Acromio humeral distance less than six millimeter: Its meaning in full-thickness rotator cuff tear

The present study sought to identify full-thickness rotator cuff tears liable to induce an acromiohumeral distance (AHD) of less than 6mm. The hypothesis was that, less than 6mm AHD is found exclusively in association with total full-thickness infraspinatus tear. Materials: A continuous single-center series recruited 109 shoulders, free of glenohumeral osteoarthritis, presenting with full-thickness tear requiring surgery. Preoperative acromiohumeral distance, rupture location and extension on the various tendons and muscular fatty degeneration (FD) were known. Methods: Full-thickness tears were categorized by location and extension on the various tendons. For each group, the number of shoulders showing AHD < 6mm was determined. Results: Total full-thickness infraspinatus tears were almost the only tendon lesions able to induce AHD < 6mm, but this only when the infraspinatus muscle showed FD equal to or greater than 2.25: i.e., when the tear was longstanding. Discussion: Unlike previous reports, the present study took account of the total or partial nature of infraspinatus and subscapularis tendon tear. The findings may suggest that AHD < 6mm is induced by posterior migration of the humeral head secondary to longstanding total infraspinatus tear, reducing AHD projection height on X-ray. Conclusion: AHD < 6mm is a sign of rotator-cuff rupture almost systematically involving longstanding total infraspinatus tear, not always amenable to suture repair due to advanced fatty degeneration. AHD equal to or greater than 6mm is of no diagnostic relevance and in no way indicates whether there is subscapularis tear and, if so, whether suture repair is feasible.