Effect of Articular Surface Compression on Cartilage Extracellular Matrix Deformation

Area of Science:

• Biomedical Engineering
• Orthopedics
• Biomechanics

Background:

• Early osteoarthritis involves superficial zone (SZ) disruption, collagen damage, and proteoglycan loss, leading to cartilage "mechanical softening".
• The SZ's role in fluid exudation and imbibition under loading/unloading is critical for cartilage function.

Purpose of the Study:

• To investigate the role of the superficial zone (SZ) in controlling fluid exudation and imbibition during cartilage loading and unloading.
• To assess the impact of SZ integrity on cartilage mechanical properties under static and cyclic loading.

Main Methods:

• Confined creep compression tests were performed on bovine osteochondral (OC) plugs.
• Tests involved static (88 kPa) or cyclic (0-125 kPa, 1 Hz) compressive stress, with measurements of cartilage deformation and recovery.
• The superficial zone (SZ) was removed in some tests, and comparisons were made between covered (porous platen) and uncovered unloading conditions.

Main Results:

• Static creep strain was generally greater than cyclic creep strain.
• Uncovered unloading led to faster cartilage thickness recovery than covered unloading.
• Superficial zone removal increased static and cyclic creep strains and the cyclic strain envelope.

Conclusions:

• An intact superficial zone (SZ) is essential for normal articular cartilage mechanical function.
• The SZ regulates fluid exudation and imbibition, thereby controlling extracellular matrix (ECM) deformation and recovery during joint loading and unloading.