Reports using the Constant-Murley score often lack details regarding how strength measurement was performed, which may have
an important impact on the results obtained. A description of the measurement is especially important when patients are unable
to adopt the prescribed position of 90° shoulder abduction, leading to invalid or highly discrepant scores. We investigated
the influence of shoulder abduction and torso position on strength measurement with special emphasis on intraobserver reliability.
Thirty-three healthy volunteers were examined using a handheld dynamometer (Isobex®) in 30°, 60°, and 90° abduction with or without stabilization of the torso. A linear correlation between strength measurements
in different degrees of abduction was observed, with values at 90° abduction on average 15% lower than at 60° and 45% lower
than at 30°. In multivariate analysis, gender and weight had a substantial impact on the strength of individual measurement
positions. Intraobserver reliability was related to arm and torso position (intraclass correlation coefficients, 0.71–0.93)
and was highest for 90° abduction without torso stabilization. These findings emphasize the importance of standardized torso
and arm positions ensuring high reliability when performing the strength measurement of the Constant-Murley score.
Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest,
patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.
Each author certifies that his or her institution has approved the human protocol for this investigation, that all investigations
were conducted in conformity with ethical principles of research, and that informed consent for participation in the study
was obtained.
This work was performed at Department of Orthopaedic Surgery and Traumatology, Kantonsspital Bruderholz.