The purpose of this study was to examine the independent effects of anterior knee pain (AKP) on bilateral ground reaction force (GRF) during running, with a focus on GRF applied to the uninvolved leg, which, prior to this study, had never been evaluated. Twelve volunteers completed three data collection sessions, that corresponded to one of three conditions (control, sham, and pain), in a counterbalanced order. For each session, subjects ran for five minutes. For the pain and sham sessions, respectively, hypertonic and isotonic saline were infused into the infrapatellar fat pad of the right leg during the running, while no infusion was involved in the control session. GRF data were collected during the final 30 seconds of running. Functional statistics were used to determine the effects of session and leg (right and left) on vertical and anterior-posterior GRF throughout the stance phase of running. A mixed model ANOVA was used to determine the effect of session and leg on vertical GRF load rate, impulse due to vertical, propulsive, and braking GRFs. A repeated measures ANOVA was used to determine the effect of session and time on subject-perceived pain. Alpha was set to 0.05 for all statistical comparisons. Unexpectedly, no significant session × leg interaction existed for vertical GRF at any time point during stance phase of running. Similarly, the experimental AKP did not affect impulse due to vertical GRF or load rate for the vertical GRF. There was, however, a significant session × leg interaction for anterior-posterior GRF. For the pain session, involved-leg braking GRF was 11% greater than uninvolved-leg braking GRF, during the first 9% of stance phase. There was also a significant between-session difference for involved-leg braking impulse (p = 0.023) and uninvolved-leg propulsive impulse (p = 0.027). The mean involved-leg braking impulses were 11.3 Ns (± 0.6), 13.2 Ns (± 0.6) and 13.2 Ns (± 0.6) for the pain, control, and sham sessions, respectively. Mean uninvolved-leg propulsive impulses were 14.8 Ns (± 1.3), 13.6 Ns (± 1.3), and 13.5 Ns (± 1.3) for the pain, control, and sham sessions, respectively. These differences in anterior-posterior GRF might reflect a compensatory unloading of the involved leg due to AKP.

The use of wearable sensors in consumer health and medicine is a rapidly developing topic of interest. The main purpose of the series of studies in this thesis is to identify novel uses of technology that can provide clinicians and scientists clinically feasible, low cost approaches to obtain meaningful information about functional limb symmetry in patients with knee injuries. In Study 1, individuals undergoing knee surgery were evaluated as they walked and stepped down onto a force platform in a manner similar to how one would step off a curb to cross a street. When subjects stepped onto their uninvolved leg, peak vertical ground reaction force was greater and occurred earlier than when stepping onto their involved leg. Asymmetries were greater in those with higher quadriceps neuromuscular impairment. In Study 2, the reliability and validity of using wearable accelerometer sensors was evaluated for estimating single leg vertical hop height in healthy people and individuals after ACL reconstruction surgery. The reliability and concurrent validity of using accelerometers to estimate single leg hop height were excellent, and were similar for healthy and ACL-reconstructed subjects. Error for this method was low, in particular when the accelerometer was worn at the lower leg. Asymmetry in hop height was greater in those with higher quadriceps neuromuscular impairment. In Study 3, wearable accelerometers were compared to a system of motion capture cameras and force platform as a method to assess functional movement asymmetry in healthy people and individuals after ACL reconstruction. While walking and stepping down, accelerometers worn at the waist were able to detect underlying movement asymmetry when it exists in people after ACL reconstruction. Acceleration at the waist was strongly associated with vertical ground reaction force and moderately associated with knee extension moments. Collectively, these studies provide evidence that functional movement symmetry can be measured with simple, inexpensive methods that can be used in a variety of clinical or field-based settings.

It has been suggested that simulating physiological loading of the knee during magnetic resonance imaging (MRI) is a promising technique for assessing soft and hard tissues in the knee joint. We have developed a novel MRI-compatible lower limb loading and positioning device to assess knee biomechanics in a physiologically relevant environment using MRI. The objectives of this study were (1) to evaluate inter- and intra-examiner reliability for using our custom-built loading system to maintain a desired load magnitude and direction during each loading trial and over repeated subject visits and (2) to determine the effect of the applied load on motion of the subject's knee over the duration of a loading trial. The pneumatic-controlled loading system was tested on ten subjects at a compression load of 50% of the subject's bodyweight. Two examiners separately positioned and loaded each subject for three loading trials per visit, repeated for three visits. The primary outcome measure was the magnitude of the primary axial load (proximal/distal force) applied to the subject's foot over a loading trial. Secondary outcome measures included average magnitude of medial/lateral and anterior/posterior forces as well as valgus/varus, flexion/extension, and external/internal moments applied to the subject's foot during a loading trial. Location of center of loading at the foot was also recorded. Primary axial load was found to be maintained to within 44-47% of subject bodyweight. Following load-application, the subject's knee exhibited movement throughout the duration of each loading trial. We found that 61.0% of proximal/distal knee displacement occurred within the first 2 minutes following loading. Between minutes 4 and 12, knee positioning was maintained to within 0.92 mm in the medial/lateral direction and 1.24 mm in the proximal/distal direction. We conclude that our loading device can apply controllable and reproducible loading over repeated trials as well as limit subject motion throughout each trial.

Contact stress exposure is thought to play a significant role in many aspects of joint degradation and pathology. Effective and accurate contact stress computation in native or pathological subject specific joints is an important tool in determining the role of contact stress in OA onset and worsening as well as eventually developing and monitoring interventions to prevent joint degradation. In the past FEA modeling has allowed for studies to be completed which relate contact stress exposure human ankle joint to the presence of radiographic OA. While promising, contact FEA for subject specific models is significantly limited by the number of cases that can be computed due to the difficulty of FEA modeling, as well as numerical convergence issues present in contact FEA. To obtain truly statistically powerful conclusions about the causes of joint degradation and OA onset large numbers of subject specific models will need to be created, run and analyzed. Rigid body spring modeling or RBSM has proven to be an effective method of contact stress measurement for both expedited evaluation of PTOA risk following tibial plafond fractures as well as for evaluation of BMLs worsening in a cohort of 38 at risk patients. RBSM treats cartilage as a bed of springs attached to an underlying rigid bone surface. It is a significant simplification from FEA in that it does not allow computation of internal stresses of an object, elaborate material treatments, or true deformation of an object. This simplification comes with the benefit of reduced computational and investigator burden due to the lack of numerical convergence issues as well as no FEA meshing step. A custom written RBSM algorithm was created in MATLAB which works in conjunction with a load balancing algorithm to iteratively solve contact solutions in both load and displacement control. This algorithm was first validated against a previously done physical validation study using two human cadaver ankles in a custom built fixture. The RBSM method was then used to replicate previously obtained FEA results in a study of 22 human ankle joints following tibial plafond fracture. FEA models and loadings were adapted for the RBSM method and run. The RBSM offered a significant speed increase while maintaining comparable results to the FEA. The ability of RBSM to predict PTOA development using a contact stress-time-area exposure metric was virtually unchanged (95% KL grade concordance and 100% OA concordance vs. 94% KL grade concordance and 100% OA concordance, for RBSM and FEA, respectively). The RBSM method was then combined with a feature based 3D-2D alignment routine custom written in MATLAB. This alignment routine uses a ray casting method to recreate a virtual x-ray silhouette edge for a 3D model. This model is then aligned to a 2D edge tracing based off an input radiograph depicting a functional pose of the bone. A global optimizer (simulated annealing) is used to determine the best Euler transform to place the bone in an accurate position in the recreated virtual scene. 38 subject specific knee models segmented from the MOST cohort were aligned to functional appositions bases off of fixed flexion standing radiographs. Contact stresses were then obtained from these aligned joints using RBSM to evaluate the relationship between contact stress level and bone marrow lesion worsening. It was found that as contact stress level increases so does the risk of BMLs worsening. As the worsening of BMLs is associated with joint pain, degradation, and pathology an expedited contact stress method which can accurately predict BML worsening is especially valuable.

Typical rehabilitation strategies and performance tests after knee surgery are often based on peak lower extremity strength. However, people rarely generate maximal knee force in both daily and sports activities, which are characterized by brief periods of rapid muscle activation and relaxation. Thus, the ability to rapidly develop or modulate force may be more meaningful and more relevant to function. It is unclear how knee surgery influences the neuromuscular mechanisms controlling the ability to rapidly develop leg muscle force and produce power, or the functional relevance of these characterizations of muscle performance in relation to injury, surgery, and recovery. The primary purpose of this collection of studies was to assess rapid quadriceps muscle activation and lower extremity force production in people undergoing arthroscopic knee surgery for meniscal debridement and anterior cruciate ligament (ACL) reconstruction. People undergoing arthroscopic partial meniscectomy (APM) presented with significant deficits in knee extensor rate of torque development (RTD), leg press power, and rapid quadriceps muscle activation both prior to and in the initial month following surgery. Subjective knee function was significantly correlated with RTD variables but not with peak strength or quadriceps volume. Limitations in the ability to rapidly activate the involved quadriceps suggests that impaired centrally mediated neural function of the involved quadriceps may limit RTD and lower extremity power post-surgery. Next, the speed and intensity of quadriceps exercise performed in the early post-surgical period of patients post-APM and the relationships between training parameters, strength, quadriceps RTD, and subjective knee function were investigated. Subjects performed high intensity quadriceps contractions 2-3x/week in the first month following surgery. All subjects increased quadriceps strength, but people who trained with greater RTD following APM demonstrated greater improvements in RTD and had better patient-based outcomes scores than those who trained with a slower rate of torque rise. Finally, power and rate of force development (RFD) in people ≤ 1 year following ACL reconstruction were evaluated along with movement biomechanics, typical clinical measures of readiness to return to activity, and patient-based outcomes. Significant side-to-side asymmetries in quadriceps strength, RFD, leg press strength and power, and knee joint kinetics were noted. Deficits in voluntary quadriceps strength paralleled the deficits in early phase RFD, indicating that in this population RFD was limited by the intrinsic properties and force production capacity of the quadriceps, not the ability to rapidly activate the muscle. However, strong to very strong correlations were found between quadriceps RFD, movement biomechanics and subjective knee function, which were predominantly stronger than the correlations with peak quadriceps strength. Leg press strength, power, and acceleration were very strongly correlated with movement biomechanics and subjective knee function. In summary, this series of studies provides important insight into the neuromuscular mechanisms related to rapid lower extremity force development and muscle activation in the context of knee joint injury and recovery after arthroscopic knee surgery. Collectively, this work suggests that the inability to quickly develop or modulate quadriceps force may have significant functional consequences, and that rehabilitation efforts following arthroscopic knee surgery to incorporate both specific dosage of and earlier performance of rapid leg muscle contractions should be explored.

Osteoarthritis is a chronic, deleterious disease of the joints. It currently affects nearly 25 million Americans. Clinically, osteoarthritis presents as joint pain and verified by radiographic evidence of joint space narrowing. Unfortunately, symptomatic osteoarthritis describes the later stages of disease, at which point irreversible cartilage and bone damage has occurred. Cross-sectional imaging modalities offer the promise of visualizing early features of disease, enabling the development and evaluation of interventions to forestall or prevent degenerative change. Modalities of clinical interest include magnetic resonance imaging (MRI) and multi-detector computed tomography (MDCT). The following work describes the efficacy of MRI-derived measures for the identification and accurate quantification of local and whole joint changes in articular cartilage thickness changes in vivo. This was performed as part of a study investigating the diagnostic potential of clinical morphometric and compositional MRI to identify early features of osteoarthritis in a large animal model of traumatic knee joint injury. Surgically induced trauma consisted of a partial medial meniscectomy and blunt impact of either 0 J, 0.6 J, or 1.2 J to the weight-bearing cartilage of the medial femur. The study was six months in duration. To evaluate the accuracy of MRI-derived measures of cartilage thickness, imaging acquired at time of euthanasia was compared to high-resolution contrast-enhanced micro-computed tomography (micro CT). 3-dimensional multimodal analysis demonstrated that morphometric MRI imaging is sensitive to sub-voxel changes in cartilage thickness. Therefore, MRI is a clinically relevant modality to quantify subtle cartilage damage, thereby presenting an opportunity to identify patients earlier in the disease process.

Millions of people each year spend some portion of their time using mobility aids to facilitate periods of non-weight bearing ambulation. The use of these devices changes the loading conditions of the lower extremities, which may result in skeletal muscle adaptations. The purpose of this work was to evaluate the effects of 3 types of mobility aids on lower-extremity muscle activity. Evaluation was based on 1) measured muscle activation signals using electromyography (EMG), and 2) measured joint kinematics and ground reaction forces, which were used to predict muscle forces. 16 healthy subjects (7 female, 9 male), ages 18-27 participated in the study. Subjects were instructed to ambulate using each of three mobility aids (crutches, a knee scooter and a temporary-injury prosthesis) as well as normal walking. EMG and motion capture were used to obtain bilateral data from the lower half of the body during ambulation on each of these mobility aids and walking (10 trials on each per subject). Muscles studied were right and left vastus lateralis (VLR, VLL), rectus femoris (RFR, RFL), Biceps femoris long head (BFR, BFL), and gastrocnemius medialis (GMR, GML). Joint kinematics and ground reaction force data (joint kinetics) were acquired using a standard camera-based motion capture system. The measured joint kinetics were used as inputs to the open source musculoskeletal biomechanics software OpenSim (SimTK, Stanford, CA), which allowed prediction of muscle force data for a representative subject during each mode of ambulation. As compared to walking, the following differences in EMG activation were significant. For the knee scooter, increases in VLR, RFR, BFL and decreases in GMR. For the TI prosthesis, increases in VLR, RFR, BFR, VLL, RFL, GML and decreases in GMR. For crutches, increases in BFR, VLL, RFL, BFL, GML and decreases in VLR, GMR. Muscle force results were similar, but demonstrated inadequacy of current musculoskeletal simulation software to resolve muscle forces during non-weight bearing portions of gait based solely on kinetic data. Results for walking data were similar to what is reported in the literature for normal gait. This study provides useful bilateral data that describe measured lower-extremity EMG activation amplitudes and muscle force predictions based on kinetic data during ambulation using three different ambulatory aids, compared to normal walking. Based on a criteria of maintaining muscle activation, the TI prosthesis proved most effective among the devices tested. The data presented will be valuable to clinicians in providing insight into which mobility aid may be best suited for a particular patient. It is anticipated that these data will provide designers of mobility aids with a protocol for evaluation of designs based on their potential to cause or prevent muscle adaptations.

The objective of this study was to investigate the influence of cyclic loading on the extensibility of hamstring muscle-tendon units in vivo.Study Design: A test-retest randomised controlled trial with repeated measures was undertaken.Background: Stretching has been commonly promoted to increase the passive extensibility of the muscle-tendon units, yet the mechanism behind its proposed effects remains ambiguous. In vivo studies of stretching have mostly been limited to the viscoelastic characteristic of stress-relaxation. Few studies have investigated the characteristic of creep. Animal and cadaver in vitro creep experiments have consistently shown increases in the length of the soft tissues, with associated changes in their resistance and stiffness. These results however, might not be representative of human muscle-tendon units under in vivo conditions. Additionally, those in vivo human studies that have investigated creep phenomenon have contrasting results. To date, no known in vivo study has examined passive cyclic loading of human hamstrings to a constant load level.Method: Using a repeated measures design the extensibility of the hamstring muscles were assessed by a passive knee extension test (PKE) to maximal stretch tolerance using a KinCom® dynamometer. Those participants in the intervention group underwent 45 continuous passive cyclic loadings as the KinCom® dynamometer moved the knee joint into extension until torque reached 85% of maximal passive resistance torque measured in the passive knee extension test. The control group sat quietly relaxed during the intervention period. Measurements of hamstring passive extensibility using the PKE test were repeated at the end of the intervention.Results: Following the intervention, the PKE test showed for the cyclic loading group there was a significant (p < 0.05) increase in both maximal passive resistance torque (mean 23%) and knee joint angle (mean 6.3%). A significant (p < 0.05) decrease in passive resistance torque (mean 11.8%) when re-measured at the baseline position of maximal passive knee angle was observed. A significant increase (p < 0.05) was found for passive stiffness over the final 10% of the knee torque-angle curve. No significant difference (p > 0.05) was found for passive stiffness for the full (100%) of the torque-angle curve. Of the control group, no significant differences (p > 0.05) were observed for all variables of the PKE test. Analysis of cycle one compared to forty-five of the cyclic loading intervention procedure showed a significant (p < 0.05) increase in both passive knee joint angle (mean 5.2%) and passive stiffness (mean 28.6%) over the final 10% of the knee joint torque-angle. No significant difference (p > 0.05) was found for passive stiffness across the full (100%) knee joint torque-angle.Conclusion: The findings of the current study demonstrated that after cyclic loading the hamstring muscles lengthened and became stiffer over the final gained range of knee joint motion. Although the current study cannot determine the mechanism behind the changes in the variables of interest, these findings do provide some evidence that most likely a combination of altered stretch tolerance and local mechanical effects within the muscle-tendon unit, i.e. creep lengthening were responsible.

The effect of a preseason conditioning program of balance and jump landing training exercises was studied to evaluate its influence on static and dynamic balance and the occurrence of ankle and knee injuries in Basketball. Fifty-eight female representative Basketball players (aged 9 – 17 years) were studied over one season. Twenty-nine of these players participated in a six week training program implemented during the preseason. Pre and post tests measured balance and injuries documented over one season. The experimental group’s static and dynamic balance improved significantly as measured by a stork stand test and a multiple single-leg hop-stabilisation test In a post hoc analysis of dynamic balance, participants in the 12 – 13 years experimental group performed significantly better on dynamic balance, whereas the 12 – 13 years control group performed poorest compared with all other age cohorts. The lower limb injury rate for the 29 experimental group participants was .78 injuries per 1 000 hours, while the control group sustained no lower limb injuries in the 2001 season, based on the injury definition utilised in the study. This finding was statistically significant although three of the four injuries sustained were contact injuries. The study findings indicate that appropriately defined balance training can be beneficial for improving balance ability in female Basketball players. Evidence was found in the study for the existence of a critical age when balance training should be introduced to maximise the benefit for young female adolescent Basketball players. / Master of Education (Hons)

Gait biomechanics of forty male subjects was evaluated at normal and fast walking speeds. The forty subjects composed four groups based on their body mass index, with ten subjects in each of the groups: underweight, normal weight, overweight and obese. To our knowledge this is the first comprehensive 3-dimensional kinetic and kinematic gait analysis of all four groups based on body mass index. The obese subjects walked with significantly slower gait speed by taking shorter steps and strides, while having significantly higher step widths and longer gait cycle times than the other subjects. The obese subjects spent significantly less time in single support and more time in double support than their non-obese counterparts. These adjustments in temporal characteristics for the obese participants may be as a result of the gait compensation for the additional body weight in order to give them the most efficient, stable and balanced walking ability. Body mass index affected significantly the forces and moments at the ankle, knee and hip in the medial-lateral plane while speed effects were more prominent in the sagittal and transverse planes. These results suggest that an increase in the body weight would affect the gait stability while increasing the speed will affect the gait progression. Contrary to most researchers beliefs that an increase of the body weight would increase the forces and moments of the knee in all three planes, this study was able to prove that the actual forces and moments in the medial-lateral plane for the knee joint decrease while the ones in the sagittal plane increase. On the other hand, the hip joint in the medial-lateral plane displays the highest forces and moment for the obese subjects. These results are indicative of a gait compensation related to increasing body weight in the medial-lateral compartment of the lower extremity joints. Recommendations for further studies and follow up experiments are enclosed.