The reliability of three-dimensional scapular attitudes in healthy people and people with shoulder impingement syndrome

Abstract

Background: Abnormal scapular displacements during arm elevation have been observed in people with shoulder impingement syndrome. These abnormal scapular displacements were evaluated using different methods and instruments allowing a 3-dimensional representation of the scapular kinematics. The validity and the intrasession reliability have been shown for the majority of these methods for healthy people. However, the intersession reliability on healthy people and people with impaired shoulders is not well documented. This measurement property needs to be assessed before using such methods in longitudinal comparative studies. The objective of this study is to evaluate the intra and intersession reliability of 3-dimensional scapular attitudes measured at different arm positions in healthy people and to explore the same measurement properties in people with shoulder impingement syndrome using the Optotrak Probing System.

Methods: Three-dimensional scapular attitudes were measured twice (test and retest interspaced by one week) on fifteen healthy subjects (mean age 37.3 years) and eight subjects with subacromial shoulder impingement syndrome (mean age 46.1 years) in three arm positions (arm at rest, 70 degrees of humerothoracic flexion and 90 degrees of humerothoracic abduction) using the Optotrak Probing System. Two different methods of calculation of 3-dimensional scapular attitudes were used: relative to the position of the scapula at rest and relative to the trunk. Intraclass correlation coefficient (ICC) and standard error of measure (SEM) were used to estimate intra and intersession reliability.

Results: For both groups, the reliability of the three-dimensional scapular attitudes for elevation positions was very good during the same session (ICCs from 0.84 to 0.99; SEM from 0.6 degrees to 1.9 degrees ) and good to very good between sessions (ICCs from 0.62 to 0.97; SEM from 1.2 degrees to 4.2 degrees ) when using the method of calculation relative to the trunk. Higher levels of intersession reliability were found for the method of calculation relative to the trunk in anterior-posterior tilting at 70 degrees of flexion compared to the method of calculation relative to the scapula at rest.

Conclusion: The estimation of three-dimensional scapular attitudes using the method of calculation relative to the trunk is reproducible in the three arm positions evaluated and can be used to document the scapular behavior.

Figure 1

Digitizing the scapular body landmarks. Three non collinear landmarks on the scapula were digitized using the Optotrak probing accessory.

Figure 2

Representation of the scapular rotations around the Y, X and Z axes. The scapular rotations are defined in accordance with the ISB recommendations. The sequence of rotations used is YsXsZs.

Figure 3

Intersession intraclass correlation coefficients of 3D scapular attitudes using two methods of calculation. The intersession intraclass correlation coefficients (ICCs) of 3D scapular attitudes (anterior/posterior tilting (A-PT), lateral/medial rotation (L-MR) and protraction/retraction (PRO-RET)) were measured in three static shoulder positions (arm at rest, 70° of flexion, 90° of abduction) using two methods of calculation (with respect (w/r) to the trunk and with respect (w/r) to the scapula at rest) in healthy subjects (n = 30 shoulders). The intersession ICCs were also measured using the mean of the three trials of each session (Trial 1-2-3) and the mean of the two first trials of each session (Trial 1–2). The error bar represents the 95% confidence interval of the ICCs.

Figure 4

Intersession standard error of measurement of 3D scapular attitudes using two methods of calculation. The intersession standard error of measurement (SEM) of 3D scapular attitudes (anterior/posterior tilting (A-PT), lateral/medial rotation (L-MR) and protraction/retraction (PRO-RET)) were measured in three static shoulder positions (arm at rest, flexion, abduction) using two methods of calculation (with respect (w/r) to the trunk and with respect (w/r) to the scapula at rest) in healthy subjects (n = 30 shoulders). The intersession SEM were also measured using the mean of the three trials of each session (Trial 1-2-3) and the mean of the two first trials of each session (Trial 1–2). The error bar represents the 95% confidence interval of the SEM.

Figure 5

Intersession intraclass correlation coefficients of 3D scapular attitudes for the two populations. The intersession intraclass correlation coefficients (ICCs) of 3D scapular attitudes (anterior/posterior tilting (A-PT), lateral/medial rotation (L-MR) and protraction/retraction (PRO-RET)) was measured in three static shoulder positions (arm at rest, 70° of flexion, 90° of abduction) using the method of calculation relative to the trunk in healthy subjects (n = 30 shoulders) and subjects with SIS (n = 8 shoulders for impaired shoulders and non-impaired shoulders).