A procedure to validate three-dimensional motion assessment systems

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.

A Quality Control Check to Ensure Comparability of Stereophotogrammetric Data between Sessions and Systems

Optoelectronic stereophotogrammetric (SP) systems are widely used in human movement research for clinical diagnostics, interventional applications, and as a reference system for validating alternative technologies. Regardless of the application, SP systems exhibit different random and systematic errors depending on camera specifications, system setup and laboratory environment, which hinders comparing SP data between sessions and across different systems. While many methods have been proposed to quantify and report the errors of SP systems, they are rarely utilized due to their complexity and need for additional equipment. In response, an easy-to-use quality control (QC) check has been designed that can be completed immediately prior to a data collection. This QC check requires minimal training for the operator and no additional equipment. In addition, a custom graphical user interface ensures automatic processing of the errors in an easy-to-read format for immediate interpretation. On initial deployment in a multicentric study, the check (i) proved to be feasible to perform in a short timeframe with minimal burden to the operator, and (ii) quantified the level of random and systematic errors between sessions and systems, ensuring comparability of data in a variety of protocol setups, including repeated measures, longitudinal studies and multicentric studies.

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.

Mechanical testing for three-dimensional motion analysis reliability

The purpose of this study was to use simple mechanical tests to evaluate the reliability of three-dimensional motion analysis systems and biomechanical models. Three different tests were conducted at four motion analysis laboratories where clinical care and research studies are routinely performed. The laboratories had different motion capture systems, different types and number of cameras, different types and numbers of force plates and different biomechanical models. These mechanical tests evaluated the accuracy of the motion capture system, the integration of the force plate and the motion capture system, and the strength of the biomechanical model used to calculate rotational kinematics. Results of motion capture system accuracy tests showed that, for all labs, the error between the measured and calculated distances between markers was less than 2mm and 1° for marker separations which ranged from 24mm to 500mm. Results from the force plate integration tests demonstrated errors in center of pressure calculation of less than 4mm across all labs, despite varied force plate and motion system configurations. Finally, errors across labs for single joint rotations and for combined rotations at the hip and knee were less than 2° at the hip and less than 10° at the knee. These results demonstrate that system accuracy and reliability can be obtained allowing the collection of comparable data across different motion analysis laboratories with varying configurations and equipment. This testing is particularly important when multi-center studies are planned in order to assure data consistency across labs.

Quantifying prosthetic gait deviation using simple outcome measures

AIM: To develop a subset of simple outcome measures to quantify prosthetic gait deviation without needing three-dimensional gait analysis (3DGA).

METHODS: Eight unilateral, transfemoral amputees and 12 unilateral, transtibial amputees were recruited. Twenty-eight able-bodied controls were recruited. All participants underwent 3DGA, the timed-up-and-go test and the six-minute walk test (6MWT). The lower-limb amputees also completed the Prosthesis Evaluation Questionnaire. Results from 3DGA were summarised using the gait deviation index (GDI), which was subsequently regressed, using stepwise regression, against the other measures.

RESULTS: Step-length (SL), self-selected walking speed (SSWS) and the distance walked during the 6MWT (6MWD) were significantly correlated with GDI. The 6MWD was the strongest, single predictor of the GDI, followed by SL and SSWS. The predictive ability of the regression equations were improved following inclusion of self-report data related to mobility and prosthetic utility.

CONCLUSION: This study offers a practicable alternative to quantifying kinematic deviation without the need to conduct complete 3DGA.

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.

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 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.

Virtual axis finder: a new method to determine the two kinematic axes of rotation for the tibio-femoral joint

The tibio-femoral joint has been mechanically approximated with two fixed kinematic axes of rotation, the longitudinal rotational (LR) axis in the tibia and the flexion-extension (FE) axis in the femur. The mechanical axis finder developed by Hollister et al. (1993, "The Axes of Rotation of the Knee," Clin. Orthop. Relat. Res., 290, pp. 259-268) identified the two fixed axes but the visual-based alignment introduced errors in the method. Therefore, the objectives were to develop and validate a new axis finding method to identify the LR and FE axes which improves on the error of the mechanical axis finder. The virtual axis finder retained the concepts of the mechanical axis finder but utilized a mathematical optimization to identify the axes. Thus, the axes are identified in a two-step process: First, the LR axis is identified from pure internal-external rotation of the tibia and the FE axis is identified after the LR axis is known. The validation used virtual simulations of 3D video-based motion analysis to create relative motion between the femur and tibia during pure internal-external rotation, and flexion-extension with coupled internal-external rotation. The simulations modeled tibio-femoral joint kinematics and incorporated 1 mm of random measurement error. The root mean squared errors (RMSEs) in identifying the position and orientation of the LR and FE axes with the virtual axis finder were 0.45 mm and 0.20 deg, and 0.11 mm and 0.20 deg, respectively. These errors are at least two times better in position and seven times better in orientation than those of the mechanical axis finder. Variables, which were considered a potential source of variation between joints and/or measurement systems, were tested for their sensitivity to the RMSE of identifying the axes. Changes in either the position or orientation of a rotational axis resulted in high sensitivity to translational RMSE (6.8 mm of RMSE per mm of translation) and rotational RMSE (1.38 deg of RMSE per degree of rotation), respectively. Notwithstanding these high sensitivities, corresponding errors can be reduced by segmenting the range of motion into regions where changes in either position or orientation are small. The virtual axis finder successfully increased the accuracy of the mechanical axis finder when the axes of motion are fixed with respect to the bones, but must be used judiciously in applications which do not have fixed axes of rotation.

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.

Pendulum-based method for determining the temporal accuracy of digital video-based motion capture systems

OBJECTIVE

To develop a simple method to determine the temporal accuracy of motion analysis systems incorporating commercial digital video cameras.

METHODS

A planar column pendulum with a natural frequency of 0.872 Hz was used to analyse five systems incorporating commercially available cameras and a single codec.

FINDING

The frame rate for each camera was measured to be within 3% of the US National Television Systems Committee (NTSC) broadcasting digital video standard of 29.97 fps; however some cameras produced a frame duplication artefact. Least squares curve-fitting using a sinusoidal function revealed RMS differences between 3-5% for angular position and 5-15% for angular speed compared to the captured motion data.

CONCLUSION

A simple method of evaluating temporal accuracy of a digital-based motion capturing system is demonstrated and it is shown that some digital-video cameras and computer playback software contain data compression technology that may produce substantial temporal frame inaccuracies in recovered video sequences. The results indicate that temporal accuracy should be evaluated in digital-based human motion analysis systems prior to their use in experimentation.

A computational method for recording and analysis of mandibular movements

This study proposed the development of a new clinical tool capable of quantifying the movements of opening-closing, protrusion and laterotrusion of the mandible. These movements are important for the clinical evaluation of the temporomandibular function and muscles involved in mastication. Unlike current commercial systems, the proposed system employs a low-cost video camera and a computer program that is used for reconstructing the trajectory of a reflective marker that is fixed on the mandible. In order to illustrate the clinical application of this tool, a clinical experiment consisting on the evaluation of the mandibular movements of 12 subjects was conducted. The results of this study were compatible with those found in the literature with the advantage of using a low cost, simple, non-invasive, and flexible tool customized for the needs of the practical clinic.

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.

Tibiofemoral joint contact forces and knee kinematics during squatting

Axial tibiofemoral joint contact forces were non-invasively determined for two high range of motion (high flexion) squatting activities. An electromagnetic motion tracking system and a non-conductive force platform were used to collect kinematic and kinetic data. An innovative scaling method was used to model subject-specific muscle group moment arms. One subject attained a peak axial tibiofemoral joint contact force of 49.7 N/kg during squatting at 149.9 degrees knee flexion. Average joint angles and average axial joint contact forces were calculated for each of the activities in order to facilitate a comparison with stair climbing data. Compared to stair climbing, the maximum average joint contact forces during the squatting activities occurred at significantly higher flexion angles (p<0.05.) The relative simplicity of the method makes it useful for application to large subject groups from diverse regions. The results of this study can be applied to the diagnosis and treatment of pathologies, and to the development of high range of motion (ROM) knee replacements.

Are patient-specific joint and inertial parameters necessary for accurate inverse dynamics analyses of gait?

Variations in joint parameter (JP) values (axis positions and orientations in body segments) and inertial parameter (IP) values (segment masses, mass centers, and moments of inertia) as well as kinematic noise alter the results of inverse dynamics analyses of gait. Three-dimensional linkage models with joint constraints have been proposed as one way to minimize the effects of noisy kinematic data. Such models can also be used to perform gait optimizations to predict post-treatment function given pre-treatment gait data. This study evaluates whether accurate patient-specific JP and IP values are needed in three-dimensional linkage models to produce accurate inverse dynamics results for gait. The study was performed in two stages. First, we used optimization analyses to evaluate whether patient-specific JP and IP values can be calibrated accurately from noisy kinematic data, and second, we used Monte Carlo analyses to evaluate how errors in JP and IP values affect inverse dynamics calculations. Both stages were performed using a dynamic, 27 degrees-of-freedom, full-body linkage model and synthetic (i.e., computer generated) gait data corresponding to a nominal experimental gait motion. In general, JP but not IP values could be found accurately from noisy kinematic data. Root-mean-square (RMS) errors were 3 degrees and 4 mm for JP values and 1 kg, 22 mm, and 74 500 kg * mm2 for IP values. Furthermore, errors in JP but not IP values had a significant effect on calculated lower-extremity inverse dynamics joint torques. The worst RMS torque error averaged 4% bodyweight * height (BW * H) due to JP variations but less than 0.25% (BW * H) due to IP variations. These results suggest that inverse dynamics analyses of gait utilizing linkage models with joint constraints should calibrate the model's JP values to obtain accurate joint torques.

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.

Direct comparison of kinematic data collected using an electromagnetic tracking system versus a digital optical system

The purpose of this study was to quantify the dynamic accuracy of kinematics measured by a digital optical motion analysis system in a gait analysis laboratory (capture volume approximately 20m(3)) compared to a standard range direct-current electromagnetic (EM) tracking device (capture volume approximately 1m(3)). This is a subset of a larger effort to establish an appropriate marker set for the optical system to quantify upperlimb kinematics simultaneously with gait, in comparison to previous studies of isolated upperlimb movements that have employed EM tracking devices. Rigid clusters of spherical reflective markers and EM sensors were attached to a mechanical articulator that mimicked three-dimensional joint rotations, similar to the elbow. As the articulator was moved through known ranges of motion (i.e. gold standard), kinematic data were collected simultaneously using both tracking systems. Both systems were tended to underestimate the range of motion; however, the application of post hoc smoothing and least-squares correction algorithms reduced these effects. When smoothing and correction algorithms were used, the magnitude of the mean difference between the gold standard and either the EM or optical system did not exceed 2 degrees for any of the compound motions performed. This level of agreement suggests that the measurements obtained from either system are clinically comparable, provided appropriate smoothing and correction algorithms are employed.

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.

Human movement analysis using stereophotogrammetry. Part 2: instrumental errors

This paper reviews the main aspects involved with the management of instrumental errors associated with video-based optoelectronic stereophotogrammetry. Insights on how such errors propagate to kinematic quantities are of great interest in the field of human movement analysis to improve the precision and reliability of measurements. The review focuses on the technical assessment and analytical compensation procedures to cope with instrumental errors. Relevant contributions dealing with intrinsic sources of systematic and random errors, such as the issues concerning camera calibration and filtering and smoothing of marker position data, are presented. Procedures for marker imaged processing, and missing marker recovery are also surveyed. Methods for checking the accuracy and precision of stereophotogrammetric systems are then reviewed. Finally, since the desired outcome of the movement measurements is a reliable estimate of body segment kinematics, state-of-the-art techniques proposed for minimization of error propagation arising from a cluster of external markers are described.

Accuracy of a System for Measuring Three-Dimensional Torso Kinematics during Manual Materials Handling

This paper describes a procedure developed and validated to assess the accuracy of an infrared-based motion measurement system used to perform a kinematic analysis of the torso with respect to the pelvis during simulated lifting tasks. Two rigid reflective marker triads were designed and fabricated for attachment to the thorax over the 6th thoracic vertebra and the pelvis. System accuracy was assessed for planar rotation as well as rotations about multiple orthogonal axes. A test fixture was used to validate known triad orientations. The spatial coordinates of these triads were collected at 120 Hz using a ProReflex motion measurement system. Single value decomposition was used to estimate a rotation matrix describing the rigid body motion of the thorax triad relative to the sacral triad at each point in time. Euler angles corresponding to flexion, lateral bending, and twisting were computed from the rotation matrix. All measurement error residuals for flexion, lateral bending, and twisting were below 1.75°. The estimated mean measurement errors were less than 1° in all three planes. These results suggest that the motion measurement system is reliable and accurate to within approximately 1.5° for the angles examined.

A proposed test to support the clinical movement analysis laboratory accreditation process

This paper describes a testing methodology and resultant set of four variables that can be used to quickly and easily document the correct installation, configuration, and combined working status of force platform (FP) and three-dimensional (3D) motion capture components of a clinical movement analysis (CMA) laboratory. Using a rigid, rod-shaped testing device, CMA laboratory data are collected simultaneously from the FP and motion capture components (typically, video-based kinematic measurements) as the device is manually loaded while being pivoted broadly about a point on the FP. Using a computational method based on static equilibrium, it is possible to independently measure the rod's orientation and tip position during the moving trial, using FP derived data exclusively, and to compare these estimates to rod orientation and tip position estimates derived exclusively from the motion capture component. The motion laboratory accreditation test (MLAT) variables include: the difference (angle) between the orientation of the long axis of the testing device as independently determined from kinematic measures (motion capture component) and the FP derived data; and the difference (x, y, z) between the center of pressure position (FP derived) and the position of the testing device tip (motion capture derived) that loads the FP. A numerical dynamics model was explored to evaluate the appropriateness of the static equilibrium-based FP data model and to determine guidelines for testing device movement frequency and FP loading. The MLAT technique provides a simple means of detecting the combined presence of errors from many sources, several of which are explored in this paper. The MLAT has been developed to help meet one criteria of the CMA laboratory accreditation process, and to serve as a routine quality assessment tool.

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.

Minimum measured-input models for the assessment of motor ability

The problem of assessing the physical functional limitation of a given individual and establishing the relationship between impairment/s and disability using a biomechanical approach is addressed. This endeavour was pursued with reference to the locomotor system and in order to address the following specific clinical issues: prognosis, eligibility for health services, measure of the outcome of a therapy, and therapeutic programming. A thorough biomechanical analysis of selected motor tasks would be effective but awkward to apply for subject-specific evaluation in clinical practice by reason of the complexity of both instrumentation and experimental protocols. In addition, as illustrated in the paper, the adequacy of the accuracy with which this type of analysis provides relevant information may be argued. Therefore, different methods were devised in the attempt to join objectivity with field applicability. These entailed the measurement of a minimum number of biomechanical variables during the execution of the selected motor task and these quantities were acquired using a low cost experimental apparatus least perceivable to the test subject, that is a dynamometric plate. However, since data thus obtained do not necessarily lend themselves to straightforward interpretation in terms of function assessment, models of the musculo-skeletal system that embodied the invariant aspects of both the modelled system and the specific motor task were devised. Using such "minimum measured-input models", physiology-related, and thus easier to interpret, information was obtained. Two different sets of mathematical models are presented: one deals with the lowest level of detail and normally aims at assessing a global physical performance score, the other discloses joint function and segmental mechanics and therefore contributes to establishing a relationship between impairment and disability. The validation of these models, carried out in the laboratory, has shown that they possess a potential for application in clinical practice.

Review of arm motion analyses

Interest in arm movements has increased tremendously in recent years. This interest has been motivated by different goals: the desire for a more scientific approach to replacement or support of the joints of the upper limb, the need for input to biomechanical computer models, and the clinical interest in comparing normal movements with pathological movements. The availability of commercial marker-tracking systems has facilitated achieving these goals. However, the complex nature of arm movements and the lack of standardized movements raises many challenges. In comparison with gait analysis, few arm motion analyses have been conducted. The purpose of this review is to aid researchers and clinicians interested in conducting an arm motion study in choosing the appropriate methodology. This is accomplished both by describing the methods used in past investigations and by highlighting important findings. Due to the variety of research goals, there is sometimes more than one appropriate method and the choice is left to the reader. Nevertheless, since it is extremely desirable to record and express the data in a standardized way, standardization proposals are described. This review, which focuses on methodology rather than results, addresses the following topics: motivations and tasks studied, tracking methods, the shoulder complex, joint centres and rotation axes, marker positions, coordinate system definitions, terminology and rotations, accuracy, and presentation methods.

Measurement of the screw-home motion of the knee is sensitive to errors in axis alignment

Measurements of joint angles during motion analysis are subject to error caused by kinematic crosstalk, that is, one joint rotation (e. g., flexion) being interpreted as another (e.g., abduction). Kinematic crosstalk results from the chosen joint coordinate system being misaligned with the axes about which rotations are assumed to occur. The aim of this paper is to demonstrate that measurement of the so-called "screw-home" motion of the human knee, in which axial rotation and extension are coupled, is especially prone to errors due to crosstalk. The motions of two different two-segment mechanical linkages were examined to study the effects of crosstalk. The segments of the first linkage (NSH) were connected by a revolute joint, but the second linkage (SH) incorporated gearing that caused 15 degrees of screw-home rotation to occur with 90 degrees knee flexion. It was found that rotating the flexion axis (inducing crosstalk) could make linkage NSH appear to exhibit a screw-home motion and that a different rotation of the flexion axis could make linkage SH apparently exhibit pure flexion. These findings suggest that the measurement of screw-home rotation may be strongly influenced by errors in the location of the flexion axis. The magnitudes of these displacements of the flexion axis were consistent with the inter-observer variability seen when five experienced observers defined the flexion axis by palpating the medial and lateral femoral epicondyles. Care should be taken when interpreting small internal-external rotations and abduction-adduction angles to ensure that they are not the products of kinematic crosstalk.

Precise laser incisions, corrected for patient respiration with an intelligent aiming system

BACKGROUND AND OBJECTIVE

Patient motion due to respiration and blood flow can negatively affect the precision of a laser incision.

STUDY DESIGN/MATERIALS AND METHODS

The video image of the surgical field is monitored by a computer system, and trends in the motion are "learned" by the computer. The laser beam is then adjusted to compensate for predicted motion. Occasional erratic motion sometime causes a false prediction. In this event, the prediction is corrected with real-time feedback.

RESULTS

Our experience shows that even with occasional false predictions, the motion compensation still gives a better incision. The surgeon always maintains control of the laser. The net effect of the intelligent aiming system is to subtract away nearly all patient motions.

CONCLUSION

Laser surgery can be performed with greater accuracy and reduced unwanted tissue damage with the predictive tracking of motion.

A spot check for estimating stereophotogrammetric errors

Good practice rules in the management of a movement analysis laboratory recommend that photogrammetric measurement errors are assessed, prior to every experimental session, using an ad hoc experiment referred to as a spot check. The paper proposes an inexpensive and easy to make spot check. The test uses a rigid rod carrying two markers and a target point taken on the line joining them and coinciding with the rod tip. The latter point is placed in a fixed and measured position in the laboratory frame and the markers are tracked while the rod is kept stationary and while it is manually made to rotate about the target point. Several target points are used within the measurement volume. The instantaneous errors with which the laboratory co-ordinates of the latter points are reconstructed are determined and submitted to statistical analysis. A normalisation procedure is illustrated that aims at making the test results independent from the geometry of the test object. The experimental and analytical methods underlying the proposed spot check were validated experimentally in two movement analysis laboratories using repeated tests. A rod, 1.5 m long, carrying four markers was used. In this way, several test-object geometries were tested. Results confirmed that the photogrammetric error could be divided into a zero-mean random and a systematic component. It was shown that the normalisation procedure was effective for the standard deviation of both error components when the two markers were located at a distance between them 1.5 times larger than the distance of their centroid from the tip of the rod. The systematic component bias could not be normalised, however a conservative value of it could be estimated. The two above-mentioned normalised standard deviations and the bias value can be taken as descriptors of the photogrammetric error of the specific measuring system tested. These parameters may also be used to assess the precision and the accuracy with which the laboratory position of a target point, defined relative to any specified marker cluster, may be reconstructed during movement analysis.

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.

Pelvis and lower limb anatomical landmark calibration precision and its propagation to bone geometry and joint angles

Human movement analysis using stereophotogrammetry is based on the reconstruction of the instantaneous laboratory position of selected bony anatomical landmarks (AL). For this purpose, knowledge of an AL's position in relevant bone-embedded frames is required. Because ALs are not points but relatively large and curved areas, their identification by palpation or other means is subject to both intra- and inter-examiner variability. In addition, the local position of ALs, as reconstructed using an ad hoc experimental procedure (AL calibration), is affected by photogrammetric errors. The intra- and inter-examiner precision with which local positions of pelvis and lower limb palpable bony ALs can be identified and reconstructed were experimentally assessed. Six examiners and two subjects participated in the study. Intra- and inter-examiner precision (RMS distance from the mean position) resulted in the range 6-21 mm and 13-25 mm, respectively. Propagation of the imprecision of ALs to the orientation of bone-embedded anatomical frames and to hip, knee and ankle joint angles was assessed. Results showed that this imprecision may cause distortion in joint angle against time functions to the extent that information relative to angular movements in the range of 10 degrees or lower may be concealed. Bone geometry parameters estimated using the same data showed that the relevant precision does not allow for reliable bone geometry description. These findings, together with those relative to skin movement artefacts reported elsewhere, assist the human movement analyst's consciousness of the possible limitations involved in 3D movement analysis using stereophotogrammetry and call for improvements of the relevant experimental protocols.

Some effects of camera placement on the accuracy of the Kinemetrix three-dimensional motion analysis system

OBJECTIVE

To assess the accuracy of the Kinemetrix motion analysis system to measure horizontal movement by a single reflective marker away from two cameras with differing camera placements.

DESIGN

Trial of the effects of nine different camera arrangements on precision of non-human movement.

BACKGROUND

In many cases the ability to arrange cameras to allow a separation of 60 degrees is not possible. Little is known about the precision of motion analysis systems for small camera angle separations.

METHODS

The accuracy of the Kinemetrix system was assessed with camera horizontal separations of 15 degrees, 30 degrees and 45 degrees, and vertical separations of 0 degrees, 15 degrees and 30 degrees rendering nine different camera placements. The distance between the cameras and the object was always maintained at 4 m. During each test the marker was moved a known horizontal distance along a line bisecting the horizontal angular separation of the two cameras. The mean absolute errors of the Kinemetrix measurement were calculated.

RESULTS

At the smallest camera separation tested (15 degrees horizontal, 0 degrees vertical), the Kinemetrix was unable to calculate the three-dimensional co-ordinate of the marker. For all other camera positions tested, the errors in measurements were small (mean absolute errors < 2 mm).

CONCLUSIONS

Maintaining camera horizontal and vertical separations above a sum of 30 degrees is sufficient for clinical testing.

RELEVANCE

Motion analysis systems are becoming more common for clinical evaluation where only confined testing areas are available. These confined areas often make positioning of cameras at greater than 60 degrees impossible; therefore, there is a need to explore the errors involved in placing two cameras at less than 60 degrees.

Factors influencing accuracy of screw displacement axis detection with a D.C.-based electromagnetic tracking system

Recent technical improvements and cost reductions in electromagnetic motion tracking systems invite their application to motion axis determination in the surgical setting. After evaluation of the accuracy of a state-of-the-art D.C. electromagnetic tracking system, which generates complete three-dimensional kinematic outputs from just a single receiver, we calculated screw displacement axes (SDA's) from its source data. The accuracy of SDA determination from such source data was evaluated for various rotational increment sizes around a revolute joint. A novel smoothing procedure, customized for this type of source data, was developed, enabling SDA detection from incremental rotations of less than 1 deg, at an accuracy appropriate for intra-operative measurement of human joint motion. Examples of SDA determination are given for motion tracking of a ball joint and of the elbow articulation.

The relative skin movement of the foot: a 2-D roentgen photogrammetry study

OBJECTIVE: This paper describes a validation of the relative motions of skin-mounted markers on the foot. DESIGN: The movement of a skin-mounted marker on the foot was evaluated by the use of 2-D roentgen photogrammetry. BACKGROUND: Validations of skin-mounted markers are needed in order to assess whether clinical use of motion analysis systems is accurate. METHODS: Six healthy volunteers participated in the study. Measurements were made with 2-D roentgen photogrammetry from the medial aspect of the foot. Spherical lead markers, with a diameter of 2 mm, were glued on the skin over the following landmarks: the medial malleolus, the navicular bone, the medial part of calcaneus, the base and the head of the first metatarsal bone, and the base of the fifth metatarsal bone. The foot was placed on a platform that was adjustable in three directions: horizontal, 20 degrees upward (towards dorsal flexion), and 30 degrees downward (towards plantar flexion). RESULTS: In relation to the underlying bones, the markers were found to move up to 4.3 mm. The markers with the largest movements were the ones over the medial malleolus, the navicular bone and the calcaneus. For the distally placed markers i.e. at the base and the head of the first metatarsal bone, and the base of the fifth metatarsal bone, the displacements were a maximum 1.8 mm. CONCLUSIONS: Markers mounted on the foot moved between 1.8 and 4.3 mm corresponding to the underlying bones. The most proximal attached markers demonstrated the largest movements.

A multisegment computer simulation of normal human gait

The goal of this project was to develop a computer simulation of normal human walking that would use as driving moments resultant joint moments from a gait analysis. The system description, initial conditions and driving moments were taken from an inverse dynamics analysis of a normal walking trial. A nine-segment three-dimensional (3-D) model, including a two-part foot, was used. Torsional, linear springs and dampers were used at the hip joints to keep the trunk vertical and at the knee and ankle joints to prevent nonphysiological motion. Dampers at other joints were required to ensure a smooth and realistic motion. The simulated human successfully completed one step (550 ms), including both single and double support phases. The model proved to be sensitive to changes in the spring stiffness values of the trunk controllers. Similar sensitivity was found with the springs used to prevent hyperextension of the knee at heel contact and of the metatarsal-phalangeal joint at push-off. In general, there was much less sensitivity to the damping coefficients. This simulation improves on previous efforts because it incorporates some features necessary in simulations designed to answer clinical science questions. Other control algorithms are required, however, to ensure that the model can be realistically adapted to different subjects.

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.

Relationships between alignment, kinematic and kinetic measures of the knee of normal elderly subjects in level walking

Twelve normal 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 was used to measure the static lower limb alignment and a 3D optoelectric system was used to measure the biomechanical performance of the knee in level walking. Relationships were calculated between static radiographic angular measures and dynamic knee angular measures, dynamic knee joint forces, and dynamic knee joint moments during gait in corresponding motion planes; and between dynamic knee angular measures and dynamic knee joint forces and dynamic knee moments during gait and in corresponding motion planes. The results showed that the static lower-limb alignment measures did not closely correlate with the kinetic measures of the knee in gait although about half of the static angular alignment measures were significantly related to some of the dynamic knee angular measures. Instead, six of nine dynamic angular measures of the knee were significantly related to the dynamic forces and moments of force in the corresponding motion planes. These results suggest that static alignment measures alone at the present time are not sufficient to predict the dynamic knee joint forces in intact knees.

Reliability of an optoelectric system to measure elbow kinematics

Motion analysis of the upper extremity during functional activities has only recently become more accessible. An optoelectric system (WATSMART) was subjected to testing using first a calibration dummy and then human subjects. The mean differences between the system calculated angles and those measured with potentiometers on a calibration dummy were less than 1.6° in all three planes. The test-retest reliability of the system when measuring elbow motion of human subjects yielded acceptable repeatability for measurement of functional activities. Calculation of the least significant difference found that minimum differences from 4 to 14° in flexion and from 10 to 19° in rotation can be detected using the reported set-up and protocol.

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.