Finite Element Analysis of an In Vitro Traumatic Joint Loading Model

Abstract

Osteoarthritis (OA) is characterized by the degeneration of articular cartilage resulting in eventual bone on bone contact causing pain and inflammation to musculoskeletal joints. An in vitro impact injury model that incorporated tangential loading was developed in our lab using intact porcine patellae to produce quantifiable degradation similar to that seen in early stage osteoarthritis. We carried out two separate sets of in vitro impact experiments: (1) axial impactions: an impact insult normal to the cartilage surface at a high load and relatively fast loading rate and (2) shear impactions: a compressive preload normal to the surface subsequently followed by a tangentially applied displacement generating a shear load. Cell death and matrix proteoglycan loss were quantified. After validation of the finite element model and collection of histological data, statistical analysis was used to correlate type, location and magnitude of stress and strain with cell death and proteoglycan loss. The overall hypothesis was that shear forces arising from traumatic impact injuries are more detrimental to cartilage matrix and chondrocytes than axial forces normally seen in most impact injury models.