IMAGING OF IMMATURE ARTICULAR-CARTILAGE USING ULTRASOUND BACKSCATTER MICROSCOPY AT 50 MHZ

A high frequency sonographic technique-ultrasound backscatter microsco py-was used to visualize the subsurface structure of immature porcine articular cartilage from the knee joint. In 20-week-old pigs, all part s that were scanned, except the weight bearing regions of the femoral condyles, demonstrated heterogeneous ultrasound backscatter characteri stics within the articular cartilage. A trilaminar pattern consisting of hypoechoic, hyperechoic, and anechoic layers ranging from superfici al to deep generally was observed, except in the weight-bearing region s of the femoral condyles, where a homogeneous anechoic pattern was se en. In the younger pigs (6 and 10 weeks old), the trilaminar backscatt er pattern was not observed. Small, highly echogenic structures that c orrelated with vascular channels in histologic assessment were observe d frequently in the cartilage of younger pigs, but they were seldom pr esent in the cartilage of 20-week-old pigs. Structural details, such a s disruption of the subchondral bone and presence of a thickened fibro us layer on the articular surface at the chondrosynovial junction, als o were detected with the ultrasound backscatter microscope. We conclud ed that high frequency ultrasound can be used to visualize the subsurf ace structure of immature articular cartilage and some of its developm ental changes. Further research is required to explain the mechanism u nderlying the observed backscatter characteristics of immature articul ar cartilage and to study its potential for the imaging of pathologic changes.