Heterogeneous assessment of shoulder disorders: validation of the Standardized Index of Shoulder Function

Abstract

Objective: Although 40 assessment tools are described in the literature, very few of them have been correctly validated. The Standardized Index of Shoulder Function (FI2S) encompasses pain, mobility, strength and function. The aim of this work is to describe the FI2S and to study its construct validity, reliability and responsiveness to change.

Patients: Fifty-nine patients with non-surgical (rotator cuff lesions, frozen shoulders, osteoarthritis) or post-surgical (acromioplasty, repairs of rotator cuff tears, arthroplasty) shoulder disorders were included.

Methods: The FI2S was compared with the Disabilities of the Arm, Shoulder and Hand questionnaire (DASH), with the Constant-Murley Score (CMS), and with a visual analogue scale for pain.

Results: Inter-test reliability and inter-rater reliability are excellent, with intra-class correlation coefficient of 0.93 (0.88-0.96) and 0.94 (0.90-0.96), respectively. Under a convergent hypothesis, the Spearman's correlation coefficients with the CMS and DASH score are 0.91 (p < 0.0001) and -0.64 (p < 0.0001), respectively. Correlations between the FI2S and the CMS are excellent for mobility and strength, but moderate for pain and functional capacities. Under a divergent hypothesis, no correlation is observed between the FI2S total score and age. Responsiveness to change is excellent.

Conclusion: The FI2S appears to be a proper assessment tool for pain, mobility, strength and function in shoulder disorders, easy to administer and of good metric value.