The function level influence of an intact rotator cuff on the unweighted Constant score and its corresponding items is unknown. The aim of this study was to evaluate this contribution. The hypothesis was that the shoulder muscles other than the rotator cuff ones ensure a “basic” shoulder function level that is improved by the rotator cuff depending on its fatty degeneration index (FDI)
Material and methods
This study was based on a continuous series of 29 non-osteoarthritic shoulders whose sutured rotator cuff tears remained intact after 9 years of follow-up. The preoperative FDI was 0.9 (0–2) and 1.26 (0.2–2.2) at the final follow-up. The Constant score was 76.85 at the final follow-up (range 42–93). There was a strong negative correlation between preoperative and follow-up FDI’s and all the Constant scores at the final follow-up. Linear regression analysis was performed. The two linear regression lines were superimposed.
For a given FDI value, all Constant scores were lower when linear regression was based on preoperative FDI scores that included postoperative deterioration of the FDI. The two linear regression lines converged as the FDI increased and intersected at an FDI of 2.25. Thus, the impact of intact repaired rotator cuff function was null when the FDI was above 2.25, leaving other shoulder muscles (including the deltoid), to ensure “basic” shoulder function at a Constant score of approximately 62 points.
The “basic” shoulder function found in this study is supported by the similar Constant scores found in reverse shoulder prostheses, and in painless shoulders with full thickness rotator cuff tears.
The deltoid and the shoulder muscles other than the rotator cuff seem to be responsible for “basic” shoulder function and represent 60% of the unweighted Constant score. The lower the FDI, the more the function of an intact repaired cuff improves this “basic” function level.
Level of evidence
Keywords : Rotator cuff function, Shoulder function, Unweighted Constant score, Muscle fatty degeneration, Fatty degeneration index