Equine subchondral bone failure threshold under impact compression applied through articular cartilage

Area of Science:

• Biomechanics
• Biomaterials Science
• Orthopedics

Background:

• Subchondral bone microdamage from high-impact loading is a primary cause of post-traumatic knee osteoarthritis.
• Understanding the tissue-level mechanical characteristics of subchondral bone is vital for elucidating the mechanisms of impact-induced microdamage.

Purpose of the Study:

• To quantify the elastic tissue modulus and local stresses/strains in equine subchondral bone (including calcified cartilage: CCSB) associated with micro-fractures.
• To establish failure thresholds for CCSB tissue under impact loading.

Main Methods:

• Combined mechanical impact testing of equine cartilage-bone specimens with micro-computed tomography (µCT) image-based finite element models (μFEM).
• Iteratively adjusted μFEM material properties to match experimental stress-strain curves.
• Assumed isotropic homogeneous material properties for uncalcified cartilage (UC) and CCSB, simulating UC large-deformation with hyperelastic properties.

Main Results:

• Achieved final material properties: UC shear modulus (G) of 38±20MPa and CCSB tissue elastic modulus (E(t)) of 3.3±0.7GPa.
• Identified initial failure in CCSB at local stresses of 29.47±5.34 MPa (tensile) and 64.3±21.3MPa (compressive).
• Determined initial failure strains in CCSB at 1.12±0.06% (tensile) and 1.99±0.41% (compressive).

Conclusions:

• Tissue-level material properties derived are applicable for finite element modeling of diarthrodial joints under impact loading.
• These findings can inform the design of artificial cartilage-bone prosthetics for damaged joint tissues.
• Provides an estimate for the threshold of initial failure in subchondral bone tissue subjected to impact compression.