# Associations between fatty infiltration of rotator cuff muscles and tear size or location of rotator cuff tendon

## TL;DR

This study shows that fatty infiltration in rotator cuff muscles is linked to the size of tears in those muscles and in adjacent muscles, and it increases with age.

## Contribution

The study reveals that fatty infiltration in rotator cuff muscles is associated with both the tear size in the same muscle and in adjacent muscles.

## Key findings

- Fatty infiltration grades were significantly associated with tear size in the same muscle (P < 0.01).
- Fatty infiltration in one muscle was also significantly associated with tear size in adjacent muscles (P < 0.01).
- Age at surgery was significantly linked to fatty infiltration progression (P < 0.01).

## Abstract

Fatty infiltration (FI) of rotator cuff muscles in patients with rotator cuff tears is an important imaging factor for determining surgical indications. However, the associations between FI grade and the size or location of adjacent rotator cuff tears are not well-known. This study aimed to primarily determine whether tear size and location, especially for the SSc tendon, are associated with FI of adjacent rotator cuff muscles. The secondary aim was to clarify which patient factors are associated with rotator cuff muscle FI in rotator cuff tear cases.

This study examined 373 shoulders of 348 patients (264 males and 109 females; mean age of 62.8 years) who underwent arthroscopic rotator cuff surgery. The FI grades of the supraspinatus (SSP), infraspinatus (ISP), and subscapularis (SSc) muscles were assessed using preoperative magnetic resonance imaging (MRI) using the Goutallier classification modified by Fuchs. According to the preoperative MRI and intraoperative findings, the tear size of the posterior–superior rotator cuff (SSP–ISP) was classified using a modified six-grade scale of the Cofield classification, and that of the SSc tear was classified using a six-grade scale according to the Lafosse classification. Age at surgery, sex, body mass index (BMI), presence of diabetes mellitus (DM) or hyperlipidemia (HL), trauma history, and duration of symptoms were investigated.

The FI grades of the SSP, ISP, and SSc were significantly associated with the size of the tears in those muscles (all P < 0.01). Furthermore, the FI grades of the SSP and the ISP were significantly associated with SSc tear size (P < 0.01), and the FI grade of the SSc was significantly associated with SSP–ISP tear size (P < 0.01). Patient age at surgery was significantly associated with FI grade (P < 0.01), with significant progression of the FI grade with advancing age. However, there were no significant associations between the FI grade and sex, BMI, presence of DM or HL, trauma history, and duration of symptoms.

The FI grade of each of the rotator cuff muscles is affected by not only the tear severity of the muscle concerned but also by the severity of any tear in the adjacent rotator cuff.