Bilateral Myofascial Trigger Points and Pressure Pain Thresholds in the Shoulder Muscles in Patients With Unilateral Shoulder Impingement Syndrome

Objectives: To identify the presence of myofascial trigger points (TrPs) and pressure pain threshold (PPT) levels in the shoulder muscles of both involved and uninvolved sides in patients with unilateral shoulder impingement syndrome (SIS). Methods: Twenty-seven patients with SIS and 20 matched control patients participated in this study. TrPs of 10 shoulder muscles and 8 PPTs, including tibialis anterior PPT, were assessed. Results: SIS group showed a greater number of TrPs (t=−2.697; P=0.010) than the control group. The muscles of the uninvolved side of the SIS group also presented some active TrPs. PPTs showed small differences between involved and uninvolved sides of patients with SIS and higher differences between both sides of the SIS group and dominant side of controls although with significant difference only in the supraspinatus PPT (F=3.239; P=0.045). The muscle PPTs of the patients presenting TrPs in each muscle of the involved side were lower than the PPTs of the patients without TrPs in the same muscle for both involved and uninvolved sides with few significant differences. Discussion: The high number of TrPs in the involved side of patients with SIS suggests the presence of peripheral sensitization. The results reject the presence of central alterations. Finally, the patients with unilateral SIS may present bilateral deficits related to myofascial pain.