Shoulder-Pacemaker Treatment Concept for Posterior Positional Functional Shoulder Instability: A Prospective Clinical Trial

Abstract

Background: Pathological muscle activation patterns of the external rotators and periscapular muscles can result in posterior positional functional shoulder instability (PP-FSI). In several patients, physical therapy and surgical treatment are not successful.

Purpose: The shoulder-pacemaker treatment concept was evaluated prospectively in patients with PP-FSI and previously failed conventional therapy attempt.

Study design: Case series; Level of evidence, 4.

Methods: A negative selection of 24 consecutive cases of noncontrollable PP-FSI in 16 patients with previously failed conventional therapy were included in this prospective study. The shoulder-pacemaker treatment consisted of an electrical muscle stimulation-based therapy protocol with 9 to 18 one-hour treatment sessions. Two patients were excluded because of nonadherence to the training schedule, leaving a final study cohort of 21 cases in 14 patients. Follow-up included assessment of clinical function, impairment during daily activities and sports, satisfaction, Western Ontario Shoulder Instability Index (WOSI), Rowe score, and Subjective Shoulder Value at 0 weeks, 2 weeks, 4 weeks, 3 months, 6 months, 12 months, and 24 months after intervention.

Results: WOSI, Subjective Shoulder Value, and Rowe score showed a highly significant improvement at all time points of follow-up (P < .001). Young age (P = .005), low weight (P = .019), shoulder activity level (P = .003), unilateral affliction (P = .046), and higher baseline WOSI score (P = .04) were associated with a better treatment effect. Cases with increased glenoid retroversion, posterior scapulohumeral decentering, and dysplastic bony glenoid shape showed a trend toward shorter treatment effect duration. No complications during the intervention or follow-up period were observed.

Conclusion: The shoulder-pacemaker therapy concept is an effective treatment with rapid improvement and sustained outcome over the course of 2 years in patients with noncontrollable PP-FSI with previously failed conventional treatment. Young and more athletic patients with lower weight and unilateral pathology respond best to the treatment.

Keywords: EMS treatment; functional shoulder instability; posterior positional functional shoulder instability; posterior shoulder instability; rehabilitation; shoulder-pacemaker; voluntary shoulder instability.

Figure 1.

Clinical and radiological presentation of PP-FSI in a young female patient (see Table 1). (A) The neutral position without signs of posterior instability. (B) The corresponding fluoroscopic image with centered humeral head. (C) Changes in the shoulder contour can be observed. (D) The posterior subluxation of the humeral head during motion is revealed.

Figure 2.

Example of transdermal electric muscle stimulation by means of a dedicated device (Shoulder Pacemaker, NCS Lab) to activate hypoactive muscle groups during (A) concentric, (B) eccentric, and (C) functional training (eg, throwing motion). Concentric exercises aim for activation and tonic contraction of hypoactive muscle groups through maximum tolerable intensity of the device. Eccentric exercises aim for strengthening of hypoactive muscle groups by eccentric exercises against the tonic contraction induced by the electrical stimulus. Functional exercises aim for electrically assisted activation of hypoactive muscles during movement exercises that are intended to restore an instability-free motion of the shoulder joint during complex movements (eg, patient-oriented sports training).

Figure 3.

Longitudinal assessment of the clinical outcome scores before the treatment intervention (PRE) and 0 weeks (POST), 2 weeks (2W), 4 weeks (4W), 3 months (3M), 6 months (6M), 12 months (12M), and 24 months (24M) after treatment. *P < .001, vs baseline. Values are presented as median (line), interquartile range (box), and maximum and minimum except outliers and extremes (bars). ROWE, Rowe score; SSV, Subjective Shoulder Value; WOSI, Western Ontario Shoulder Instability Index.

Figure 4.

Longitudinal assessment of the functional impairment during daily and sporting activities before the treatment intervention (PRE) and 0 weeks (POST), 2 weeks (2W), 4 weeks (4W), 3 months (3M), 6 months (6M), 12 months (12M), and 24 months (24M) after treatment. *P < .01, vs baseline. Values are presented as mean ± SD.