A. de Lange

Finite centroid and helical axis estimation from noisy landmark measurements in the study of human joint kinematics

Recent work on joint kinematics indicates that the finite centroid (centre of rotation) and the finite helical axis (axis of rotation, screw axis, twist axis) are highly susceptible to measurement errors when they are experimentally determined from landmark position data. This paper presents an analytical model to describe these effects, under isotropic conditions for the measurement errors and for the spatial landmark distribution. It appears that the position and direction errors are inversely proportional to the rotation magnitude, and that they are much more error-prone than the relatively well-determined rotation and translation magnitudes. Furthermore, the direction and rotation magnitude errors are inversely proportional to the landmark distribution radius, and the position and translation magnitude errors are minimal if the mean position of the landmarks coincides with the centroid or helical axis. For the planar centroid, the use of rigid-body constraints results in considerable precision improvement relative to the classical, finite Reuleaux method for centroid reconstruction. These analytical results can be used to define suitable measurement configurations, and they are used in this paper to explain experimental results on Röntgenphotogrammetrically acquired in vitro wrist joint movement.

Helical axes of passive knee joint motions

The purpose of this study was to determine finite helical axes for passive knee joint motions in vitro and to evaluate the descriptive value of the finite helical axes for step-by-step flexion motions, with respect to consistency and reproducibility. An accurate Roentgenstereophotogrammetric system was used for motion measurements. Four knees were tested in a motion and loading rig with one and the same experimental protocol. A fifth specimen was used to study the effects of some of the experimental conditions on the axis parameters. On the basis of earlier reported motion characteristics in terms of Euler rotations and translations, two motion pathways were chosen to be reported here: a flexion motion with an internal torque of 3 Nm and one with an external torque of 3 Nm on the tibia. The positions and orientations of the axes were described relative to the insertions of the four major ligaments and the geometry of the articular surfaces of the femur, and also as intersections with a medial and a lateral sagittal plane. The three-dimensional patterns of the helical axes of the four knee specimens were found to be highly reproducible and consistent for each of the two motion pathways. The axis patterns were not unique, but reflected the particular combination of flexion and axial rotation for each particular motion pathway. Although small, the helical translations indicated medial motions of the tibia relative to the femur. This medial helical translation was more pronounced for the internal pathway compared with the external pathway. Above 70 degrees flexion, the axes move posteriorly relative to the femur.

Analytical stereophotogrammetric determination of three-dimensional knee-joint geometry

An analytical stereophotogrammetric method is introduced to measure the three-dimensional geometry of articular surfaces in vitro. Information of this kind is particularly useful for mathematical joint models and anthropological studies. The method requires no specific equipment, such as a stereocomparator, contrarily to other techniques reported (e.g. Ghosh, 1983) and is relatively simple and inexpensive. The background of the method is outlined in the present paper, and results of accuracy and precision tests are presented. It is shown that an accuracy on the order of 0.2 mm (95% confidence interval) is well feasible in actual knee-joint evaluations, if the measuring procedure is conducted carefully. The method is illustrated by measuring and comparing the articular surface geometries of a bilateral pair of knee joints.

Instantaneous Helical Axis Estimation Via Natural, Cross-Validated Splines

In studies of biological joint motion, quantification of translations and rotations by means of a reference point and attitude angles does not provide a clear insight in the relation between kinematics and joint geometry. Because of its geometric simplicity, a better picture can be obtained by means of the Instantaneous Helical Axis (IHA), also known as the instantaneous screw axis, twist axis, or axis of rotation. At each moment in time, joint motion is seen as the movement of one body segment with respect to an adjacent segment (usually distal with respect to proximal), with a translation component along, and a rotation component about a directed line in space which is uniquely determined as long as the rotatory component does not vanish: see Figure 1. The total amounts of translation and rotation along the path of motion can be defined as the time integrals of the instantaneous translation and rotation velocities at the IHA from a given reference time.

Kinematics of the Human Knee Joint

The human knee joint is probably one of the most complicated joint structures from a kinematics point of view, and certainly more complex than any technical joint design known. Viewed as a mechanical system it consists of two relatively irregular bearing surfaces, the tibial and femoral condyles, covered with articular cartilage. Interposed between these relatively rigid structures are the compliant menisci. The bones are connected by collageneous fibers organised in a capsule and several ligaments, of which the two cruciate ligaments and the two collateral ligaments are the most important (Figs. 1 and 2).

Using an eHealth Intervention to Stimulate Health Behavior for the Prevention of Cognitive Decline in Dutch Adults: A Study Protocol for the Brain Aging Monitor.

Background Internet-delivered intervention programs are an effective way of changing health behavior in an aging population. The same population has an increasing number of people with cognitive decline or cognitive impairments. Modifiable lifestyle risk factors such as physical activity, nutrition, smoking, alcohol consumption, sleep, and stress all influence the probability of developing neurodegenerative diseases such as Alzheimer’s disease. Objective This study aims to answer two questions: (1) Is the use of a self-motivated, complex eHealth intervention effective in changing multiple health behaviors related to cognitive aging in Dutch adults in the work force, especially those aged 40 and over? and (2) Does this health behavior change result in healthier cognitive aging patterns and contribute to preventing or delaying future onset of neurodegenerative syndromes? Methods The Brain Aging Monitor study uses a quasi-experimental 2-year pre-posttest design. The Brain Aging Monitor is an online, self-motivated lifestyle intervention program. Recruitment is done both in medium to large organizations and in the Dutch general population over the age of 40. The main outcome measure is the relationship between lifestyle change and cognitive aging. The program uses different strategies and modalities such as Web content, email, online newsletters, and online games to aid its users in behavior change. To build self-regulatory skills, the Brain Aging Monitor offers its users goal-setting activities, skill-building activities, and self-monitoring. Results Study results are expected to be published in early 2016. Conclusions This study will add to the body of evidence on the effectiveness of eHealth intervention programs with the combined use of state-of-the-art applied games and established behavior change techniques. This will lead to new insights on how to use behavior change techniques and theory in multidimensional lifestyle eHealth research, and how these techniques and theories apply when they are used in a setting where no professional back-end is available. Trial Registration Nederlands Trial Register: NTR4144; http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=4144 (Archived by WebCite at http://www.webcitation.org/6cZzwZSg3)

On the Application of a Smoothing Procedure in the Kinematical Study of the Human Wrist Joint In-Vitro

In most biomechanical studies, the motions of a rigid body (e.g. bone) are described in terms of Euler rotation angles and translation vectors or in terms of helical axis (e.g. axis of rotation, screw axis). Each description has its own benefits. An attractive aspect of the helical axis representation is its illustrative quality, giving a more direct impression of the joint motion. Other advantages are that the helical axis facilitates relating joint kinematics to joint geometry and that the values for translations and rotations are invariant under a co-ordinate system transformation.

Changing Behavioral Lifestyle Risk Factors Related to Cognitive Decline in Later Life Using a Self-Motivated eHealth Intervention in Dutch Adults

Background Our labor force is aging, but aged workers are not yet coached on how to stay cognitively fit for the job. Objective In this study, we tested whether a self-motivated, complex eHealth intervention could improve multiple health-related behaviors that are associated with cognitive aging among working Dutch adults. Methods This quasi-experimental prospective study with a pre-post design was conducted with employees of Dutch medium to large companies. All employees with Internet access, a good understanding of the Dutch language, and who provided digital informed consent were eligible to participate. In total, 2972 participants (2110/2972, 71.11% females) with a mean (standard deviation, SD) age of 51.8 (SD 12.9) years were recruited; 2305 became active users of the intervention, and 173 completed the 1-year follow-up. This self-motivated eHealth lifestyle intervention stimulates participants to set personally relevant, monthly health behavior change goals using Goal Attainment Scaling and to realize these goals by implementing behavior change techniques grounded in behavior change theory. The primary outcomes were the goal-setting success rate and the change in overall lifestyle score from baseline to the 1-year follow-up; the score was based on physical activity, diet, smoking, alcohol, sleep, and stress scores. The secondary outcomes were the changes in body weight, body mass index, specific lifestyle characteristics, and website usage. Results A total of 1212 participants set 2620 behavior change goals; 392 participants assessed 1089 (1089/2288, 47.59%) goals and successfully achieved 422 (422/1089, 38.75%) of these goals. Among the goal-setting participants in follow-up, this led to a +0.81-point improvement (95% CI 0.49-1.13, P<.001) in overall lifestyle (d=0.32) and weight loss of 0.62 kg (95% CI −1.16 to −0.07, P=.03). These participants also showed significant improvement in 8 out of 11 specific lifestyle components. Conclusions Among an adult Dutch population, this eHealth intervention resulted in lifestyle changes in behavioral risk factors associated with cognitive decline, and these improvements lasted over the period of 1 year. Given the general aging of our workforce, this eHealth intervention opens new avenues for the widespread use of cost-effective self-motivated prevention programs aimed at prevention of early-stage cognitive decline and more self-management of their risk factors. Trial Registration Nederlands Trial Register: NTR4144; http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=4144 (Archived by WebCite at http://www.webcitation.org/6cZzwZSg3).

The three-dimensional freedom-of-motion characteristics of the human knee joint

The present study attempts to quantify the three-dimensional freedom-of-motion characteristics of the knee-joint in vitro, and their dependence on external forces, knee ligaments and menisci. This information provides descriptions of knee-joint kinematic behaviour in general, which can be applied to the development of improved diagnostic tools and operative procedures.