Computer simulation of syringomyelia in dogs

Syringomyelia is a pathological condition in which fluid-filled cavities (syringes) form and expand in the spinal cord. Syringomyelia is often linked with obstruction of the craniocervical junction and a Chiari malformation, which is similar in both humans and animals. Some brachycephalic toy breed dogs such as Cavalier King Charles Spaniels (CKCS) are particularly predisposed. The exact mechanism of the formation of syringomyelia is undetermined and consequently with the lack of clinical explanation, engineers and mathematicians have resorted to computer models to identify possible physical mechanisms that can lead to syringes. We developed a computer model of the spinal cavity of a CKCS suffering from a large syrinx. The model was excited at the cranial end to simulate the movement of the cerebrospinal fluid (CSF) and the spinal cord due to the shift of blood volume in the cranium related to the cardiac cycle. To simulate the normal condition, the movement was prescribed to the CSF. To simulate the pathological condition, the movement of CSF was blocked

Cerebral circulation during acceleration stress

grantor: University of TorontoA mathematical model of the cerebrovascular system has been developed to examine the influence of acceleration on cerebral circulation. The objective is to distinguish the main factors that limit cerebral blood flow in pilots subjected to accelerations which exceed the gravitational acceleration of the earth (Gz > 1). The cerebrovascular system was approximated by an open-loop network of elastic tubes and the flow in blood vessels was modeled according to a one-dimensional theory of flow in collapsible tubes. Since linear analysis showed that the speed of pulse propagation in the intracranial vessels should not be modified by the skull constraint, the same governing equations were used for the intracranial vessels as for the rest of the network. The steady and pulsatile components of the cerebrospinal fluid pressure were determined from the condition that the cranial volume must be conserved. After the qualitative aspects of the model results were verified experimentally, the open-loop geometry was incorporated into a global mathematical model of the cardiovascular system. Both the mathematical models and the experiment show that cerebral blood flow diminishes for Gz > 1 due to an increase in the resistance of the large veins in the neck, which collapse as soon as the venous pressure becomes negative. In contrast, the conservation of the cranial volume requires that the cerebrospinal and venous pressure always be approximately the same, and the vessels contained in the cranial cavity do not collapse. Positive pressure breathing provides protection by elevating blood arterial and venous pressures at the heart, thus preventing the venous collapse and maintaining the normal cerebral vascular resistance.Ph.D

Slosh Simulation in a Computer Model of Canine Syringomyelia

The exact pathogenesis of syringomyelia is unknown. Epidural venous distention during raised intrathoracic pressure (Valsalva) may cause impulsive movement of fluid (“slosh”) within the syrinx. Such a slosh mechanism is a proposed cause of syrinx dissection into spinal cord parenchyma resulting in craniocaudal propagation of the cavity. We sought to test the “slosh” hypothesis by epidural excitation of CSF pulse in a computer model of canine syringomyelia. Our previously developed canine syringomyelia computer model was modified to include an epidural pressure pulse. Simulations were run for: cord free of cavities; cord with small syringes at different locations; and cord with a syrinx that was progressively expanding caudally. If small syringes are present, there are peaks of stress at those locations. This effect is most pronounced at the locations at which syringes initially form. When a syrinx is expanding caudally, the peak stress is typically at the caudal end of the syrinx. However, when the syrinx reaches the lumbar region; the stress becomes moderate. The findings support the “slosh” hypothesis, suggesting that small cervical syringes may propagate caudally. However, when the syrinx is large, there is less focal stress, which may explain why a syrinx can rapidly expand but then remain unchanged in shape over years

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 between 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 previously established. Hypothesis/Purpose: The aim of this study is to quantify variation in the shape of the Glenohumeral joint and investigate whether the scapula and humerus geometries affect axial rotational range of the Glenohumeral joint. Study Design: Cross-sectional study. Methods: The range of active and passive internal-external rotation of the Glenohumeral joint was quantified for 10 asymptomatic subjects using optical motion tracking at 60º, 90º and 120º humeral elevations in the Coronal, Scapular and Sagittal planes. Bone geometrical parameters were acquired from shoulder MRI scans and correlations between geometric parameters and maximum internal and external rotations were investigated. Three-dimensional subject-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 geometrical parameters and were limited by bony collisions. Generally, the active axial rotational range was greater with increased articular cartilage and glenoid curvature; whilst 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<0.01 at 60° elevation), a greater subacromial depth in the Coronal plane (r=0.74, p<0.01 at 90° elevation), and a greater articular cartilage curvature in the Sagittal plane (r=0.75, p<0.01 at 90° 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 which limit the range-of-motion of Glenohumeral joint. This information can be used to predict full range-of-motion and set patient specific rehabilitation targets for patients recovering from shoulder pathologies. It can improve positioning and choice of shoulder implants during pre-operative planning by considering points of collision which could limit range-of-motion

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

A computational model of the cerebrospinal fluid system incorporating lumped-parameter cranial compartment and one-dimensional distributed spinal compartment

The dynamic transmission of pressure through the cerebro-circulatory system may play a role in the genesis of pathological conditions of the brain and spinal cord. This study aims to lay down the foundations for computer modelling of the cerebrospinal (CSF) pressure dynamics in the cranio-spinal cavity as a single entity. The cerebro-vascular system was modelled as a set of resistors and capacitors. The model of the CSF space comprised a lumped cranial compartment and a distributed spinal compartment. Apart from simulating normal (baseline) conditions, the effects of jugular vein compression, and thoracic pressure elevation by coughing were investigated by applying pressure waveforms at the appropriate points in the model. The Chiari malformation was simulated by assigning high resistance to the circulation of the CSF between the cranium and the spine. The model was capable of reproducing physiologically plausible results for all forms of excitation. The spinal cavity behaved effectively as a lumped compartment, except for the cough excitation where wave-type behaviour was evident. In that case, the Chiari obstruction resulted in prolonged periodic straining of the spinal cord. This result can be of significance for understanding the mechanism of the formation of cysts in the spinal cord

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 400 μs. 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

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 400 μs. 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

Evaluating the Effect of Changes in Bone Geometry on the Trans-femoral Socket-Residual Limb Interface Using Finite Element Analysis

A prosthetic socket used by a lower limb amputee should accommodate the patient’s geometry and biomechanical needs. The creation of a geometrically accurate subject-specific finite element model can be used to provide a better understanding of the load transfer between socket and limb. There has been a limited number of finite element studies of trans-femoral sockets with all current models only including the femur and ignoring the pelvis. This study looked to evaluate the effect that including the pelvic bone as well as the femur in a finite element model has on the contact interface between the prosthetic socket and residual limb. This was done by creating a finite element model from a computerised tomography scan of a trans-femoral amputee. This model included three-dimensional geometry, nonlinear material properties and frictional contact between the residual limb and prosthetic socket. It was found that without the pelvic bone the contact pressures peaked at the distal end region of the residual limb (peak of 95 kPa). However by including the pelvic bone the contact pressures were instead concentrated at the ischial loading region (peak of 364 kPa). The shear stresses experienced on the socket-residual limb interface were also simulated. The results obtained in this study can be used to provide more of an understanding of the loading on the residual limb for the design and creation of future trans-femoral sockets