ISB recommendation on definitions of joint coordinate system of various joints for the reporting of human joint motion--part I: ankle, hip, and spine. International Society of Biomechanics

The Standardization and Terminology Committee (STC) of the International Society of Biomechanics (ISB) proposes a general reporting standard for joint kinematics based on the Joint Coordinate System (JCS), first proposed by Grood and Suntay for the knee joint in 1983 (J. Biomech. Eng. 105 (1983) 136). There is currently a lack of standard for reporting joint motion in the field of biomechanics for human movement, and the JCS as proposed by Grood and Suntay has the advantage of reporting joint motions in clinically relevant terms. In this communication, the STC proposes definitions of JCS for the ankle, hip, and spine. Definitions for other joints (such as shoulder, elbow, hand and wrist, temporomandibular joint (TMJ), and whole body) will be reported in later parts of the series. The STC is publishing these recommendations so as to encourage their use, to stimulate feedback and discussion, and to facilitate further revisions. For each joint, a standard for the local axis system in each articulating bone is generated. These axes then standardize the JCS. Adopting these standards will lead to better communication among researchers and clinicians.     

Quantifying translations in the radiohumeral joint: application of a floating axis analysis

The purpose of this study was to apply the Floating Axis analysis technique to the elbow joint, and to verify its ability to quantify clinically relevant radiohumeral translation in vitro using an electromagnetic tracking device. Of particular interest was the ability to quantify changes in anterior-posterior radial head translation, which is associated with the clinical condition of posterolateral rotatory instability of the elbow. Following the method proposed by Grood and Suntay to determine motions in the knee, an elbow coordinate system with axes representing the flexion-extension axis of the humerus, the long axis of the radius, and their mutual perpendicular, was developed. The algorithm was tested using a mechanical articulator that modeled the Floating Axis approach. Translation errors using this articulator were 0.1+/-0.1mm. The algorithm was applied to kinematic data collected from 12 cadaveric elbows that underwent a pivot shift test prior and subsequent to transection of the lateral collateral ligament. Anterior-posterior radiohumeral translation increased significantly in these elbows following the ligament sectioning (p<0.0001), with the average magnitude of posterior translation increasing from 0.9 to 19.8mm at 90 degrees of flexion. This approach will provide valuable information related to alterations in elbow motion pathways, especially for studies aimed at quantifying changes in joint stability.     

Assessment of the functional method of hip joint center location subject to reduced range of hip motion

Motion analysis of the lower extremities usually requires determination of the location of the hip joint center. The results of several recent studies have suggested that kinematic and kinetic variables calculated from motion analysis data are highly sensitive to errors in hip joint center location. "Functional" methods in which the location of the hip joint center is determined from the relative motion of the thigh and pelvis, rather than from the locations of bony landmarks, are promising but may be ineffective when motion is limited. The aims of the present study were to determine whether the accuracy of the functional method is compromised in young and elderly subjects when limitations on hip motion are imposed and to investigate the possibility of locating the hip joint center using data collected during commonly studied motions (walking, sit-to-stand, stair ascent, stair descent) rather than using data from an ad hoc trial in which varied hip motions are performed. The results of the study suggested that functional methods would result in worst-case hip joint center location errors of 26mm (comparable to the average errors previously reported for joint center location based on bony landmarks) when available hip motion is substantially limited. Much larger errors ( approximately 70mm worst-case), however, resulted when hip joint centers were located from data collected during commonly performed motions, perhaps because these motions are, for the most part, restricted to the sagittal plane. It appears that the functional method can be successfully implemented when range of motion is limited but still requires collection of a special motion trial in which hip motion in both the sagittal and frontal planes is recorded.     

A comparison of passive flexion-extension to normal gait in the ovine stifle joint

Obtaining accurate values of joint tissue loads in human subjects and animals in vivo requires exact 3D-reproduction of joint kinematics and comparisons of in vivo motions between subjects and animals, and also necessitates an accurate reference position. For the knee, passive flexion-extension of isolated joints by hand has been assumed to produce bony motions similar to those of normal gait. We hypothesized that passive flexion-extension kinematics would not accurately reproduce in vivo gait, and, further, that such kinematics would vary significantly between testers. In vivo gait motions of four ovine stifle joints were measured in six degrees of freedom, as were passive flexion-extension motions after sacrifice. Passive flexion-extension motions were performed by three testers on the same stifle joints used in vitro. Results showed statistically significant differences in all degrees of freedom, with the largest differences in the proximal-distal and internal-external directions. Differences induced by muscle loads and kinetic factors in vivo were most evident during stance and hoof-off phases of gait. The in vitro passive paths generated by hand created motions with large variability both between and within individual testers. The user dependence and "area" of motion of passive flexion-extension indicates that passive flexion-extension is contained in a volume of motion, rather than constrained to a unique path. The assumption that the passive path has relevance to precise bone positions during normal in vivo gait is not supported by these results. Thus, using passive flexion-extension as a reference between joints may introduce large motion variability in the observed outcome, and large potential errors in determining joint tissue loads.     

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.     

Determination of patient-specific multi-joint kinematic models through two-level optimization

Dynamic patient-specific musculoskeletal models have great potential for addressing clinical problems in orthopedics and rehabilitation. However, their predictive capability is limited by how well the underlying kinematic model matches the patient's structure. This study presents a general two-level optimization procedure for tuning any multi-joint kinematic model to a patient's experimental movement data. An outer level optimization modifies the model's parameters (joint position and orientations) while repeated inner level optimizations modify the model's degrees of freedom given the current parameters, with the goal of minimizing errors between model and experimental marker trajectories. The approach is demonstrated by fitting a 27 parameter, three-dimensional, 12 degree-of-freedom lower-extremity kinematic model to synthetic and experimental movement data for isolated joint (hip, knee, and ankle) and gait (full leg) motions. For noiseless synthetic data, the approach successfully recovered the known joint parameters to within an arbitrarily tight tolerance. When noise was added to the synthetic data, root-mean-square (RMS) errors between known and recovered joint parameters were within 10.4 degrees and 10 mm. For experimental data, RMS marker distance errors were reduced by up to 62% compared to methods that estimate joint parameters from anatomical landmarks. Optimized joint parameters found using a loaded full-leg gait motion differed significantly from those found using unloaded individual joint motions. In the future, this approach may facilitate the creation of dynamic patient-specific musculoskeletal models for predictive clinical applications.     

Reduction of knee range of motion during continuous passive motion due to misaligned hip joint centre

When using continuous passive motion (CPM) devices, appropriate setting of the device and positioning of the patient are necessary to obtain maximum range of motion (ROM). In this study, the ROMs in both the knee joint and CPM device during CPM treatment were measured using a motion analysis system for three different CPM devices. Additionally, the trajectories of the angles at the knee for hip joint misalignments were evaluated using kinematic models of the three CPM devices. The results showed that discrepancies in ROM between the knee joints and the CPM device settings during CPM treatment were revealed regardless of the CPM device and that the effect of misalignment is dependent on the design of the CPM device. The present technology could be applied for the development of a better design configuration for the CPM device to reduce the discrepancy in ROM at the knee joint.     

Reduction of knee range of motion during continuous passive motion due to misaligned hip joint centre

When using continuous passive motion (CPM) devices, appropriate setting of the device and positioning of the patient are necessary to obtain maximum range of motion (ROM). In this study, the ROMs in both the knee joint and CPM device during CPM treatment were measured using a motion analysis system for three different CPM devices. Additionally, the trajectories of the angles at the knee for hip joint misalignments were evaluated using kinematic models of the three CPM devices. The results showed that discrepancies in ROM between the knee joints and the CPM device settings during CPM treatment were revealed regardless of the CPM device and that the effect of misalignment is dependent on the design of the CPM device. The present technology could be applied for the development of a better design configuration for the CPM device to reduce the discrepancy in ROM at the knee joint.     

Cross-Talk Correction Method for Knee Kinematics in Gait Analysis Using Principal Component Analysis (PCA): A New Proposal

Background

In 3D gait analysis, the knee joint is usually described by the Eulerian way. It consists in breaking down the motion between the articulating bones of the knee into three rotations around three axes: flexion/extension, abduction/adduction and internal/external rotation. However, the definition of these axes is prone to error, such as the “cross-talk” effect, due to difficult positioning of anatomical landmarks. This paper proposes a correction method, principal component analysis (PCA), based on an objective kinematic criterion for standardization, in order to improve knee joint kinematic analysis.

Methods

The method was applied to the 3D gait data of two different groups (twenty healthy subjects and four with knee osteoarthritis). Then, this method was evaluated with respect to three main criteria: (1) the deletion of knee joint angle cross-talk (2) the reduction of variance in the varus/valgus kinematic profile (3) the posture trial varus/valgus deformation matching the X-ray value for patients with knee osteoarthritis. The effect of the correction method was tested statistically on variabilities and cross-talk during gait.

Results

Cross-talk was lower (p<0.05) after correction (the correlation between the flexion-extension and varus-valgus kinematic profiles being annihilated). Additionally, the variance in the kinematic profile for knee varus/valgus and knee flexion/extension was found to be lower and higher (p<0.05), respectively, after correction for both the left and right side. Moreover, after correction, the posture trial varus/valgus angles were much closer to x-ray grading.

Conclusion

The results show that the PCA correction applied to the knee joint eliminates the cross-talk effect, and does not alter the radiological varus/valgus deformation for patients with knee osteoarthritis. These findings suggest that the proposed correction method produces new rotational axes that better fit true knee motion.     

Effects of data smoothing on the reconstruction of helical axis parameters in human joint kinematics

In biomechanical joint-motion analyses, the continuous motion to be studied is often approximated by a sequence of finite displacements, and the Finite Helical Axis (FHA) or "screw axis" for each displacement is estimated from position measurements on a number of anatomical or artificial landmarks. When FHA parameters are directly determined from raw (noisy) displacement data, both the position and the direction of the FHA are ill-determined, in particular when the sequential displacement steps are small. This implies, that under certain conditions, the continuous pathways of joint motions cannot be adequately described. The purpose of the present experimental study is to investigate the applicability of smoothing (or filtering) techniques, in those cases where FHA parameters are ill-determined. Two different quintic-spline smoothing methods were used to analyze the motion data obtained with Roentgenstereophotogrammetry in two experiments. One concerning carpal motions in a wrist-joint specimen, and one relative to a kinematic laboratory model, in which the axis positions are a priori known. The smoothed and non-smoothed FHA parameter errors were compared. The influences of the number of samples and the size of the sampling interval (displacement step) were investigated, as were the effects of equidistant and nonequidistant sampling conditions and noise invariance.     

The use of sequential MR image sets for determining tibiofemoral motion: reliability of coordinate systems and accuracy of motion tracking algorithm

The use of magnetic resonance imaging has been proposed by many investigators for establishment of joint reference systems and kinematic tracking of musculoskeletal joints. In this study, the intraobserver and interobserver reliability of a strategy to establish anatomic reference systems using manually selected fiducial points were quantified for seven sets of MR images of the human knee joint. The standard error of the measurement of the intraobserver and interobserver errors were less than 2.6 degrees, and 1.2 mm for relative tibiofemoral orientation and displacement, respectively. An automated motion tracking algorithm was also validated with a controlled motion experiment in a cadaveric knee joint. The controlled displacements and rotations prescribed in our motion tracking validation were highly correlated to those predicted (Pearson's correlation = 0.99, RMS errors = 0.39 mm, 0.38 degree). Finally, the system for anatomic reference system definition and motion tracking was demonstrated with a set of MR images of in vivo passive flexion in the human knee.     

Validation of net joint loads calculated by inverse dynamics in case of complex movements: application to balance recovery movements

The joint forces and moments driving the motion of a human subject are classically computed by an inverse dynamic calculation. However, even if this process is theoretically simple, many sources of errors may lead to huge inaccuracies in the results. Moreover, a direct comparison with in vivo measured loads or with "gold standard" values from literature is only possible for very specific studies. Therefore, assessing the inaccuracy of inverse dynamic results is not a trivial problem and a simple method is still required. This paper presents a simple method to evaluate both: (1) the consistency of the results obtained by inverse dynamics; (2) the influence of possible modifications in the inverse dynamic hypotheses. This technique concerns recursive calculation performed on full kinematic chains, and consists in evaluating the loads obtained by two different recursive strategies. It has been applied to complex 3D whole body movements of balance recovery. A recursive Newton-Euler procedure was used to compute the net joint loads. Two models were used to represent the subject bodies, considering or not the upper body as a unique rigid segment. The inertial parameters of the body segments were estimated from two different sets of scaling equations [De Leva, P., 1996. Adjustments to Zatsiorsky-Suleyanov's segment inertia parameters. Journal of Biomechanics 29, 1223-1230; Dumas, R., Chèze, L., Verriest, J.-P., 2006b. Adjustments to McConville et al. and Young et al. Body Segment Inertial Parameters. Journal of Biomechanics, in press]. Using this comparison technique, it has been shown that, for the balance recovery motions investigated: (1) the use of the scaling equations proposed by Dumas et al., instead of those proposed by De Leva, improves the consistency of the results (average relative influence up to 30% for the transversal moment); (2) the arm motions dynamically influence the recovery motion in a non negligible way (average relative influence up to 15% and 30% for the longitudinal force and the transversal moment, respectively).     

A model of semitendinosus muscle sarcomere length, knee and hip joint interaction in the frog hindlimb

The interaction between the semitendinosus muscle and both hip and knee joint angles was examined in the frog (Rana pipiens) hindlimb. Sarcomere length was measured by laser diffraction in passive muscle during hip and knee rotation. A model was then developed to predict semitendinosus sarcomere length as a function of both hip and knee flexion angle. Based on published frog muscle fiber length-tension [Gordon, A. M. et al., J. Physiol. 184, 170-192 (1966)] and force-velocity [Edman, K. A. P., J. Physiol. 291, 143-159 (1979)] properties, and published joint angles during hopping [Calow, L. J. and Alexander, R. McN., J. Zool. (Lond.) 171, 293-321 (1973)], muscle sarcomere length, force and hip and knee torque during a hop were predicted. The semitendinosus muscle generally operated on the descending limb of the length-tension curve at normal joint angle combinations. The model predicted that, during a single coordinated movement, a period of sarcomere shortening (concentric) was followed by a period of sarcomere lengthening (eccentric). Based on calculated torque profiles at the hip and knee joints, this study suggested that the semitendinosus muscle probably functions more as a hip extensor than a knee flexor. In addition, based on the nature of the shortening-lengthening cycle, the semitendinosus may act to mechanically link the force of knee extension to hip extension.     

Weightlifting performance is related to kinematic and kinetic patterns of the hip and knee joints

The purpose of this study was to investigate the correlations between biomechanical outcome measures and weightlifting performance. Joint kinematics and kinetics of the hip, knee, and ankle were calculated while 10 subjects performed a clean at 85% of 1 repetition maximum (1RM). Kinematic and kinetic time-series patterns were extracted with principal components analysis. Discrete scores for each time-series pattern were calculated and used to determine how each pattern was related to body mass-normalized 1RM. Two hip kinematic and 2 knee kinetic patterns were significantly correlated with relative 1RM. The kinematic patterns captured hip and trunk motions during the first pull and hip joint motion during the movement transition between the first and second pulls. The first kinetic pattern captured a peak in the knee extension moment during the second pull. The second kinetic pattern captured a spatiotemporal shift in the timing and amplitude of the peak knee extension moment. The kinematic results suggest that greater lift mass was associated with steady trunk position during the first pull and less hip extension motion during the second-knee bend transition. Further, the kinetic results suggest that greater lift mass was associated with a smaller knee extensor moments during the first pull, but greater knee extension moments during the second pull, and an earlier temporal transition between knee flexion-extension moments at the beginning of the second pull. Collectively, these results highlight the importance of controlled trunk and hip motions during the first pull and rapid employment of the knee extensor muscles during the second pull in relation to weightlifting performance.     

The envelope of passive knee joint motion

The purpose of this study is to create an accurate experimental database for the passive (in vitro) freedom-of-motion characteristics of the human knee joint on a subject to subject basis, suitable for the verification and enhancement of mathematical knee-joint models. Knee-joint specimens in a six degree-of-freedom motion rig are moved through flexion under several combinations of external loads, including tibial torques, axial forces and AP-forces. Euler rotation angles and translation vectors, describing the relative, spatial motions of the joint are measured using an accurate Roentgen Stereo Photogrammetric system. Conceptually the joint is considered as a two degrees-of-freedom of motion mechanism (flexion-tibial rotation), whereby the limits of internal and external tibial rotation are defined at torques of +/- 3 Nm. The motion pathways along these limits are defined as the envelopes of passive knee joint motion. It is found that these envelope pathways are consistent and hardly influenced by additional axial forces up to 300 N and AP-forces of 30 N. Within the envelope of motion, however, the motion patterns are highly susceptible to small changes in the external load configuration. It is shown that the external tibial rotation during extension ('screw-home mechanism') is not an obligatory effect of the passive joint characteristics, but a direct result of the external loads. Anatomical differences notwithstanding, the inter-individual discrepancies in the motion patterns of the four specimens tested, showed to be relatively small in a qualitative sense. Quantitative differences can be explained by small differences in the alignment of the coordinate systems relative to the joint anatomy and by differences in rotatory laxity.     

A spatial mechanism with higher pairs for modelling the human knee joint

By generalizing a previous model proposed in the literature, a new spatial kinematic model of the knee joint passive motion is presented. The model is based on an equivalent spatial parallel mechanism which relies upon the assumption that fibers within the anterior cruciate ligament (ACL), the medial collateral ligament (MCL) and the posterior cruciate ligament (PCL) can be considered as isometric during the knee flexion in passive motion (virtually unloaded motion). The articular surfaces of femoral and tibial condyles are modelled as 3-D surfaces of general shapes. In particular, the paper presents the closure equations of the new mechanism both for surfaces represented by means of scalar equations that have the Cartesian coordinates of the points of the surface as variables and for surfaces represented in parametric form. An example of simulation is presented in the case both femoral condyles are modelled as ellipsoidal surfaces and tibial condyles as spherical surfaces. The results of the simulation are compared to those of the previous models and to measurements. The comparison confirms the expectation that a better approximation of the tibiofemoral condyle surfaces leads to a more accurate model of the knee passive motion.     

The efficacy of a video-based marker-less tracking system for gait analysis

Most clinical gait analyses are conducted using motion capture systems which track retro-reflective markers that are placed on key landmarks of the participants. An alternative to a three-dimensional (3D) motion capture, marker-based, optical camera system may be a marker-less video-based tracking system. The aim of our study was to investigate the efficacy of the use of a marker-less tracking system in the calculation of 3D joint angles for possible use in clinical gait analysis. Ten participants walked and jogged on a treadmill and their kinematic data were captured with a marker and marker-less tracking system simultaneously. The hip, knee and ankle angles in the frontal, sagittal and transverse planes were computed. Root Mean Square differences (RMS_diff) between corresponding angles for each participant’s support phase were calculated and averaged to derive the mean within-subject RMS_diff. These within-subject means were averaged to obtain the mean between-subject RMS_diff for the relevant joint angles in the two gait conditions (walking and jogging). The RMS_diff between the two tracking systems was less than 1° for all rotations of the three joint angles of the hip and knee. However, there were slightly larger differences in the ankle joint angles. The results of this study suggest a potential application in gait analysis in clinical settings where observations of anatomical motions may provide meaningful feedback.     

Congruency effects on load bearing in diarthrodial joints

Modelling load bearing in diarthrodial joints is challenging, due to the complexity of the materials, the boundary and interface conditions and the geometry. The articulating surfaces are covered with cartilage layers that are filled with a fluid that plays a major role in load bearing [Mow, V.C., Holmes, M.H., Lai, W.M. (1984) "Survey article: fluid transport and mechanical properties of articular cartilage: a review", Journal of Biomechanics 17(5), 377-394]. Researchers have tended to approximate joint geometry using axisymmetry [Donzelli, P.S., Spilker, R.L., Ateshian, G.A., Mow, V.C. (1999) "Contact analysis of biphasic transversely isotropic cartilage layers and correlations with tissue failure", Journal of Biomechanics 32, 1037-1047], often with a rounded upper articulating surface, creating a form of Hertz problem [Donzelli, P.S., Spilker, R.L., Ateshian, G.A., Mow, V.C. (1999) "Contact analysis of biphasic transversely isotropic cartilage layers and correlations with tissue failure", Journal of Biomechanics 32, 1037-1047]. However, diarthrodial joints (shoulder, hip and knee) are equipped with peripheral structures (glenoid labrum, acetabular labrum and meniscus, respectively) that tend to deepen the joint contact and thus cause initial contact to be established at the periphery of the joint rather than "centrally". The surface geometries are purposefully incongruent, and the incongruency has a significant effect on the stresses, pressures and pressure gradients inside the tissue. The models show the importance of the peripheral structures and the incongruency from a load-bearing perspective. Joint shapes must provide a compromise between demands for load-bearing, lubrication and the supply of nutrients to the chondrocytes of the cartilage and cells of the peripheral structures. Retention and repair of the functionality of these peripheral structures should be a prime consideration in any surgical treatment of an injured joint.