Biomechanics

Improved Prosthetic Gait Following Amputee-Specific Physical Therapy.

Following amputation, an amputee must learn to walk again using a prosthesis. A goal of prosthetic rehabilitation is to reduce and eliminate asymmetries between the prosthetic leg and sound leg which may decrease the negative effects of long term force and work demands on the sound leg. An amputee-specific physical therapy program provides structured motor learning to aid in developing proper gait mechanics. However, physical therapy is not standard of care for all individuals receiving their first prosthesis due to limited evidence showing improved gait. Thus, the purpose of this study was to determine whether amputees receiving physical therapy have better gait mechanics than those that do not. It was hypothesized that those who underwent an amputee-specific physical therapy program would display a more symmetrical gait pattern. Transtibial amputees walked overground at self-selected pace while kinetic (600Hz) and kinematic (60Hz) data were collected. The therapy group had previously received 2-3 therapy sessions per week for 3 months. Asymmetries were determined through dependent t-tests (α=0.05) comparing sound leg and prosthetic leg kinetic variables. Of the 23 kinetic variables tested, 17 variables showed significant difference between the sound leg and prosthetic leg for the group that did not receive the amputee-specific physical therapy. For the group that had previously received the therapy, only 4 variables showed differences between the sound and prosthetic leg. Thus, we showed that individuals partaking in amputee-specific physical therapy have a more symmetrical gait which results on less force and energy demands on the sound leg.
Listed In: Biomechanics, Gait, Physical Therapy


Gait biomechanics are not improved following supervised treadmill exercise in patients with peripheral arterial disease.

Introduction Pain, tingling, or numbness in the calves, thighs, and/or buttocks brought on by physical activity is called intermittent claudication (IC). IC is the primary symptom of peripheral arterial disease (PAD) that occurs because blockages in the lower extremity arteries hinder blood flow to the legs. Current conservative treatment for patients with PAD consists of supervised treadmill walking exercise (STW). After STW, patients with PAD exhibit improvement in maximum walking distances(1), but little is known regarding gait biomechanics. This study was conducted to determine the effectiveness of the current conservative treatment on gait biomechanics and lower extremity strength in patients with PAD. Methods Fifteen patients (total of 26 claudicating limbs; age: 66±1.9 years, height: 1.75±2.24 m, weight: 89.23± 5.01 kg), diagnosed with PAD were recruited from the Omaha Veterans’ Affairs Medical Center. Patients visited the lab prior to and after completing a prescribed 12-week, 3 times/week STW. Five over-ground walking trials for each leg were performed while kinematics (60 Hz; Motion Analysis Corp., USA) and kinetics (600 Hz; Kistler Instruments, USA) were recorded pre and post 12-weeks STW. Absolute claudication distance (max walk distance) was determined through a progressive, graded treadmill protocol (2 miles/hour, 0% grade with 2% increase every 2 minutes) until maximal claudication pain. Inverse dynamics was used to calculate peak joint torques and powers for the ankle, knee, and hip (Visual 3D, C-Motion, Inc., USA). Peak plantar flexor strength was assessed using an isokinetic dynamometer (Biodex Medical Systems, USA). Differences pre to post STW were determined using paired t-tests (α=0.05). Results/Conclusion In agreement with the previous literature, absolute claudication distance significantly increased post STW. No significant differences between baseline and post STW were detected for joint torques and powers, or lower extremity strength. Supervised treadmill walking appears to address a cardiovascular mechanism in PAD. STW may only be helping to improve stamina. The lack of any functional training may be reinforcing poor mechanics, which will continue to hinder patient function with a poor chance for long term benefits to be realized. Future investigation should include functional exercises in patients with PAD.
Listed In: Biomechanics


Stud Type Affects Knee Biomechanics on Infilled Synthetic Turf during a 180° Cut, but not during a Single-Leg Land-Cut Task

Higher ACL injury frequencies have been reported on synthetic turfs compared to natural turfs. However, assessments of cleat stud type on lower extremity biomechanics worn on these surfaces are limited. The purpose of this study was to examine the knee biomechanics of a non-studded running shoe (RS), a football shoe with natural turf studs (NTS), and with synthetic turf studs (STS) during single-leg land-cut and 180°-cut tasks on synthetic turf. Fourteen recreational football players performed five trials of 180°-cut and land-cut tasks in the three shoe conditions on an infilled synthetic turf. Knee biomechanics were analyzed using a 2x3 (task x shoe) repeated measures ANOVA followed by post-hoc paired samples t-tests (p<0.05). For the 180° cut, 1st peak internal knee adduction moments were increased in RS and STS compared to NTS (Table) and in 1st peak knee extensor moments in RS compared NTS and STS. The peak negative knee extensor power was increased in RS compared to NTS and STS. The land-cut had significantly greater peak extensor moments, sagittal plane powers, and abduction angles, and significantly lower adduction moments compared to the 180°-cut. As expected, the land-cut movement involved increased power absorption, power generation, and extensor moment compared to the 180°-cut. However, shoe effects lie only in the 180°-cut. Decreased medial ground reaction force1, knee adduction and extensor moments in NTS suggest the knee may be in a safer environment using these studs during cutting maneuvers. Reduced knee adduction moments in NTS could have implications in non-contact ACL injury.
Listed In: Biomechanics, Gait, Sports Science


Positive Ankle Work is Decreased in Peripheral Arterial Disease Before the Onset of Claudication Pain

Peripheral arterial disease (PAD) is a vascular disease characterized by atherosclerotic blockages restricting blood flow to the lower extremities causing pain and discomfort with physical activity. Several studies have previously found decrements in ambulation associated with PAD, such as decreased joint moments and powers before and after the onset of claudication pain [1]. With decreases in moments and powers, the joint work may also be decremented as well. Thus, the purpose of this study was to investigate the positive and negative work at the ankle, knee and hip of PAD patients in a pain-free condition and compare them to gait-velocity matched controls. Five patients with PAD and five healthy older controls were consented for participation. Subjects walked along a 10-meter walkway at their own self-selected speed while kinematics and kinetics were recorded. Each subject rested one minute between trials to mitigate fatigue and prevent ischemic pain. The positive and negative joint work for the PAD patients’ affected limb and the right limb of each control were analyzed and compared through independent t-tests (α=0.05). Five PAD patients (66.6 + 6.2 years; 178.2 + 9.3 cm; 102.6 + 18.5 kg; 1.16 + 0.07 m/s) and five controls (69 + 4.6 years; 174.5 + 1.6 cm; 79.4 + 8.14 kg; 1.30 + 0.09 m/s) were used for analysis. From this study it was found that patients with PAD exhibit a 26% reduction in positive ankle joint work during stance phase than their healthy counterparts (p=0.012).
Listed In: Biomechanics


Effects of Adiposity on Walking Muscle Function in Children: Implications for Bio-Feedback and Assistive Devices

Altered gait biomechanics associated with pediatric obesity may increase the risk of musculoskeletal injury/pathology during physical activity and/or diminish a child’s ability to engage in sufficient physical activity. The biomechanical mechanisms responsible for the altered gait in obese children are not well understood, particularly as they relate to increases in adipose tissue. The purpose of this study was to investigate the role of adiposity (i.e. body fat percentage, BF%) on lower extremity kinematics, muscle force requirements and their individual contributions to the acceleration of the center of mass (COM) during walking. We scaled a musculoskeletal model to the anthropometrics of each participant (n=14, 8-12 years old, BF%: 16-41%) and generated dynamic simulations of walking to predict muscle forces and their contributions to the acceleration of the COM. Muscle force output was normalized to muscle mass. BF% was correlated with average knee flexion angle during stance (r=−0.54) and pelvic obliquity range of motion (r=0.78), as well as with relative vasti (r=−0.60), gluteus medius (r=0.65) and soleus (r=0.59) force production. Contributions to COM acceleration from the vasti were negatively correlated to BF% (vertical: r=−0.75, posterior: r=−0.68, respectively), but there was no correlation between BF% and COM accelerations produced by the gluteus medius. The functional demands and relative force requirements of the hip abductors during walking in pediatric obesity may contribute to altered gait kinematics. Our results provide insight into the muscle force requirements during walking in pediatric obesity that may be used to improve the quality/quantity of locomotor activity in this population.
Listed In: Biomechanical Engineering, Biomechanics, Gait


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


BEHAVIOR OF VASTUS LATERALIS FASCICLE LENGTH UNDER DIFFERENT FORCE LEVEL OF ECCENTRIC CONTRACTION

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