Discussion: A technique for measuring the compressive modulus of articular cartilage under physiological loading rates with preliminary results

Abstract

Abstract

On the issue of ultrasound measurement of cartilage thickness, in his Reply to my initial Communication [1] Dr Shepherd asserts that we ‘assume’ a velocity for the speed of sound in cartilage in our ultrasonic measurement of acetabula cartilage thickness and topography [2]. Page 254 of our 1981 Journal of Biomechanics article [2] states: ‘Sound velocity in the respective media was experimentally determined using samples of known geometry.’ A prior publication of the Leeds group in 1989 [3] cited reference [2] and stated ‘Efforts by the present authors to measure cartilage thickness using ultrasound indicate… Thickness measurements were difficult to obtain and even with immaculate cartilage, signal attenuation was pronounced. The unreliability in obtaining measurements prevented even a rudimentary repeatability study from being performed.’ Dr Shepherd also cites in his Reply to my Communication [1] a brief abstract [4] by his group which also dismisses ultrasound measurement with ‘ultrasonic measurement … its accuracy in measuring the thickness of human articular cartilage in situ has not been rigorously tested, nor has the potential of ultrasonic measurements for measuring mechanical properties of cartilage been evaluated’; abstract [4] cites no references.