Repeatability of gait data using a functional hip joint centre and a mean helical knee axis.

Requirements for upper extremity motions during activities of daily living.

Inertial and magnetic measurement systems (IMMSs) are a new generation of motion analysis systems which may diffuse the measurement of upper-limb kinematics to ambulatory settings. Based on the MT9B IMMS (Xsens Technologies, NL), we therefore developed a protocol that measures the scapulothoracic, humerothoracic and elbow 3D kinematics. To preliminarily evaluate the protocol, a 23-year-old subject performed six tasks involving shoulder and elbow single-joint-angle movements. Criteria for protocol validity were limited cross-talk with the other joint-angles during each task; scapulohumeral-rhythm close to literature results; and constant carrying-angle. To assess the accuracy of the MT9B when measuring the upper-limb kinematics through the protocol, we compared the MT9B estimations during the six tasks, plus other four, with the estimations of an optoelectronic system (the gold standard), in terms of RMS error, correlation coefficient (r), and the amplitude ratio (m). Results indicate that the criteria for protocol validity were met for all tasks. For the joint angles mainly involved in each movement, the MT9B estimations presented RMS errors 0.99 and 0.9 < m < 1.09. It appears therefore that (1) the protocol in combination with the MT9B is valid for, and (2) the MT9B in combination with the protocol is accurate when, measuring shoulder and elbow kinematics, during the tasks tested, in ambulatory settings.

Ambulatory measurement of shoulder and elbow kinematics through inertial and magnetic sensors

A survey of formal methods for determining functional joint axes

When developing robotic exoskeletons, the design of physical connections between the device and the human limb to which it is connected is a crucial problem. Indeed, using an embedment at each connection point leads to uncontrollable forces at the interaction port, induced by hyperstaticity. In practice, these forces may be large because in general the human limb kinematics and the exoskeleton kinematics differ. To cope with hyperstaticity, the literature suggests the addition of passive mechanisms inside the mechanism loops. However, empirical solutions that are proposed so far lack proper analysis and generality. In this paper, we study the general problem of connecting two similar kinematic chains through multiple passive mechanisms. We derive a constructive method that allows the determination of all the possible distributions of freed degrees of freedom across different fixation mechanisms. It also provides formal proofs of global isostaticity. Practical usefulness is illustrated through two examples with conclusive experimental results: a preliminary study made on a manikin with an arm exoskeleton controlling the movement (passive mode) and a larger campaign on ten healthy subjects performing pointing tasks with a transparent robot (active mode).

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Connecting a Human Limb to an Exoskeleton

Determination of the optimal elbow axis for evaluation of placement of prostheses.

Determining the optimal flexion-extension axis of the elbow in vivo - a study of interobserver and intraobserver reliability

OBJECTIVES: (1) To investigate the measurement characteristics of the
Hospital for Special Surgery (HSS) and Mayo Clinic elbow assessment
instruments, utilizing methodological criteria including feasibility,
reliability, validity, and discriminative ability; and (2) to develop an
efficient and disease-specific rating system for elbow function assessment
(EFA) in adult patients with RA, using a combination of self-reported
subjective items and objective measures, and comparing its characteristics
with the HSS and Mayo Clinic scales. METHODS: (1) Selection of
elbow-specific items. (2) Investigation of reliability and validity of all
separate items, as well as the total HSS and Mayo Clinic scores, in 42
patients with RA (mean age 60 yrs). Direct observation of functional elbow
performance was defined as the gold standard against which criterion
validity was compared. (3) Reaching agreement within a team of
professionals on the different scale dimensions and the assigned weight.
(4) Item reduction by eliminating unreliable, inaccurate, unfeasible, and
ambiguous items. Finally, the EFA scale was constructed by selecting the
most reliable and accurate items. RESULTS: The EFA scale showed a superior
or equal degree of reliability as reflected in intraclass correlation
coefficients of more than 0.88, and also superior validity, compared with
the HSS and Mayo Clinic measures. CONCLUSION: Although the elbow scoring
systems currently available provide a reliable measure, they seem
restricted in evaluating elbow-specific functional ability. The EFA scale
was found to be most suitable to measure elbow functional ability in RA,
and was also shown to be highly reliable and practical in clinical
practice. (aut.ref.)

Y.A. de Boer

Papers

Determination of the optimal elbow axis for evaluation of placement of prostheses.

Determining the optimal flexion-extension axis of the elbow in vivo - a study of interobserver and intraobserver reliability

Clinical reliability and validity of elbow functional assessment in rheumatoid arthritis.