Skin blood flow as an objective measure for lateral elbow tendinopathy

PURPOSE: To investigate the test-retest reliability, side-to-side difference, responsiveness, and concurrent validity of skin blood flow (SkBF) measured by laser Doppler flowmetry (LDF) in individuals with acute or subacute lateral elbow tendinopathy (LET). METHODS: Eighteen individuals with acute or subacute LET were recruited for this study. SkBF was measured over the lateral epicondyle and common extensor origin on both ipsilateral and contralateral sides. The intraclass correlation coefficient (ICC3,1) was used to evaluate test-retest reliability. A paired t-test was used for comparing the side-to-side difference. Responsiveness was reported with a change score, paired t-test, effect size (ES), and standardized response mean (SRM). The concurrent validity of SkBF was investigated by correlating with a visual analog scale (VAS) pain intensity during resisted wrist extension isometric contraction using the Spearman correlation coefficient. RESULTS: Test-retest reliability was good at lateral epicondyle (ICC3,1 = 0.899), and at common extensor origin (ICC3,1 = 0.803). A side-to-side difference was found between the two sides (p <  0.001). For responsiveness, the change score for SkBF at the lateral epicondyle was – 8.04, and the common extensor origin was – 3.54. The ES and SRM ranged from – 0.71 to – 0.78. Concurrent validity was reported with a strong correlation with pain intensity (r = – 0.637). DISCUSSION: SkBF is a reliable and responsive variable for investigating the elbows with acute or subacute LET providing clinical information according to its inflammatory responses. However, the concurrent validity can be found only for SkBF at common extensor origin, which correlates with pain during resisted wrist extension isometric contraction.