Ultrasonic measurement of the thickness of human articular cartilage in situ

Objective. The objective of the present study was to explore the possibilit y of using the ultrasonic pulse-echo technique for the non-invasive measure ment of cartilage thickness in situ during a joint arthroscopic examination . The accuracy of the ultrasonic measurement was assessed in vitro against that of an established needling technique which is destructive. Methods. The velocity of sound in articular cartilage was measured in an in vitro study of one set of ipsilateral human ankle and hip joints at 69 tes t sites. Its variability was determined. Results. The velocity of sound in human articular cartilage measured in sit u varied widely (1419-2428 m/s; mean: 1892 m/s; S.D. 183 m/s) and therefore the error in the thickness of cartilage obtained from ultrasonic measureme nt based upon a constant velocity of sound could be as large as 33.6% (mean 7.38%; S.D. 6.25%). Conclusions. The ultrasonic pulse-echo technique is not accurate for the me asurement of the thickness of cartilage in situ. An alternative (albeit min imally invasive) would be the needling technique. This requires the develop ment of a specialized probe.