Understanding stresses within the joint is central to understanding the etiology and progression of osteoarthritis (OA), as well as the effects of clinical interventions meant to slow or halt OA progression. It’s been hypothesized that a change in stress is a significant factor in the initiation and progression of post-traumatic osteoarthritis. Without a reliable method for measuring stress this hypothesis has largely gone untested. This study was aimed at testing this hypothesis by developing and implementing an alternative stress sensing technology.

Currently the most widely used method for measuring contact stresses is stress sensitive films. Their use requires a significant amount of dissection and removal of biomechanically relevant structures. Their presence in the joint alters the natural mechanics and the lubrication properties of the joint. There are also significant errors associated with the thickness and curvature, and modulus dependency resulting in large errors and unreliable data.

To address the existing knowledge gap small fibre optic sensors capable of measuring normal stress between contact surfaces in diarthrodial joints were developed. The small size of these sensors (diameter of 125-300 μm and sensing length of 1 mm) allows these sensors to be inserted into the joint space without the removal of biomechanically relevant structures.

Fibre optic sensors specifically designed to be inserted into ovine knee joints were used to measure in-vivo stresses on the surface of the cartilage for both healthy and surgically damaged joints. Undeniably the most important finding of this study was the correlation iii between changes in average and peak stress values following trauma and the likelihood of the development of focal damage at each position signaling the onset of post-traumatic osteoarthritis. Another important result in the non-uniformity of stress under the meniscus.

This study successfully addressed many of the challenges associated with the use of fibre optic sensors to obtain repeatable in vivo stress measurements, validating an innovative technique for measuring stresses in the knee joint. Along with our capability to reproduce invivo motions accurately and the improvements of fibre optic technology, this study is the first accurate, direct measurement of stress in a joint during in-vivo gait replication.