Predictions of Vertebral Strength using QCT and Intra-Vertebral Heterogeneity in Density vs. DXA

Submitted by Amira Hussein

Trabecular bone is highly non-uniform throughout the vertebra. This intra-vertebral heterogeneity has often been proposed as a main reason why average measures of bone mineral density (BMD) explain only ~60% of the variance in vertebral strength. The goal of this study was to determine the influence of the intra-vertebral heterogeneity in density on strength predictions. Thirty-one fresh-frozen, human, L1 functional spine units were scanned via quantitative computed tomography (QCT) and then compressed to failure to measure the ultimate force. Heterogeneity was quantified using the inter-quartile range (IQR) of the BMD values for 5mm cubes distributed throughout the centrum. Average BMD (vBMD) and cross-sectional area (CSA) were calculated for the largest elliptical cylinder that fits within the vertebra. The images were also used to calculate areal BMD (aBMD) simulating DXA, and axial rigidity (EA; the resistance to axial loading). Linear regressions were used to determine the dependence of ultimate force on: 1) vBMD*CSA; 2) vBMD*CSA and IQR; 3) aBMD; 4) EA, and to rank the different models. Accounting for intra-vertebral heterogeneity in density in addition to mean density significantly improved strength predictions. Including IQR in addition to vBMD*CSA in the regression model improved the R2 value from 0.43 to 0.58 (p<0.002), resulting in the best regression model. Model 3 was inferior to model 2, and model 4 was not significant. These findings show that non-invasive assessments of the intra-vertebral heterogeneity in density improve predictions of vertebral strength compared to current clinical standards that use only average BMD from QCT or DXA.


Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering 




  

    			
Decoding kinetic parameters of grasping movements from single unit activity in monkey motor cortex

		    
        

      Submitted by Tomislav Milekovic
    

    
        	

    		
    		

    			    			    		

    		

    			
Development of neuronal prosthetics, where neuronal activity is used to control artificial limbs, has so far relied on decoding kinematic parameters of movements, such as movement position or velocity. In addition to kinematic control, proper control of forces exerted by the prosthetic device is necessary for successful interaction with the environment. In our study, we analysed the possibility of classifying and decoding different grasp related forces during active grasping. Two macaque monkeys were trained to reach, grasp and pull an object in response to visual cues. Cues instructed the monkeys to grasp the object with one out of two grip types (precision or side grip) and pull the object with one of two different forces (0.5N or 2N). Monkeys obtained a food reward after successfully performing the instructed grip and pull. During the task execution, we recorded electrophysiological signals from the multielectrode arrays implanted intracortically in the hand and arm area of the monkey’s motor cortex. Six different parameters of the grip: four pressure forces on each side of the object, pull force on the object and the object displacement, were recorded simultaneously with the neuronal activity. Recorded neuronal activity was used to classify different grip types or loading forces, and to decode the continuous traces of different forces during the grip. Our results show that kinetic grip parameters can be decoded with high accuracy, thereby improving the feasibility of constructing fully functional anthropomorphic neuronal prosthesis that relies on kinetic (force) control.



    			Listed In: Biomechanical Engineering, Neuroscience
    		

    	

        
      









  

    			
Age-related changes in motor adaptation to novel dynamics

		    
        

      Submitted by Alison Pienciak
    

    
        	

    		
    		

    			    			    		

    		

    			
Skilled movement relies on our ability to learn and adapt internal models of our bodies and the environment. Older adults move less accurately and efficiently than young adults; we hypothesize that this may indicate an impaired ability to learn novel internal models. We used an experimental paradigm testing motor adaptation of reaching movements to novel reaching dynamics that has been well-characterized in young adults, but not in older adults. We tested whether older adults showed impaired movement adaptation, and further, whether they showed impaired internal model learning, as compared to young adults. We found that both groups showed similar adaptation in terms of movement error and velocity. However, in terms of force learning, the old group learned the novel dynamics more slowly and to a lesser extent than the young group. The old group also showed larger increases in arm muscle coactivation, which may help to explain the discrepancy between error and force learning rates; i.e., the old adults may have compensated for impaired force learning by using a more coactivated strategy to increase limb stiffness.



    			Listed In: Biomechanical Engineering, Biomechanics, Neuroscience
    		

    	

        
      









  

    			
Mechanical Behavior and Failure of Scaffold Free Tissue Engineered Cartilage

		    
        

      Submitted by Mostafa Motavalli
    

    
        	

    		
    		

    			    			    		

    		

    			
Articular cartilage covers the articulating bones within synovial joints. It provides a bearing surface with low friction and wear properties. Although cartilage can function effectively for decades, it has limited ability to repair itself. Damage to articular cartilage is linked to degenerative diseases like Osteoarthritis (OA), which is a leading cause of disability in the United States. While severe cases of OA may be treated with a total joint replacement, tissue engineered (TE) cartilage is now emerging as a potential alternative treatment. TE constructs must function in the highly loaded environment of diarthrodial joints for many years. We have been investigating the mechanical behavior of tissue-engineered cartilage under combined compression and shear. Previous studies showed failure of TE cartilage under combined cyclic shear and static compressive loads, while native cartilage remained intact. Subsequent investigations identified a cell rich (matrix deficient) region in the middle layer of TE cartilage, which is sandwiched between matrix rich outer layers with lower cellularity. The objectives of this study are to determine the mechanical behavior of TE articular cartilage throughout its depth under static compressive and shear deformation. Failure under shear deformation, and the relationship between failure and the previously identified matrix deficient and matrix rich regions are of particular interest.



    			Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering
    		

    	

        
      









  

    			
A POLYMER-BASED MICROFLUIDIC RESISTIVE SENSOR FOR DETECTING DISTRIBUTED LOADS 

		    
        

      Submitted by Wenting gu
    

    
        	

    		
    		

    			    			    		

    		

    			This poster presents a polymer-based microfluidic resistive sensor for detecting distributed loads. The sensor is comprised of a polymer rectangular microstructure with an embedded electrolyte-filled microchannel and an array of electrodes aligned along the microchannel length. Electrolyte solution in the microchannel serves as impedance transduction. Distributed loads acting on the polymer microstructure give rise to different deflection along the microstructure length, which is recorded as the resistance change in electrolyte solution. This sensor can detect distributed loads by monitoring the resistance change at each pair of electrodes. Owing to great simplicity of the device configuration, a standard polymer-based fabrication process is employed to fabricate this device. With custom-built electronic circuits and custom LabVIEW programs, fabricated devices filled with two different electrolytes, 0.1M NaCl electrolyte and 1-Ethyl-3-methylimidazolium dicyanamide electrolyte, are characterized, demonstrating the capability of detecting distributed static and dynamic loads with a single device.  

    			Listed In: Biomechanical Engineering
    		

    	

        
      









  

    			
Upper Extremity Biomechanical Model for Evaluation of Pediatric Joint Demands during Wheelchair Mobility

		    
        

      Submitted by Alyssa Paul
    

    
        	

    		
    		

    			    			    		

    		

    			
Current methods for evaluating upper extremity (UE) dynamics during pediatric wheelchair use are limited. We propose a new model to characterize UE joint kinematics and kinetics during pediatric wheelchair mobility. The bilateral model is comprised of the thorax, clavicle, scapula, upper arm, forearm, and hand segments. The modeled joints include: sternoclavicular, acromioclavicular, glenohumeral, elbow and wrist. The model is complete and is currently undergoing pilot studies for clinical application. Results may provide considerable quantitative insight into pediatric UE joint dynamics to improve wheelchair prescription, training and long term care of children with orthopaedic disabilities.



    			Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research
    		

    	

        
      









  

    			
OPTIMAL CONTROL AND FORWARD DYNAMICS OF PERIODIC FOREARM  MOTIONS USING FOURIER SERIES FOR MUSCLE EXCITATIONS

		    
        

      Submitted by Mohammad Sharif Shourijeh
    

    
        	

    		
    		

    			    			    		

    		

    			Dynamic musculoskeletal models are well-established tools to simulate, predict, and analyze human movements. Furthermore, although forward dynamics studies are slow and time consuming due to forward integrations, they are preferred over inverse dynamics models due to being predictive. A forward dynamics musculoskeletal simulation often involves solving an optimal control problem (OCP).  In this study, a model for the forward dynamic simulation of a forearm performing a periodic motion is presented. Using a new parametrization function based on Fourier series for the muscle excitation functions (u), the OCP is converted to an optimization problem, which is solved for the optimal motion and muscle excitations. 


    			Listed In: Biomechanical Engineering
    		

    	

        
      









  

    			
A Phenomenological Human Energy Expenditure Model in Joint Space

		    
        

      Submitted by Dustyn Roberts
    

    
        	

    		
    		

    			    			    		

    		

    			
Humans act as transducers that transform chemical energy from food, water, and air into mechanical work and the thermal energy of heat loss. Although this energy expenditure can be experimentally measured, methods of predicting energy expenditure have not been broadly studied. This work introduces a new formulation of metabolic energy consumption based on muscle physiology and the equations of motion for the human body. Kinematic and kinetic data from a gait experiment and an over-arm throwing simulation are used to illustrate and validate this new model. The results extend the capabilities of dynamic human modeling to include metabolic energy prediction in general tasks. This novel formulation is useful for the investigation of human performance with applications in physical therapy, rehabilitation, and sports.



    			Listed In: Biomechanical Engineering, Biomechanics, Gait, Mechanical Engineering, Sports Science
    		

    	

        
      









  

    			
Between Landing Kinetic and Kinematic Differences in  a Drop Vertical Jump

		    
        

      Submitted by Nathaniel Bates
    

    
        	

    		
    		

    			    			    		

    		

    			
ACL ruptures are catastrophic injuries that are debilitating to athletes. Specific kinematic and kinetic variables observed in landing and cutting are associated with increased ACL injury risk. The drop vertical jump (DVJ) test has been established as an ideal task to evaluate neuromuscular control and simulate motions and moments that place athletes at risk for ACL injuries. A DVJ involves an athlete landing from a 31 cm drop followed by a maximal vertical jump and subsequent landing. This study aimed to examine kinetic and kinematic differences between the first and second landing of a DVJ. 239 middle and high school athletes each performed 3 trials of a DVJ task for a 10 camera motion analysis system while landing on AMTI force platforms. Kinematic variables demonstrated a decrease in peak hip and knee flexion, hip adduction, and knee abduction angles from the first to second landing. Kinetic variables demonstrated smaller peak knee flexion, knee abduction, and hip flexion moments in the second landing. Overall, the second landing exhibited mechanics characteristic of a higher intensity athletic task or lower neuromuscular control. The second landing may serve as a better screening tool for sagittal plane risk factors, while the first landing may prove optimal for the assessment of frontal plane control and injury risk.



    			Listed In: Biomechanical Engineering, Biomechanics, Physical Therapy, Sports Science
    		

    	

        
      









  

    			
Directed Injection of Vertebroplastic Cement at the Site of a Lytic Metastatic Lesion Restores Strength with Minimum Injection Volume

		    
        

      Submitted by Ata Kiapour
    

    
        	

    		
    		

    			    			    		

    		

    			While Vertebroplasty (VP) has existed for years, most studies address osteoporotic fracture due to diffuse, low energy failure of the vertical trabeculae. Neoplastic vertebral disruption promotes focal lysis of vertical and horizontal trabeculae, often with pedicle involvement. VP used for metastases increases complication rates. Restoration of axial strength in metastatic disease is not well characterized.

32 specimens were harvested from 6 cadavers (T5-S1, age 74±14, BMD 0.7±0.2). Each consisted of one full vertebra and 2 adjacent hemi-vertebrae. Lytic lesions with peripedicular cortical disruption were created and filled with adipose tissue to simulate tumor bulk. Specimens were randomly distributed between 3 groups: lesion alone (control), standard VP, and directed peripedicular augmentation. Specimens then underwent unconstrained compression using a material-testing machine and an embedded bilateral cable system passing through the approximate center of rotation. Linear and angular body collapse, PMMA injection volume and vertebral body volume were measured. 
Height reduction was significantly higher in the anterior body (p=0.003). Mean height loss was least for the group with directed VP. Directed VP demonstrated the least increase in kyphosis. Average injected cement volume for the directed VP was 49% less than the standard VP (p<0.0005). Percent body fill was lower for directed than for standard VP. VP significantly increased normalized failure stress (p=0.04).
An optimum threshold cement injection volume may exist, at which vertebral body strength is improved with minimum cement volume. Fixation by directed VP can achieve similar augmentation to standard VP with an anterior fill, while requiring half the cement injection volume.


    			Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Orthopedic Research