through-thickness cylindrical hole (diameter = 4 mm) completely filled with a bolus of augmentation material - was used to compare two BKP augmentation materials with very different chemistries (a high-viscosity acrylic bone cement (PMMA) and a calcium phosphate bone substitute (CP)) in cyclic compression life tests. The test conditions were considered physiologically relevant: the model was immersed in phosphate buffered saline solution, at 37°C; the frequency was 3 Hz; and the maximum load was either 1150 N or 2300 N (corresponding to a maximum stress of 1.7 or 3.4 MPa). At the high load, all four PMMA and two out of seven CP specimens ran out to 1 million cycles. CP specimens consistently ran out at the low load. The use of this model for rapid and reliable ex vivo screening of BKP augmentation materials was considered both valid (because of the clear demarcation seen in the qualitative and quantitative results obtained with the two materials tested) and appropriate (that is, clinically relevant to BKP). © 2008 Wiley Periodicals, Inc