The osteoarthritis pain enigma and how biomechanics research can lead to new solutions

The primary function of our joints is to provide pain-free movement. However, with osteoarthritis (OA), the joint's structures are damaged, potentially leading to chronic joint pain. While it is logical to assume chronic OA pain relates to tissue destruction, a direct relationship between joint structure and pain is not the full story. For the last 25 years, epidemiologic data estimates that there are as many asymptomatic cases of OA as symptomatic cases in the United States. Thus, the relationship between OA pathology and painful symptoms is more complex than "more damage leads to more pain." This OA pain enigma is one of the outstanding challenges in the field. Since the ultimate function of the joint is to provide pain-free movement, this narrative review discusses our opinions on how biomechanics can continue to advance our understanding of joint function within the context of chronic OA pain. Using multiscale mechanics, we have learned critical lessons on how loads are transferred during movement. Tissue structure-function modeling has begun to reveal how articular cartilage produces its extraordinary mechanical functions. Moreover, biomechanics principles are being incorporated into rehabilitation and "prehabilitation" strategies in the clinic. Within these biomechanical lessons, a critical challenge remains for the OA joint-is our goal pain free movement or restoration of the joint? Within the OA pain enigma, the relationship between pain and function remains closely entwined, and our outlook sees a critical role for biomechanics research advancing our understanding of chronic OA pain.