Cartilage collagen matrix reorientation and displacement in response to surface loading

Area of Science:

• Biomechanics
• Materials Science
• Orthopedics

Background:

• Articular cartilage is crucial for joint function.
• Understanding its response to mechanical load is vital for treating joint diseases.
• Collagen fibers provide structural integrity to cartilage.

Purpose of the Study:

• To investigate collagen fiber reorientation in equine articular cartilage and subchondral bone under compressive loads.
• To analyze fluid and matrix movement within the cartilage.
• To compare the mechanical response of healthy and diseased cartilage.

Main Methods:

• Small angle X-ray scattering (SAXS) measurements.
• Optical microscopy and polarized light for fiber orientation analysis.
• Tracer-based displacement measurements for matrix and fluid movement.

Main Results:

• Reversible compression of superficial fibers up to 1.5 MPa.
• Reorientation propagated to deeper zones with increased load.
• Fiber "crimping" observed at higher loads (4.8-6.0 MPa).
• Radial splitting in deep cartilage at failure, with intact surface zone.
• Disrupted fiber organization and initial fiber rupture in diseased cartilage.
• Anisotropic solid and fluid displacement dependent on tissue depth.

Conclusions:

• Cartilage exhibits complex, depth-dependent responses to mechanical loading.
• Collagen fiber architecture significantly influences cartilage mechanics.
• Diseased cartilage shows altered mechanical behavior and potential for early fiber failure.
• Findings provide insights into cartilage degeneration and injury mechanisms.