Srdjan Cirovic

A One-Dimensional Model of the Spinal Cerebrospinal-Fluid Compartment

Modeling of the cerebrospinal fluid (CSF) system in the spine is strongly motivated by the need to understand the origins of pathological conditions such as the emergence and growth of fluid-filled cysts in the spinal cord. In this study, a one-dimensional (1D) approximation for the flow in elastic conduits was used to formulate a model of the spinal CSF compartment. The modeling was based around a coaxial geometry in which the inner elastic cylinder represented the spinal cord, middle elastic tube represented the dura, and the outermost tube represented the vertebral column. The fluid-filled annuli between the cord and dura, and the dura and vertebral column, represented the subarachnoid and epidural spaces, respectively. The system of governing equations was constructed by applying a 1D form of mass and momentum conservation to all segments of the model. The developed 1D model was used to simulate CSF pulse excited by pressure disturbances in the subarachnoid and epidural spaces. The results were compared to those obtained from an equivalent two-dimensional finite element (FE) model which was implemented using a commercial software package. The analysis of linearized governing equations revealed the existence of three types of waves, of which the two slower waves can be clearly related to the wave modes identified in previous similar studies. The third, much faster, wave emanates directly from the vertebral column and has little effect on the deformation of the spinal cord. The results obtained from the 1D model and its FE counterpart were found to be in good general agreement even when sharp spatial gradients of the spinal cord stiffness were included; both models predicted large radial displacements of the cord at the location of an initial cyst. This study suggests that 1D modeling, which is computationally inexpensive and amenable to coupling with the models of the cranial CSF system, should be a useful approach for the analysis of some aspects of the CSF dynamics in the spine. The simulation of the CSF pulse excited by a pressure disturbance in the epidural space, points to the possibility that regions of the spinal cord with abnormally low stiffness may be prone to experiencing large strains due to coughing and sneezing.

Finite element modelling of radial shock wave therapy for chronic plantar fasciitis

Abstract Therapeutic use of high-amplitude pressure waves, or shock wave therapy (SWT), is emerging as a popular method for treating musculoskeletal disorders. However, the mechanism(s) through which this technique promotes healing are unclear. Finite element models of a shock wave source and the foot were constructed to gain a better understanding of the mechanical stimuli that SWT produces in the context of plantar fasciitis treatment. The model of the shock wave source was based on the geometry of an actual radial shock wave device, in which pressure waves are generated through the collision of two metallic objects: a projectile and an applicator. The foot model was based on the geometry reconstructed from magnetic resonance images of a volunteer and it comprised bones, cartilage, soft tissue, plantar fascia, and Achilles tendon. Dynamic simulations were conducted of a single and of two successive shock wave pulses administered to the foot. The collision between the projectile and the applicator resulted in a stress wave in the applicator. This wave was transmitted into the soft tissue in the form of compression–rarefaction pressure waves with an amplitude of the order of several MPa. The negative pressure at the plantar fascia reached values of over 1.5 MPa, which could be sufficient to generate cavitation in the tissue. The results also show that multiple shock wave pulses may have a cumulative effect in terms of strain energy accumulation in the foot.

Assessment of the glenohumeral joint's active and passive axial rotational range

BACKGROUND Assessment of the range of axial rotation of the glenohumeral joint will improve understanding of shoulder function, with applications in shoulder rehabilitation and sports medicine. However, there is currently no complete description of motion of the joint. The study aimed to develop a reliable protocol to quantify the internal and external axial rotations of the glenohumeral joint during active and passive motion at multiple humeral positions. METHODS Optical motion tracking was used to collect kinematic data from 20 healthy subjects. The humerus was positioned at 60°, 90°, and 120° of humerothoracic elevation in the coronal, scapular, and sagittal planes. Internal and external rotations were measured at each position for active and passive motion, where intrasubject standard deviations were used to assess variations in internal-external rotations. RESULTS The protocol showed intrasubject variability in the axial rotational range of <5° for active and passive rotations at all humeral positions. Maximum internal rotation was shown to be dependent on humeral position, where a reduced range was measured in the sagittal plane (P < .001) and at 120° elevations (P < .001). Conversely, maximum external rotations were not affected by humeral position. CONCLUSION The results describe normal ranges of internal-external rotation of the glenohumeral joint at multiple humeral positions. The protocols low variability means that it could be used to test whether shoulder pathologic conditions lead to changes in axial rotational range at specific humeral positions.

Cadaveric experiments to evaluate pressure wave generated by radial shockwave treatment of plantar fasciitis

BACKGROUND Shockwave treatment is increasingly used for plantar fasciitis and Achilles tendinopathy. To be effective it is believed that high pressure must be achieved in the tissues. We report on the first human cadaveric experiments to characterize pressure from radial shockwave therapy (rSWT) for plantar fasciitis. METHODS The pressure from rSWT was measured in two cadaveric feet using a needle hydrophone. Maximal pressure and energy flux were calculated from the measurements. RESULTS The pressure persisted longer than supposed, for up to 400μs. The peak negative pressure was up to two Mega Pascal. The predicted energy in the tissue strongly depended on the time interval used in calculations. CONCLUSIONS The measured pressure may be sufficiently high to cause cavitation in the tissue, which is one of the proposed healing mechanisms associated with rSWT. The results suggest that the energy is imparted to the tissues for much longer than previously thought.

Shaken Mannequin Experiments: Head Motion Pattern and Its Potential Effect on Blood Pressure

Shaken baby syndrome (SBS) describes a group of symptoms observed in young infants that are associated with a high level of fatality. There is currently no consensus on whether shaking alone can cause the observed injuries. We performed experiments on anthropometric test devices (dummies) to analyze the head motion generated by shaking. Volunteers were asked to violently shake the dummies whose motion was tracked with a camera-based system; a model of the cardiovascular system was mounted on a dummy to assess the effect of shaking on the blood pressure. Over the duration of shaking episodes the acceleration along the inferior-superior axis of the head had a mean of up to four times the gravitational acceleration. The results from the cardiovascular model indicate that this could lead to an increase of the blood pressure in the head. It is possible that this mechanism contributes to some ocular symptoms associated with SBS.

Investigation of fullerenol-induced changes in poroelasticity of human hepatocellular carcinoma by AFM-based creep tests

In this study, atomic force microscopy (AFM) is used to investigate the alterations of the poroelastic properties of hepatocellular carcinoma (SMMC-7721) cells treated with fullerenol. The SMMC-7721 cells were subject to AFM-based creep tests, and a corresponding poroelastic indentation model was used to determine the poroelastic parameters by curve fitting. Comparative analyses indicated that the both permeability and diffusion of fullerenol-treated cells increased significantly while their elastic modulus decreased by a small amount. From the change in the trend of the determined parameter, we verified the corresponding alternations of cytoskeleton (mainly filaments actin), which was reported by the previous study using confocal imaging method. Our investigation on SMMC-7721 cell reveals that the poroelastic properties could provide a better understanding how the cancer cells are affected by fullerenol or potentially other drugs which could find possible applications in drug efficacy test, cancer diagnosis and secure therapies.

Shoulder Bone Geometry Affects the Active and Passive Axial Rotational Range of the Glenohumeral Joint

Background: The range of motion of the glenohumeral joint varies substantially among individuals and is dependent on humeral position. How variation in shape of the humerus and scapula affects shoulder axial range of motion at various positions has not been established. Purpose: To quantify variation in the shape of the glenohumeral joint and investigate whether the scapula and humerus geometries affect the axial rotational range of the glenohumeral joint. Study Design: Descriptive laboratory study. Methods: The range of active and passive internal-external rotation of the glenohumeral joint was quantified for 10 asymptomatic participants with optical motion tracking at 60º, 90º, and 120º humeral elevations in the coronal, scapular, and sagittal planes. Bone geometrical parameters were acquired from shoulder magnetic resonance image scans, and correlations between geometrical parameters and maximum internal and external rotations were investigated. Three-dimensional participant-specific models of the humerus and scapula were used to identify collisions between bones at the end of range. Results: Maximum internal and external rotations of the glenohumeral joint were correlated to geometric parameters and were limited by bony collisions. Generally, the active axial rotational range was greater with increased articular cartilage and glenoid curvature, while a shorter acromion resulted in greater passive range. Greater internal rotation was correlated with a greater glenoid depth and curvature in the scapular plane (r = 0.76, P < .01, at 60° of elevation), a greater subacromial depth in the coronal plane (r = 0.74, P < .01, at 90° of elevation), and a greater articular cartilage curvature in the sagittal plane (r = 0.75, P < .01, at 90° of elevation). At higher humeral elevations, a greater subacromial depth and shorter acromion allowed a greater range of motion. Conclusion: The study strongly suggests that specific bony constraints restrict the maximum internal and external rotations achieved in active and passive glenohumeral movement. Clinical Relevance: This study identifies bony constraints that limit the range of motion of the glenohumeral joint. This information can be used to predict full range of motion and set patient-specific rehabilitation targets for those recovering from shoulder disorders. It can improve positioning and choice of shoulder implants during preoperative planning by considering points of collision that could limit range of motion.

DEVELOPMENT OF KINEMATIC CRITERIA FOR DETECTION OF SUBMARINING

Since the implementation of seat-belts and child restraint systems (CRSs) as a legal requirement, the number of child road fatalities has greatly decreased. However, new patterns of injuries have occurred in relation to restraint use, affecting the thorax and the abdomen. Submarining is a major cause for the latter. Submarining is defined as a slouching motion occurring in frontal impacts consisting of a backward pelvis tilt, rounding of the spine, and slipping forward of the pelvis, resulting in poor routing and interaction of the seat-belt with the body, potentially causing injuries to the abdomen.