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Pubmed for Handhelds

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  • Title: Neck mobility measurement by means of the 'Flock of Birds' electromagnetic tracking system.
    Author: Koerhuis CL, Winters JC, van der Helm FC, Hof AL.
    Journal: Clin Biomech (Bristol); 2003 Jan; 18(1):14-8. PubMed ID: 12527242.
    Abstract:
    OBJECTIVE: To establish the accuracy and reliability of a six-degrees-of-freedom electromagnetic tracking device, the "Flock of Birds", for measuring neck rotations and to identify the main sources of error. DESIGN: Ten human subjects made the same types of maximal neck rotation, both actively and passively: axial rotation in neutral position, from a flexed position and from an extended position, flexion/extension and lateral flexion. The same movements were mimicked in a 'dummy head' set-up. METHODS: One Flock of Birds receiver was mounted on the thorax, one on the head. By means of a third receiver, mounted on a stylus, bony landmarks on head and thorax were palpated. These served to define two anatomically based local coordinate systems, to which the rotations were referred. RESULTS: Measurements were accurate with a maximal measurement error of 2.5 degrees. No significant difference between active and passive rotation was seen. The intra-subject variation was low within the same session, SD between 2 degrees and 4 degrees. Between sessions the variability was considerable, SD between 5 degrees and 16 degrees. CONCLUSION: The Flock of Birds method is reliable and sufficiently precise. The variability in measured range of motion between sessions is a point of concern in interpreting follow-up studies in patients. RELEVANCE: A reduced range of neck motion is a major complaint in pathologies of the cervical spine or the shoulder. A method is described in which neck rotations are related to well-defined bony landmarks. In combined rotations, e.g. flexion combined with axial rotation, the measured range of motion can sometimes fluctuate strongly (up to 30 degrees ) between measurements, without apparent pathology.
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