Health (Faculty of)

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The Faculty was known as the Faculty of Applied Health Sciences prior to its name change in January 2021.

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Development of a full flexion 3D musculoskeletal model of the knee considering intersegmental contact and deep muscle activity during high knee flexion
(University of Waterloo, 2019-01-24) Kingston, David C.; Acker, Stacey; Callaghan, Jack
Habitual kneeling in high knee flexion postures is a risk factor for knee joint dysfunction yet critical parameters for modeling this range of motion remain unknown or untested in three dimensions. High flexion is defined as postures exceeding 120° at the knee joint to a maximum of approximately 165°. Specific occupational and ethnic populations that regularly use high knee flexion postures have increased prevalence of degenerative knee diseases. This could suggest a causal relationship between habitual kneeling and disease prevalence resulting from repeated exposures. Therefore, this thesis was designed to explore two critical components for high knee flexion biomechanical modeling: intersegmental (thigh-calf and heel-gluteal) contact forces and lower limb muscular activation patterns across the full range of knee flexion. The global objective of this work was to develop a 3D musculoskeletal (MSK) model of the knee to estimate tibial contact forces in high knee flexion postures for determining the effect of intersegmental contact on these calculations. Two experimental studies, verification against a ‘gold-standard’ dataset, and an application study supported this global objective. Study 1: The purposes of this study were: 1) to measure total intersegmental contact force magnitude and centre of force (CoF) location during six high knee flexion movements and 2) to define regression models, based on anthropometrics, for the estimation of intersegmental contact parameters. Fifty eight participants completed six high knee flexion movements while motion capture and pressure data from the right lower limb were recorded. High knee flexion movements had average peak total intersegmental contact force magnitudes ranging from ~50-200N or ~8-30 %BW. Intersegmental CoF locations were segregated between thigh-calf and heel-gluteal regions with CoF, at peak total force, being ~6.2 cm and ~32.7 cm distal from the functional knee joint center about the long axis of the femur respectively. Five parameters of intersegmental contact (onset, maximum knee flexion angle, total contact force, thigh-calf CoF, and thigh-calf contact area) were then assessed for anthropometric based regression model fit. Strong correlations and linear regression models were found for maximum knee flexion angle and thigh-calf CoF, but only moderate to weak results were found for all other intersegmental contact parameters. The overall poor fit and variance explained by the linear regression models for onset, total force, and contact area suggest further work is needed to provide estimations of these parameters for use in future modeling efforts. Study 2: The purposes of this study were: 1) to measure surface and fine-wire EMG activation profiles in six high knee flexion movements and 2) to establish if surface EMG sites can be used as a proxy for fine-wire activation profiles. Sixteen participants completed the same high knee flexion movements, and level walking, as study 1 while activation waveforms from three deep muscles—vastus intermedius (VI), adductor magnus (AM), and semimembranosus (SM)—were recorded using fine-wire electrodes for comparison to easily accessible surface sites. Average peaks of VI, AM, and SM fine-wire activations during high knee flexion movements were approximately 30, 85, and 35 %MVC respectively. None of the surface sites recorded satisfied our criteria to successfully model fine-wire recordings. This was largely due to the considerable variability of surface-indwelling comparisons between participants. Our findings would suggest that the use of fine-wire EMG to obtain representative activation waveforms from VI, AM, or SM may be required if isolated muscle/motor unit activity is needed. MSK model: A full range of knee motion MSK model was developed for the estimation of tibial contact forces. Verification of the MSK model was completed by calculating the error between tibial compressive force estimates and measurements from an instrumented knee implant (gold standard). Vertex based object files of participant bones and CAD files of implant components were obtained from a public repository for gold standard data with muscle geometry scaled from our MSK model. Tibial compression estimates strongly fit implant data shape during walking (R2 0.83), squatting (R2 0.93), and ‘bouncy’ walking (R2 0.74) with an RMSD of 0.47, 0.16 and 0.58 BW respectively. Qualitative assessments of recorded EMG and muscle force estimations showed poor agreement between time-series data. Therefore, the strong fit of MSK tibial compression estimates to gold standard data would suggest this model is phenomenological in nature and does not accurately represent neuromuscular control. Application: The purpose of this study was to quantify the effect of including intersegmental contact on external knee joint moments and tibial contact force estimations. This study used participant data collected from study 2. There was an average RMSD of 3.56, 0.16, and 0.06 %BW*HT in flexion/extension, ab/adduction, and int/external external moments respectively when considering intersegmental contact parameters. Reductions in external moments caused changes to mean RMSD tibial contact force estimates: 0.14 BW lower compression, 0.2 BW lower posterior shear, and 0.03 BW higher lateral shear. Muscle force estimates generally followed EMG waveforms in shape for vastii, gluteus medius, and AM with SM having an improved agreement using its indwelling signal compared to surface measurements. General conclusions: Intersegmental contact forces must be considered when reporting tibial contact forces during high knee flexion movements as significant reductions to tibial posterior shear and increases in lateral shear were observed. Further work is required to refine MSK models in these ranges of knee motion as pressure sensor technology and soft tissue artifact are considerable limitations. Measurement of populations who habitually perform these activities needs to be completed to assess the translation of these findings to appropriate individuals.
Development of a Wearable Sensor-Based Framework for the Classification and Quantification of High Knee Flexion Exposures in Childcare
(University of Waterloo, 2022-12-19) Laudanski, Annemarie F.; Acker, Stacey
Repetitive cyclic and prolonged joint loading in high knee flexion postures has been associated with the progression of degenerative knee joint diseases and knee osteoarthritis (OA). Despite this association, high flexion postures, where the knee angle exceeds 120°, are commonly performed within occupational settings. While work related musculoskeletal disorders have been studied across many occupations, the risk of OA development associated with the adoption of high knee flexion postures in childcare workers has until recently been unexplored; and therefore, occupational childcare has not appeared in any systematic reviews seeking to prove a causal relationship between occupational exposures and the risk of knee OA development. Therefore, the overarching goal of this thesis was to explore the adoption of high flexion postures in childcare settings and to develop a means by which these could be measured using non-laboratory-based technologies. The global objectives of this thesis were to (i) identify the postural demands of occupational childcare as they relate to high flexion exposures at the knee, (ii) apply, extend, and validate sensor to segment alignment algorithms through which lower limb flexion-extension kinematics could be measured in multiple high knee flexion postures using inertial measurement units (IMUs), and (iii) develop a machine learning based classification model capable of identifying each childcare-inspired high knee flexion posture. In-line with these global objectives, four independent studies were conducted. Study I – Characterization of Postures of High Knee Flexion and Lifting Tasks Associated with Occupational Childcare Background: High knee flexion postures, despite their association with increased incidences of osteoarthritis, are frequently adopted in occupational childcare. High flexion exposure thresholds (based on exposure frequency or cumulative daily exposure) that relate to increased incidences of OA have previously been proposed; yet our understanding of how the specific postural requirements of this childcare compare to these thresholds remains limited. Objectives: This study sought to define and quantify high flexion postures typically adopted in childcare to evaluate any increased likelihood of knee osteoarthritis development. Methods: Video data of eighteen childcare workers caring for infant, toddler, and preschool-aged children over a period of approximately 3.25 hours were obtained for this investigation from a larger cohort study conducted across five daycares in Kingston, Ontario, Canada. Each video was segmented to identify the start and end of potential high knee flexion exposures. Each identified posture was quantified by duration and frequency. An analysis of postural adoption by occupational task was subsequently performed to determine which task(s) might pose the greatest risk for cumulative joint trauma. Results: A total of ten postures involving varying degrees of knee flexion were identified, of which 8 involved high knee flexion. Childcare workers caring for children of all ages were found to adopt high knee flexion postures for durations of 1.45±0.15 hours and frequencies of 128.67±21.45 over the 3.25 hour observation period, exceeding proposed thresholds for incidences of knee osteoarthritis development. Structured activities, playing, and feeding tasks were found to demand the greatest adoption of high flexion postures. Conclusions: Based on the findings of this study, it is likely that childcare workers caring for children of all ages exceed cumulative exposure- and frequency-based thresholds associated with increased incidences of knee OA development within a typical working day. Study II – Evaluating the Robustness of Automatic IMU Calibration for Lower Extremity Motion Analysis in High Knee Flexion Postures Background: While inertial measurement units promise an out- of-the-box, minimally intrusive means of objectively measuring body segment kinematics in any setting, in practice their implementation requires complex calculations in order to align each sensor with the coordinate system of the segment to which they are attached. Objectives: This study sought to apply and extend previously proposed alignment algorithms to align inertial sensors with the segments on which they are attached in order to calculate flexion-extension angles for the ankle, knee, and hip during multiple childcare-inspired postures. Methods: The Seel joint axis algorithm and the Constrained Seel Knee Axis (CSKA) algorithm were implemented for the sensor to segment calibration of acceleration and angular velocity data from IMUs mounted on the lower limbs and pelvis, based on a series of calibration movements about each joint. Further, the Iterative Seel spherical axis (ISSA) extension to this implementation was proposed for the calibration of sensors about the ankle and hip. The performance of these algorithms was validated across fifty participants during ten childcare-inspired movements performed by comparing IMU- and gold standard optical-based flexion-extension angle estimates. Results: Strong correlations between the IMU- and optical-based angle estimates were reported for all joints during each high flexion motion with the exception of a moderate correlation reported for the ankle angle estimate during child chair sitting. Mean RMSE between protocols were found to be 6.61° ± 2.96° for the ankle, 7.55° ± 5.82° for the knee, and 14.64° ± 6.73° for the hip. Conclusions: The estimation of joint kinematics through the IMU-based CSKA and ISSA algorithms presents an effective solution for the sensor to segment calibration of inertial sensors, allowing for the calculation of lower limb flexion-extension kinematics in multiple childcare-inspired high knee flexion postures. Study III – A Multi-Dimensional Dynamic Time Warping Distance-Based Framework for the Recognition of High Knee Flexion Postures in Inertial Sensor Data Background: The interpretation of inertial measures as they relate to occupational exposures is non-trivial. In order to relate the continuously collected data to the activities or postures performed by the sensor wearer, pattern recognition and machine learning based algorithms can be applied. One difficulty in applying these techniques to real-world data lies in the temporal and scale variability of human movements, which must be overcome when seeking to classify data in the time-domain. Objectives: The objective of this study was to develop a sensor-based framework for the detection and measurement of isolated childcare-specific postures (identified in Study I). As a secondary objective, the classification accuracy movements performed under loaded and unloaded conditions were compared in order to assess the sensitivity of the developed model to potential postural variabilities accompanying the presence of a load. Methods: IMU-based joint angle estimates for the ankle, knee, and hip were time and scale normalized prior to being input to a multi-dimensional Dynamic Time Warping (DTW) distance-based Nearest Neighbour algorithm for the identification of twelve childcare inspired postures. Fifty participants performed each posture, when possible, under unloaded and loaded conditions. Angle estimates from thirty-five participants were divided into development and testing data, such that 80% of the trials were segmented into movement templates and the remaining 20% were left as continuous movement sequences. These data were then included in the model building and testing phases while the accuracy of the model was validated based on novel data from fifteen participants. Results: Overall accuracies of 82.3% and 55.6% were reached when classifying postures on testing and validation data respectively. When adjusting for the imbalances between classification groups, mean balanced accuracies increased to 86% and 74.6% for testing and validation data respectively. Sensitivity and specificity values revealed the highest rates of misclassifications occurred between flatfoot squatting, heels-up squatting, and stooping. It was also found that the model was not capable of identifying sequences of walking data based on a single step motion template. No significant differences were found between the classification of loaded and unloaded motion trials. Conclusions: A combination of DTW distances calculated between motion templates and continuous movement sequences of lower limb flexion-extension angles was found to be effective in the identification of isolated postures frequently performed in childcare. The developed model was successful at classifying data from participants both included and precluded from the algorithm building dataset and insensitive to postural variability which might be caused by the presence of a load. Study IV – Evaluating the Feasibility of Applying the Developed Multi-Dimensional Dynamic Time Warping Distance-Based Framework to the Measurement and Recognition of High Knee Flexion Postures in a Simulated Childcare Environment Background: While the simulation of high knee flexion postures in isolation (in Study III) provided a basis for the development of a multi-dimensional Dynamic Time Warping based nearest neighbour algorithm for the identification of childcare-inspired postures, it is unlikely that the postures adopted in childcare settings would be performed in isolation. Objectives: This study sought to explore the feasibility of extending the developed classification algorithm to identify and measure postures frequently adopted when performing childcare specific tasks within a simulated childcare environment. Methods: Lower limb inertial motion data was recorded from twelve participants as they interacted with their child during a series of tasks inspired by those identified in Study I as frequently occurring in childcare settings. In order to reduce the error associated with gyroscopic drift over time, joint angles for each trial were calculated over 60 second increments and concatenated across the duration of each trial. Angle estimates from ten participants were time windowed in order to create the inputs for the development and testing of two model designs wherein: (A) the model development data included all templates generated from Study III as well as continuous motion windows here collected, or (B) only the model development data included only windows of continuous motion data. The division of data into the development and testing datasets for each 5-fold cross-validated classification model was performed in one of two ways wherein the data was divided: (a) through stratified randomized partitioning of windows such that 80% were assigned to model development and the remaining 20% were reserved for testing, or (b) by partitioning all windows from a single trial of a single participant for testing while all remaining windows were assigned to the model development dataset. When the classification of continuously collected windows was tested (using division strategy b), a logic-based correction module was introduced to eliminate any erroneous predictions. Each model design (A and B) was developed and tested using both data division strategies (a and b) and subsequently their performance was evaluated based on the classification of all data windows from the two subjects reserved for validation. Results: Classification accuracies of 42.2% and 42.5% were achieved when classifying the testing data separated through stratified random partitioning (division strategy a) using models that included (model A, 159 classes) or excluded (model B, 149 classes) the templates generated from Study III, respectively. This classification accuracy was found to decrease when classifying a test partition which included all windows of a single trial (division strategy b) to 35.4% when using model A (where templates from Study III were included in the model development dataset); however, this same trial was classified with an accuracy of 80.8% when using model B (whose development dataset included only windows of continuous motion data). This accuracy was however found to be highly dependent on the motions performed in a given trial and logic-based corrections were not found to improve classification accuracies. When validating each model by identifying postures performed by novel subjects, classification accuracies of 24.0% and 26.6% were obtained using development data which included (model A) and excluded (model B) templates from Study III, respectively. Across all novel data, the highest classification accuracies were observed when identifying static postures, which is unsurprising given that windows of these postures were most prevalent in the model development datasets. Conclusions: While classification accuracies above those achievable by chance were achieved, the classification models evaluated in this study were incapable of accurately identifying the postures adopted during simulated childcare tasks to a level that could be considered satisfactory to accurately report on the postures assumed in a childcare environment. The success of the classifier was highly dependent on the number of transitions occurring between postures while in high flexion; therefore, more classifier development data is needed to create templates for these novel transition movements. Given the high variability in postural adoption when caring for and interacting with children, additional movement templates based on continuously collected data would be required for the successful identification of postures in occupational settings. Global Conclusions Childcare workers exceed previously reported thresholds for high knee flexion postures based on cumulative exposure and frequency of adoption associated with increased incidences of knee OA development within a typical working day. Inertial measurement units provide a unique means of objectively measuring postures frequently adopted when caring for children which may ultimately permit the quantification of high knee flexion exposures in childcare settings and further study of the relationship between these postures and the risk of OA development in occupational childcare. While the results of this thesis demonstrate that IMU based measures of lower limb kinematics can be used to identify these postures in isolation, further work is required to expand the classification model and enable the identification of such postures from continuously collected data.
Do East Asians Achieve Greater Knee Flexion than Caucasian North Americans, and are East Asian Kneeling and Squatting Styles Kinetically Different from North American Norms?
(University of Waterloo, 2016-01-20) Chong, Helen; Acker, Stacey
High flexion postures (specifically, kneeling and squatting) are used with greater regularity in East Asian (Chinese, Japanese, Korean, and Vietnamese) cultures for many activities of daily living (ADL). Furthermore, the favored style of kneeling and squatting is different between ethnicities: Caucasians typically flex their forefoot while kneeling and squatting, whereas East Asians tend to keep the top or bottom of the foot flat to the ground. Most, but not all, research suggests that East Asians are able to achieve a greater knee flexion angle during high flexion postures, but it is unknown if any differences between ethnicity extends to kinetic outcomes. A direct comparison between ethnicities with respect to kinetics has not been made. Where a difference in maximal attainable flexion angle exists, it is unclear whether the cause is cultural or innate. Therefore, this thesis project aimed to answer three related questions: 1) Do East Asian populations achieve a greater flexion angle than North American Caucasians; 2) If there is in fact a difference, is it a result of cultural upbringing or innate ability?; and, 3) Do different styles of kneeling and squatting alter the moments of force at the knee? To accomplish these aims, 43 participants were recruited from the University of Waterloo and fit into one of three groups: Caucasian, born and raised in North America (20 participants); East Asian, born and raised in North America (18 participants); or, East Asian, born in East Asia, living in North America for less than two years (five participants) (however, the East Asian born in East Asia group was excluded from statistical processing since the group size was considerably smaller). Kinetic, kinematic, neuromuscular, and passive range of motion data were collected and compared between different ethnicity groups. East Asians did not achieve a greater mean knee flexion angle during kneeling compared to Caucasians (Canadian born East Asians=152.01° (±4.85°); Caucasians=153.07° (±7.46°), p=0.2859), but a greater mean flexion angle was found during squatting (Canadian born East Asians =147.96° (±6.62°); Caucasians = 141.69° (±17.48°), p=0.0014). Between Caucasians and Canadian born East Asians, there was also no difference in peak knee flexion angle during passive range of motion testing (Canadian born East Asians = 152.05° (±8.16°); Caucasians = 149.54° (±7.75°)), which indicates that there is no difference in ability to achieve greater high flexion between groups. Finally, it was found that different styles of squatting altered the kinetics at the knee, but different styles of kneeling were not significantly different. Flat foot squatting, a posture more commonly seen in East Asian cultures, had significantly (p<0.05) lower flexion and adduction moments at the knee than heels raised squatting (which is more commonly used by Caucasian North Americans) during descent, ascent, and static squatting. The mean static flexion moment (which is similar in magnitude to the peak flexion moment during descent and ascent) for flat foot squatting was 4.37 (±1.47) %BW*Ht, and for heels raised squatting was 5.99 (±1.84) %BW*Ht. The mean static frontal plane moment for flat foot squatting was -0.45 (±1.33) and for heels raised squatting was 0.59 (±1.02). (Negative values indicate an external abduction moment and positive values indicate an external adduction moment.) When performing high flexion postures, reduced knee moments are desirable since higher moments are associated with greater joint loading and injury risk.
Effect of Club Selection and Clubhead Speed on the Knee Joint during the Golf Swing
(University of Waterloo, 2018-05-23) Maier, Dustin; Acker, Stacey
Golf is a sport that can be played throughout one’s lifetime providing an opportunity for competition, socialization, and improved physical activity. Golf is commonly recommended by physicians to those with knee ailments, under the assumption given that golf is considered a low impact sport. Previous research shows large forces and moments in the frontal plane of the knee, with magnitudes high enough to cause concern for injury and progression of overuse/degenerative conditions, especially with repeated exposure. In addition, changes to the golf swing across clubs have been seldom analyzed, while variations in clubhead speed using multiple clubs have yet to be investigated. Because shot ranges overlap between golf clubs, multiple clubs could be used for a given shot. A certain club’s shot distance at given speed can also be achieved by using the next longest club in the set and swinging 6 mph slower. The purpose of this study was to determine if male golfers with a handicap below 18 can reduce their peak frontal plane moments by swinging 6 mph slower while using the next longest club in the set. It was hypothesized that swinging slower with a longer club, would reduce the peak adduction and abduction moments at the knee joint. Kinetics and kinematics of the lower body were analyzed from 11 intermediate to highly skilled participants (handicap: 10.1 ± 6.3) during the golf swing using 7 golf clubs (Driver, 4i, 5i, 6i, 7i, 8i, and 9i) and two participant-specific clubhead speeds (normal and slow). The normal speed was defined as the participant’s self-selected clubhead speed, while the slow speed was set as 6 mph slower using the paired longer club. Normal (N) and slow (S) clubhead speed pairings of adjacent clubs were analyzed, including 5iN/4iS, 6iN/5iS, 7iN/6iS, 8iN/7iS, and 9iN/8iS. The shape of the moment waveforms were consistent within and between participants. Peak knee adduction moments ranged from 0.86-0.95 Nm/kg (N), and 0.84-0.9 Nm/kg (S). A two-way ‘condition (2) x pair (5)’ repeated measures analyses of variance was used to address the hypotheses. Peak abduction moments ranged from 0.58-0.77 iv Nm/kg (N), and 0.52-0.56 Nm/kg (S). There was a main effect of condition, but not of pair or an interaction for the peak abduction moments (P<0.05). There was no main effect, of condition or pair, or interaction for the peak adduction moments (P>0.2). While not statistically significant, peak adduction moments were lower with the slower swings. The magnitudes of these frontal plane moments are greater than those previously reported, potentially indicating differing swing mechanics compared to this study, resulting in altered kinetics of the lower limbs during the golf swing.
Effect of Cyclic and Sustained Squatting Exposures on Hemodynamics and Subsequent Changes in Lower Limb Jumping Mechanics
(University of Waterloo, 2019-07-29) Ivanochko, Natasha; Acker, Stacey
Occupational exposure to high knee flexion postures such as squatting or kneeling is associated with an increased risk of developing knee osteoarthritis. The exact mechanisms behind the increased risk are currently unknown. The literature is inconclusive on whether the duration spent in knee bending postures or the act of cycling through these postures is more detrimental to the knee. The goal of the study was to investigate whether the type of squat (cyclic or sustained) leads to different changes in power, neuromuscular control and lower-limb muscular blood flow parameters. It was hypothesized that sustained squatting would cause more detrimental effects to biomechanical and hemodynamic measures that are related to injury than cyclic squatting. Knee joint power, knee extensor muscle activation patterns, and lower limb kinematics were recorded before and after exposures to cyclic and sustained squats, whereas vastus medialis muscle oxygenation was measured during squat exposures. Thirty healthy young participants (15 Male/15 Female, age: 22.3 ± 2.2 years, height: 1.70 ± 0.09 m, weight: 66.88 ± 11.16 kg) were recruited for the study. Participants completed a cyclic and sustained squatting exposure. The total time spent in a squat posture was equivalent between exposures. The cyclic squat consisted of a 40-second squat followed by 20 seconds of rest, repeated for six cycles. The sustained squat was a static squat hold of four minutes. Two countermovement jumps were performed pre and post each squatting exposure, for a total of eight countermovement jumps. Between squat exposures, a four minute standing recovery occurred. Vastus medialis muscle oxygenation was measured using near-infrared spectroscopy. Lower limb kinematics were collected using 3D-motion capture, kinetics were measured using two embedded force plates, and vastus medialis and vastus lateralis muscle activity was collected with surface electromyography. The sustained squatting exposure was found to cause a significantly greater decrease to peak knee power from baseline compared to the cyclic squat (−0.71 W/kg and −0.33 W/kg respectively, p = .016). A sex difference was also found, with males experiencing greater decreases in knee power than females (−0.73 W/kg vs. −0.32 W/kg, p = .013). A significant interaction occurred for integrated EMG (iEMG) between muscle and phase (p = .037). During the deceleration phase on average iEMG values decreased from baseline values, and increased during the preparatory phase (− 2.48 mV∙s vs. 0.62 mV∙s), with vastus medialis activity being reduced by a larger degree than vastus lateralis. Changes to tissue saturation index % during the squat exposure also displayed a sex main effect (p = .012), with on average males experiencing decreases and females increases (−1.97% vs. 2.60%). Regardless of squat type, the squatting exposure did not cause significant changes to frontal plane motion, delays in muscle onset or changes in percent normalized muscle oxygenation. Historically, occupational squatting and its relationship to knee osteoarthritis has been studied from an epidemiological framework, therefore, the current study was novel in that it provided a more systematic and quantitative assessment of squatting exposures. The study demonstrated that acute exposures to high knee flexion postures cause detrimental changes to power generation, neuromuscular control and hemodynamics. The results suggested that sustained exposures were more detrimental than cyclic exposures. Sex effects indicated that males were more affected by the squatting exposures than females. Our work highlights the importance for workplace guidelines in occupations with frequent squatting to limit the duration of static high knee flexion activities, and provide ample rest between exposures.
Effects of a Single Shift of Occupational Childcare on Knee Mechanics during Gait
(University of Waterloo, 2024-04-16) Peckett, Kimberly; Acker, Stacey
The current literature shows that there are ergonomic challenges in occupational childcare, such as inappropriate heights of furniture for adults, and that childcare educators engage in high knee flexion positions beyond levels that have been previously associated with an increased risk of developing knee osteoarthritis. However, what has not yet been investigated is the possibility that childcare educators’ knee mechanics during everyday activities, such as walking, differ after their shift, likely as a result of their daily work activities and work environment. This study aimed to evaluate the differences in childcare educators’ knee kinematics and kinetics before and after their workday, in gait measures that, when compared to controls, have been associated with knee joint injury and disease, including knee flexion angle at heel strike, peak knee adduction angle, peak knee flexion moment, and peak knee adduction moment during gait. For this study, 21 childcare educators were recruited from early learning centres in the Waterloo/Wellesley areas. In their place of work, before (baseline) and after their workday, each participant completed walking trials until three successful trials, defined as their entire foot contacting the first force plate and the heel of the same foot contacting a second force plate in the same gait cycle, were obtained for each leg. Motion data and ground reaction forces were collected using markerless motion capture cameras and force plates, respectively. Two-tailed paired samples t-tests were run to evaluate changes in all outcome variables for both legs, except for peak adduction moment on the non-dominant leg, which was evaluated using the non-parametric equivalent test (Wilcoxon signed-rank test). There was a statistically significant increase in peak knee flexion moment (p = 0.031) after the shift compared to baseline. No statistically significant pre- to post-shift differences for any other dependent variable on either leg was found (all p > 0.05). Inter-trial error was calculated for the pre-shift gait trials as a measure of the natural variability in the participants’ gait outcome measures. Participants who experienced a change (post minus pre-shift) larger than the inter-trial error can be said to have exhibited a change over their work shift that cannot be explained by natural variability alone. For at least one leg, there were 19 such participants for the kinetic outcomes and 16 such participants for the kinematic outcomes. The results from this study suggest that a single shift of occupational childcare does have an effect on the childcare educators’ knee mechanics during gait.
An Evaluation of Knee Joint Laxity, Mechanics and Muscle Activation Following Sustained Deep Flexion Kneeling
(University of Waterloo, 2016-01-22) Mines, Daniel; Acker, Stacey
Knee osteoarthritis (OA) is a complex disease with several proposed mechanisms for both the initiation and progression of the disease. Within the next 30 years, 1 in 4 Canadians are expected to have OA and 30% of the workforce will have difficulty performing occupational activities due to OA. One at-risk group is workers whose occupations require frequent and intermittent kneeling: habitual kneelers. To better our understanding of how knee OA is initiated in this population, biomechanical studies are needed to support or refute current hypothesized pathways that link occupational kneeling to knee OA. It is well documented that frontal plane knee laxity changes throughout the progression of knee OA but it is not known whether laxity changes are a cause or a result of the disease. This thesis work explores a laxity mechanism for knee OA initiation in habitual kneelers. Study 1 aimed to reliably capture frontal plane knee joint laxity using an improved device. Ten healthy, young participants volunteered (5 males, 5 females). ICC scores ranged from 0.95 to 0.99 suggesting excellent reliability of the device. An MDD of 1.22˚ was calculated and used to inform laxity decisions in Study 2. Study 2 was novel as it was the first to determine what changes occur in passive frontal plane knee joint laxity - in addition to gait mechanics and muscle activation - following a kneeling exposure. Fifteen healthy, young participants volunteered (8 males, 7 females). Contrary to what was expected, frontal plane knee joint laxity did not change following the kneeling exposure. However, during gait, knee flexion angle at heel contact and peak knee flexion angle during early stance phase were both affected by the kneeling exposure. These findings link kneeling exposure to immediate changes in measures indicative of knee joint instability and altered loading that have the potential to damage knee joint cartilage. Thus, the findings support the epidemiological evidence of a higher risk of knee OA development in habitual workers, though likely through some other mechanism than increased frontal plane knee joint laxity.
Gait Characteristics Change Following an Acute Exposure to Kneeling and Filtering Considerations for Gait Analysis
(University of Waterloo, 2023-02-03) Weeks, Terri; Acker, Stacey
Following sustained kneeling in young adults, kinetic and kinematic changes at the knee and ankle during gait have been observed (Gaudreault et al., 2013; Kajaks & Costigan., 2015a; Tennant et al., 2014). It is possible that a change in the cyclic gait pattern after sustained deep knee bending (greater than 120 degrees of flexion) could deferentially load the cartilage in the knee and modify the mechanical stress exerted on the tissues, at least acutely, leading to increased risk of knee osteoarthritis development (Edd et al., 2018; Kajaks & Costigan, 2015). Gait changes that have been observed in those with knee osteoarthritis include decreases in knee flexion at heel strike, knee flexion range of motion, knee power, ankle power and knee flexion moment, and increases in knee adduction moment, and vertical loading rate. The primary purpose of this thesis was to explore whether differences in gait kinematics and kinetics following sustained kneeling mirror those occurring in osteoarthritic gait. It was hypothesized that prolonged kneeling would increase external peak knee adduction moment (KAM), and vertical loading rate (VLR), and would decrease knee flexion angle at heel strike (HS), knee flexion range of motion (ROM), external peak knee flexion moment (KFM) in early stance, positive peak ankle power (PAP) in late stance, and the second positive peak knee power (PKP) in late stance. There is also a need to low-pass filter marker data to remove random noise, especially because noise is amplified when differentiating position and orientation for the calculation of linear and angular velocities and accelerations for inverse dynamics calculations such as joint moments and joint powers (Kristianslund et al., 2012; Sinclair et al., 2013). It has become common practice to filter raw marker and raw ground reaction force (GRF) data differently to preserve ground reaction force peaks and impact due to heel strike while walking. Papers reviewed for this project include a range of marker cut off frequencies from 5-8Hz and a range of GRF cut-off frequencies from raw (no filtering) to 40Hz. Selecting different cut-off frequencies for marker and GRF data can result in large oscillations in joint moments around heel strike during running that are not representative of the actual movement (Bezodis et al., 2013). It is possible that these effects could exist in any form of gait. The secondary purpose of this thesis was to determine the effects of various low-pass filter cut-offs on all dependent variables calculated for the primary objective. It was hypothesized that large differences in the filter cut-offs between marker and GRF data would result in significantly different knee flexion angles at HS, knee flexion ROM, first peak KAM, first peak KFM, PAP, PKP, and peak VLR. As part of a previous study, fourteen participants (8M/6F) performed three pre- and post-kneeling gait trials at their self-selected pace while motion (Optotrak, NDI, Waterloo, Canada) and ground reaction force (AMTI, Watertown, MA, USA) data were recorded for the right leg. The kneeling protocol consisted of three ten-minute bouts of sustained plantarflexed kneeling separated by five-minutes of seated rest. Ground reaction force and motion capture data were filtered at 6Hz using a 4th order Butterworth filter using Visual 3D software (C-Motion Inc., Germantown, MD) to determine outcome measures. For the primary objective, seven two-tailed paired t-tests (one per outcome measure) were performed to compare subject mean values pre- and post- kneeling (α=0.05). For the secondary objective, marker and GRF data were filtered using a 4th order zero-lag Butterworth filter with 16 different cuff-off combinations. Each combination of GRF and marker input data was then used to calculate KFM, KAM, PAP and PKP for each subject’s pre- and post- kneeling gait trials. For measures where only kinematic data or only ground reaction forces were involved in their calculation (knee angle at HS knee ROM and peak VLR), only six different cut-off frequencies were used. A two-way repeated measures ANOVA was used to compare the mean outcome variables across different filtering conditions, and between the pre- and post-kneeling time points. Any main effect of filtering condition would indicate that filtering condition had a significant effect on the outcome measure. Any interaction would indicate that the effect of the kneeling exposure (part of the primary objective) depended on the filtering condition. From the primary objective analysis, acute exposure to kneeling produced significant increases in knee flexion angle at HS, and peak KFM. An increase in knee flexion angle at HS and KFM peak (which typically occurs during early stance) suggests that participants could be attempting to reduce knee joint rate of loading more by accepting their weight with more knee flexion, as opposed to more knee extension which is typical of osteoarthritic gait and is related to greater axial loading rate at the knee. The increase in external KFM is balanced by the internal knee extensor muscle moment, suggesting that following kneeling, contradictory to what we hypothesized, participants are placing greater demand on their quadriceps. High flexion activities such as kneeling are associated with an increased risk of knee OA development. This work suggests that prolonged kneeling has the potential to compromise the integrity of the knee joint such that kneeling can acutely alter the loading patterns experienced at the knee joint (and thus potentially other lower limb joints) during the subsequent ambulation. For the secondary objective of this thesis there was a significant main effect between pre- and post-kneeling for knee flexion at HS (p=0.034), and KFM (p=0.0063). The significant main effects between pre- and post-kneeling conditions for knee flexion at HS and KFM were expected, these results were found when investigating the primary objective. Interestingly there was also a main effect for filtering condition of peak VLR (p=0). The raw filtering condition was significantly larger than all other conditions, followed by the 25Hz being larger then 6Hz and 10Hz, and finally 20Hz being significantly larger then 6Hz. Since there was no significant main effect for filtering condition for any of the remaining dependent variables used, we can conclude that these peak measures are robust to filtering condition. With the lack of filter x kneeling condition interactions for all variables, we can infer that pre- and post- differences between subjects discreate variables are also robust to filtering condition. The lack of significant filtering condition effect for all outcome measures but the peak VLR is likely due to these measures being far enough away from heel strike, that the additional noise from oscillations caused by the impact at heel strike, like that seen during running, had minimal effect on these peaks except for peak VLR. This work shows that, in young asymptomatic participants, post-kneeling changes in kinetic and kinematic outcomes commonly used in the osteoarthritis literature are robust to changing filter cut-off frequencies. This finding may suggest that the wide variety of cut-off frequencies (when reported at all) in the literature on gait characteristics in osteoarthritis may not be of significant concern when comparing these outcome measures between studies.
Investigation of a Double Calibration Technique to Reduce Soft Tissue Artifact Error in High Flexion
(University of Waterloo, 2022-02-01) Tworzyanski, Madalyn; Acker, Stacey
High knee flexion tasks (knee flexion angle > 120 degrees) are performed frequently in both daily living activities (gardening, religious practice, exercise, etc.) and occupational settings (childcare, roofing, construction, floor laying, etc.). These tasks are associated with an increased risk of knee osteoarthritis development, which can alter movement patterns. These types of movement differences can be captured when analyzing high flexion postures using optical motion capture; however, we do not know how accurate reported kinematic outcomes are because of an inherent source of error known as soft tissue artifact (STA). This error is defined as the movement of skin markers relative to the underlying bone and affects the thigh markers more than the shank. It cannot be filtered out of data after processing because it has a similar frequency content to the movements themselves (~5-10 Hz). Therefore, all reported measures of knee kinematics obtained using optical motion capture include an unknown level of error and can affect clinical and biomechanical interpretations of knee pathologies. This thesis investigated the use of a double calibration technique to improve the accuracy of landmarks tracked in high flexion postures with an anterolaterally located marker cluster in the mid-thigh region. Thirty-three participants performed flatfoot squatting, heels-up squatting, dorsiflexed kneeling and plantarflexed kneeling movements. The position of the functional hip joint center was defined in a standing reference position using a functional calibration trial. This landmark was then simultaneously tracked with the thigh cluster and pelvis cluster during high flexion movements. The landmark tracking with the thigh cluster was referred to as the femoral head center and was obtained in two ways: using either single or double calibration techniques. The landmark tracking with the pelvis, referred to as the hip joint center, was considered the gold standard and thus was the position to which the single and double calibration-based femoral head center positions were compared. Root-mean squared (RMS) error was calculated between the hip joint center and femoral head centers in the global x, y, and z directions. Resultant error (distance between the hip joint center and the femoral head centers) was also determined. The bias and limits of agreement on the resultant error were used to evaluate the accuracy of locating the femoral head center using each calibration technique relative to the location of the hip joint center. Paired t-tests revealed RMS error and resultant error were not significantly lower using the double calibration technique, and the limits of agreement were wider in the double calibration. Data were then separated into percentile groups to evaluate the double calibration technique after controlling for mid-thigh circumference, a subject-specific variable. RMS errors in the global y and z directions and resultant error were significantly greater in the double calibration for the 25th and 50th percentile groups, while there were no significant differences in RMS error nor resultant error between calibration techniques in the 15th and 75th percentile group. Resultant error also increased from 15th to 50th percentile groups and limits of agreement increased with higher percentiles. Due to poor performance of the double calibration despite separating data into mid-thigh percentile groups, the double calibration method was evaluated using a different landmark to predict the position of the femoral head center in the seated calibration posture (as the functional hip joint center trial was only able to be applied to the standing posture). Double calibration using the lateral femoral condyle performed only slightly superior than using the greater trochanter, the landmark initially used in the double calibration method; however single calibration continued to perform best. Therefore, the double calibration was not recommended for use with the studied high flexion movements. The conclusions of this thesis direct future research to evaluate the composition of the thigh (adipose tissue vs muscular tissue) and its relation to STA, and to assess ways to improve palpation of landmarks in high flexion postures (e.g., using fluoroscopy measures). Once accurate palpation is achieved in high flexion, the double calibration technique could be revisited to evaluate its effectiveness to reduce STA.
An Investigation of Methods to Attenuate Soft Tissue Artifact of the Thigh in High Knee Flexion
(University of Waterloo, 2020-08-26) Buchman-Pearle, Jessa; Acker, Stacey
Soft tissue artifact during optical motion capture, or the movement of skin markers relative to bone, is widely accepted as a significant source of error in estimations of angles and moments. In some cases, the error associated with soft tissue movement exceeds that of the physiological motion of the joint, thereby calling into question the accuracy of the data obtained and casting doubt on the ability to determine mechanical demands of a given task. While previous studies have attempted to quantify soft tissue artifact, the variability in error with placement of skin markers (i.e. location specificity), the subject investigated (i.e. subject specificity), and the requirements of the task examined (i.e. task specificity), severely compromises the ability to develop methods which minimize and compensate for soft tissue artifact. Thus, the global objective of this thesis was to investigate soft tissue artifact of the thigh in high knee flexion movements and develop recommendations to standardize data collection and processing techniques. High knee flexion was examined because knee flexion beyond approximately 100° lacks investigation despite the unique deformation of soft tissue that occurs in this range (i.e. thigh-calf contact). Additionally, the repetitive adoption of high knee flexion is associated with knee joint injury and disease; thus, to more clearly elucidate mechanisms for these injuries and disease, improvements in the accuracy and reliability of collection and processing procedures is required. Fifty participants performed squatting and kneeling movements while motion of the pelvis and lower limb was recorded with optical motion capture and force data was synchronously recorded from four embedded force plates. Six identical rigid marker clusters were distributed on the distal and middle third of the thighs, and on the anterior, lateral, and anterolateral aspect of the thighs, while one marker cluster was adhered to the pelvis, shanks, and feet. Anthropometric measures were also taken for each subject including sex, height, mass, waist circumference, thigh length, thigh proximal, middle, and distal circumference, and thigh skinfold thickness. Data processing was divided into two studies. The first study developed a non-invasive method to estimate soft tissue artifact for each thigh marker cluster which consisted of measuring the mean of the peak difference in the hip joint center position when tracked with the pelvis cluster (i.e. the gold standard) versus each of the six thigh marker clusters. Bland-Altman methods were then utilized to compare agreement between the pelvis and thigh marker clusters for each task during maximal knee flexion. Across the tasks, the mean difference ranged from -4.93 to 0.03 cm while the lower and upper limits of agreement ranged from -11.86 to -3.27 cm and -0.87 to 5.33 cm, respectively. The mid-anterolateral cluster tended to be least susceptible to soft tissue artifact across the tasks and thus would be recommended, while the lateral clusters were most susceptible and should be avoided. Utilizing the anthropometric measures for each subject, regression models were also developed to determine the association between subject anthropometry and the mean difference in hip joint center position for each marker cluster. Ten of eighteen regression models significantly predicted soft tissue artifact with poor to moderate fit (R = 0.37 to 0.63) and explained between 14 and 40% of variation in the sample. These results suggest that while soft tissue artifact is somewhat associated with measures of anthropometry, marker placement should not be adjusted based on anthropometry alone. Additionally, negative unstandardized beta coefficients and partial correlations for thigh skinfold thickness and proximal thigh circumference revealed that adipose tissue may act to dampen artifact resulting from muscular contractions. The second study evaluated the difference in peak knee joint angles and moments between the thigh marker clusters and assessed the ability of global optimization, implemented in Visual3D utilizing IK constraints, to increase precision and reliability between marker clusters. Without global optimization, there were significant differences in estimated angles and moments between the marker clusters, wherein the mean difference was up to 8.9° and 0.6 %BW*H for flexion, 5.2° and 1.0 %BW*H for abduction, 4.9° and 0.7 %BW*H for adduction, 7.5° and 0.1 %BW*H external rotation, and 9.5° and 0.1 %BW*H for internal rotation. Global optimization was partially effective in compensating for differences between marker clusters in the sagittal plane (peak mean difference decreased 2.7° and 0.4 %BW*H) but less so in the frontal and transverse plane. Additionally, while global optimization decreased the partial eta squared (i.e. measure of effect of marker cluster location) for 12 of 30 outcome measures, intraclass correlation coefficients (i.e. measure of marker cluster reliability) only increased for 2 of 30 outcome measures. These findings highlight the importance of consistent marker placement for a given subject (i.e. between legs and laboratory sessions) and between subjects, as well as the need for researchers to report marker placement and all processing methods.
Lower Limb Biomechanics in Walking, Running and Cycling: Implications for Overuse Injury
(University of Waterloo, 2019-09-27) Chuang, Tyler; Acker, Stacey
A common anecdotal theory among endurance athletes is that cycling results in fewer knee injuries compared to running. This is thought to be due in part to a lower impact ground reaction force in cycling, compared to running. Thus, as these endurance athletes age, there is a tendency to shift from running participation to cycling participation in order to avoid injury. However, the knee has been reported to be the most commonly injured region in both sports, with similar injury rates (Clarsen, Krosshaug, & Bahr, 2010; James, 1995). While it has been found that cycling does typically result in a lower peak ground reaction force compared to running (Gatti et al., 2017), it is unknown how other mechanisms (which could potentially lead to injuries such as iliotibial band syndrome and patellofemoral pain syndrome) differ between these exercise modalities. There has been an abundance of research conducted assessing the impacts of cycling on subsequent running performance (i.e. triathlon performance), specifically from a physiological point of view (Heiden & Burnett, 2003; Hue, Le Gallais, Chollet, Boussana, & Préfaut, 1998). No study to date, however, has explicitly compared the biomechanics of running and cycling. The purpose of the current study was to compare dynamic joint stiffness, co-contraction of the muscles surrounding the knee, segment coordination variability and iliotibial band impingement measures between walking, running and cycling in young, experienced runner/cyclists, in order to elucidate the risk of developing knee injury in one activity over the other. Fifteen healthy, trained runner/cyclists (11M, 4F, age: 25.1 ± 4.7 years, height: 1.80 ± 0.1 m, mass: 72.1 ± 8.2 kg) were recruited. Muscle activity for 7 lower limb muscles were collected using wireless surface electromyography. External ground reaction forces were collected using force plates for the walking and running trials and an instrumented force pedal for the cycling trials. 3D kinematics were collected using an active motion capture system. Participants performed 6 trials of walking at a self-selected pace, 6 trials of running at a pace equivalent to 70% of their maximal heart rate and 6 minutes of cycling at an intensity of 65% of their maximal heart rate. These intensities were selected to represent a typical, social weekend activity. A walking or running trial consisted of one progression overground on a 20m runway and a cycling trial consisted of 30 second efforts extracted from a continuous, steady state, 6-minute trial on the cycle ergometer. Walking was assumed to be a relatively low injury-risk activity and was performed to act as a baseline to which running and cycling could be compared. Kinematic, kinetic and electromyographical signals were analyzed during the stance phase of walking/running and the downstroke of cycling. These portions of the respective activities were chosen since they are the main propulsion producing phases of their respective activities. Compared to walking and cycling, running generally had a larger dynamic joint stiffness and co-contraction index. For the entire stance/downstroke, and when it was broken into an initial and terminal phase, running had the largest DJS, followed by walking and then cycling (all p<0.0001). For stance/downstroke as well as the terminal phase, for all muscle groupings, running had a greater CCI compared to walking and cycling (all p<0.05/4), which were not different from each other. For the initial phase, for the VLLG and VMMG muscle groupings, running had a greater CCI compared to walking and cycling (both p<0.05/4), which were not different from each other. For the VLBF muscle grouping, running had a greater CCI compared to walking, which was greater than cycling (p=0.002) and for the VMST muscle grouping, walking and running were larger than cycling, but were not different from each other (p=0.002). The coordination variability was not different between walking, running or cycling for the sagittal thigh / sagittal shank or sagittal shank / sagittal foot segment coupling (both p>0.05). In terms of IT band impingement measures, running had a larger ITBEX compared to walking and cycling, which were not different from each other (p=0.0001). In terms of IT band impingement duration over an equivalent cumulative load, there were no differences between walking, running and cycling (p=0.164). The outcome measures that were different from walking (assumed to be a relatively low-injury risk activity) might be a contributor to injury for that activity. Of the outcomes analyzed in the current study, joint stiffness and co-contraction thus could potentially play a role in running injuries. None of the studied outcomes, however, when interpreted in isolation, likely play a role in cycling injuries. At the large knee flexion angles, such as those exhibited during the downstroke of cycling, the patellofemoral contact pressure, area and force have been found to be increased compared to full extension (Lewallen, Riegger, Myers, & Hayes, 1990). Thus, perhaps large flexion angles may be an important factor, either in isolation in combination with the outcome measures analyzed such as the co-contraction indices and coordination variability, to overuse injuries in cycling. This was the first study to explicitly compare the biomechanics of running and cycling in the same study. When comparing walking, running, and cycling, significant differences were found in the dynamic joint stiffness and co-contraction index. Since injury rates between the two sports are very similar, these findings suggest that the same injuries could manifest from different injury mechanisms. Runners may opt to cross train in cycling but should be warned that due to large knee flexion angles under load, there are mechanisms of injury during cycling that may also result in overuse injury.
Neuromuscular Control of Gait and Squatting Following a Simulated Occupational Kneeling Exposure
(University of Waterloo, 2016-01-20) Tennant, Liana M.; Acker, Stacey
Frequent and prolonged occupational high knee flexion postures such as kneeling and squatting are associated with an increased risk for the initiation and development of knee osteoarthritis. In order to reduce the prevalence of knee osteoarthritis in this population, a better understanding of the link between these postures and the onset of joint degeneration is needed. The goal of this thesis was to investigate the effects of a 30-minute simulated occupational kneeling exposure on the mechanics of gait and squat transitions, as well as knee joint proprioception, in order to evaluate any negative adaptations that may be associated with an increased risk for knee osteoarthritis development. It was expected that increased joint loading during gait following the kneeling exposure would be linked to deficits in proprioceptive acuity. Greater frontal plane knee motion during squat transitions was also hypothesized. These hypotheses were based on the concept that a prolonged kneeling exposure may induce proprioceptive and neuromuscular control changes by way of ligamentous creep, muscle stretch, pain, or joint capsule deformation. Forty healthy, young participants volunteered for this study (20M, 20F, age: 21.4 ± 2.5 years, height: 1.69 ± 0.10 m, mass: 68.8 ± 16.1 kg). Vastus medialis muscle activity was recorded with surface electromyography, external ground reaction forces were collected using force plates, and 3D lower limb kinematics were measured using an active motion capture system. A knee joint position sense task was used to evaluate proprioception. Gait was evaluated in both an unloaded condition and a loaded condition. In the loaded condition, participants carried a load normalized to 20% of their body mass in a crate held in both hands in front of the torso to simulate how loads are carried occupationally. Participants also performed squat transitions at both a slow and a fast pace. Participants then completed a 30-minute simulated occupational kneeling exposure, following which proprioception, gait, and squatting measures were re-collected. All values were collected for a third time, 30 minutes from the time the kneeling exposure ended. The kneeling exposure resulted in a significant increase in both the peak and mean knee frontal plane motion during the squat transition. The average baseline values for both peak and mean absolute frontal plane knee deviation (peak: 0.207 m (SD 0.110 m); mean: 0.084 m (SD 0.048 m)) were significantly smaller than post-kneeling values (peak: 0.229 m (SD 0.107 m), p = .0057; mean: 0.091 m (SD 0.048 m), p = .0186). The knee joint was still deviated during squat transitions 30 minutes post-kneeling (peak: 0.227 m (SD 0.108 m), p = .0267; mean: 0.093 m (SD 0.049 m), p = .0061). During gait, vastus medialis activation onset was delayed with respect to initial contact following the kneeling exposure (pre: -0.159 s (SD 0.034 s); post: -0.152 s (SD 0.035 s), p = .0004; 30post: -0.148 s (SD 0.032 s), p = .0003); however, the biological significance of this small change in activation onset is questionable. The kneeling protocol did not elicit a change in knee proprioception, or in the measures of external loading evaluated during gait. Greater frontal plane knee motion following the kneeling exposure suggests a negative adaptation in movement control that may act to increase the risk of traumatic joint injury that could lead to secondary knee osteoarthritis. The lack of change in proprioceptive acuity implies that changes in knee joint position sense are not responsible for the observed change in squat control. In addition, the dynamic kneeling exposure used in the current study seems to reduce the potential for inducing adaptations in motor control during gait. This reasoning is based on a comparison to previous work that found alterations in gait mechanics following a 30-minute static full-flexion kneeling exposure. Further research is needed on the effects of prolonged and cyclic kneeling on ligamentous creep, joint laxity, and neuromuscular control during gait, as well as other occupationally relevant tasks such as squat transitions.
Passive Frontal Plane Knee Joint Laxity Following Anterior Cruciate Ligament Reconstruction Within 6 Months to 5 Years
(University of Waterloo, 2022-01-28) Loo, Michelle; Acker, Stacey
Following an anterior cruciate ligament rupture, surgical reconstructions aim to restore the joint stability. Increased frontal plane laxity has been observed in the anterior cruciate ligament deficient knee, intra-operatively immediately following reconstruction compared to contralateral knees, and in osteoarthritic knees. This indicates that surgical intervention may not have fully mitigated the increased frontal plane laxity associated with an anterior cruciate ligament tear. The primary objective of this study was to compare passive frontal plane laxity in a relatively young study cohort (aged 19-24) across three knee statuses (anterior cruciate ligament reconstructed knees (between 6 months to 5 years post-operation), contralateral knees, and knees from a control group), taking into account sex. It was hypothesized that the anterior cruciate ligament reconstructed knees would have the greatest frontal plane laxity, followed by the contralateral knees, and finally the control knees, where females would have a greater laxity compared to males across all three knee statuses. A secondary objective of this study was to quantify the repeatability and sensitivity of the frontal plane measurement system following design modifications that: removed the effect of the gravitational force from the plane of measurement, applied a consistent load between participants, allowed rotation about the knee’s natural joint center, and monitored muscle activity that ensured passive laxity measures. It was hypothesized that the frontal plane measurement system of this study would have a greater repeatability and sensitivity compared to previous designs reported in the literature. Twenty-four university aged participants (twelve females mean age 20.5 ± 1.8 and twelve males mean age 21.7 ± 2.3) were recruited for this cohort study. There were two groups: twelve participants with one ACL reconstructed knee and one contralateral knee (that had no previous ACL tear or repair) and twelve age- and sex-matched controls. Of the ACL reconstructed participants, six received a bone-patellar tendon-bone autograft and six received a hamstring autograft during their ACL reconstruction. Passive bilateral lower limb kinematic data was collected using infrared marker clusters while vastus lateralis and vastus medialis electromyographic readings were recorded. The mean laxity from three trials was measured using a free moving sled apparatus. Frontal plane laxity was defined as the passive varus-valgus tibiofemoral angular excursion in response to a varus-valgus moment of 10 Nm. For controls, the knee with the greatest measured mean frontal plane laxity was used. The standard error of measurement and minimal detectable difference was calculated using the mean of the three repeated laxity measures for the right limb across all participants. The means of the three repeated laxity measures for each knee status (ACL reconstructed knees, contralateral knees, and controls knees) were used in one two-way mixed model analysis of variance between ACL reconstructed knees and contralateral knees (status x sex) with an alpha level of 0.05 and two additional two-way ANOVA between ACL reconstructed knees and controls knees, and contralateral knees and control knees (status x sex) with an alpha level of 0.05. One t-test with an alpha level of 0.05 was used to determine if there were any statistically significant differences between the type of surgical reconstruction (bone-patellar tendon-bone graft or hamstring graft). The standard error of measurement and mean detectable difference was 0.7° and 1.8° respectively. No statistically significant knee status main effect, sex main effect and knee status x sex interaction occurred (all p>0.05). There was no significant difference in laxity between reconstruction types (p>0.05). This sample population achieved normal frontal plane knee laxity at short-term follow-up. This supports the possibility that the laxity previously measured in long-term follow-up is not residual laxity from the anterior cruciate ligament rupture that was insufficiently addressed by the reconstruction procedure. Increased frontal plane laxity that has been observed in anterior cruciate ligament reconstructed and osteoarthritic knees may instead be an outcome of the disease itself or other risk factors.

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