How a radial focal incision influences the internal shear distribution in articular cartilage with respect to its zonally differentiated microanatomy

Abstract

Articular surface fibrillation and the loss of both transverse interconnectivity and zonal differentiation are indicators of articular cartilage (AC) degeneration. However, exactly how these structural features affect the load-redistributing properties of cartilage is still poorly understood. This study investigated how a single radial incision made to varying depths with respect to the primary zones of AC influenced its deformation response to compression. Three depths of incision were applied to cartilage-on-bone tissue blocks: one not exceeding the transition zone; one into the mid-radial zone; and one down to the calcified cartilage. Also included were non-incised controls. All samples were compressed to a near-equilibrium strain using a flat-faced indenter that incorporated a central relief channel within which the incision could be positioned lengthwise along the channel axis. Employing fixation under load followed by decalcification, the structural responses of the cartilage-on-bone samples were investigated. The study provides an analysis of the micro-morphological response that is characteristic of a completely normal cartilage-on-bone system but which contains a defined degree of disruption induced by the focal radial incision. The resulting loss of transverse continuity of the cartilage with respect to its zonally differentiated structure is shown to lead to an altered pattern of internal matrix shear whose intensity varies with incision depth.

Comparison between in vitro and in vivo cartilage overloading studies based on a systematic literature review

“…In contrast, cartilage is less prone to fracture when the most superficial layer is removed, or when a pre‐strain of 10% or higher is applied prior to overloading . The amount and depth of surface fissures in cartilage decreases its surface strain‐limiting abilities, induces tissue swelling, and alters the compressive load distribution, which may lead to further mechano‐biological damage …”