Quantifying stair gait stability and plantar pressure in an aging community, with modifications to insoles and lighting

Introduction: Stair gait is an activity performed daily. Inherently falls during stair gait continue to be a concern especially for older adults 65 years +. Recently falls have become the most common cause of injury-related deaths in individuals over the age of 75 y.o. Stair descent falls account for 75% of stair falls and also present a greater injury severity. Poor shoes or insoles and lighting condition can contribute to an increased risk of falls during stair locomotion. Stability can be measured using the COM-BOS ‘stability margin’ relationship. Center of pressure (COP), another stability measure,can be calculated from a multi-axis force-plate system. As well, plantar pressure is an important indicator of gait pattern efficiency. Aim: To identify aspects of stair gait that increase the risk of falls. By measuring the COM-BOS ‘stability margin’, the COP and plantar pressure patterns of individuals during stair gait, while modifying insoles and lighting. Methods: Young and older adults will ascend and descend a 4 level staircase, with two imbedded AMTI-force platforms in varying lighting condition (low, normal). Participants will be fitted with standardized footwear with Medi-logic insoles placed under varying hardnesses of insoles. An Optotrak motion capture system will record 12 IRED markers placed on the individual to determine the COM trajectory and BOS of location. Hypothesis: Partipants should demonstrate a greater lateral displacement in the single support phase during dim lighting as opposed to normal lighting. The stability of older adults will be compromised with alteration to the insoles (soft and hard).

Listed In: Biomechanics, Gait, Other

Influence of Experimental Knee Pain on Bilateral Loading Patterns during Walking in Healthy Individuals

Purpose: Knee pain is a chief symptom of knee pathology. Both acute and chronic knee pain result in altered joint loads during walking, which potentially result in mechanical and biological changes in knee articular cartilage. Due to confounding factors in clinical knee pain (effusion, muscle weakness, inflammation, structural changes), it is difficult to examine the independent effect of knee pain on walking mechanics. The purpose of this study is to examine whether unilateral experimentally induced knee pain influences bilateral loading patterns during walking in healthy individuals. Methods: This study was a controlled laboratory, cross-over trial. Each of 30 able-bodied subjects (M = 20, F = 10; 23 ± 2.4 yrs, 71 ± 12.7 kg, 178 ± 8.2 cm) completed three experimental sessions: pain (5.0% NaCl infusion), sham (0.9% NaCl infusion), and control (no infusion) in a counterbalanced order, 2 days apart (a washout period). For the experimental sessions, hypertonic (5% NaCl) or isotonic (0.9% NaCl) saline was continuously infused into the right (involved limb) infrapatellar fat pad using a portable infusion pump, which produced a continuous saline flow of 0.154mL/min (total 2.16 mL) for 14 min for the pain or sham session, respectively. No infusion was administered to the control session. Subjects and investigators were blinded regarding the saline solution which was being infused. During each of three experimental sessions, subjects performed 30-sec gait trials at a self-selected speed at two time points (pre- and post-infusion). Ground reaction force (GRF) data were collected using an AMTI instrumented force-sensing tandem treadmill (1200 Hz). The first 4 successful gait cycles in each limb were used for data analysis. A functional data analysis approach (α = .05) was used to detect time (pre- and post-infusion) x limb (involved vs. uninvolved) interactions for the vertical, anterior-posterior, and medial-lateral GRF. Results: Significant time x limb interactions were observed during the pain session (hypertonic saline; 5.0% NaCl; p < .05). Experimental knee pain resulted in up to (i) 0.05 N/kg less vertical GRF and 0.02 N/kg more vertical GRF during various stance phases, (ii) 0.01 N/kg less breaking GRF during loading response, and (iii) 0.007 N/kg less lateral GRF and 0.007 N/kg more lateral GRF during various stance phases in the involved limb. Conclusions: Relative to the pre-infusion condition, subjects during the knee pain condition tended to walk with less vertical, posterior and lateral GRF in the involved limb (painful limb) across various portions of stance, which simultaneously increased loads in the uninvolved limb (non-painful limb). Our data suggest that compensatory loading patterns occur simultaneously for the involved and uninvolved limbs. This unloading pattern in the involved limb may be due to perception of knee pain, which can make subjects feel fear for damaging or provoking pain more during walking. Moreover, voluntary and/or involuntary quadriceps inhibition (e.g., neuromuscular activation and strength) due to experimentally induced knee pain may play a role in reducing the loads in the involved limb because the quadriceps support the center of body mass eccentrically from initial loading response to midstance to prevent collapse of the lower limbs. These asymmetrical loading patterns due to knee pain and associated with neural inhibition may be a risk factor for knee joint disease progression via changes in mechanical components.
Listed In: Biomechanics, Gait

Bilateral assessment of cartilage with UTE-T2* quantitative MRI and associations with knee center of rotation following anterior cruciate ligament reconstruction

Purpose: Anterior cruciate ligament (ACL) tear greatly increases the risk of knee osteoarthritis (OA), even when patients undergo ACL reconstruction surgery (ACLR). Changes to walking kinematics following ACLR have been suggested to play a role in this degenerative path to post-traumatic OA by shifting the location of repetitive joint contact loads that occur during walking to regions of cartilage not conditioned for altered loads. Recent work has shown that changes to the average knee center of rotation during walking (KCOR) between 2 and 4 years after ACLR are associated with long term changes in patient reported outcomes at 8 years. Changes to KCOR result in changes to contact patterns between the femur and the tibial plateau. However, it is unknown if changes to this kinematic measure are reflected by changes to cartilage as early as 2 years after surgery. Ultrashort TE-enhanced T2* (UTE-T2*) mapping has been shown to be sensitive to subsurface changes occurring in deep articular cartilage early after ACL injury and over 2 years after ACLR that were not detectable by standard morphological MRI. Thus, the purpose of this study was to test the hypothesis that side to side differences in KCOR correlate with side to side differences in UTE-T2* quantitative MRI (qMRI) in the central weight bearing regions of the medial and lateral tibial plateaus at 2 years following ACLR. Methods: Thirty-five human participants (18F, Age: 33.8±10.5 yrs, BMI: 24.1±3.3) with a history of unilateral ACL reconstruction (2.19±0.22 yrs post-surgery) and no other history of serious lower limb injury received bilateral examinations on a 3T MRI scanner. UTE-T2* maps were calculated via mono-exponential fitting on a series of T2*-weighted MR images acquired at eight TEs (32μs -16 ms, non-uniform echo spacing) using a radial out 3D cones acquisition. All subjects completed bilateral gait analysis. Medial-lateral (ML) and anterior-posterior (AP) coordinates of average KCOR during stance of walking were calculated for both knees. Side to side differences in KCOR were tested for correlations with side to side differences in mean full thickness UTE-T2* quantitative values in the central weight bearing regions of the medial and lateral tibial plateau using Pearson correlation coefficients. Results: There was a distribution in UTE-T2* values, with some subjects having higher UTE-T2* and some lower in the ACLR knee relative to the contralateral knee. A significant correlation (R=0.407, p=0.015, Figure 1A) was observed between UTE-T2* and the ML KCOR with a more lateral KCOR corresponding to higher values of UTE-T2* for the medial tibia. Similarly, for the lateral tibia, a lower UTE-T2* was correlated with a more posterior KCOR (R=0.363, p=0.032, Figure 1B). Significant correlations were not observed for UTE-T2* in the lateral tibia with the ML position of KCOR or for UTE-T2* in the medial tibia with the AP position of KCOR. Conclusions: The results of this study support the hypothesis that side to side differences in mean full thickness UTE-T2* qMRI correlate with side to side differences in knee kinematics at 2 years after ACLR. The finding that a more lateral KCOR in the ACLR knee correlates with UTE T2* values in the medial tibia that were higher than the contralateral side suggests that this kinematic change, which has been previously shown to result in more relative motion between the femur and tibia in the medial compartment, could be affecting subsurface matrix integrity, inducing changes detectable by UTE-T2* mapping. Additionally, the finding that a more posterior KCOR in the ACLR knee correlated with UTE-T2* values in the lateral tibia that were lower than the contralateral knee further suggests that the UTE-T2* metric may reflect early changes in cartilage health. When interpreted within the context of prior work showing that a posterior shift in KCOR from 2 to 4 years post-surgery correlated with improved clinical outcomes at 8 years, the observed lower UTE-T2* with a more posterior KCOR, which is reflective of improved quadriceps recruitment, suggests positive cartilage matrix properties. In spite of the limitations of this cross-sectional and exploratory study, and the difficulty accounting for changes in the contralateral knee, these results support future studies of the relationship between UTE-T2* and KCOR to provide new insight into predicting the risk for OA after ACLR.
Listed In: Biomechanical Engineering, Biomechanics, Gait, Mechanical Engineering, Orthopedic Research, Sports Science

The effect of fatigue on knee mechanics in older adults: Does physical activity matter?

INTRODUCTION. Increased age is associated with changes in gait mechanics and decreased muscle function. As the knee extensors (KE) are prime movers in gait, altered KE function (strength, power, fatigability) could alter knee mechanics. This study aimed to determine whether a bout of exercise induces KE fatigue and changes in knee mechanics in two older groups with different physical activity levels: sedentary adults and runners. METHODS. Adults aged 55-70 who were either runners (≥15 miles/wk) or sedentary (≤3x30 min exercise bouts/wk) completed gait and strength testing before and after a 30 minute treadmill walk (30MTW). Joint kinematics were calculated using the point cluster technique. Externally-referenced moments were calculated using inverse dynamics. KE power and isometric strength were assessed via isokinetic dynamometry. Changes in KE power and knee mechanics were calculated; within-group changes were examined using paired t-tests (p<0.1). RESULTS. Sedentary adults displayed a drop in KE power at 6/8 contraction velocities vs. 2/8 in runners (poster Figure 2). Both groups showed an increase in knee flexion angle at heel strike and runners displayed decreased knee flexion moments post-30MTW (poster Figure 3). CONCLUSIONS. Vigorous physical activity may allow older adults to maintain fatigue resistance. Sensitivity of knee mechanics to KE fatigue remains unclear as few changes were seen even in a fatigued group. Global, rather than discrete, measures of joint function may provide more sensitive measures of the response of gait mechanics to muscle fatigue and may allow for a more complete picture of the impact of muscle function on gait.
Listed In: Biomechanics, Gait

Effects of Total Knee Replacement Material Pairing on Implant Kinematics and Stability

Physical testing of TKR systems to assess stability is an important aspect in screening candidate TKR designs which can be expensive and time consuming. Costs can be reduced by utilizing 3D printed plastic components. The objective is to compare the kinematics and intrinsic constraint of metal-on-plastic (M-P) and plastic-on-plastic (P-P) implants under physiologically relevant loading, with and without simulated ligament contributions, in order to elucidate the effects of material pairings. A cruciate retaining TKR implant was created by combining a 3D printed ABS plastic tibial component with the standard cobalt chrome femoral component, as well as a 3D printed ABS plastic replica femoral component. This results in both M-P and P-P articulations that were mounted to a VIVO 6-DOF joint motion simulator (AMTI, Watertown, MA), which was used for in vitro constraint testing using functional laxity tests. Anterior-posterior (AP) and internal-external (IE) constraint was measured based on resulting deviations from the normal path when superimposed AP and IE loads were applied. Ligaments were simulated as tension-only point-to-point springs using the soft tissue modelling capabilities of the VIVO. Different kinematics were observed between the M-P and P-P implants which could be the result of different initial implant positioning on the joint motion simulator or due to “stiction” of the P-P implant. The functional laxity of the implant system tested appears to be relatively insensitive to the material pairing and ligament presence. These relationships are complex and hard to predict, which underscores the importance of pre-clinical in vitro testing.
Listed In: Biomechanical Engineering, Biomechanics, Gait, Mechanical Engineering, Orthopedic Research


Accelerometers have become extremely popular in the measurement of stride frequency as well as other related stride variables with current sensors capable of recording both accelerations and electromyography. The purpose of this preliminary investigation was to assess the estimation of stride frequency during running using a single tri-axial accelerometer compared to a commonly used infrared device the OptojumpTM system. Five healthy participants wore a Delsys Trigno tri-axial accelerometer attached to the right anterior shin and participants repeatedly ran at a submaximal pace through a four metre section of OptojumpTM. Stride frequency was calculated as stride time divided by one. For the OptojumpTM, stride time was the sum of contact and flight times from two consecutive steps. For the accelerometer, stride time was calculated as the time between two consecutive foot contacts on the right side. Foot contact was identified by local maxima in the Y (medial-lateral) acceleration trace. Estimates of stride frequency were compared using paired samples t- tests, intraclass correlation coefficients (ICCs) and Bland and Altman 95% limits of agreement (LOA) with significance set at p < 0.05. The mean difference between estimates was 0.01 Hz (95% LOA: -0.05-0.07 Hz) with single and average ICCs for stride frequency of 0.93 and 0.96 respectively. The results suggest that an accelerometer attached to the shin can accurately estimate stride frequency in running. Discrepancies in stride frequencies can be partially explained by differences in device sampling rates i.e. 137.15 Hz versus 1,000 Hz
Listed In: Biomechanics, Gait, Sports Science

Locomotor Stability Control and Vestibular Function among Older Adults: Implications for Falls Prevention and Research

In the following project, we explored the relationships between age, vestibulopathy and stability control, in order to determine the age and vestibulopathy-related effects on stability control, and to establish if a relationship existed between static and dynamic stability task performance. The first study examined the response to repeated trip perturbations of healthy middle aged adults and vestibulopathy patients, the second examined feedforward adaptation of gait in young, middle aged and older adults to a sustained mechanical perturbation and the third examined the relationship between standing balance and recovery following a tripping perturbation in vestibulopathy patients. The results showed that vestibulopathy is related to a diminished ability to control and recover gait stability after an unexpected perturbation, and to a deficient reactive adaptation potential. With ageing, the ability to recalibrate locomotor commands to control stability is preserved, although this recalibration may be slower in old age compared to middle and young age. Given that a decline in vestibular function is seen with increasing age, we suggest that assessment of vestibular function may be necessary when investigating locomotor stability and falls risk in both research and clinical settings. Finally, despite static balance tasks and parameters being commonly used in clinical settings, we did not find a consistent relationship between static and dynamic stability task performance, indicating the importance of dynamic stability tests when assessing falls risk in clinical settings.
Listed In: Biomechanics, Gait, Posturography

Effects of an 8-week cadence gait training program on knee loading in individuals following ACL reconstruction

While normalization of gait is a primary goal of early rehabilitation, between limb asymmetries in knee extensor moment can persist 6-24 months later and previous literature assessing gait interventions is limited. The purpose of this study was to assess the influence of subject-specific cadence gait training program on knee loading mechanics following ACLr. Nine individuals completed an 8-week cadence training program (20min, 3x/week; Table1) and nine sex- and surgery-matched individuals served as controls. All eighteen participants received standard physical therapy and were tested at 1 and 3 months post-op. Kinematic and kinetic data were collected during walking at a self-selected speed. Repeated measures ANOVAs were used for comparisons; significance α≤0.05. Main effects of limb and time were observed: knee ROM (kROM;p<0.001;p=0.044;Fig.1) and knee extensor moment (kEXT;p=0.003;p=0.002) in the cadence and control groups, respectively. No main effects of group for kROM (p=0.136) or kEXT (p=0.229) were found. A trend toward a significant group x time x limb interaction was observed in kEXT (p=0.092), but not kROM (p=0.412). Post-hoc analyses of kEXT (Fig.2) revealed a significant time x limb interaction for the cadence group (p=0.053) but not the control group (p=0.884). In the cadence group, the time x limb interaction was driven by a 131% increase in kEXT in the surgical limb versus a 42% increase in the non-surgical limb between T1 and T2. Consistent with previous findings, these pilot data show promising results as the cadence intervention resulted in improvements in sagittal plane knee loading compared to controls.

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

Spatiotemporal gait parameters are affected by footwear stiffness in toddler-aged children.

Footwear plays a significant role in, and can influence children’s gait. Footwear type is especially important as a child grows and develops from a novice to an expert walker. Compared to barefoot walking, children generally have increased spatiotemporal (ST) gait parameters while walking with footwear. Gait variability has also shown to be affected by footwear. The degree of stiffness in footwear could have a large influence on children’s gait and variability. This study investigated effects of footwear stiffness on ST gait parameters and gait variability in novice walkers. Children with an average age of 33.3 ( 7.0) months participated in a single data collection. Heel and toe marker positions were acquired for one minute of walking per condition. Participants walked on the treadmill in three levels of footwear stiffness (rigid: hard-soled stiff shoe, semi-rigid: EVA sole athletic shoe, compliant: moccasin soft-sole shoe) and barefoot. ST gait parameters and gait variability were calculated for each condition using marker. and treadmill forces. ST parameters all increased in the rigid and semi-rigid footwear conditions compared to soft-sole and barefoot. Interestingly, there were no differences between barefoot and wearing a moccasin for any of the ST variables. There were no differences in SD and COV between any of the footwear conditions. The moccasin shoe promotes walking most similar to normal barefoot walking. Standard measures of variability failed to detect differences between footwear conditions. Further investigation into different measurements is necessary to parse out what effect footwear has on children’s gait variability.
Listed In: Biomechanics, Gait

Pushoff Work is Increased Following Prosthesis Adaptation

The purpose of this study was to quantify adaptation to a new prosthesis in terms of mechanical work profiles. Currently, there is a lack of knowledge on how individuals adapt to a new prosthesis, with many studies investigating different prosthetic feet but not adaptation over time. Thus, there is a need for objective measures to quantify the process of adaptation. Mechanical power and work profiles are a prime subject for modern energy-storage-and-return type prostheses, as the amount of energy a prosthesis stores and returns (i.e., positive and negative work) during stance is directly related to how a user loads and unloads the limb. 22 individuals with unilateral, transtibial amputation were given a new prosthesis at their current mobility level (K3 or above) and wore it for a three-week adaptation period. Kinematic and kinetic measures were recorded from walking on overground force plates at 0, 1.5, and 3 weeks into the adaptation period. Positive and negative work done by the prosthesis and intact ankle-foot was calculated using a unified deformable segment model. Positive work from the prosthesis side increased by 6.1% and intact side by 5.7% after 3 weeks (p = .041, .036). No significant changes were seen in negative power from prosthesis or intact side (p = .115, .192). Analyzing work done by a prosthesis may be desirable for tracking a patient’s gait rehabilitation over time. Future work may analyze how mechanical work profiles relate to more traditional clinical measures.

Listed In: Biomechanics, Gait, Physical Therapy