Range-of-motion affects cartilage fluid load support: functional implications for prolonged inactivity.

Area of Science:

• Biomechanics
• Biomaterials Science
• Orthopedics

Background:

• Joint movements are crucial for maintaining cartilage fluid load support (FLS) via contact migration and bath exposure.
• Previous theories suggested prolonged inactivity might disrupt load-induced exudation, but this study experimentally investigates the required range of motion.

Purpose of the Study:

• To experimentally test the hypothesis that joint range-of-motion must exceed contact length to sustain non-zero FLS.
• To quantify the relationship between migration length, contact stress, and FLS in osteochondral explants.

Main Methods:

• Bovine osteochondral explants were subjected to controlled sliding movements against glass spheres.
• In situ deformation measurements quantified FLS under varying normal loads and migration lengths (0.05-7 mm).
• Péclet numbers >100 confirmed fluid exudation conditions.

Main Results:

• Non-zero FLS was sustained even at migration lengths below 10% of the contact diameter.
• FLS peaked when migration track lengths were over 10 times the contact diameter.
• Below this threshold, FLS decreased with increasing contact stress.

Conclusions:

• Small movements like fidgeting and drifting can mitigate FLS loss during prolonged inactivity.
• Quantitative limits for the biomechanical benefits of small movements were identified.
• Movement patterns, load, and mobility significantly impact long-term FLS.