Lateral versus posterior approach to shoulder injection in patients with subacromial impingement syndrome: A mixed methods study

Objectives: To determine the effectiveness of lateral approach to subacromial injection compared to posterior approach for the treatment of subacromial impingement syndrome (SAIS); and to establish the experiences of SAIS patients receiving these injections associated with better clinical outcomes. Design: This study used a mixed methods approach that combines a pragmatic randomised control trial to investigate which injection approach is better and a semi-structured qualitative interview to investigate the experiences of SAIS patients receiving these injections. Settings: Out-patients community musculoskeletal service Sample: 80 patients with SAIS for the randomised control study and 20 participants for the semi-structured qualitative interview. Interventions: The Intervention group received a single subacromial injection with a 21-gauge Green needle with a 40 mg/ml of Kenalog and a 4 ml 1% of Lidocaine through a lateral approach. The Control group received an identical treatment except that the location was by a posterior approach. Outcome measures: Difference in improvements in the overall patient reported outcome measures (PROMs) and shoulder pain and disability index score (SPADI) at 8 and 12 weeks follow-up between the two groups. Results: A moderate but statistically and clinically significant difference in improvement in day-time pain (mean change score) occurred in favour of the lateral group (mean = 3.7) compared with the posterior group (mean = 2.3) between week 0 to 8 (1.4 points [95% CI 0.3 to 2.6, p = 0.018]). However, there were no statistically significant differences between the groups in night-time pain, shoulder function and SPADI scores. There was a statistically and clinically significant difference (p = 0.001) within the groups for all clinical outcomes between week 0 to 8 and between week 0 and 12. This was confirmed by participants from the semi-structured interviews which were conducted 12 weeks after the injection. Conclusion: There were no real significant differences in the treatments; however, both forms of treatment were associated with significant improvement in shoulder pain, function and disability. This was confirmed by participants from the semi-structured interviews, who felt that they improved not only because of the effect of the cortisone injection, but also because of other factors such as education about their treatment, exercise information, the experience and skills of the injecting clinicians, access to treatment as well as good customer service.