Use of shoulder pacemaker for treatment of functional shoulder instability

BACKGROUND Functional shoulder instability (polar type III) is caused by underactivity of rotator cuff and periscapular muscles, which leads to subluxation or dislocation during shoulder movement. While surgical treatment has shown no benefits, aggravates pain, and frequently diminishes function even further, conservative treatment is often ineffective as well. OBJECTIVES The aim was to investigate the effectiveness of a "shoulder pacemaker" device that stimulates underactive muscles in patients with functional instability during shoulder movement in order to re-establish glenohumeral stability. PATIENTS AND METHODS Three patients with unsuccessfully treated functional shoulder instability causing pain, emotional stress, as well as limitations during daily activities and sports participation were enrolled in this pilot project. The device was used to stimulate the external rotators of the shoulder and retractors of the scapula. Pain level, subjective shoulder instability, range of motion, visible aberrant muscle activation, and signs of dislocation were compared when the device was switched on and off. RESULTS No changes were observed when the device was attached but switched off. When the device was switched on, all patients were able to move their arms freely without pain, discomfort, or subjective or objective signs of instability. All patients rated this as an excellent experience and volunteered to train further with the device. No complications were observed. CONCLUSION The electric stimulation of hypoactive rotator cuff and periscapular muscles by means of the shoulder pacemaker successfully re-establishes stability in patients with functional shoulder instability during the time of application.  VIDEO ONLINE The online version of this article (doi: 10.1007/s11678-017-0399-z) contains the video: "The Shoulder-Pacemaker: treatment of functional shoulder instability with pathological muscle activation pattern". Video by courtesy of P. Moroder, M. Minkus, E. Böhm, V. Danzinger, C. Gerhardt and M. Scheibel, Charité Universitätsmedizin Berlin 2017, all rights reserved.