Evaluation of Haversian Bone Fracture Healing in Simulated Microgravity

The inherent reduction in mechanical loading associated with microgravity has been shown to result in dramatic decreases in the bone mineral density (BMD) and mechanical strength of skeletal tissue. Importantly, there is a concomitant increase in fracture risk during long-duration spaceflight missions. Thus, the objective of this study was to investigate the effects of microgravity loading on long-bone fracture healing in a previously-developed Haversian bone model of simulated microgravity over a 4-week period. For in vivo mechanical evaluation, strains of an implanted orthopaedic fixation plate were quantified for known hindlimb ground reaction forces with a six degree-of-freedom load cell (AMTI, Watertown, MA). In vivo strain measurements demonstrated significantly higher orthopaedic plate strains in the Microgravity Group as compared to the Control Group following the 28-day healing period due to inhibited healing in the microgravity environment. DEXA BMD in the treated metatarsus of the Microgravity Group decreased 17.6% at the time of the ostectomy surgery and decreased an additional 5.4% during the 28-day healing period. Four-point bending stiffness of the Microgravity Group was 4.4 times lower than that of the Control Group (p<0.01), while µCT and histomorphometry demonstrated reduced periosteal callus area, mineralizing surface, mineral apposition rate (p<0.001), bone formation rate, and periosteal/endosteal osteoblast numbers as well as increased periosteal osteoclast number. These data provide strong evidence that the mechanical loading environment dramatically affects the fracture healing cascade and resultant mineralized tissue strength, and that the microgravity loading environment has negative effects on fracture healing in Haversian systems.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Orthopedic Research

Are static and dynamic squatting activities comparable?

Background: Numerous studies have described 3D kinematics, 3D kinetics and electromyography (EMG) of the lower limb during quasi-static or dynamic squatting activities. However there is only little information on the comparison of these two squatting conditions. Only one study compared these activities in terms of 3D kinematics, but no information was available on 3D kinetics and EMG. The purpose of this study was to compare simultaneous recordings of 3D kinematics, 3D kinetics and EMG of the lower limb during quasi-static and fast dynamic squats. Methods: Ten subjects were recruited. 3D knee kinematics was recorded with a motion capture system, 3D kinetics was recorded with a force plate, and EMG of 8 muscles was recorded with surface electrodes. Each subject performed a quasi-static squat and several fast dynamic squats from 0° to 70° of knee flexion. Findings: Mean differences between quasi-static and dynamic squats were 1.6° for rotations, 1.8 mm for translations, 38 N ground reaction forces (2.1 % of subjects’ body weight), 6 Nm for torques, 13.0 mm for center of pressure, and 7 µV for EMG (6.3% of the maximum dynamic electromyographic activities ). Some significant differences (P < 0.05) were found in anterior-posterior translation, vertical forces and EMG. Interpretation: All differences found between quasi-static and fast dynamic squats can be considered small. 69.5% of the compared data were equivalent. In conclusion, this study show for the first time that quasi-static and dynamic squatting activities are comparable in terms of 3D kinematics, 3D kinetics and EMG.

Listed In: Biomechanical Engineering, Biomechanics, Gait, Orthopedic Research, Posturography

Suprathreshold Galvanic Vestibular Stimulation as an analog of vestibular dysfunction

In the past we have shown that exposure to increasing amplitudes of Galvanic vestibular stimulation (GVS) induces a corresponding increasing deficit in postural control, cognition and autonomic function. Previous studies have suggested that suprathreshold GVS induces a similar pattern of postural instability as the one observed on bilateral vestibular loss. The aim of the present study was to determine whether different current intensities would affect somatosensory, visual, and vestibular sensory system similarly to patient affected by vestibular deficits. We assessed postural control in unilateral (right and left) and bilateral vestibular loss patients, an aged matched healthy control group, and during pseudorandom binaural bipolar GVS in healthy subjects at one of three current amplitudes (1 mA, 3.5 mA, 5 mA). Balance was assessed with sensory organization test (SOT) that quantifies the effectiveness of vestibular, visual and somatosensory input to postural control. Results showed that GVS significantly affects vestibular control of posture compared to baseline at all current amplitudes, whereas somatosensory and visual performance was unaffected. Vestibular patients showed a significant decrease in vestibular and visual response compared to control. Suprathreshold GVS 5 mA showed a similar large effect size to unilateral and bilateral vestibular loss patients relative to their aged matched control. NASA NCC 9-58 and NNX09AL14G

Listed In: Biomechanical Engineering, Neuroscience, Posturography

Sensorimotor adaptation to Galvanic Vestibular Stimulation: a longitudinal study

Our previous study showed that exposure to Galvanic Vestibular Stimulation (GVS) induces temporary postural deficits similar to the ones experienced by astronauts after microgravity exposure. Preliminary evidence suggests that repeated exposures to GVS might induce adaptation of sway response. We studied whether repeated exposure to pseudorandom GVS over a 3 month period facilitates the adaptation response. Twenty healthy subjects were randomly assigned into 2 groups: suprathreshold (5mA) GVS, and subthreshold (1mA). The test battery included: Romberg, sensory organization test (posturography), dynamic visual acuity, and torsional eye movement. Each test was performed with no GVS, and then with 10 min of GVS per session for 12 consecutive weeks. Sensorimotor adaptation was also measured during two follow up sessions at weeks 18 and 36. Results showed that subthreshold GVS did not affect vestibular scores. Suprathreshold GVS significantly decreased vestibular scores during the first few weeks, with postural performance returning to baseline around the 6th week of exposure. This improvement was maintained during the follow up sessions. Our results suggest that 60 min of subthreshold GVS are sufficient to elicit adaptation to the stimulus. No significant changes were shown in low-level vestibulo-ocular reflexes during torsional eye movement, or vestibulo-spinal reflexes during Romberg; confirming that adaptation only occurs at the level of the CNS. NASA NCC 9-58; NNX09AL14G
Listed In: Biomechanical Engineering, Neuroscience, Posturography

Impacts of Stifle Joint Remodeling on Vertical Ground Reaction Forces Following MCL Transection and Medial Meniscectomy

Functional demands placed on the human knee’s anterior cruciate ligament (ACL) vary with activity but remain impossible to measure directly in-vivo. Our lab is characterizing these demands in the sheep model by recording in vivo knee kinematics and ACL transducer voltages during activities of daily living (ADLs), reproducing these motions using the instrumented limb, and measuring the 3D forces in the ligament. However, up to 13% of patients sustaining ACL injuries will also sustain dual medial meniscus (MM) injuries and up to 10% will sustain dual medial collateral ligament (MCL) injuries. These structures are frequently left unrepaired, which may alter the ACL’s functional demands, resulting in inadequate ACL reconstruction outcomes for patients with dual injuries. Although these structures have been shown to alter ACL loading in cadaveric studies, the extent to which they impact ACL functionality during in vivo ADLs remains unknown. Moreover, changes in ACL functionality over time due to joint healing and remodeling have yet to be investigated. In this study, we aimed to track stifle joint remodeling in response to surgically imposed MCL transections and medial meniscectomies through monitoring vertical ground reaction forces (VGRFs) for three ADLs over 12 weeks. Results of this study may then be used in conjunction with future robotic studies as a tool to estimate in vivo load requirements for ACL reconstructions in patients with dual injuries.

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

Accelerometry for outdoor effort quantification

Assessing the lower limb properties in-situ is of a major interest for analyzing the athletic performance. From a physical point of view, the lower limb could be modeled as single linear spring which supports the whole body mass. The main mechanical parameter studied when using this spring-mass-model is the leg-spring stiffness (k). In laboratory conditions, the movements are assessed using a force plate (Meth1) which measures the ground reaction force (GRF), and a motion capture system which could estimate the displacement of the centre of mass (CoM). In this way, k is calculated as shown in equation (2).More recent methods allow to calculate k in field conditions by using either foot switches (Meth2) or accelerometry-based instruments (Meth3) which are both wireless devices. The associated calculated methods assume that force-time signal is a sine wave, described by the equation (3) with equation (4) (CT: contact time; FT: flight time). In these cases, the kinematic measurement (CoM) could be calculated either by a mathematical approach (Eq.(5)) (meth2), or by double integrating the acceleration (meth3) in order to calculate k.Thanks to their transportability, the methods 2 and 3 offer not only the possibility to assess the lower limb movements, but also, to objectively follow up the athletic abilities (performance, reactivity, force and power, stiffness) in-situ.

Listed In: Biomechanical Engineering, Biomechanics, Sports Science


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