Arthroscopic repair of massive rotator cuff tears using a suture bridge technique has a relatively high retear rate, and these structural failures appear to have a significant difference in clinical outcomes compared with the healed group. Degree of fatty infiltration of the infraspinatus and extent of retraction are the 2 most important factors associated with a retear. Orthopaedic surgeons should predict the possibility of retear before surgery and counsel patients about their expected functional results.

Retears occurred infrequently in the late postoperative period (after 3 months) in well-healed tendons that had shown intact cuff repair integrity with sufficient mechanical and biological healing within the first 3 postoperative months.

Purpose The purpose of this study was to identify the relationship between an acromion index (AI) and the size of a rotator cuff tear. The hypothesis of our study was that an AI will be higher in patients with a full-thickness tear than in patients with a partial-thickness articular-side tear, and that it can be used as a predictor for the size of a rotator cuff tear. Methods We included 284 patients who had been diagnosed with rotator cuff tears and had undergone arthroscopic rotator cuff repair at our institute. All patients were divided into five distinct groups (partial-thickness articular side tear, and four subgroups of full-thickness tears) depending on the size of the rotator cuff tear on arthroscopy. In each patient, an AI was measured on the pre-operative oblique coronal MR images and then analysed to determine the difference between groups. Results There were statistically significant differences between the partial-thickness articular side rotator cuff tear and large-tomassive rotator cuff tear groups (p<0.01), and the mean value of an AI was highest in the large-sized full-thickness tear group. The AI of the partial-thickness articular-side rotator cuff tear group was statistically different from the large-to-massive rotator cuff tear groups. ConclusionsThe AI can be a predictor which can differentiate a partial-thickness articular-side tear and a large-to-massive rotator cuff tear pre-operatively. However the AI could not provide useful guidance on predicting the differences in tear size in full-thickness tear patients. We suggest that a high AI can be one of the associated factors for progression to large-to-massive rotator cuff tears in a rotator cuff disease.