Condition category
Musculoskeletal Diseases
Date applied
Date assigned
Last edited
Prospectively registered
Overall trial status
Recruitment status

Plain English Summary

Background and study aims
Functional posterior shoulder instability (FPSI) is a force imbalance of stabilizing shoulder muscles which mainly affects teenagers and young adults with severe effects on shoulder function. Patients with FPSI suffer from repetitive posterior displacements every time the shoulder passes a particular phase of movement in the mid-range of motion. Severely restricted shoulder function and symptoms such as pain, loss of range of motion due to weakness or blockage that inhibits any further movement, as well as a strong feeling of instability, are reported by the affected patients. Current therapy includes conservative as well as surgical stabilization attempts. In daily clinical practice, however, standard physiotherapy is often ineffective and after years of unsuccessful conservative treatment, patients affected with FPSI finally undergo a surgical stabilization attempt with results that are often worse than before. In a study with 5 participating centres, a promising therapy concept based on electric muscle stimulation shall be compared to the current standard care physiotherapy. If the results of the new treatment approach show better results than the existing standard physiotherapy, a much-needed step forward in the treatment of patients with FPSI will be achieved and likely lead to a complete change in the existing therapy for this challenging pathology. For the patients themselves, this new treatment concept possibly could represent a true „game-changer“ that might free them of the burden of FPSI.

Who can participate?
Participants over the age of 14 with FPSI will be included in this study irrespective of gender or duration of symptoms. Exclusion criteria focus on structural pathologies (static posterior migration, connective tissue diseases, degenerative joint diseases, structural defects) and other pathologies (multidirectional instability, neurological disorder or nerve injuries, existing pain syndrome, medical contraindication to EMS treatment) hindering, impeding, or prohibiting to complete the control or experimental treatment. Additionally, participants with previous participation in a pathology-targeted standardized EMS or physiotherapy protocol are excluded in order to avoid potential unwillingness to participate in or preformed mindset towards an intervention that they previously tried already without success.

What does the study involve?
The study will compare two treatment groups. The experimental intervention consists of an EMS-based training protocol to stimulate specific muscle groups of the shoulder. The training involves a combination of certain exercises with increasing difficulty and intensity. The control intervention includes a pathology-targeted standardized physiotherapy protocol which has been developed and agreed on by international renowned shoulder experts. Both experimental and control treatment will include 18 one-hour trainings evenly distributed over a time period of 6 weeks and will be performed by the same physiotherapist at each participating centre based on standardized protocols. In the case of subjectively unsatisfying results, an optional switch (cross-over) into the other treatment group is allowed to make both potentially superior therapies available to all participants within a reasonable time (3 months after the beginning/6 weeks after the end of the intervention).

What are the possible benefits and risks of participating?
Each participant benefits by receiving an intensive, targeted and potentially equal physiotherapeutic treatment concept. The training concepts aim to increase endurance and coordination including functional training as well as strengthen specific stabilizing shoulder muscles. In addition, as part of clinical routine, each participant will receive a clinical evaluation and individualized consultation on the likelihood of reoccurring shoulder displacements. No adverse events or complications of the experimental EMS-based therapy have been observed in a pilot study.

Where is the study run from?
This study will be available in centres across Germany and Switzerland and supervised by the Charité- Universitaetsmedizin Berlin as lead centre. Further centres include the ATOS Clinic, Munich, Germany; the Annastift Hospital, Hannover, Germany; the St. Vincentius Kliniken, Karlsruhe, Germany; Schoen Clinic Düsseldorf and University Clinic Düsseldorf, Germany; and the Schulthess Clinic, Zurich, Switzerland.

When is the study starting and how long is it expected to run for?
June 2019 to June 2022

Who is funding the study?
This project is currently initiated and funded by the investigators

Who is the main contact?
1. PD Dr. med. univ. Philipp Moroder
2. Victor Danzinger

Trial website

Contact information



Primary contact

Mr Victor Danzinger


Contact details

Department of Shoulder and Elbow Surgery
Center for Musculoskeletal Surgery- Campus Virchow
Charitè Universitaetsmedizin
Augustenburgerplatz 1



Additional contact

Dr Philipp Moroder


Contact details

Department of Shoulder and Elbow Surgery
Center for Musculoskeletal Surgery- Campus Virchow
Charitè Universitaetsmedizin
Augustenburgerplatz 1

Additional identifiers

EudraCT number

Nil known number

Nil known

Protocol/serial number


Study information

Scientific title

Electric muscle stimulation for treatment of non-controllable positional functional posterior shoulder instability



Study hypothesis

Electrical muscle stimulation (EMS) based therapy has the same clinical effect as conventional state-of-the art physiotherapy treatment for FPSI.

Ethics approval

Approved 30/08/2018, Ethics Committee of Charité – Universitaetsmedizin Berlin (Charitéplatz 1, Virchowweg 10, 10117 Berlin; +49 30 450 517 222;, ref: EA2/077/18

Study design

Multi-centric randomized controlled therapeutic trial active control no masking optional cross-over design

Primary study design


Secondary study design

Randomised cross over trial

Trial setting


Trial type


Patient information sheet

Not available in web format, please use contact details to request a participant information sheet


Non-controllable positional functional posterior shoulder instability (FPSI).


In a multicentric prospective randomized controlled trial, we would like to objectively assess a promising new EMS-based treatment concept which was evaluated at our institution in a prospective pilot trial involving 24 cases with previously unsuccessful conventional physiotherapy treatment of FPSI. Pathology-targeted physiotherapy is the current standard treatment of FPSI and will serve as the control intervention in the proposed trial. All involved centers as well as independent experts have specified and agreed on a standardized exercise protocol for the control intervention during a Delphi survey. The control intervention will have the same duration, intervals, and instructing physiotherapist (at each center) as the experimental intervention. An optional bi-directional cross-over into the other intervention group (experimental or control) is possible after follow-up examination at the time-point T2 (3 months after the beginning/6 weeks after the end of the intervention) in the case of subjectively unsatisfying results despite completion of the originally assigned intervention to offer both possibly superior interventions to all participants.

Experimental intervention: electrical muscle stimulation based therapy protocol
Control intervention: conventional state-of-the art physiotherapy protocol
Follow-up per patient: 0 weeks (T0), 6 weeks (T1), 3 months (T2), 6 months (T3), 12 months (T4)
Duration of intervention per patient: 6 weeks

The strict inclusion and exclusion criteria create a homogeneous group of study participants. After a patient has decided to enter the study and provided written informed consent, he/she will be randomized in one of the two treatment groups (allocation ratio 1:1). A randomization sequence will be generated electronically using Stata (StataCorp LP, Texas USA) separately for each participating center and loaded within an online study database in REDCap17 (Research Electronic Data Capture) for automatic concealed allocation. Block-randomization with blocks of 2 and 4 will be used to minimize the risk of unequal group sizes. The randomization process allows to divide the study participants into two cohorts of comparable characteristics. We will compare these cohorts with regards to potential confounding factors before the outcome analyses and adjust statistically for any observed imbalance as appropriate.

Since the main outcome measurement is a subjective score, blinding of the examiner is not necessary. Blinding of the patients themselves is not possible due to the nature of experimental and control intervention. This circumstance can potentially introduce a confirmation bias from the patients’ side. However, according to the trial design, all patients with previous participation in a pathology-targeted standardized EMS or physiotherapy protocol are excluded which reduces the risk for a pre-conditioned mindset in patients.

Intervention type



Drug names

Primary outcome measure

Western Ontario Shoulder Instability Index (WOSI) at T2

Secondary outcome measures

1. WOSI at T1, T3, and T4.
At 0 weeks (T0), 6 weeks (T1), 3 months (T2), 6 months (T3), 12 months (T4):
2. Subjective shoulder value
3. Impairment of daily activities
4. Sports impairment
5. Pain level
6. Range of motion
7. Strength
8. Satisfaction with treatment

Assessment of safety: Based on the complication-free pilot trial, no adverse events are pre-specified but continuous recording of unexpected adverse events will be executed in both treatment arms.

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Non-controllable positional functional posterior shoulder instability (FPSI)
2. Aged 13 or over

Participant type


Age group




Target number of participants

To be assessed for eligibility: n = approximately 87 (expected exclusion rate of approximately 25%); To be assigned to the trial: n = 65 (accounting for an expected drop-out rate of approximately 20%); To be analysed: n = 52 (calculated sample size for a power of 80%, alpha error probability of 5%, and an estimated effect size of 0.8 at 12 months)

Participant exclusion criteria

1. Multidirectional instability
2. Static posterior instability/migration
3. Connective tissue disease
4. Degenerative joint disease
5. Structural defects visible on pre-treatment MRI
6. Neurological disorder or nerve injury
7. Existing pain syndrome (defined by pain at rest or during motion, which is not caused by dislocation but impedes physiotherapeutic training and/or EMS)
8. Non-tolerance of EMS treatment (e.g. cardiac pacemaker)
9. Previous participation in a pathology-specific standardized EMS or physiotherapy protocol

Added 21/02/2020:
5. Structural defects visible on pre-treatment MRI:
5.1. Any acquired glenoid bone defect
5.2. Glenoid dysplasia with more than 10° of retroversion (of cartilagineous surface) according to Imhoff et al.
5.3. Convex cartilagineous glenoid articular surface
5.4. Static posterior glenohumeral decentering >55% according to Walch et al.
5.5. Degenerative changes (any visible cartilage damage or OA)

Recruitment start date


Recruitment end date



Countries of recruitment

Germany, Switzerland

Trial participating centre

Charité University Hospital
Centrum für Muskuloskeletale Chirurgie Augustenburger Platz 1

Trial participating centre

Annastift Hospital
Anna-von-Borries-Straße 1-7

Trial participating centre

ATOS Clinic
Effnerstraße 38

Trial participating centre

St. Vincentius Clinic
Südendstr. 32

Trial participating centre

Schulthess Clinic
Lengghalde 2

Trial participating centre

Schoen Clinic Düsseldorf
Am Heerdter Krankenhaus 2

Trial participating centre

University Clinic Düsseldorf
Moorenstraße 5

Sponsor information


Charité - Universitaetsmedizin Berlin

Sponsor details

Department of Shoulder and Elbow Surgery
Center for Musculoskeletal Surgery
Campus Virchow Klinikum
Augustenburger Platz 1
+49 30 450 - 50

Sponsor type




Funder type

Research organisation

Funder name

Deutsche Forschungsgemeinschaft

Alternative name(s)


Funding Body Type


Funding Body Subtype


Results and Publications

Publication and dissemination plan

The results of the study are presented in a manuscript in accordance with the CONSORT guidelines and published in a scientific journal. To ensure general availability, the publication is made freely accessible. Moreover, the results will be presented at national and international conferences.

IPD sharing statement:
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request

Intention to publish date


Participant level data

Available on request

Basic results (scientific)

Publication list

Publication citations

Editorial Notes

11/01/2021: The following changes were made to the trial record: 1. The recruitment end date was changed from 01/01/2021 to 01/01/2022. 2. The overall trial end date was changed from 01/06/2021 to 01/06/2022. 3. The intention to publish date was changed from 01/10/2021 to 01/10/2022. 08/07/2020: The recruitment end date was changed from 01/06/2020 to 01/01/2021. 04/06/2020: The following changes were made to the trial record: 1. Recruitment resumed on 03/06/2020. 2. Uploaded protocol version 4.0, 08 April 2020, (not peer reviewed) as an additional file. 16/04/2020: Due to current public health guidance, recruitment for this study has been paused. 25/03/2020: Uploaded protocol version 3.0, 25 March 2020 (not peer reviewed). 21/02/2020: The exclusion criteria were updated and the trial participating centres were updated to add Schoen Clinic Düsseldorf and University Clinic Düsseldorf. 18/02/2020: Uploaded protocol version 2.0, 18 February 2020 (not peer reviewed). 02/12/2019: Uploaded protocol version 1.0, 30 November 2019 (not peer reviewed). 03/04/2019: Trial’s existence confirmed by IRB