How long does the prevention effect last? A comparison of two case studies of different FES stimulation frequencies in stroke shoulder subluxation follow up period

There is strong evidence on the positive effect of functional electrical stimulation (FES) in preventing shoulder subluxation (SS) following stroke. However, the extent of such intervention has not been weekly documented with regards to different stimulation frequencies. It is unknown whether high or low frequency (35 Hz or 20 Hz) has better potential in maintaining the FES effect in preventing SS during the follow-up period. Two participants underwent standard prescribed physiotherapy sessions in a rehabilitation centre during their hospitalisation period. Electrical stimulation was administered to their supraspinatus and posterior deltoid muscles for up to 2 hours a day for 4 weeks. All stimulation parameters were set constant except the stimulation current, which depended on the subject tolerance, and stimulation frequency, which was set to high (35Hz: Subject A) and low (20 Hz: Subject B). No SS among the intervened subjects during the 4 weeks FES therapy period. The high (35 Hz) stimulation frequency prevented subluxation until the end of 4 weeks follow up period in Subject A while low stimulation (20 Hz) frequency stimulation maintained the effect for up to 2 weeks in Subject B. The effect of FES on SS could be maintained up to 4 weeks upon withdrawal without undergoing subsequent FES therapy. Given all parameters fixed and the stimulation current dependent on the subject´s tolerance, high frequency stimulation (35Hz) may be recommended in a subluxation prevention programs to further maintain the stability of the shoulder joint.