Amputee socks: how does sock ply relate to sock thickness?

Area of Science:

• Prosthetics and Orthotics
• Biomechanical Engineering
• Materials Science

Background:

• The term 'sock ply' in prosthetics can be misleading due to inconsistent relationships with actual sock thickness.
• This ambiguity can impact prosthetic fitting and patient comfort.

Purpose of the Study:

• To investigate the relationship between sock ply and sock thickness across various prosthetic sock materials.
• To assess how mechanical loading conditions affect prosthetic sock thickness.

Main Methods:

• Mechanical assessment of seven different prosthetic sock materials with varying ply and sheath constructions.
• Measurement of sock thickness under eight compressive stress and two biaxial tensile strain conditions.

Main Results:

• For single-material socks, 1, 3, and 5-ply thicknesses averaged 0.7, 1.2, and 1.5 mm, respectively.
• For multi-material socks, 1, 3, and 5-ply thicknesses averaged 0.4, 0.7, and 0.8 mm, respectively.
• Sock ply did not correlate linearly with thickness; a 3-ply sock was not thrice the thickness of a 1-ply sock.

Conclusions:

• Prosthetic sock thickness and compressive stiffness are significantly influenced by material composition.
• Interface pressure and in-plane biaxial strain are critical factors affecting sock thickness under load.