Indentation probing of human articular cartilage: Effect on chondrocyte viability.

BACKGROUND: Clinical arthroscopic probes based on indentation testing are being developed. However, the biological effects of certain design parameters (i.e., tip geometry and size) and loading protocols (i.e., indentation depth, rate, and repetition) on human articular cartilage are unclear.
OBJECTIVE: Determine if indenter design and indentation protocol modulate mechanical injury of probed cartilage samples.
METHODS: The objectives of this study were to determine the effects of indentation testing using clinically applicable tips (0.4mm radius, plane- or sphere-ended) and protocols (indentation depths of 100, 200, or 300 microm, applied at a rate of 50 or 500 microm/s) on the extent and the pattern of chondrocyte death, should it occur. Grossly normal osteochondral blocks were harvested from human talar dome, indented, stained with live/dead dyes, and imaged en face on a fluorescence microscope.
RESULTS: The occurrence and the extent of cell death generally increased with indentation depth, being undetected at an indentation depth of 100 microm but marked at 300 microm. In addition, tip geometry affected the pattern of cell death: ring- and solid circle-shaped areas of cell deaths were apparent when compressed to 300 microm using plane- and sphere-ended indenters.
CONCLUSION: Indenter design and indentation protocol modulated the extent and the pattern of chondrocyte death. These results have implications for designing indentation probes and protocols, as well as clinicians performing arthroscopic probing.