Objective assessment, repeatability, and agreement of shoulder ROM with a 3D gyroscope

Abstract

Background: Assessment of shoulder mobility is essential for diagnosis and clinical follow-up of shoulder diseases. Only a few highly sophisticated instruments for objective measurements of shoulder mobility are available. The recently introduced DynaPort MiniMod TriGyro ShoulderTest-System (DP) was validated earlier in laboratory trials. We aimed to assess the precision (repeatability) and agreement of this instrument in human subjects, as compared to the conventional goniometer.

Methods: The DP is a small, light-weight, three-dimensional gyroscope that can be fixed on the distal upper arm, recording shoulder abduction, flexion, and rotation. Twenty-one subjects (42 shoulders) were included for analysis. Two subsequent assessments of the same subject with a 30-minute delay in testing of each shoulder were performed with the DP in two directions (flexion and abduction), and simultaneously correlated with the measurements of a conventional goniometer. All assessments were performed by one observer. Repeatability for each method was determined and compared as the statistical variance between two repeated measurements. Agreement was illustrated by Bland-Altman-Plots with 95% limits of agreement. Statistical analysis was performed with a linear mixed regression model. Variance for repeated measurements by the same method was also estimated and compared with the likelihood-ratio test.

Results: Evaluation of abduction showed significantly better repeatability for the DP compared to the conventional goniometer (error variance: DP = 0.89, goniometer = 8.58, p = 0.025). No significant differences were found for flexion (DP = 1.52, goniometer = 5.94, p = 0.09). Agreement assessment was performed for flexion for mean differences of 0.27° with 95% limit of agreement ranging from -7.97° to 8.51°. For abduction, the mean differences were 1.19° with a 95% limit of agreement ranging from -9.07° to 11.46°.

Conclusion: In summary, DP demonstrated a high precision even higher than the conventional goniometer. Agreement between both methods is acceptable, with possible deviations of up to greater than 10°. Therefore, static measurements with DP are more precise than conventional goniometer measurements. These results are promising for routine clinical use of the DP.

Figure 1

Three-dimensional gyroscope DynaPort MiniMod TriGyro ShoulderTest.

Figure 2

Conventional goniometer.

Figure 3

Calibration-check by MiRA®-software: left for flexion and right for abduction.

Figure 4

Bland-Altman-Plot for flexion. x-axis: mean value of ROM, y-axis: difference between conventional goniometer and DP in °. Thick blue line: mean difference between conventional goniometer and DP. Thin blue lines: lower and upper 95% limits of agreement.

Figure 5

Bland-Altman-Plot for abduction. x-axis: mean value of ROM, y-axis: difference between conventional goniometer and DP in °. Thick blue line: mean difference between conventional goniometer and DP. Thin blue lines: lower and upper 95% limits of agreement.