Comparison between tripod and skin-fixed recording of scapular motion.
Non-invasive dynamical measurements of 3D scapular motion can be performed easily by attachment of a 6 DOF electromagnetic receiver onto the skin above the acromion. To quantify the introduction of possible errors due to skin displacement, we assessed 3D scapular positions on n=8 subjects by both tripod and skin-fixed method. Error analysis included the variables method (tripod, skin-fixed simultaneously with tripod, separate skin-fixed at 0 and 0.25Hz of elevation speed), plane of elevation (0 degrees and 90 degrees ) and observation (receiver replacement: n=3). Inter-individual 'group' differences depended on elevation plane and showed an average underestimation of scapular rotation of 6.5 degrees (worst case 13 degrees ) using the skin-fixed method. Only the group RMSE, not the individual RMSE, could be successfully lowered using linear regression (to about 2 degrees ). Inter-trial reliability (RMSE <3.24 degrees , ICC>0.94) and RMSE between 0 and 0.25Hz recordings (about 2.5 degrees ) were satisfactory. Intra-observer RMSE after replacement of the skin-fixed receiver was 5 degrees . The skin-fixed method is suitable for dynamic recordings of scapular rotations; however, measurements are precise only when the acromion receiver is not replaced. Combined with a relatively low accuracy, we conclude that the skin-fixed method should be used only in combination with tripod 'calibration'.
Laboratory for Motion Analysis, Department of Orthopaedic Surgery, Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands. c.g.m.meskers@lumc.nl
Carel G M
CG
Meskers
Michiel A J
MA
van de Sande
Jurriaan H
JH
de Groot
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D012540:Scapula / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology*