Effects of in vivo fatigue-induced subchondral bone microdamage on the mechanical response of cartilage-bone under a single impact compression.

The research investigates how fatigue-induced microdamage in subchondral bone – a common issue in competitive horses and athletes – can affect the mechanical response of the joint surfaces under a single point of impact compression. The main outcome demonstrates that higher levels of microdamage result in increased rigidity and decreased shock absorption in the tested equine third metacarpal bone.

Research Design and Methodology

• The researchers’ primary aim was to quantify the mechanical properties of cartilage-bone from equine third metacarpal (MC3) condyles, since this is an area often subject to accumulated microdamage due to repetitive impact loading.
• The researchers chose a non-destructive technique, high-resolution microcomputed tomography (µCT) imaging, to identify varying degrees of in vivo microdamage prior to conducting mechanical testing.
• The study sought to identify potential variables in the horse’s racing and training history that could offer additional insight into the prior loading history of the samples.
• The team then performed unconfined high-rate compression to simulate a cycle of galloping, alongside real-time strain measurements using digital image correlation (DIC) techniques to find the stiffness and shock-absorbing abilities of the cartilage-bone unit and associated cartilage and SCB.

Main Research Findings

• The results revealed that stiffness in the cartilage-bone and the SCB decreased with an increasing degree of microdamage.
• Whole specimen stiffness increased, and relative energy loss decreased with higher bone mineral density (BMD), while the bone volume fraction of the SCB had a negative association with the stiffness of bone.
• The primary predictor of stiffness and relative energy loss of the third metacarpal bone’s articular surface was the degree of subchondral bone damage, as observed with µCT imaging.

Relevance of the Research

• This investigation offers valuable insight into the effect of focal fatigue-induced microdamage on the mechanical response of tissue in horses, which can contribute to the improved understanding of joint surface injuries and osteoarthritis development.
• Such understandings can be potentially instrumental in the development of more effective therapeutic and preventive strategies against osteoarthritis and joint damage specifically in athletic horses, and potentially in high-impact sports athletes.