| Summary: | Category: Hindfoot Introduction/Purpose: Stage 1 posterior tibial tendon dysfunction (PTTD) may be present without intra-substance tendon pathology. We hypothesize that in individuals with the clinical diagnosis of Stage 1 PTTD, with no MRI-detectable intra-substance tendon pathology, that sheath fluid amount is a confirmatory finding of PTTD. This purpose of this study was to quantify the amount of PTT sheath fluid in 1) individuals with the clinical diagnosis of Stage 1 PTTD and no MRI-detectable intra-substance tendon pathology and compare to controls with medial ankle pain (causes other) also without MRI-detectable intra-substance PTT pathology, and 2) test if there was a sheath fluid measurement predictive of the clinical diagnosis of PTTD. Methods: 326 individuals with medial ankle pain, no intra-substance PTT pathology, were studied, 48 with the clinical diagnosis of Stage 1 PTT dysfunction and 278 with medial ankle pain, causes other. Geometric methods defined MRI-based sheath fluid volume, maximum cross-sectional fluid area, and maximum fluid width. Fluid measurements were compared between groups and a predictive measurement calculated to identify individuals with PTTD. Measurement reliability was tested. Results: Individuals with PTT dysfunction had larger PTT sheath fluid volume, area, and width than controls (p’s < 0.001). An 9 mm threshold maximum fluid width was associated with PTTD (sensitivity 84%, specificity 85%). Measurements were reliable (p’s <0.03). Conclusion: The amount of PTT sheath fluid, in individuals with medial ankle pain and no intra-substance PTT pathology, was associated with Stage 1 PTTD and a maximum PTT sheath fluid width of > 9 mm predicted PTTD. This is clinically significance as MRI-detected sheath fluid can now be used as a confirmatory finding in individuals with the clinical diagnosis of Stage 1 PTTD who do not have MRI-detectable intra-substance pathology
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