A scapular coordinate frame for clinical and kinematic analyses

The aim of this study was to define a body-fixed coordinate frame for the scapula that minimises axes variability and is closely related to the clinical frame of reference. Medical images of 21 scapulae were used to quantify 14 different axes from identifiable landmarks. The plane of the blade of the scapula was defined. The orientations of the quantified axes were calculated. The angular relationships between axes were quantified and applied to grade the sensitivity of each axis to inter-scapular variations in the others. The volume of data required to define an axis was noted for its dependency on pathology and the three criteria were weighted according to relative importance. The two axes with the highest weighting were applied to define a body-fixed Cartesian coordinate frame for the scapula. A least square medio-lateral line through the centre of the spine root was the most optimal axis. The plane formed by the spine root line and a least square line through the centre of the lateral border ridge was the most optimal scapular plane. This body-fixed Cartesian coordinate frame is closely aligned to the cardinal planes in the anatomical position and thus is a clinically applicable, specimen invariant coordinate frame that can be used in patient-specific kinematics modelling.     

Automatic determination of anatomical coordinate systems for three-dimensional bone models of the isolated human knee

The combination of three-dimensional (3-D) models with dual fluoroscopy is increasingly popular for evaluating joint function in vivo. Applying these modalities to study knee motion with high accuracy requires reliable anatomical coordinate systems (ACSs) for the femur and tibia. Therefore, a robust method for creating ACSs from 3-D models of the femur and tibia is required. We present and evaluate an automated method for constructing ACSs for the distal femur and proximal tibia based solely on 3-D bone models. The algorithm requires no observer interactions and uses model cross-sectional area, center of mass, principal axes of inertia, and cylindrical surface fitting to construct the ACSs. The algorithm was applied to the femur and tibia of 10 (unpaired) human cadaveric knees. Due to the automated nature of the algorithm, the within specimen variability is zero for a given bone model. The algorithm’s repeatability was evaluated by calculating variability in ACS location and orientation across specimens. Differences in ACS location and orientation between specimens were low (<1.5 mm and <2.5°). Variability arose primarily from natural anatomical and morphological differences between specimens. The presented algorithm provides an alternative method for automatically determining subject-specific ACSs from the distal femur and proximal tibia.     

On the kinematic modeling and the parameter estimation of the human knee joint.

This paper presents some results on the modeling and the parameter estimation of the human knee joint. Based on the geometric characteristics of the femur condyle and the tibia plateau, a part of femoro-tibial joint model includes an involute-on-plane submodel. Data recorded by camera type device are used to analyze the kinematic characteristics of the knee joint and to estimate the corresponding submodel parameters. Experimental results are presented and the model is further validated.     

Articular-surface-based automatic anatomical coordinate systems for the knee bones

Increasing use of patient-specific surgical procedures in orthopaedics means that patient-specific anatomical coordinate systems (ACSs) need to be determined. For knee bones, automatic algorithms constructing ACSs exist and are assumed to be more reliable than manual methods, although both approaches are based on non-unique numerical reconstructions of true bone geometries. Furthermore, determining the best algorithms is difficult, as algorithms are evaluated on different datasets. Thus, in this study, we developed 3 algorithms, each with 3 variants, and compared them with 5 from the literature on a dataset comprising 24 lower-limb CT-scans. To evaluate algorithms’ sensitivity to the operator-dependent reconstruction procedure, the tibia, patella and femur of each CT-scan were each reconstructed once by three different operators.Our algorithms use principal inertia axis (PIA), cross-sectional area, surface normal orientations and curvature data to identify the bone region underneath articular surfaces (ASs). Then geometric primitives are fitted to ASs, and the ACSs are constructed from the geometric primitive points and/or axes. For each bone type, the algorithm displaying the least inter-operator variability is identified. The best femur algorithm fits a cylinder to posterior condyle ASs and a sphere to the femoral head, average axis deviations: 0.12°, position differences: 0.20 mm. The best patella algorithm identifies the AS PIAs, average axis deviations: 0.91°, position differences: 0.19 mm. The best tibia algorithm finds the ankle AS center and the 1st PIA of a layer around a plane fitted to condyle ASs, average axis deviations: 0.38°, position differences: 0.27 mm.     

An alternative definition of the scapular coordinate system for use with RSA

When performing radiostereometric analysis (RSA), computed tomography scans are often taken to obtain the landmarks used to create anatomical coordinate systems (CSs) for quantifying joint kinematics. Different conventions for defining CSs lead to an inability to compare results among studies. The International Society of Biomechanics (ISB) has proposed a set of CSs; however, the landmarks needed to create the recommended scapular CS require the entire scapula to be scanned, thereby also exposing breast and other tissues to radiation. The main purpose of this work was to investigate an alternate definition of the CS that has repeatably attainable landmarks and axes as close as possible to those recommended by the ISB, while limiting the portion of the scapula requiring scanning. Intra- and inter-investigator variabilities of landmark digitization were quantified in one model of a scapula and one cadaveric specimen. Based on the variability of the digitizations, an alternative CS was defined. The differences between the ISB and alternative CSs were evaluated on 11 cadaveric specimens. Beaded biplanar RSA was performed on the glenohumeral joint model in 15 different configurations and the resulting kinematics were calculated for each set of landmark digitizations using both sets of coordinate systems. While the kinematic angles obtained using the alternative CS were statistically different from those obtained using the ISB standard, these differences were small (on the order of 5°) and therefore considered to be of little clinical significance. In all likelihood, the benefits of decreasing radiation exposure outweigh these differences in angles.     

A model of the human knee, derived from kinematic principles and its relevance for endoprosthesis design

A mainly deductive kinematic model of the human knee is described. The modelling procedure is based upon the application of a four-bar mechanism. Emphasis has been laid upon elucidating the functional anatomical relationship between several morphological characteristics concerning the shape of the articular surfaces and the constellation of the cruciate ligaments. Starting from a simple planar model, which simulates motions in a sagittal plane only, a spatial model was developed, which allowed an additional longitudinal rotation of the tibia also. The conclusions drawn from this modelling procedure have been used to evaluate from an functional anatomical point of view the current designs of presently available endoprostheses for the knee.     

A finite helical axis as a landmark for kinematic reference of the knee

Reference coordinates based on the finite helical axis for flexion of the knee from 0 to 90 deg are proposed. Six degree-of-freedom tracking allows the use of such a helical axis as a kinematic landmark for knee motion representation. Data from five human subjects in vivo are presented as a path of finite helical axes for flexion of the knee from 20 to 80 deg. The finite helical axis rotates by an average of 11.4 deg, the centrode translates an average of 19.8 mm, and the total axial translation averages 0.1 mm during flexion from 20 to 80 deg. Error due to the transducer was measured on a fixed-pivot pendulum and found to be 1.0 deg and 1.9 mm rms for the helical axis orientation and position, respectively, and 0.1 mm for the axial translation. Reproducibility and soft tissue effects on the measurements were repeatable to 4.0 deg and 2.7 mm rms in orientation and position, respectively, and 0.1 mm for the axial translations. Soft tissue errors averaged 4.9 deg and 3.6 mm in position and orientation, and 0.3 mm in the axial translations.     

The effect of coordinate system choice and segment reference on RSA-based knee translation measures

Roentgen stereophotogrammetric analysis (RSA) can be utilized to accurately describe joint kinematics, but even when measuring small displacements within radiographically discernible structures, standardized reference frames are imperative for useful comparison across patients and across studies. In the current paper, accurately controlled laboratory models demonstrated the considerable influence that a mere 1.9-cm offset of the origin of the coordinate system from the rotation axes could exert on translation measures when rotations were occurring. In addition, the use of two different coordinate systems to gauge translation on a radiographic anterior-posterior (A-P) knee laxity exam resulted in a significant correlation (R(2)=0.562) between the two systems; however, differences of up 9.28 mm were found between corresponding measurements. This implies that clinical conclusions can potentially be upheld or refuted, based on the same data set, subject to coordinate system definition. Although the data analyzed presently involved the knee joint, similar issues surround the RSA motion analysis of other joints as well.     

A new system for analyzing swim fin propulsion based on human kinematic data

The use of swim fins has become popular in various water sport activities. While numerous models of swim fin with various innovative shapes have been subjectively designed, the exact influence of the fin characteristics on swimming performance is still much debated, and remains difficult to quantify. To date, the most common approach for evaluating swim fin propulsion is based on the study of “swimmer-fins” as a global system, where physiological and/or biomechanical responses are considered. However, reproducible swimming technique is difficult (or even impossible) to obtain on human body and may lead to discrepancies in data acquired between trials. In this study, we present and validate a new automat called HERMES which enables an evaluation of various swim fins during an adjustable, standardized and reproducible motion. This test bench reliably and accurately reproduces human fin-swimming motions, and gives resulting dynamic measurements at the ankle joint. Seven fins with various geometrical and mechanical characteristics were tested. For each swim fin, ankle force and hydromechanical efficiency (useful mechanical power output divided by mechanical power input delivered by the motors) were calculated. Efficiencies reported in our study were high (close to 70% for some swim fins) over a narrow range of Strouhal number (St) and peaks within the interval 0.2<St<0.4, as shown in previous studies on flying or swimming animals. Therefore, an interesting prospect in this work would be to accurately study the impact of adjustable fin kinematics and material (design and mechanical properties) on the wake structure and on efficiency.     

An automated coordinate recorder for biometry

Many measuring devices used in micropaleontology are unsatisfactory because observations must be recorded manually. Moreover, most use a linear scale that depends on the presence of predetermined morphological loci. An x, y recorder, largely adapted from instruments available in geological laboratories, is discussed. It obviates manual recording, frees data collection from the constraint of homologous loci and. in some applications, permits more shape information to be collected.     

Trafficking coordinate description of intracellular transport control of signaling networks

Many cellular networks rely on the regulated transport of their components to transduce extracellular information into precise intracellular signals. The dynamics of these networks is typically described in terms of compartmentalized chemical reactions. There are many important situations, however, in which the properties of the compartments change continuously in a way that cannot naturally be described by chemical reactions. Here, we develop an approach based on transport along a trafficking coordinate to precisely describe these processes and we apply it explicitly to the TGF-β signal transduction network, which plays a fundamental role in many diseases and cellular processes. The results of this newly introduced approach accurately capture the distinct TGF-β signaling dynamics of cells with and without cancerous backgrounds and provide an avenue to predict the effects of chemical perturbations in a way that closely recapitulates the observed cellular behavior.     

A kinematic model of the human ankle

The spatial gross motion of the foot with respect to the shank is modelled as rotations about two fixed ankle axes: the upper ankle rotation axis (plantarflexion/dorsiflexion) and the subtalar rotation axis (inversion/eversion). The positions of the axes are determined by externally visible bony landmarks of the lower leg and are measured for a living subject. The model input data are the plantarflexion/dorsiflexion and inversion/eversion rotation angles; the model output is a 4 × 4 transformation matrix which quantitatively describes the relative position of a foot coordinate system with respect to a shank coordinate system.     

Development and evaluation of the measurement system for the human shoulder joint based on the 6 DOF kinematic modelling

Although numerical models on the shoulder complex joint are currently available, many are impractical because of the procedural complexity coupled with limited and mere simple simulations. The present study defined the clavicle-scapula system as the "base of the humerus" in determining the position of proximal head of humerus, rendering conclusive innovation of a six degree of freedom (DOF) shoulder complex joint model. Furthermore, a complete measurement system where evaluation by calibrating the actual values via the use of an electromagnetic tracking device (ETD) was developed based on the innovated model. The special calibration method using optimizing calculation to work out the rotational center of humerus was employed and actually tested if the theoretical consideration was practically available. As a result of accuracy check experiments, the measurement error was defined within 2-3 mm, indicating sufficient accuracy in studies for human movement. Our findings strongly advocate that the benefit of this novel measurement system would contribute to studies related to shoulder movements in physiological anthropology.     

OpenSim as a preliminary kinematic testing platform for the development of total knee arthroplasty implants

The design of a total knee replacement implant needs to take account the complex surfaces of the knee which it is replacing. Ensuring design performance of the implant requires in vitro testing of the implant. A considerable amount of time is required to produce components and evaluate them inside an experimental setting. Numerous adjustments in the design of an implant and testing each individual design can be time consuming and expensive.Our solution is to use the OpenSim simulation software to rapidly test multiple design configurations of implants. This study modeled a testing rig which characterized the motion and laxity of knee implants. Three different knee implant designs were used to test and validate the accuracy of the simulation: symmetrical, asymmetric, and anatomic. Kinematics were described as distances measured from the center of each femoral condyle to a plane intersecting the most posterior points of the tibial condyles between 0 and 135° of flexion with 15° increments. Excluding the initial flexion measurement (∼0°) results, the absolute differences between all experimental and simulation results (neutral path, anterior-posterior shear, internal-external torque) for the symmetric, asymmetric, and anatomical designs were 1.98 mm ± 1.15, 1.17 mm ± 0.89, and 1.24 mm ± 0.97, respectively. Considering all designs, the accuracy of the simulation across all tests was 1.46 mm ± 1.07. It was concluded that the results of the simulation were an acceptable representation of the testing rig and hence applicable as a design tool for new total knees.     

Evaluation of alternative technical markers for the pelvic coordinate system

In this study, we evaluated alternative technical markers for the motion analysis of the pelvic segment. Thirteen subjects walked eight times while tri-dimensional kinematics were recorded for one stride of each trial. Five marker sets were evaluated, and we compared the tilt, obliquity, and rotation angles of the pelvis segment: (1) standard: markers at the anterior and posterior superior iliac spines (ASIS and PSIS); (2) markers at the PSIS and at the hip joint centers, HJCs (estimated by a functional method and described with clusters of markers at the thighs); (3) markers at the PSIS and HJCs (estimated by a predictive method and described with clusters of markers at the thighs); (4) markers at the PSIS and HJCs (estimated by a predictive method and described with skin-mounted markers at the thighs based on the Helen-Hayes marker set); (5) markers at the PSIS and at the iliac spines. Concerning the pelvic angles, evaluation of the alternative technical marker sets evinced that all marker sets demonstrated similar precision across trials (about 1°) but different accuracies (ranging from 1° to 3°) in comparison to the standard marker set. We suggest that all the investigated marker sets are reliable alternatives to the standard pelvic marker set.