Semiautomatic three-dimensional knee motion assessment system

Gait biomechanics phenotypes among total knee arthroplasty candidates by machine learning cluster analysis

Knee osteoarthritis patient phenotyping is relevant to developing targeted treatments and assessing the treatment efficacy of total knee arthroplasty (TKA). This study aimed to identify clusters among TKA candidates based on demographic and knee mechanic features during gait, and compare gait changes between clusters postoperatively. TKA patients underwent 3D gait analysis 1-week pre (n = 134) and 1-year post-TKA (n = 105). Principal component analysis was applied to frontal and sagittal knee angle and moment waveforms, extracting major patterns of variability. Age, sex, body mass index, gait speed, and frontal and sagittal pre-TKA angle and moment PC scores previously identified as relevant to TKA outcomes were standardized (mean = 0, SD = 1, [134 × 15]). Multidimensional scaling and machine learning-based hierarchical clustering were applied. Final clusters were validated by examining intercluster differences pre-TKA and gait feature changes (Post_PCscore  - Pre_PCscore ) by k-way Χ² and ANOVA tests. Four TKA candidate phenotypes yielded optimum clustering metrics, interpreted as higher and lower functioning clusters that were predominantly male and female. Higher functioning clusters pre-TKA (clusters 1 and 4) had more dynamic sagittal flexion moment (p < 0.001) and frontal plane adduction moment (p < 0.001) loading/un-loading patterns during stance. Post-TKA, higher functioning clusters demonstrated less knee mechanic improvements during gait (flexion angle p < 0.001; flexion moment p < 0.001). TKA candidates can be characterized by four clusters, predominately separated by sex and knee joint biomechanics. Post-TKA knee kinematics and kinetics improvements were cluster-specific; lower functioning clusters experienced more improvement. Cluster-based patient profiling may aid in triaging and developing OA management and surgical strategies meeting group-level function needs.

The Effect of Lumbar Belts with Different Extensibilities on Kinematic, Kinetic, and Muscle Activity of Sit-to-Stand Motions in Patients with Nonspecific Low Back Pain

Although lumbar belts can be used for the treatment and prevention of low back pain, the role of the lumbar belt remains unclear without clear guidelines. This study aimed to investigate the effect of lumbar belts with different extensibilities on the kinematics, kinetics, and muscle activity of sit-to-stand motions in terms of motor control in patients with nonspecific low back pain. A total of 30 subjects participated in the study: 15 patients with nonspecific low back pain and 15 healthy adults. Participants performed the sit-to-stand motion in random order of three conditions: no lumbar belt, wearing an extensible lumbar belt, and wearing a non-extensible lumbar belt. The sit-to-stand motion's kinematic, kinetic, and muscle activity variables in each condition were measured using a three-dimensional motion analysis device, force plate, and surface electromyography. An interaction effect was found for the time taken, anterior pelvic tilt angle, and muscle activity of the vastus lateralis and biceps femoris. The two lumbar belts with different extensibilities had a positive effect on motor control in patients with nonspecific low back pain. Therefore, both types of extensible lumbar belts can be useful in the sit-to-stand motion, which is an important functional activity for patients with nonspecific low back pain.

Association of Low Physical Activity Levels With Gait Patterns Considered at Risk for Clinical Knee Osteoarthritis Progression

Objective

Although gait analysis provides an estimate of joint loading magnitude and patterns during a typical step, accelerometry provides information about loading frequency. Understanding the relationships between these components of loading and knee osteoarthritis (OA) progression may improve conservative management, as gait interventions may need to account for physical activity levels or vice versa. The primary objective was to examine relationships between gait patterns that have previously been associated with OA progression and accelerometer‐derived metrics of loading frequency. The secondary objective examined the association of accelerometer‐derived metrics and total knee arthroplasty (TKA) at a mean follow‐up of 3.5 years.

Methods

Fifty‐seven individuals with knee OA underwent gait analysis and 1 week of accelerometer wear. Spearman correlations were calculated between accelerometer‐derived metrics and gait patterns. Differences across quartiles of step count were examined with Jonckheere‐Terpstra tests. In a subsample, baseline differences between TKA and no TKA groups were examined with Mann‐Whitney U‐tests.

Results

Gait variables previously related to progression were correlated to both step count and moderate‐ to vigorous‐intensity, but not lower‐intensity, physical activity. Individuals in the lowest quartile (~4000 steps/day) exhibited gait patterns previously related to progression. There were no differences in any baseline accelerometer‐derived metrics between those that did and did not undergo TKA at follow‐up.

Conclusion

Complex relationships exist between gait, physical activity, and OA progression. Accelerometer‐derived metrics may contribute unique information about overall loading for individuals above a certain activity threshold, but for those with lower activity levels, gait may be sufficient to predict clinical progression risk, at least over the short term.

Individual Gait Features Are Associated with Clinical Improvement After Total Knee Arthroplasty

Background:

Over 20% of patients do not report clinically relevant pain relief or functional improvements after total knee arthroplasty (TKA). The aim of this study was to investigate the effect of demographics, pre-TKA knee-joint biomechanics, and postoperative changes in knee biomechanics on meaningful improvements in self-reported pain and function after TKA.

Methods:

Forty-six patients underwent 3-dimensional gait analysis and completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire before and 1 year after TKA. Response to treatment in terms of pain relief and functional improvement (“pain and function responders”) was defined as improvements in WOMAC scores that met minimal clinically important difference thresholds in the pain and function domains. Differences between responder and non-responder demographics, severity of the osteoarthritis as seen radiographically, and knee kinematics and kinetics before TKA were explored using the t test and Mann-Whitney U test. Correlations and regression models were used to examine demographics, baseline knee kinematics and kinetics, and post-TKA kinematic and kinetic improvements associated with being a pain responder and a function responder separately. Analyses were conducted using a hypothesis-driving approach.

Results:

Of the 46 patients, 34 were pain responders and 36 were function responders. Preoperatively, both responder groups had a higher radiographic severity (Kellgren-Lawrence) grade (p = 0.03) and pain responders were more symptomatic according to their WOMAC score (p < 0.04). Less preoperative stance-phase flexion-extension angle range (p ≤ 0.03), lower preoperative stance-phase adduction (varus) angle magnitude (p = 0.01), and less postoperative reduction in the adduction angle magnitude (p ≤ 0.009) were independently associated with more self-reported improvement in pain and function.

Conclusions:

Patients with a higher radiographic severity grade, with specific frontal and sagittal knee kinematic patterns during gait before TKA, and who demonstrated less reduction in frontal plane angles during gait after TKA had greater self-reported pain and function score improvements after standard TKA. Gait analysis may aid preoperative identification of kinematic subgroups associated with self-reported improvements after TKA, and provide evidence that may inform triaging, surgical planning, and expectation management strategies.

Level of Evidence:

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Differences in Baseline Joint Moments and Muscle Activation Patterns Associated With Knee Osteoarthritis Progression When Defined Using a Clinical Versus a Structural Outcome

Both structural and clinical changes can signify knee osteoarthritis progression; however, these changes are not always concurrent. A better understanding of mechanical factors associated with progression and whether they differ for structural versus clinical outcomes could lead to improved conservative management. This study examined baseline gait differences between progression and no progression groups defined at an average of 7-year follow-up using 2 different outcomes indicative of knee osteoarthritis progression: radiographic medial joint space narrowing and total knee arthroplasty. Of 49 individuals with knee osteoarthritis who underwent baseline gait analysis, 32 progressed and 17 did not progress using the radiographic outcome, while 13 progressed and 36 did not progress using the arthroplasty outcome. Key knee moment and electromyography waveform features were extracted using principal component analysis, and confidence intervals were used to examine between-group differences in these metrics. Those who progressed using the arthroplasty outcome had prolonged rectus femoris and lateral hamstrings muscle activation compared with the no arthroplasty group. Those with radiographic progression had greater mid-stance internal knee rotation moments compared with the no radiographic progression group. These results provide preliminary evidence for the role of prolonged muscle activation in total knee arthroplasty, while radiographic changes may be related to loading magnitude.

Gait analysis in short-term follow-up of medial opening wedge high tibial osteotomy

BACKGROUND

Biomechanical gait changes are proposed as adaptations to medial knee osteoarthritis (OA), and little is known about which parameters can be modified early by high tibial osteotomy (HTO) surgery. The aim of this study was to identify early gait changes in a postoperative period of 6 months as compared to a control group, in three different spatial planes.

METHODS

Twenty-one patients with OA were submitted to three-dimensional gait analysis preoperatively and 6 months after HTO surgery. Sixteen healthy individuals were selected for the control group.

RESULTS

Compared to the control group, OA patients walked more slowly, with a shorter stride length, and with a higher knee varus and flexion angles. The gait changes detected in the postoperative of 6 months were a significant reduction in knee varus angle and adductor moment in coronal plane; an important reduction in knee extension and an increased extensor moment in sagittal plane; also an increased foot external rotation angle in axial plane was observed. Flexion angle peak in swing phase, adductor and flexor moments were the gait parameters with postoperatively results that were closer to those of the control group.

CONCLUSIONS

Even in a short follow-up of 6 months, HTO determines positive results in biomechanical gait, not only in the coronal plane but also in the sagittal and axial planes and should be taken into account during the rehabilitation process.

Obesity is associated with higher absolute tibiofemoral contact and muscle forces during gait with and without knee osteoarthritis

BACKGROUND

Obesity is an important risk factor for knee osteoarthritis initiation and progression. However, it is unclear how obesity may directly affect the mechanical loading environment of the knee joint, initiating or progressing joint degeneration. The objective of this study was to investigate the interacting role of obesity and moderate knee osteoarthritis presence on tibiofemoral contact forces and muscle forces within the knee joint during walking gait.

METHODS

Three-dimensional gait analysis was performed on 80 asymptomatic participants and 115 individuals diagnosed with moderate knee osteoarthritis. Each group was divided into three body mass index categories: healthy weight (body mass index<25), overweight (25≤body mass index≤30), and obese (body mass index>30). Tibiofemoral anterior-posterior shear and compressive forces, as well as quadriceps, hamstrings and gastrocnemius muscle forces, were estimated based on a sagittal plane contact force model. Peak contact and muscle forces during gait were compared between groups, as well as the interaction between disease presence and body mass index category, using a two-factor analysis of variance.

FINDINGS

There were significant osteoarthritis effects in peak shear, gastrocnemius and quadriceps forces only when they were normalized to body mass, and there were significant BMI effects in peak shear, compression, gastrocnemius and hamstrings forces only in absolute, non-normalized forces. There was a significant interaction effect in peak quadriceps muscle forces, with higher forces in overweight and obese groups compared to asymptomatic healthy weight participants.

INTERPRETATION

Body mass index was associated with higher absolute tibiofemoral compression and shear forces as well as posterior muscle forces during gait, regardless of moderate osteoarthritis presence or absence. The differences found may contribute to accelerated joint damage with obesity, but with the osteoarthritic knees less able to accommodate the high loads.

Relationship between knee adduction moment patterns extracted using principal component analysis and discrete measures with different amplitude normalizations: Implications for knee osteoarthritis progression studies

BACKGROUND

Knee adduction moment discrete features (peaks and impulses) are commonly reported in knee osteoarthritis gait studies, but they do not necessarily capture loading patterns. Principal component analysis extracts dynamic patterns, but can be difficult to interpret. This methodological study determined relationships between external knee adduction moment discrete measures and principal component analysis features, and examined whether amplitude-normalization methods influenced differences in those with knee osteoarthritis who progressed to surgery versus those that did not.

METHODS

54 knee osteoarthritis patients had three-dimensional biomechanical measures assessed during walking. Knee adduction moments were calculated and non-normalized and amplitude-normalized waveforms using two common methods were calculated. Patterns were extracted using principal component analysis. Knee adduction moment peak and impulse were calculated. Correlation coefficients were determined between two knee adduction moment patterns extracted and peak and impulse. T-tests evaluated between-group differences.

FINDINGS

An overall magnitude pattern was correlated with peak (r=0.88-0.90, p<0.05) and impulse (r=0.93, p<0.05). A pattern capturing a difference between early and mid/late -stance knee adduction moment was significantly correlated with peak (r=0.27-0.40, p<0.05), but explained minimal variance. Between-group peak differences were only affected by amplitude-normalization method.

INTERPRETATION

Findings suggest that the overall magnitude knee adduction moment principal pattern does not provide unique information from peak and impulse measures. However, low correlations and minimal variance explained between the pattern capturing ability to unload the joint during mid-stance and the two discrete measures, suggests that this pattern captured a unique waveform feature.

Three-dimensional biomechanical gait characteristics at baseline are associated with progression to total knee arthroplasty

Objective

To determine if baseline 3-dimensional (3-D) biomechanical gait patterns differed between those patients with moderate knee osteoarthritis (OA) who progressed to total knee arthroplasty (TKA) and those that did not, and whether these differences had predictive value.

Methods

Fifty-four patients with knee OA had ground reaction forces and segment motions collected during gait. 3-D hip, knee, and ankle angles and moments were calculated over the gait cycle. Amplitude and temporal waveform characteristics were determined using principal component analysis. At followup 5–8 years later, 26 patients reported undergoing TKA. Unpaired t-tests were performed on baseline demographic and waveform characteristics between TKA and no-TKA groups. Receiver operating curve analysis, stepwise discriminate analysis, and logistic regression analysis determined the combination of features that best classified TKA and no-TKA groups and their predictive ability.

Results

Baseline demographic, symptomatic, and radiographic variables were similar, but 7 gait variables differed (P < 0.05) between groups. A multivariate model including overall knee adduction moment magnitude, knee flexion/extension moment difference, and stance–dorsiflexion moment had a 74% correct classification rate, with no overtraining based on cross-validation. A 1-unit increase in model score increased by 6-fold the odds of progression to TKA.

Conclusion

In addition to the link between higher overall knee adduction magnitude and future TKA, an outcome of clear clinical importance, novel findings include altered sagittal plane moment patterns indicative of reduced ability to unload the joint during midstance. This combination of dynamic biomechanical factors had a 6-fold increased odds of future TKA; adding baseline demographic and clinical factors did not improve the model.

Changes in knee joint muscle activation patterns during walking associated with increased structural severity in knee osteoarthritis

PURPOSE

To determine whether alterations in knee joint muscle activation patterns during gait were related to structural severity determined by Kellgren-Lawrence (KL) radiographic grades, for those with a moderate knee OA classification.

SCOPE

Eighty-two individuals with knee OA, classified as moderate using a functional and clinical criterion were stratified on KL-grade (KL II, KL III and KL IV). Thirty-five asymptomatic individuals were matched for age and walking velocity. Lower limb motion and surface electromyograms from rectus femoris plus lateral and medial sites for the gastrocnemii, vastii and hamstring muscles were recorded during self-selected walking. Gait velocity and characteristics from sagittal plane knee angular displacement waveforms were calculated. Principal component analysis extracted amplitude and temporal features from electromyographic waveform. Analysis of variance models tested for main effects (group, muscle) and interactions (α=0.05) for these features. No differences in anthropometrics, velocity, knee muscle strength and symptoms were found among the three OA groups (p>0.05). Specific features from medial gastrocnemius, lateral hamstring and quadriceps amplitude and temporal patterns were significantly different among OA groups (p<0.05).

CONCLUSIONS

Systematic alterations in specific knee joint muscle activation patterns were associated with increasing structural severity based on KL-grades whereas other alterations were associated with the presence of OA.

Body mass index affects knee joint mechanics during gait differently with and without moderate knee osteoarthritis

OBJECTIVE

Obesity is a highly cited risk factor for knee osteoarthritis (OA), but its role in knee OA pathogenesis and progression is not as clear. Excess weight may contribute to an increased mechanical burden and altered dynamic movement and loading patterns at the knee. The objective of this study was to examine the interacting role of moderate knee OA disease presence and obesity on knee joint mechanics during gait.

METHODS

Gait analysis was performed on 104 asymptomatic and 140 individuals with moderate knee OA. Each subject group was divided into three body mass categories based on body mass index (BMI): healthy weight (BMI<25), overweight (25≤BMI≤30), and obese (BMI>30). Three-dimensional knee joint angles and net external knee joint moments were calculated and waveform principal component analysis (PCA) was applied to extract major patterns of variability from each. PC scores for major patterns were compared between groups using a two-factor ANOVA.

RESULTS

Significant BMI main effects were found in the pattern of the knee adduction moment, the knee flexion moment, and the knee rotation moment during gait. Two interaction effects between moderate OA disease presence and BMI were also found that described different changes in the knee flexion moment and the knee flexion angle with increased BMI with and without knee OA.

CONCLUSION

Our results suggest that increased BMI is associated with different changes in biomechanical patterns of the knee joint during gait depending on the presence of moderate knee OA.

Effect of a high intensity quadriceps fatigue protocol on knee joint mechanics and muscle activation during gait in young adults

The purpose of this study was to determine the effect of impaired quadriceps function on knee joint biomechanics and neuromuscular function during gait. Surface electromyograms, three-dimensional motion and ground reaction forces were collected during gait before and after 20 healthy adults completed a high intensity quadriceps fatigue protocol. Pattern recognition techniques were utilized to examine changes in amplitude and temporal characteristics of all gait variables. The fatigue protocol resulted in decreased knee extensor torque generation and quadriceps median power frequencies for 18 of 20 participants (p < 0.05). The gait data from these 18 participants was analyzed. The knee external rotation angle increased (p < 0.05), the net external flexion and external rotation moments decreased (p < 0.05), and the net external adduction moment increased (p < 0.05). Post-fatigue changes in periarticular muscle activation patterns were consistent with the biomechanical changes, but were not significantly altered. Even for this low demand task of walking the knee motion and loading characteristics were altered following a high intensity fatigue protocol in a manner that may place the knee joint at greater risk for joint pathology and injury.

The association between knee joint biomechanics and neuromuscular control and moderate knee osteoarthritis radiographic and pain severity

OBJECTIVE

The objective of this study was to determine the association between biomechanical and neuromuscular factors of clinically diagnosed mild to moderate knee osteoarthritis (OA) with radiographic severity and pain severity separately.

METHOD

Three-dimensional gait analysis and electromyography were performed on a group of 40 participants with clinically diagnosed mild to moderate medial knee OA. Associations between radiographic severity, defined using a visual analog radiographic score, and pain severity, defined with the pain subscale of the WOMAC osteoarthritis index, with knee joint kinematics and kinetics, electromyography patterns of periarticular knee muscles, BMI and gait speed were determined with correlation analyses. Multiple linear regression analyses of radiographic and pain severity were also explored.

RESULTS

Statistically significant correlations between radiographic severity and the overall magnitude of the knee adduction moment during stance (r²=21.4%, P=0.003) and the magnitude of the knee flexion angle during the gait cycle (r²=11.4%, P=0.03) were found. Significant correlations between pain and gait speed (r²=28.2%, P<0.0001), the activation patterns of the lateral gastrocnemius (r²=16.6%, P=0.009) and the medial hamstring (r²=10.3%, P=0.04) during gait were found. The combination of the magnitude of the knee adduction moment during stance and BMI explained a significant portion of the variability in radiographic severity (R(2)=27.1%, P<0.0001). No multivariate model explained pain severity better than gait speed alone.

CONCLUSIONS

This study suggests that some knee joint biomechanical variables are associated with structural knee OA severity measured from radiographs in clinically diagnosed mild to moderate levels of disease, but that pain severity is only reflected in gait speed and neuromuscular activation patterns. A combination of the knee adduction moment and BMI better explained structural knee OA severity than any individual factor alone.

The effect of total knee arthroplasty on knee joint kinematics and kinetics during gait

This study determined how total knee arthroplasty (TKA) altered knee motion and loading during gait. Three-dimensional kinematic and kinetic gait patterns of 42 patients with severe knee osteoarthritis were collected 1 week prior and 1-year post-TKA. Principal component analysis extracted major patterns of variability in the gait waveforms. Overall and midstance knee adduction moment magnitude decreased. Overall knee flexion angle magnitude increased due to an increase during swing. Increases in the early stance knee flexion moment and late stance knee extension moment were found, indicating improved impact attenuation and function. A decrease in the early stance knee external rotation moment indicated alteration in the typical rotation mechanism. Most changes moved toward an asymptomatic pattern and would be considered improvements in motion, function, and loading.

Patients with osteoarthritic knees have shorter orientation and tangent indicatrices during gait

BACKGROUND

This study introduces two novel outcomes that could be used to identify people with knee osteoarthritis from healthy controls. These outcomes examine the lengths of paths on a sphere derived from knee angle and knee position during gait.

METHODS

Participants with moderate knee osteoarthritis (n=47) and no knee pathology (n=51) walked overground. The time-varying orientation matrices and position vectors of the knee (leg relative to the thigh) were measured, then arclength (constant speed) parameterized. The orientation matrix column aligned with the long axis of the leg, and the tangent, normal and binormal vectors (Frenet Frame) along the position vectors were calculated. These unit length vectors all scribe paths (indicatrices) on a unit sphere. The path lengths of these indicatrices, for all or part of a gait cycle, were the novel outcomes. A stepwise discriminant analysis defined a linear function that included those outcomes that best allocated a participant to the osteoarthritis or control group.

FINDINGS

Group differences were best detected with the indicatrix lengths associated with the orientation of the leg's long axis over a gait cycle (P<0.001) and the tangent vector over the stance phase (P=0.014). Both outcomes were smaller in the knee osteoarthritis compared to control group. Walking speed was poorly correlated with all indicatrix lengths (rho<|0.484|) and a discriminate analysis correctly classified 83.7% of the participants.

INTERPRETATION

Smaller indicatrix measures distinguished those with knee osteoarthritis from healthy controls. These outcomes introduce a promising new kinematic approach when examining gait data.

Differentiation of young and older adult stair climbing gait using principal component analysis

INTRODUCTION

Principal component analysis (PCA) has been used to reduce the volume of gait data and can also be used to identify the differences between populations. This approach has not been used on stair climbing gait data. Our objective was to use PCA to compare the gait patterns between young and older adults during stair climbing.

METHODS

The knee joint mechanics of 30 healthy young adults (23.9 + or - 2.6 years) and 32 healthy older adults (65.5 + or - 5.2 years) were analyzed while they ascended a custom 4-step staircase. The three-dimensional net knee joint forces, moments, and angles were calculated using typical inverse dynamics. PCA models were created for the knee joint forces, moments and angles about the three axes. The principal component scores (PC scores) generated from the model were analyzed for group differences using independent samples t-tests. A stepwise discriminant procedure determined which principal components (PCs) were most successful in differentiating the two groups.

RESULTS

The number of PCs retained for analysis was chosen using a 90% trace criterion. Of the scores generated from the PCA models nine were statistically different (p < .0019) between the two groups, four of the nine PC scores could be used to correctly classify 95% of the original group.

CONCLUSIONS

The PCA and discriminant function analysis applied in this investigation identified gait pattern differences between young and older adults. Identification of stair gait pattern differences between young and older adults could help in understanding age-related changes associated with the performance of the locomotor task of stair climbing.

The free moment in walking and its change with foot rotation angle

BACKGROUND

This investigation characterized the time-history pattern of the free moment (FM) during walking and, additionally, assessed whether walking with either an internally or externally rotated foot position altered the FM's time-history.

METHODS

Force plate and foot kinematic data were acquired simultaneously for 11 healthy subjects (6 males, 5 females) while walking at their self-selected comfortable speed in 3 foot rotation conditions (normal, internal and external). The FM was calculated and normalized by the product of each participant's body weight and height prior to extraction of peak FM, occurrence of peak FM in stance and net relative impulse. Differences in these values across foot rotation conditions were assessed using separate one-way, repeated measures analysis of variance and subsequent pair-wise comparisons.

RESULTS

The average FM pattern during normal walking exhibits a biphasic shape: resisting inward rotation during approximately the first half of stance and outward rotation during the latter part of stance. While no differences in peak FM or net relative impulse were observed between the internal foot rotation condition and normal walking, the external foot rotation condition resulted in significantly greater peak FM and relative net impulse in comparison to normal walking.

CONCLUSION

The differences in selected FM variables between normal walking and the external foot rotation condition are attributable to individual subject response to walking with an externally rotated foot. In this condition, some subjects displayed a FM pattern that was similar to that recorded during normal walking, while others displayed markedly larger FM patterns that are comparable in magnitude to those reported for running. The larger FM values in these latter subjects are speculated to be a result of excessive transverse plane body movements. Whilst further investigation is warranted regarding the FM time-history characteristics during walking, our results indicate that the FM may provide useful information in assessment of gait.

Co-activation differences in lower limb muscles between asymptomatic controls and those with varying degrees of knee osteoarthritis during walking

BACKGROUND

Increased muscle co-activation during gait has been identified as a neuromuscular alteration associated with knee osteoarthritis, however levels of co-activation among different osteoarthritis severity have not been established. The purpose of this study was to determine if differences in co-activation could be detected among asymptomatic controls, those with moderate and those with severe osteoarthritis using a co-activation index and a pattern recognition technique.

METHODS

Surface electromyograms from vastus lateralis and medialis, lateral and medial hamstring and gastrocnemius pairs were recorded from 63 asymptomatic, 59 moderate and 48 severe osteoarthritic subjects during self-selected walking. A co-activation index was calculated over the initial stance for four medial and lateral muscle pairs. The four co-activation indices were tested among groups using a one factor ANOVA (alpha=0.05). Gait waveform pattern recognition procedures were applied to yield a principal pattern, scored for each muscle site and subject. A mixed model ANOVA (group-muscle) tested for principal pattern score differences.

FINDINGS

A significant group effect was found (P<0.05) for all four co-activation indices. Principal pattern one captured the amplitude and general shape of activity throughout the entire stance phase. ANOVA revealed a significant (P<0.05) group by muscle interaction for the principal pattern scores. Significant differences were found among all three groups and between the two osteoarthritic groups for both measures.

INTERPRETATION

The co-activation indices and principal patterns identified that lateral site differences occurred among all three groups with medial site differences between the two osteoarthritic groups. These findings suggest that measures of muscle co-activity provide additional information related to knee osteoarthritis severity.

Explaining the hip adduction moment variability during gait: Implications for hip abductor strengthening

BACKGROUND

There is emerging interest in hip abductor function during gait and its potential relationship to knee joint pathology. During gait, the hip abductor muscles are primarily responsible for generating moments of force to control frontal plane movement. The current study investigated the relationship between hip abductor muscle function and frontal plane hip moments of force during gait.

METHODS

Frontal plane hip moments of force and electromyographic features of gluteus medius were measured during walking in 22 healthy individuals. Hip abductor strength, subject anthropometrics and gait velocity were recorded. Multiple regression models were used to evaluate the relationship between the anthropometric, velocity, strength and electromyographic variables and the initial and mid-stance magnitude of the hip adduction moment.

FINDINGS

A positive relationship was found between the initial peak moment (Nm), and both body mass and gait speed (R(2)=90%). Body mass (positive) and hip abductor strength (negative) explained significant levels of mid-stance magnitude variability (R(2)=62.5%). Gait speed (positive) explained significant levels of variability in the normalized initial peak moment (Nm/kg) (R(2)=52%). No variables were included in the normalized mid-stance moment model (P>0.05).

INTERPRETATION

Body mass was the key factor associated with high hip adduction moments during initial and mid-stance of the gait cycle. Increased gait velocity was associated with higher initial peaks and higher muscle strength was associated with lower mid-stance magnitude of the external hip adductor moment during walking. These findings suggest that in a healthy adult population, hip abductor strength and activation were not directly related to the hip adduction moment magnitude during gait.

The effect of internal and external foot rotation on the adduction moment and lateral–medial shear force at the knee during gait

It has been hypothesised that those with medial compartment knee osteoarthritis tend to externally rotate their foot during gait in order to unload the diseased compartment. This has been found to decrease the adduction moment at the knee during late stance, although the effects of foot rotation on shear forces at the knee have not yet been determined. Also, the effects of internal foot rotation on the knee during gait are not clear. This study performed a gait analysis on 11 healthy participants (M: 6; mean age 22.9+/-1.8 years) in three conditions: (1) natural foot rotation position; (2) internal foot rotation and (3) external foot rotation. Three-dimensional gait analysis calculated the knee adduction moment and lateral-medial shear force for all three foot rotation conditions. Internal rotation of the foot increased the knee adduction moment and lateral-medial shear force magnitude during late stance, while external rotation of the foot decreased the magnitude of both these measures. This implies that walking with an externally and internally rotated foot may unload the diseased compartment for those with medial and lateral compartment knee OA, respectively. Also, the relationship of foot rotation angle to the adduction moment and lateral-medial shear force was strengthened when data were corrected for the subject's normal walking condition. Knee OA subject data revealed that they were able to reduce the knee adduction moment more than normal subjects during late stance, indicating that other factors besides the rotation of the foot need to be investigated.

Mechanical factors relate to pain in knee osteoarthritis

BACKGROUND

Pain experienced by people with knee osteoarthritis is related to psychosocial factors and damage to articular tissues and/or the pain pathway itself. Mechanical factors have been speculated to trigger this pain experience; yet mechanics have not been identified as a source of pain in this population. The purpose of this study was to identify whether mechanics could explain variance in pain intensity in people with knee osteoarthritis.

METHODS

Data from 53 participants with physician-diagnosed knee osteoarthritis (mean age=68.5 years; standard deviation=8.6 years) were analyzed. Pain intensity was reported on the Western Ontario and McMaster Universities Osteoarthritis Index. Mechanical measures included weight-bearing varus-valgus alignment, body mass index and isokinetic quadriceps torque. Gait analysis captured the range of adduction-abduction angle, range of flexion-extension angle and external knee adduction moment during level walking.

FINDINGS

Pain intensity was significantly related to the dynamic range of flexion-extension during gait and body mass index. A total of 29% of the variance in pain intensity was explained by mechanical variables. The range of flexion-extension explained 18% of variance in pain intensity. Body mass index added 11% to the model. The knee adduction moment was unrelated to pain intensity.

INTERPRETATION

The findings support that mechanical factors are related to knee osteoarthritis pain. Because limitations in flexion-extension range of motion and body size are modifiable factors, future research could examine whether interventions targeting these mechanics would facilitate pain management.

Detecting differences between asymptomatic and osteoarthritic gait is influenced by changing the knee adduction moment model

INTRODUCTION

The adduction moment measured at the knee during gait is important to the study of osteoarthritis. The purpose of this study was to explore the effect of describing the knee adduction moment using three different biomechanical models, and furthermore, how the choice of model affects differences that are identified between asymptomatic and osteoarthritic gait.

METHODS

Gait was measured for 44 asymptomatic subjects and 44 subjects with moderate osteoarthritis. The adduction moment was calculated and compared using three common biomechanical models: a 2D coordinate system, a 3D tibial coordinate system, and a 3D floating axis coordinate system. Several portions of the gait cycle waveform were compared between the two groups.

RESULTS AND DISCUSSION

It was found that the choice of biomechanical model changes the overall magnitude and shape of the adduction moment waveform (maximum value changed 8-14% and peak value changed 5-17%). Significant differences between the study groups were found for each model applied; but more importantly, the portions of the gait cycle exhibiting the differences depended on the model.

CONCLUSION

These findings support the importance of specifying the knee model and waveform feature used to compare asymptomatic and osteoarthritic groups. The overall magnitude of the adduction moment throughout stance, and the mid-stance adduction moment value were found to differentiate between the two groups regardless of the adduction moment model.

Biomechanical changes at the hip, knee, and ankle joints during gait are associated with knee osteoarthritis severity

Mechanical factors have been implicated in the progression of knee osteoarthritis (OA). Understanding how these factors change as the condition progresses would elucidate their role and help in developing interventions that could delay the progress of knee OA. In this cross-sectional study, we identified kinematic and kinetic variables at the hip, knee, and ankle joints that change between three clinically distinct levels of knee OA disease severity: asymptomatic, moderate OA, and severe OA. The severity level was based on a combined radiographic/symptomatic clinical decision for treatment with (severe) or without (moderate) total knee replacement surgery. Gait variables that changed between groups were categorized as: those that differed between the asymptomatic group and both OA groups, those that differed between the asymptomatic group and the severe OA group only, or those that changed progressively, that is, the asymptomatic differed from the moderate OA, and the moderate OA differed from the severe OA group. Changes seen in both OA subject groups compared to asymptomatic included increased mid-stance knee adduction moments, decreased peak knee flexion moments, decreased peak hip adduction moments, and decreased peak hip extension moments. Changes found only in the severe knee OA group included multiple kinematic and kinetic differences at the hip, knee, and ankle joints. Gait differences that progressed with OA severity included decreased stance phase knee flexion angles, decreased early stance knee extension moments, decreased peak stance phase hip internal rotation moments, and decreased peak ankle dorsiflexion moments.

Gender differences exist in osteoarthritic gait

BACKGROUND

Knee osteoarthritis is 2-3 times more prevalent in females than males. Biomechanical differences in gait may play a role in this gender predisposition. The purpose of this study was to determine if there are gender-based biomechanical differences in the gait patterns of people with knee osteoarthritis.

METHODS

Three-dimensional gait analysis was performed on healthy (18 males and 24 females) subjects and patients with moderate knee osteoarthritis (24 males and 15 females). Kinematics and kinetics at the hip, knee and ankle were calculated. Variables including anthropometrics, stride characteristics, strength, pain, stiffness, function and radiographic disease severity were also quantified. Multivariate statistical techniques and analysis of variance were used to test for main disease effects, main gender effects and disease vs. gender interactions.

FINDINGS

A significant interaction effect between gender and disease was found in the knee flexion angle and the knee moments in the sagittal, frontal and transverse planes. In each of these measures the females exhibited different biomechanics with osteoarthritis, while the osteoarthritic males maintained the same biomechanics as healthy males. This interaction between gender and osteoarthritis was not associated with differences in anthropometrics, stride characteristics, strength, pain, stiffness, function or radiographic disease severity between the populations.

INTERPRETATION

This study has found gait pattern differences between the genders in the osteoarthritic patients that were not apparent in the healthy subjects. This suggests that the biomechanics associated with knee osteoarthritis are gender dependent. Therefore, gender specific design of biomechanical interventions to slow the progression of osteoarthritis should be explored.

Biomechanical features of gait waveform data associated with knee osteoarthritis: an application of principal component analysis

This study compared the gait of 50 patients with end-stage knee osteoarthritis to a group of 63 age-matched asymptomatic control subjects. The analysis focused on three gait waveform measures that were selected based on previous literature demonstrating their relevance to knee osteoarthritis (OA): the knee flexion angle, flexion moment, and adduction moment. The objective was to determine the biomechanical features of these gait measures related to knee osteoarthritis. Principal component analysis was used as a data reduction tool, as well as a preliminary step for further analysis to determine gait pattern differences between the OA and the control groups. These further analyses included statistical hypothesis testing to detect group differences, and discriminant analysis to quantify overall group separation and to establish a hierarchy of discriminatory ability among the gait waveform features. The two groups were separated with a misclassification rate (estimated by cross-validation) of 8%. The discriminatory features of the gait waveforms were, in order of their discriminatory ability: the amplitude of the flexion moment, the range of motion of the flexion angle, the magnitude of the flexion moment during early stance, and the magnitude of the adduction moment during stance.

Análise biomecânica das articulações do quadril e joelho durante a marcha em participantes idosos

O objetivo desse estudo foi determinar a amplitude de movimento, o momento de força, a potência e o trabalho das articulações do quadril e joelho durante a marcha em um grupo de participantes entre 55 e 75 anos de idade. O andar é uma atividade diária comum e normalmente prescrita como exercício terapêutico na reabilitação de pessoas idosas. Dados cinemáticos e cinéticos das articulações do quadril e joelho foram obtidos usando o sistema Optotrak, associado a uma plataforma de força, raio-X padronizado para determinar com acurácia o centro de rotação das articulações do joelho e quadril e dados antropométricos. A articulação do quadril gerou mais trabalho que o joelho durante a marcha. O quadril gerou um total de 0.40J/kg, sendo que 22% ocorreram no plano frontal, 76% no sagital e 2% no plano transverso. A articulação do joelho gerou um trabalho total de 0,30J/kg durante a marcha, sendo 7% no plano frontal, 90% no sagital e 3% no transverso. O estudo biomecânico das articulações durante diferentes atividades leva a uma maior compreensão do papel de cada articulação durante o movimento, contribuindo assim para a elaboração de melhores programas físicos de reabilitação, prevenção e treinamento de performance.

The influence of gait pattern on signs of knee osteoarthritis in older adults over a 5-11 year follow-up period: a case study analysis

There is evidence that joint load is a factor in the development of osteoarthritis (OA) and, while altered gait profiles have been linked with OA, it is unknown if abnormal gait is a cause or effect of the disease. While the knee's adduction moment has been implicated in the development and progression of knee OA, it is also known that shearing forces are detrimental to the health of cartilage. The purpose of this pilot study was to examine the adduction moment and gait shear forces to determine if they may lead to signs of knee OA in older adults as they age. Knee gait kinetics, standardized radiographs and a questionnaire were collected on 28 older adults (M:13) during an initial visit, and 5 to 11 years later. Radiographic score increased (knees became more osteoarthritic in 15 of 28 subjects) over time. However, gait time-distance measures remained constant in disease free participants. Two returning participants developed symptoms and radiographic evidence of knee OA. The subject with the largest adduction moment developed signs of medial OA while the subject with the smallest adduction moment developed signs of lateral OA. In addition, there was a strong correlation between the magnitudes of the adduction moment and lateral-medial shear force that needs to be investigated further. Results suggest that gait can remain stable over time in older adults. Also, the medial and lateral OA case study findings suggest that the extreme gait profiles seen in these two participants may be important in explaining cartilage breakdown and the development of OA. This longitudinal study would suggest that perhaps it is the abnormal gait pattern that leads to the development of OA, although a much larger study would be needed to confirm this finding.

Role of knee kinematics and kinetics on performance and disability in people with medial compartment knee osteoarthritis

BACKGROUND

Although gait characteristics have been well documented in people with knee osteoarthritis, little is known about the relationships between gait characteristics and performance or disability. Our purpose was to examine the role of knee kinematics and kinetics on walking performance and disability in people with knee osteoarthritis. We also examined whether pain mediated the relationship between the knee adduction moment and performance or disability.

METHODS

Three-dimensional gait analysis was conducted on 54 people with medial compartment knee osteoarthritis. Performance was quantified with the Six Minute Walk test and disability was self-reported on the Short Form-36. The pain subscale of the Western Ontario McMaster Universities Osteoarthritis Index and the functional self-efficacy subscale of the Arthritis Self-Efficacy scale were completed.

FINDINGS

A step-wise linear regression demonstrated that the variance in Six Minute Walk test scores was explained by functional self-efficacy (50%) and the range of knee motion (8%). The variance in Short Form-36 was explained by pain (36%), the peak extension angle (19%) and the range of knee motion (4%). Pain was unrelated to the knee adduction moment so analyses of pain as a mediator of the adduction moment on either performance or disability were halted.

INTERPRETATION

Kinematic output from the motor control system is useful in understanding some variance in current performance and disability in people with knee osteoarthritis. The knee adduction moment was unrelated to these variables and pain did not mediate between the knee adduction moment and performance or disability. Therefore this moment does not explain current clinical status in people with knee osteoarthritis based on the measures of performance and disability used in this study.

A multivariate gait data analysis technique: Application to knee osteoarthritis

Modern gait analysis is a powerful non-invasive tool for calculating the mechanical factors involved in pathological processes such as knee osteoarthritis (OA). Although very accurate measurements can be made, the clinical applicability and widespread use of gait analysis have been hindered by a lack of appropriate data analysis techniques for reducing and analysing the resulting large volumes of highly correlated gait data. This paper introduces a multidimensional galt data analysis technique that simultaneously considers multiple time-varying and discrete measures, exploiting the correlation structure between and within the measures. The multidimensional analysis technique was used to detect discriminatory mechanical features of knee OA gait patterns that involved interacting changes in several gait measures, at specific time portions of the gait cycle. The two most discriminatory features described a dynamic alignment difference and a loading response difference with knee OA.

[Feet insoles and knee osteoarthritis: evaluation of biomechanical and clinical effects from a literature review]

OBJECTIVE

To determine the biomechanical and clinical effectiveness of foot insoles in patients with knee osteoarthritis.

MATERIALS AND METHODS

A systematic review of the literature (Medline, Pascal and Embase) using the MESH words knee, and insole and plantar orthosis for the biomechanical part and osteoarthritis, and insole and plantar orthosis for the clinical part. Clinical studies were classified by 2 independent readers using the Jadad scale.

RESULTS

Two biomechanical theories were found: the adduction moment theory, which explains the effect of heel wedging, and articular chain theory, which explains the effect of lateral wedged insoles. The clinical effect was explained more by an anti-algesic effect than an anatomic or functional effect: the treated group consumed fewer nonsteroidal anti-inflammatory drugs than the placebo group for up to 2-years of treatment. Evidence is lacking because of methodological weakness and few clinical trials. The information on side effects is limited.

DISCUSSION

Laterally wedged foot insoles are proposed for the treatment of knee medial compartment osteoarthritis. The clinical effect is probably limited, but the treatment may reduce the digestive and renal side effects of prolonged use of nonsteroidal anti-inflammatory drugs. Foot insoles could be recommended in clinical practice despite the lack of evidence in comparing the effectiveness of other therapeutics in knee osteoarthritis.

CONCLUSION

Use of foot insoles is a nonpharmacologic treatment of osteoarthritis of the knee medial compartment.

Estimation of bone-on-bone contact forces in the tibiofemoral joint during walking

In this study, the tibiofemoral contact forces were estimated from standard gait analysis data of adult walking. Knee angles, ground reaction forces, and external flexion-extension knee moments together with lines of action and moment arms of the force bearing structures in the knee previously determined were used to obtain bone-on-bone contact forces. The heel strike, the onset of single limb stance and terminal extension before toe-off each corresponded to a significant turning point on the force versus gait cycle curve. The tibiofemoral bone-on-bone peak forces calculated reached an estimated three times bodyweight. The estimated joint loads are clinically relevant and can either be used directly for evaluation of subjects in a gait analysis, or indirectly in studies of the knee joint where models simulating loading conditions are used to investigate various pathologies.

Changes in frontal plane dynamics and the loading response phase of the gait cycle are characteristic of severe knee osteoarthritis application of a multidimensional analysis technique

BACKGROUND

Osteoarthritis of the knee is related to many correlated mechanical factors that can be measured with gait analysis. Gait analysis results in large data sets. The analysis of these data is difficult due to the correlated, multidimensional nature of the measures.

METHODS

A multidimensional model that uses two multivariate statistical techniques, principal component analysis and discriminant analysis, was used to discriminate between the gait patterns of the normal subject group and the osteoarthritis subject group. Nine time varying gait measures and eight discrete measures were included in the analysis. All interrelationships between and within the measures were retained in the analysis.

FINDINGS

The multidimensional analysis technique successfully separated the gait patterns of normal and knee osteoarthritis subjects with a misclassification error rate of <6%. The most discriminatory feature described a static and dynamic alignment factor. The second most discriminatory feature described a gait pattern change during the loading response phase of the gait cycle.

INTERPRETATION

The interrelationships between gait measures and between the time instants of the gait cycle can provide insight into the mechanical mechanisms of pathologies such as knee osteoarthritis. These results suggest that changes in frontal plane loading and alignment and the loading response phase of the gait cycle are characteristic of severe knee osteoarthritis gait patterns. Subsequent investigations earlier in the disease process may suggest the importance of these factors to the progression of knee osteoarthritis.

Static and dynamic biomechanics of foot orthoses in people with medial compartment knee osteoarthritis

OBJECTIVE

Gait biomechanics (knee adduction moment, center of pressure) and static alignment were investigated to determine the mechanical effect of foot orthoses in people with medial compartment knee osteoarthritis.

DESIGN

Repeated measures design in which subjects were exposed to three conditions (normal footwear, heel wedge and orthosis) in random order.

BACKGROUND

The knee adduction moment is an indirect measure of medial compartment loading. It was hypothesized that the use of a 5 degrees valgus wedge and 5 degrees valgus modified orthosis would shift the center of pressure laterally during walking, thereby decreasing the adduction moment arm and the adduction moment.

METHODS

Peak knee adduction moment and center of pressure excursion were obtained in nine subjects with medial compartment knee OA during level walking using an optoelectric system and force plate. Static radiographs were taken in 12 subjects using precision radiographs.

RESULTS

There was no difference between conditions in static alignment, the peak adduction moment or excursion of the center of pressure in the medial-lateral direction. No relationship was found between the adduction moment and center of pressure excursion in the medial-lateral plane. The displacement of the center of pressure in the anterior-posterior direction, measured relative to the laboratory coordinate system, was decreased with the orthosis compared to the control condition (P=0.036) and this measure was correlated with the adduction moment (r=0.45, P=0.019).

CONCLUSIONS

The proposed mechanism was not supported by the findings. The reduction in the center of pressure excursion in the anterior-posterior direction suggests that foot positioning was altered, possibly to a toe-out position, while subjects wore the orthoses. Based on the current findings, we hypothesize that toe-out positioning may reduce medial joint load.

RELEVANCE

Knee Osteoarthritis is the most common cause of chronic disability amongst seniors. Developing inexpensive, non-invasive treatment strategies for this large population has potential to impact health care costs, quality of life and clinical outcomes.

Knee and hip kinetics during normal stair climbing

Understanding joint kinetics during activities of daily living furthers our understanding of the factors involved in joint pathology and the effects of treatment. In this study, we examined hip and knee joint kinetics during stair climbing in 35 young healthy subjects using a subject-specific knee model to estimate bone-on-bone tibiofemoral and patello-femoral joint contact forces. The net knee forces were below one body weight while the peak posterior-anterior contact force was close to one body weight. The peak distal-proximal contact force was on average 3 times body weight and could be as high as 6 times body weight. These contact forces occurred at a high degree of knee flexion where there is a smaller joint contact area resulting in high contact stresses. The peak knee adduction moment was 0.42 (0.15) Nm/kg while the flexion moment was 1.16 (0.24) Nm/kg. Similar peak moment values, but different curve profiles, were found for the hip. The hip and knee posterior-anterior shear forces and the knee flexion moment were higher during stair climbing than during level walking. The most striking difference between stair ascent and level walking was that the peak patello-femoral contact force was 8 times higher during stair ascent. These data can be used as baseline measures in pathology studies, as input to theoretical joint models, and as input to mechanical joint simulators.

Software for temporal gait data analysis

This study presents a computer program, developed to support a low-cost, portable telemetry system that has been designed to assess footfall timing. This software frees the user from data processing and allows concentration on data analysis. The new technique has been applied with accuracy and reliability to the analysis of the gait of orthopedic patients, athletes, mountaineers, etc. The subroutines developed for data acquisition, storage and analysis are explained in detail, and an example is presented.

Aging-related changes in skeletal muscle. Mechanisms and interventions

The aging-related motor handicap and the growing population of elderly citizens have enormous socioeconomic effects on the modern healthcare system. The mechanisms underlying impaired motor performance in old age are complex and involve the central and peripheral nervous systems and the muscle tissue itself. It is widely accepted that the aging-related loss of muscle mass, strength and quality has a significant detrimental impact on motor performance in old age and on the ability to recover from falls, resulting in an increased risk of fractures and dependency. Therefore, the prevention of falls and gait instability is a very important safety issue, and different intervention strategies have been used to improve motor performance among the aging population. There is general consensus that physical exercise is a powerful intervention to obtain long term benefits on muscle function, reduce the frequency of falls, and to maintain independence and a high quality of life in older persons. The results from studies using different types of hormone supplementation therapies have shown interesting and encouraging effects on skeletal muscle mass and function. However, the potential risks with both growth hormone and androgen treatment are not known and long term clinical trials are needed to address safety concerns and the effects on skeletal muscle. Recent advancements in cellular/molecular, physiological and molecular biological techniques will significantly facilitate our understanding of aging-related impairments of muscle function and contribute to the evaluation of different intervention strategies.

Arm motion and load analysis of sit-to-stand, stand-to-sit, cane walking and lifting

OBJECTIVE

To conduct a pilot study to characterize the hand loads, arm joint angles and external moments corresponding to five activities of daily living demanding of the shoulder, for healthy subjects over 50 years of age.

DESIGN

The tasks were sit-to-stand, stand-to-sit, cane walking, lifting a 5 kg box with both hands, and lifting a 10 kg suitcase.

BACKGROUND

Arm motion and loading have not been previously studied for functional daily-living tasks involving substantial external loads.Methods. Motion was tracked using an optoelectronic system. Loads were measured using an instrumented chair arm, a force plate, and gravitational and acceleration loads. Six healthy volunteers (3 male, 3 female), mean age 55, with no history of shoulder problems participated in the study.

RESULTS

Average peak external moments ranged from 12.3 N m for sitting down into a chair to 27.9 N m for lifting a suitcase. Except for lifting the box, which had much lower loads, average peak hand loads varied from 16% to 19% of body weight (114-134 N). The arcs of motion were larger than for seated activities of daily-living studied previously.

CONCLUSIONS

The five tasks studied are commonly performed, yet involve large external moments. Lifting represents the greatest potential loading at the shoulder as it resulted in the highest external moments; furthermore, loads larger than those used in this study might be commonly lifted.

RELEVANCE

External moments at the shoulder should not be underestimated, even for activities of daily living.

The effect of segment parameter error on gait analysis results

The extent to which errors in predicting body segment parameters (SP) influence biomechanical analysis of human motion is unclear. Therefore, the current study quantitatively evaluated the differences in SP estimates using literature predictive functions and computed the effect of SP variation on the kinetic output of walking. For a group of 15 young males, significant differences (P<0. 05) were observed between SP estimates for the leg and thigh using the literature predictive functions, with mass and moment of inertial values differing by more than 40%. Using kinematic and ground reaction force data collected for each subject while walking, inverse dynamic analysis was performed iteratively to compute hip forces and moments while simultaneously varying SP values over nine intervals within +/-40% of a baseline value. SP variations were found to significantly affect (P<0.05) most of the kinetic estimates produced, particularly those taken during the swing phase. However, the magnitude of these effects was generally less than 1% of body weight. The data from the current study allows researchers to estimate the errors in kinetic measures due to SP variation. The results also indicate that the accuracy of SP prediction should be of concern in biomechanical research particularly for open chain and high acceleration activities. Further study is necessary to identify the importance of SP variation on other motion skills.

Radiographic and non-invasive determination of the hip joint center location: effect on hip joint moments

OBJECTIVE

To determine which of four non-invasive measures is most accurate in locating the hip joint center.

BACKGROUND

The location of the joint centers must be accurately determined in three dimensions for calculation of the moments of force during gait. It is not known which of the several non-invasive methods available for location of the hip center is most accurate.

DESIGN

Hip center location was determined using standardized X-rays and four non-invasive methods which utilized measured distances between bony landmarks in 10 healthy subjects. Hip moments during gait were obtained from optical tracking, force plate and anthropometric data.

RESULTS

The most accurate non-invasive method of locating the hip center was by taking the midpoint of a line connecting the antero-superior iliac spine and the symphysis pubis and moving inferiorly 2 cm. Using this approach the hip center was located 0.7 cm medial and 0.8 cm superior to its true location determined using the standardized X-rays. The 95% confidence interval of the maximum error difference in moments measured between this method and the standardized X-rays ranged from -0.15 to 0.4 Nm/kg in the frontal plane, -0.03 to 0.07 Nm/kg in the sagittal plane and -0.05 to -0.03 Nm/kg in the transverse plane.

CONCLUSIONS

Locating the hip center based on the distance between the antero-superior iliac spine and the symphysis pubis is a valid technique for estimating the hip center in routine gait analysis.

Relationship between alignment and kinematic and kinetic measures of the knee of osteoarthritic elderly subjects in level walking

Eleven osteoarthritic elderly subjects were tested to analyse the relationships between static radiographic alignment and dynamic kinematic and kinetic measures at the knee in gait. A standard precision radiograph procedure (QPR) was used to measure the static lower limb alignment in two planes and a 3D optoelectronic system was used to measure the biomechanical performance of the knee in level walking. Relationships were calculated between the static radiographic angular measures and the dynamic knee angular measures, dynamic knee joint forces, and dynamic knee moments of force during gait. The results indicated that there was not a close relationship between lower limb alignment and the force estimates in gait. However, a closer relationship was observed between QPR parameters, dynamic knee joint angles, and joint moments in gait, implying that complex interrelationships may exist between static alignment, dynamic alignment, and dynamic kinetic measures. These findings suggest that the static alignment measures associated with both the kinematic and kinetic measures should be combined to better explain the biomechanical changes at the knee joint. RELEVANCE:--Values for radiograph alignment and dynamic variables obtained during walking for a group of elderly subjects with moderate osteoarthritis are provided. Joint forces obtained during walking were not related to static radiographic alignment. The findings indicate that both the coronal and sagittal plane measures were associated with the magnitude of joint moments, joint angles, and timing of the events.

Abduction-adduction moments at the knee during stair ascent and descent

To examine the relative magnitude of the knee abduction-adduction moments during stair climbing, ten normal subjects (average weight 660 N, leg length 0.962 m, height 1.74 m) were studied during repeated trials of stair ascent and descent. Data were collected using a four-camera video system and two forces plates incorporated within a flight of three stairs. The inverse dynamics approach was used to calculate internal moments at the knee, and these moments were normalized in magnitude (to percent body weight and leg length) and time (percent stance). The primary findings were: (1) knee joint moments were similar in shape and magnitude for the first and second steps during both stair ascent and descent; (2) the abduction knee moments, although comparable in magnitude (25-45 Nm), were statistically smaller than the extension moments (60-85 Nm) for stair ascent and descent; and (3) the moment patterns were exclusively abductor throughout stance, indicating that the ground reaction vector always passed medial to the knee joint center. Although the knee abduction-adduction moment is not in the primary plane of motion, its magnitude should not be ignored when trying to understand the stability and function of the knee during stair climbing.

An integrated procedure to assess knee-joint kinematics and kinetics during gait using an optoelectric system and standardized X-rays

This paper describes a 3-D gait analysis system, which combines optoelectric motion tracking and a standardized X-ray procedure, to calculate the net knee-joint forces and moments of a normal subject group during walking. The optoelectric system collects kinematic data from infra-red LED markers placed at selected skin surface locations and projecting probes attached to the lower limb. A standardized X-ray procedure is used to move surface markers into their designated bony landmarks based on individual bone structure, which reduces the error caused by uncertainty of skin-surface marker locations. Based on moved-in marker information, different joint coordinate systems are proposed for kinematic and kinetic analysis of the knee joint. Normalized data of knee angles, net reaction forces and net moments from 35 young, normal subjects are presented.