Location dependent properties of cartilage measured by ultrasound and indentation: Two case studies of ovine and minipig knee articular cartilage

INTRODUCTION: The topographic analysis of cartilage mechanical properties has been of particular interest since it is known that physiological loading patterns differ with location in a synovial joint. Site-specific in vivo material characterization of articular cartilage has previously been performed using both ultrasound and indentation techniques [1-3]. Ultrasound biomicroscopy (UBM) uses high frequency acoustic waves that allow both, non-destructive three-dimensional visualization and assessment of mechanical properties. This method, has recently been applied for the evaluation of cartilage repair in a minipig model [4]. The goal of the present study was to investigate, if mechanical parameters derived by creep indentation correlate with site-matched parameters derived from UBM. Cartilage samples from two animal species (ovine and porcine) were thus investigated mechanically i.e. under creep indentation, as well as by means of ultrasound scanning. Specimens were scanned in US immediately after preparation, and subsequently biomechanically tested at the same locations.