Objective: In asymptomatic, normal tendons, the difference in tendon thickness between sides is less than 15%. In this study, three tests were used to examine differences between symptomatic and asymptomatic shoulders.
Design: Cross-sectional study. The three tests were performed in sequence. The observer was blinded in the maximal pain-free isometric force test.
Setting: Outpatient physiotherapy clinic at Bergen University College, Norway.
Participants: Sixty-four patients with an exclusive, tentative diagnosis of unilateral shoulder tendinopathy.
Main outcome measures: Differences in maximal pain-free isometric force, tendon pain pressure and tendon thickness measured by ultrasonography.
Results: This paper follows the STARD recommendations for papers on diagnostic accuracy. When cut-off values for within-subject side differences were selected at >or=0.8mm for tendon thickness (TT(diff)), >or=10N for maximal pain-free isometric force (PFF(diff)) and >or=0.6 kg for tendon pain pressure (PPT(diff)), positive tests were found in 92% of patients. All three tests were sensitive for the detection of within-subject side differences with the selected cut-off values (TT(diff), n=60/64; PPT(diff), n=59/64; PFF(diff), n=57/64; P>0.35). There were strong agreements between the three tests: TT(diff) and PFF(diff), 0.89; TT(diff) and PPT(diff), 0.83; and PFF(diff) and PPT(diff), 0.84. When both clinical tests were positive (PFF(diff) and PPT(diff)), the positive predictive value was excellent (94%) for finding increased tendon thickness in the symptomatic side on ultrasonography.
Conclusions: Within the limitations of this partially blinded study, patients with unilateral shoulder tendinopathy exhibited significant differences between sides in all three tests. The combination of the two clinical tests seems to be valid for the detection of unilateral shoulder tendinopathy if other diagnoses have been excluded.