Summary

Abnormal critical shoulder angle or acromion index do not negatively influence mid-term functional outcomes and are not contraindications for arthroscopic rotator cuff repair.

Abstract

Introduction

Recent studies have shown a correlation between scapular geometry and the development of atraumatic rotator cuff tears. Studying the influence of CSA and AI on post-operative outcomes is important as they will aid with pre-operative patient counselling with regards to expectations for post-surgical recovery, and also determine if surgical techniques aimed at modifying CSA and AI (for example arthroscopic lateral acromion resection) will ultimately be useful in the clinical setting. However, there is a paucity of literature on the effects of Critical Shoulder Angle (CSA) and Acromial Index (AI) on functional outcomes after arthroscopic rotator cuff repair. This study aimed to investigate the influence of CSA and AI on mid-term functional outcome after arthroscopic rotator cuff repair. The hypothesis was that a larger CSA or AI would result in poorer post-operative outcomes.

Methods

147 patients who underwent arthroscopic double row rotator cuff repair for radiologically documented full-thickness supraspinatus tears were included in this study. An independent reviewer measured the CSA and AI on preoperative radiographs. These patients were prospectively followed up and evaluated pre-operatively, as well as at 3, 6, 12 and 24 months post-operatively. Functional outcome was assessed with CSS, Oxford Shoulder Score (OSS), and UCLA Shoulder Rating Scale. The patients were first divided based on CSA: 1) =35° (control CSA) and 2) >35° (abnormal CSA), and then based on AI: 1) =0.7 and 2) >0.7. The Student unpaired t-test, Pearson Chi-Square test, and Pearson correlation were performed to examine the influence of CSA and AI on post-operative functional outcome scores.
Results:At 6 months follow-up, the CSS, OSS and UCLA Shoulder Rating Scale were 10±1, 4±2 and 3±1 points poorer in the abnormal CSA group compared to the control CSA group (p=0.005, p=0.030, p=0.035 respectively). By 24 months follow-up, all outcome scores were comparable between both CSA groups. At 3 months follow-up, the CSS was 6+/-1 points poorer in the abnormal AI group compared to the control AI group (p=0.039); this difference was not seen at 24 months. There was no significant correlation between CSA or AI with CSS, OSS or UCLA Shoulder Rating Scale at 24 months follow-up.

Conclusion

This study shows that despite scapular geometry having a role to play in the development of degenerative rotator cuff tears, they may not actually influence post-operative outcomes. Hence, surgical modification of CSA or AI with the aim of correction towards the norm may not necessarily be beneficial for the patient. Furthermore, patients with abnormal CSA or AI should still undergo surgery if indicated as their mid-term outcomes are not negatively influenced.