Impact of Neuromuscular Control With and Without Electrical Stimulation and Long-term Effect of Kinetic Chain Exercises in Multidirectional Shoulder Instability Patients

Background: Shoulder instability is commonly observed in adolescents and young females, ranging from asymptomatic multidirectional instability (MDI) to symptomatic conditions. Patients with MDI often experience shoulder pain, muscle tension, and episodes of subluxation. This condition is associated with hypermobility spectrum disorder (HSD) and hypermobile Ehlers-Danlos syndrome (hEDS), both characterized by generalized joint laxity and recurrent joint dislocations, significantly affecting daily activities and athletic performance. Current literature lacks clarity on the actual humeral head displacement, shoulder joint kinetics, and muscle activity characteristics during movement in patients with MDI accompanied by HSD or hEDS. Additionally, the effects of electrical stimulation on different shoulder muscles and its impact on humeral head displacement in MDI patients remain to be validated.

Objective: The purposes of this study are to (1) examine whether patients with hEDS/HSD and MDI have increased humeral head translation compared to healthy controls during three isometric contraction ; (2) investigate the relationship between humeral head translation and associated muscle activity during three isometric exercises ; (3) examine the effect of NMES and NMCT to humerus/scapula muscles on humeral head translations in MDI patients with hEDS/HSD Outcome measurements: The primary outcomes include changes in acromiohumeral distance (AHD) or humeroglenoid distance (HGD) under four conditions (no stimulation, NMCT, BLH/Infraspinatus/MD stimulation, and SA stimulation) during three isometric contractions (shoulder flexion, horizontal adduction, and fully extended elbow holding weight).

The secondary outcomes assess muscle activation differences in BLH, infraspinatus, MD, UT, LT, and SA before and after NMCT.