Morphological characteristics of the acromion in Fosbury flop tears and their clinical outcomes after arthroscopic rotator cuff repair

Background: Rotator cuff tears that have flipped upon itself and adhered medially have been recently described as Fosbury flop tears (FFT). However, there are no reports on the cause and clinical outcomes of FFT. We investigated the preoperative anatomical factors and clinical outcomes related to the occurrence of FFT. Methods: Among patients with more than two years of follow-up, 33 patients with FFT who underwent arthroscopic rotator cuff repair (ARCR) for a small-to-medium sized tear of the supraspinatus tendon alone (Group F: mean age, 63.4 +/- 8.9 years) and 52 patients without FFT who underwent ARCR (Group C: mean age, 62.1 +/- 7.0 years) were included. Presence of diabetes mellitus, critical shoulder angle (CSA), lateral acromial angle (LAA), acromiohumeral distance (AHD), sagittal and coronal morphologies of the acromion, JOA score, and rate of rotator cuff re-tear were evaluated. Results: There were significantly more males in Group F (P = 0.017). There were no significant differences in age or rate of diabetic complications. The mean CSA, LAA, and AHD in the Groups F and C were respectively as follows: CSA, 33.7 +/- 4.0 degrees and 34.5 +/- 3.4 degrees; LAA, 82.1 +/- 9.9 degrees and 82.1 +/- 6.9 degrees; AHD, 10.2 +/- 1.4 mm and 9.8 +/- 1.4 mm. There were no significant differences between groups. The acromial morphology showed no significant difference in the sagittal plane; however, significantly more double-floor type acromia were found in the coronal plane (P < 0.001). Although the JOA score significantly improved in both groups, there was no significant difference between groups. The re-rupture rate was significantly higher in Group F than Group C (15.2% versus 1.9%; P = 0.02). Conclusions: Double-floor type acromia in the coronal plane was common in Group F. The location of osteophytes on the inferior surface of the acromion was believed to be associated with the occurrence of FFT. Furthermore, a high re-tear rate was observed in group F.