Differences in acromial morphology of shoulders in patients with degenerative and traumatic supraspinatus tendon tears.

ABSTRACT

PURPOSE: Distinct characteristics of acromial morphology seem to be one factor for the development of degenerative supraspinatus tendon tears. Thus, it is questionable whether patients with traumatic tendon tears also present these parameters. The hypothesis of the present study was that the acromial morphology of patients with degenerative supraspinatus tendon tears differs from patients with traumatic tears. METHODS: One hundred and thirty-six patients that were treated by arthroscopic rotator cuff repair from 2010 to 2013 were included in this study. Seventy-two patients had degenerative (group 1), and 64 had traumatic (group 2) supraspinatus tendon tears. On preoperative radiographs the Bigliani type, acromial slope, acromiohumeral (AH) distance, lateral acromial angle (LAA), acromion index (AI), and critical shoulder angle (CSA) were measured. Medians of these parameters as well as of age of both groups were compared using the t test. RESULTS: The percentaged distribution of the Bigliani type differed (group 1 vs. 2 type 1 18/38, type 2 56/55, type 3 26/8). All parameters showed significant differences between degenerative and traumatic tears. Slope 21.2° (SD 7.6°) versus 19.2° (SD 7.9°, p = 0.026), AH distance 8.4 mm (SD 2.3 mm) versus 9.9 mm (SD 1.9 mm, p = 0.0006), LAA 77.0° (SD 4.0°) versus 82.5° (SD 4.7°, p < 0.0001), AI 0.77 (SD 0.07) versus 0.73 (0.06, p = 0.0239), and CSA 36.8° (SD 3.6°) versus 35.3° (SD 2.9°, p = 0.007). An LAA <70° or an AH distance of <5 mm only occurred in degenerative tears. Patients with degenerative tears were significantly older (60 vs. 54 years). CONCLUSIONS: The hypothesis that the acromial morphology of patients with degenerative supraspinatus tendon tears differs from patients with traumatic tears was confirmed. Shoulders with degenerative tears show a narrower subacromial space and a larger lateral extension as well as a steeper angulation of the acromion than with traumatic tears. Thus, the results of this study support the theory of external impingement as a cause for degenerative rotator cuff tears. LEVEL OF EVIDENCE IV.