Purpose: The aim of this study was to analyse the correlation of clinical symptoms and function with the fatty degeneration of the infraspinatus in rotator cuff tears.
Methods: A total of 152 patients who had rotator cuff tears was enroled retrospectively. The infraspinatus muscle was divided into two compartments according to the bundle of fibres, and the patients were divided into four groups that reflected fatty degeneration. The muscle strength of the shoulder and clinical symptoms was investigated.
Results: The severity of the rotator cuff tear and retraction increased with fatty degeneration of both the superior and inferior parts in the infraspinatus muscles. Because of the increasing fatty degeneration of the superior part of the infraspinatus, the shoulder strength index (SSI) of abduction had poor results. Additionally, as the fatty degeneration of the inferior part of the infraspinatus increased, the SSI of abduction and external rotation had worse results.
Conclusions: Fatty degeneration of the superior part of the infraspinatus has no correlation with the power of external rotation but has a negative correlation with the power of abduction. Moreover, fatty degeneration of the inferior part of the infraspinatus has a negative correlation with both the power of abduction and external rotation.
Level of evidence: Retrospective study, Level IV.