Static indentation test for neocartilage surface hardness in repair of periosteal articular cartilage defects.

The objective of this study was to determine whether hardness of the superficial layer is a useful parameter to characterise cartilage produced by periosteal neochondrogenesis, using rabbit knee lesions as a model. A cartilage defect was created in the right hind knee of anesthetised young adult rabbits, and the defect was then covered with an autologous periosteal graft. At one and eight months postsurgery, rabbits were euthanised, and the articular cartilage lesion sites were evaluated for the histological parameters in a modified O'Driscoll scale, which is the current 'gold standard' for new cartilage properties. In addition, a static indentation test was performed, using a Shore-A sclerometer to measure surface hardness of the new cartilage. The hardness values had a statistically significant, positive correlation with the O'Driscoll parameters. This combination of a biomechanical measure and the O'Driscoll scale provided a more definitive indicator of graft quality. The results suggest that a hardness test with some type of sclerometer should be included in the functional characterisation of all engineered or grafted neocartilage.