Novel Synthetic Biolubricant Reduces Friction in Previously-Worn Cartilage Evaluated by Long-Duration Torsional Friction Test

During osteoarthritis (OA), the lubricity of synovial fluid (SF) decreases. Therefore, we synthesized a novel, 2MDa polymer biolubricant (“2M TEG”) designed to augment the lubricating properties of SF in OA. This study’s aims were 1) to compare the abilities of 2M TEG and bovine synovial fluid (BSF) to reduce the coefficient of friction (COF) for previously “worn” cartilage specimens during a long-duration, torsional, wear test, and 2) using the same regimen, examine the “reversibility” of 2M TEG’s lubricity relative to BSF. For both aims, each wear test consisted of subjecting mated, bovine osteochondral plug pairs to 10,080 rotations. To accomplish Aim 1, plug pairs were subjected to three sequential wear regimens (Wear 1-3). Wear 1&2 were used to progressively “wear” the cartilage, and Wear 3 was used to test the efficacy of either BSF (n=4) or 2M TEG (n=4) on “worn” cartilage. For Aim 2, three pairs were subjected to four sequential wear regimens, where the lubricants were BSF, BSF, 2M TEG, and BSF, respectively. The relative percent reduction in COF between Wear 3 and Wear 2 in Aim 1 was greatest for 2M TEG, followed by BSF. For Aim 2, the mean percent reduction in COF for Wear 3 relative to Wear 2 was almost exactly the same as the mean increase in COF for Wear 4 relative to Wear 3. By reducing the COF for worn cartilage in OA joints, synthetic biolubricants such as 2M TEG could help minimize further cartilage wear and ameliorate the progression of OA.
Listed In: Biomechanical Engineering, Biomechanics, Biotribology, Orthopedic Research

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

Biochemical markers of type II collagen degradation and synthesis are not associated with biomechanical variables in patients following ACL reconstruction.

This study investigated the association of serum C-propeptide (sCPII), urinary CTX-II (uCTX-II), and uCTX-II:sCPII with peak vertical ground reaction force (PVGRF) and quadriceps strength during jump-landing in patients with ACL reconstruction (ACLR). METHODS: twenty two patients with ACLR (Male=14, age=19.6 ± 4 yr) were tested 20 weeks after the surgery. Blood and urine samples were collected. sCPII and uCTX-II, biomarkers of articular degradation and synthesis respectively, were analyze using commercial ELISAs. Subjects performed 3 trials of a forward drop land and a drop vertical jump. Subjects started on a 20 cm step and landed on a force platform (AMTI). PVGRF was analyzed on the surgical side. Quadriceps strength (PKET) was assessed with an isokinetic dynamometer (60°/s). PVGRF and PKET were normalized to body weight (BW). Pearson’s correlation, with and without adjustment for age, was used to analyze associations among variables. RESULTS: Mean (± SD) log concentrations were 2.88 ± 0.19 and 3.32 ± 0.49 ng/mmol for sCPII and uCTX-II respectively; and for uCTXII:CPII was 1.16 ± 0.18. PVGRF was 3.2 BW ± 0.3 and 1.4 BW ± 0.3 for the forward drop land and drop vertical jump tasks, respectively; PKET was 0.92 BW ± 0.2. There were no significant correlations among variables (p≥0.2), except for a trend towards a positive correlation between PKET and uCTXII:sCPII (r = 406, p = .076). CONCLUSSIONS: Biomarkers of type II collagen metabolism were not associated with jump-landing forces. However, higher quadriceps strength may be associated with a shift in articular cartilage metabolism towards degradation.

Listed In: Biomechanics, Orthopedic Research, Physical Therapy, Sports Science


Eccentric training may affect the longitudinal adaptation of the muscle. Usually the muscle fiber lengthening during eccentric training is measured by the joint kinematics. Due to tendon compliance, this method offers insufficient information about the muscle fiber behavior. The present study investigated the muscle fiber behavior of the Vastus Lateralis muscle (VL) during eccentric knee contractions in humans by measuring the changes of fascicle length in vivo with ultrasonography, at force levels of 65% and 95% of the maximum voluntary isometric contraction force (MVC). Seven young adults were tested by a Biodex. They performed eccentric knee contractions with one leg at 65% and 95% of their MVC (knee angle 25°-100°, angular velocity 90°/s). Potential joint axis deviations were recorded using a Vicon camera system. Exerted knee moments were captured synchronously with the Vicon system at 1000Hz. Fascicle length of the VL muscle visualized by a 10cm Ultrasound prob. The means and standard deviations of fascicle elongation at 65% and 95% of the MVC were 42.71±8.54mm and 39.11±10.64mm respectively, with no statistically significant difference between both conditions. All subjects showed a plateau or slide decrease in fascicle length at the beginning of the movement. This slight decrease in fascicle length, which occurs despite a lengthening of the VL muscle-tendon unite, can be explained by the tendon compliance. The similar fascicle elongation between the two conditions (65% vs. 95% MVC) reveals that the amplitude of the force level during eccentric knee extension contractions does not affect the lengthening of the fascicle.

Listed In: Biomechanics, Other

The Influence of Trunk Posture on Hip and Knee Moments during Over-ground Running

A high incidence of lower extremity injuries has been reported in runners, with half of the injuries occurring at the knee joint. Sagittal plane trunk posture was shown to influence hip and knee kinetics during landing. This suggests trunk posture may be a risk factor of running injuries. The purpose of this study was aimed to examine the influence of sagittal plane trunk posture on hip and knee kinetics during running. Forty runners were recruited. Three-dimensional kinematics (250Hz, Qualisys) and ground reaction force data (1500Hz, AMTI) were collected while subjects ran with a self-selected trunk posture (speed: 3.4m/s). Mean trunk flexion angle and peak hip and knee extensor moments during the stance phase were calculated. Subjects were dichotomized into High-Flex and Low-Flex groups based on trunk flexion angles. On average, the two groups demonstrate 7.4°difference in trunk flexion. Independent t-tests showed that the Low-Flex group demonstrated significantly higher knee extensor moments and lower hip extensor moments compared to the High-Flex group. Pearson correlations showed that trunk flexion angle was positively correlated with peak hip extensor moment (r=0.44) and inversely correlated with peak knee extensor moment (r=-0.51). The results suggested a small difference in trunk flexion angle has significant influences on hip and knee kinetics. Individuals who run with a more upright trunk posture may be predisposed to a higher risk of patellar tendinopathy and patellofemoral pain. Incorporating a forward lean trunk may be utilized as an intervention strategy to reduce knee loading and risk of knee injuries in runners.

Listed In: Biomechanics, Physical Therapy, Sports Science

Residual Force Enhancement in Context of Everyday Human Movement

When an active muscle is stretched, the resulting post-eccentric steady-state force is known to be greater than the isometric force at the corresponding muscle length. The aim of our research was to clarify if residual force enhancement (RFE) is relevant for voluntary human muscle action in everyday like scenarios. Therefore 13 healthy subjects participated in our study and had to perform bilateral leg extensions using a motor-driven leg press dynamometer, measuring external reaction forces (Fext) as well as activity of 9 lower extremity muscles. In addition, ankle (Ma) and knee (Mk) joint torque were calculated using inverse dynamics. Subjects performed isometric and isometric-eccentric-isometric contractions (20° stretch, ω=60°/s) at 30% of maximum voluntary activation. Visual feedback of VL muscle activation was given to control submaximal muscle action. We did not find differences in VL activation level between contraction conditions and time points. Mean VL activity ranged between 29.1 ± 2.2% and 29.8±2.5% MVA. We found significantly enhanced Fext (p < 0.002) as well as joint torques in knee (p < 0.002) and ankle joint (p < 0.033) for all instances in time. In summary RFE seems to be relevant in everyday like human motion.

Listed In: Biomechanics, Sports Science

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

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

Effects of cortical stimulation on sensorimotor hand functions in healthy elderly individuals

Transcranial anodal stimulation (tDCS) improves manual dexterity in healthy old adults. The underlying changes in finger force behavior for this improved dexterity have not been reported. Here, we investigated the effects of tDCS (20-min) over primary motor cortex (M1) combined with repeated practice on the Grooved pegboard test (tDCS+MP) on the fingertip forces applied to an object during grasp and manipulation. Eight right-handed able-bodied individuals (60-85 years) participated in a sham-controlled, single-blinded study. Each participant received anodal and sham intervention in two sessions at least 5-day apart. Before and after intervention, they performed a ‘key-slot’ task that required inserting a slot on an object onto a stationary bar, an isometric force production task using a pinch grip, and the Grooved pegboard test. Anodal relative to sham tDCS+MP allowed participants to better retain the improved performance on the pegboard test. For the isometric task, anodal tDCS+MP significantly increased the variability of force compared to sham tDCS+MP. More importantly, the improved retention of performance post-anodal tDCS correlated with the reduction in force angle variability on the key-slot task, but not with the change in force variability on the isometric task. Our findings suggest that anodal tDCS+MP facilitated retention of learning on a skillful manual task in healthy old adults, consistent with the role of M1 in retention of learning versus skill acquisition. Furthermore, improved force steadiness is one of the potential mechanisms through which short-term anodal tDCS during motor training yields improved performance on a functional task.
Listed In: Biomechanics, Neuroscience