THE VARIABILITY OF SHOULDER MOTIONS RECORDED BY MEANS OF PALPATION

Objective. The objective of this methodological study is the quantific ation of the sources of variability in the recorded three-dimensional motions of the shoulder mechanism for comparative purposes. Background . The palpation and subsequent digitization of skeletal landmarks of t he shoulder mechanism is a non-invasive and relatively easy method to quantify shoulder orientations. Comparison of individual motions is su bject to the accuracy of the palpation method, the magnitude of kinema tic redundancy of the shoulder mechanism and intersubject differences in morphology and physiology. Quantification of these sources of varia nce, i.e. the palpation error, motoric noise and inter-subject differe nces, demonstrated the accuracy of the method and the potential validi ty of the descriptive motion parameters, e.g. Cardan angles, in intra- and inter-individual studies for clinical, ergonomical and biomechanic al studies. Methods. The orientations of the shoulder bones were recor ded five times for each of five subjects by palpation and digitization of 12 skeletal landmarks for 10 equidistant arm elevation postures in the scapular plane. The orientations were described by means of Carda n angles. The palpation error was determined at a standardized initial rest position and expressed by Cardan angles for each recorded postur e. Adding motoric noise and intersubject differences gave the inter-in dividual variance. Results. The palpation error was approximately 2 de grees. The major recorded variance originated from motoric noise (+/-3 3%) and inter-subject difference (+/-55%). Conclusions. The palpation method is an accurate means of recording the three-dimensional orienta tions of the shoulder mechanism and for intra-individual studies, Howe ver, inter-subject variability is large. Relevance The parameters desc ribing shoulder orientations are essential for biomechanical analysis by means of musculoskeletal shoulder models, and supply descriptive pa rameters for the comparative analysis and follow-up of individual shou lder motions in clinical and ergonomic settings, e.g. glenohumeral imm obility and impingement. (C) 1997 Elsevier Science Ltd. All rights res erved.