Lower-Limb Muscle Architecture and Strength in Men with Radiographic Axial Spondyloarthritis: A Cross-Sectional Ultrasound Study

Background/Objectives: To compare lower-limb muscle architecture and strength between men with radiographic axial spondyloarthritis (r-axSpA) and controls. Methods: In this controlled cross-sectional study, 30 men with r-axSpA and 30 age-matched healthy men underwent bilateral ultrasound assessment of the vastus lateralis (VL), gastrocnemius medialis (GM), gastrocnemius lateralis (GL), and tibialis anterior (TA). Fascicle length was derived trigonometrically. Strength was assessed using hand-held dynamometry. Results: Differences represent r-axSpA minus controls, with 95% confidence intervals. VL, GM, and GL thickness differences were −0.32 (−0.50 to −0.13), −0.18 (−0.34 to −0.02), and −0.21 (−0.36 to −0.05) cm, respectively. Pennation-angle differences were −2.38 (−3.48 to −1.28), −1.99 (−3.35 to −0.63), −2.46 (−3.69 to −1.23), and 0.26 (−0.68 to 1.22) degrees for VL, GM, GL, and the TA superficial region, respectively. TA superficial-region thickness and derived fascicle length were greater: +0.53 (0.29 to 0.78) and +2.40 (1.36 to 3.45) cm, respectively. Knee extensor, ankle dorsiflexor, and ankle plantar flexor strength differences were −86.3 (−123.6 to −48.8), −52.0 (−78.2 to −26.6), and −57.9 (−92.3 to −24.1) N, respectively. Conclusions: Men with r-axSpA showed greater TA superficial-region thickness and derived fascicle length alongside lower dorsiflexion strength. These preliminary findings require confirmation in independent studies using validated measurement methods.