Assessment of the Passive Tension of the First Dorsal Interosseous and First Lumbrical Muscles Using Shear Wave Elastography

Purpose Quantitative evaluation of passive tension of the intrinsic muscles of the hand is necessary to assess contracture of the intrinsic muscles accurately. The aim of this study was to evaluate the shear modulus, which is related to passive muscle tension, of the first dorsal interosseous (FDI) and first lumbrical (FL) muscles using shear wave elastography. Methods Subjects were 18 healthy males. The shear modulus of the FDI and FL muscles was assessed at several proximal interphalangeal (PIP), distal interphalangeal (DIP), metacarpophalangeal (MCP), and wrist joint positions. The position in which the MCP joint was flexed 60° past 0° with PIP-DIP joint extension and that in which the MCP joint was extended 30° past 0° with PIP-DIP joint flexion were respectively defined as the slack and stretched positions. We analyzed whether the shear modulus was affected by finger position (slack or stretched), wrist position (30° flexion past 0° and 30° extension past 0°), and muscle (FDI or FL). Results Shear modulus in the stretched position was significantly higher than that in the slack position. The shear modulus of the FL muscle at 30° wrist extension was significantly higher than that at 30° flexion. The shear modulus of the FL muscle was significantly higher than that of the FDI muscle in the stretched position with the wrist at 30° flexion and extension, and in the slack position with the wrist at 30° extension. Conclusions The shear modulus of the FDI and FL muscles increased with MCP joint extension and PIP-DIP joint flexion. The difference in the muscle characteristics between the FDI and FL muscles should be considered when evaluating or treating contractures of the intrinsic muscles. Clinical relevance Shear wave elastography can evaluate the condition of the intrinsic muscles of the hand quantitatively.