Aims

Staphylococcus aureus is a major cause of septic arthritis, and in vitro studies suggest α haemolysin (Hla) is responsible for chondrocyte death. We used an in vivo murine joint model to compare inoculation with wild type S. aureus 8325-4 with a Hla-deficient strain DU1090 on chondrocyte viability, tissue histology, and joint biomechanics. The aim was to compare the actions of S. aureus Hla alone with those of the animal’s immune response to infection.

Objectives

Staphylococcus aureus (S. aureus) is the most commonly implicated organism in septic arthritis, a condition that may be highly destructive to articular cartilage. Previous studies investigating laboratory and clinical strains of S. aureus have demonstrated that potent toxins induced significant chondrocyte death, although the precise toxin or toxins that were involved was unknown. In this study, we used isogenic S. aureus mutants to assess the influence of alpha (Hla)-, beta (Hlb)-, and gamma (Hlg)-haemolysins, toxins considered important for the destruction of host tissue, on in situ bovine chondrocyte viability.

Objectives

The purpose of this study was to create a novel ex vivo organ culture model for evaluating the effects of static and dynamic load on cartilage.

Objectives

During open orthopaedic surgery, joints may be exposed to air, potentially leading to cartilage drying and chondrocyte death, however, the long-term effects of joint drying in vivo are poorly understood. We used an animal model to investigate the subsequent effects of joint drying on cartilage and chondrocytes.

Articular cartilage is attached to subchondral bone but it is not clear whether the tissues interact and influence in situ (within the matrix) chondrocyte survival. The aim of this study was to determine whether subchondral bone influences in situ chondrocyte survival.

Articular cartilage explants harvested from the meta-carpophalangeal joints (N=6) of three-year old cows were placed into three groups:

subchondral bone excised from articular cartilage (Group A)

Explants were cultured in serum-free media over 7 days. Using confocal laser scanning microscopy, fluorescent probes and biochemical assays, in situ chondrocyte viability and biophysical parameters (cartilage thickness, cell density, culture medium composition) were quantified over time (2.5 hours vs. 7 days) for Groups A, B and C.

With excision of subchondral bone from articular cartilage (Group A), there was a marked increase in chondrocyte death over 7 days primarily within the superficial zone (p< 0.05). There was no significant increase in chondrocyte death within the superficial zone over the same time period for Groups B and C (p> 0.05). There was no significant difference in cartilage thickness or cell density between Groups A, B and C (p> 0.05). Corresponding increases in the protein content of the culture media for Groups B and C but not for Group A, suggested that the release of soluble factors from subchondral bone may have influenced chondrocyte survival.

Subchondral bone significantly influences chondrocyte survival in articular cartilage in vitro. These data support the concept of a functional bone-cartilage system in vivo.