Introduction: There is a lack of data relating the macroscopic appearance of cartilage to its ultrasound properties. The purpose of the present study was to evaluate degenerated cartilage and healthy-looking cartilage using an ultrasound system.
Methods: Ultrasound properties--signal intensity (a measure of superficial cartilage integrity), echo duration (a parameter related to the surface irregularity) and the interval between signals (that is, time of flight--which is related to the thickness and ultrasound speed of cartilage)--of 20 knees were measured at seven sites: the lateral femoral condyle (site A, anterior; site B, posterior), the medial condyle (site C), the lateral tibial plateau (site D, center; site E, under the meniscus) and the medial tibial plateau (site F, anterior; site G, posterior). The sites were evaluated macroscopically and classed using the International Cartilage Repair Society (ICRS) grading system.
Results: The signal intensity of grade 0 cartilage was significantly greater than the intensities of grade 1, grade 2 or grade 3 cartilage. Signal intensity decreased with increasing ICRS grades. The signal intensity was greater at site B than at site C, site D, site F and site G. The signal intensity of grade 0 was greater at site B than at site E. The echo duration did not differ between the grades and between the sites. The interval between signals of grade 3 was less than the intervals of grade 0, grade 1 or grade 2. The interval between signals at site C was less than the intervals at site A, site B, site D, and site E.
Conclusion: Site-specific differences in signal intensity suggest that a superficial collagen network may be maintained in cartilage of the lateral condyle but may deteriorate in cartilage of the medial condyle and the medial tibial plateau in varus knee osteoarthritis. Signal intensity may be helpful to differentiate ICRS grades, especially grade 0 cartilage from grade 1 cartilage.