Summary

Shoulder Pacemaker-enhanced physiotherapy leads to significant and clinically relevant improvement of outcomes in the treatment of functional posterior shoulder instability.

Abstract

Introduction

Functional posterior shoulder instability (FPSI) is a severe type of instability mostly affecting young adults that leads to loss of function, pain, and stigmatization. Even though physiotherapy is the gold standard treatment, it is often not successful leading to salvage surgical stabilization attempts with uncertain outcomes. An experimental non-surgical treatment protocol based on neuromuscular electrical stimulation (NMES) called the Shoulder Pacemaker concept showed very promising early results in the treatment of FPSI. However, as with most new inventions and techniques in orthopedics, the initial reports tend to be positive and subsequently over time increasing evidence challenges their benefit.
The goal of this study was to evaluate the effectiveness and general applicability of this promising but yet unproven treatment option for an unresolved clinical problem in a multi-centric, randomized controlled trial with independent data analysis and quality control by independent study supervision. The hypothesis of this study was that the Shoulder Pacemaker treatment leads to better outcome than the current gold standard of treatment in patients suffering from FPSI.

Methods

This multicentric randomized controlled trial involved 5 national shoulder centers as study sites, independent data storage and analysis, as well as an independent international study advisory board. Patients with functional posterior shoulder instability were randomly allocated in a 1:1 ratio either to a 6-weeks physiotherapy (PT) protocol including exercises determined in a prior Delphi survey or the same protocol supervised by the same physiotherapists with simultaneous Shoulder Pacemaker stimulation (SPM-PT). Baseline scores, as well as outcome scores at 6 weeks, 3 months, 6 months, and 12 months after the intervention were obtained. The 3-months WOSI was defined as primary outcome measurement with a minimally clinically important difference of 10.4%. Cross-over to the other treatment group was allowed after the 3 months follow-up. Prior to the beginning of the trial, the study design was registered online, a sample size estimation for 80% study power was performed, and ethical committee approval was obtained.

Results

49 patients were randomized and eligible for the trial. Both groups showed comparable baseline characteristics and adherence to treatment protocols. The SPM-PT group showed a significantly better outcome compared to the PT group in terms of the 3-month WOSI Score (64 ± 16% vs. 51 ± 24%; 13% difference in means with 95% CI 1% to 25%, p = 0.047). The relative improvement compared to baseline was 80 ± 102% in the SPM-PT group and 16 ± 59% in the PT group (difference in means of 64%, 95% CI 14% to 115%, p=0.017). Two thirds of the patients from the PT group crossed over to the SPM-PT group due to dissatisfaction after the 3-month follow-up and showed a significant increase in their WOSI Score from 49 ± 18% to 67 ± 24% (mean change of 17%, 95% CI 3% to 31%, p=0.023) at the 6-months follow-up and beyond. Patients in the SPM-PT group who showed clinically-relevant improvement above the MCID of 10.4% had significantly lower baseline WOSI scores (mean 37 ± 15% versus 51 ± 16%; difference in means of 14%, 95% CI 2% to 27%, p=0.043).
The frequency of instability episodes showed a significant improvement in the SPM-PT group at 3 months follow-up (p=0.001) and beyond (6 months: p=0.001, 12 months: 0.004), while in the PT group no statistically significant difference was observed (p=0.481). 95% of patients in the SPM-PT group reported a subjective improvement of their symptoms compared to 63% of patients in the PT group (RR 1.5, 95% CI 1.1 to 2.2, p=0.024). No serious adverse events were recorded in either treatment group.

Conclusion

The current study shows that SPM-PT leads to statistically significant and clinically relevant improvement of outcomes in the treatment of functional posterior shoulder instability compared to conventional physiotherapy alone. Even patients with prior unsatisfactory results after conventional physiotherapy showed a significant benefit after secondary SPM-PT.