Femoral Cartilage Ultrasound Echo Intensity Associates with Arthroscopic Cartilage Damage

Abstract

This study compared quantitative cartilage ultrasound metrics between people with (n = 12) and without (n = 12) arthroscopic cartilage damage after anterior cruciate ligament injury (age, 24.9 ± 3.7 y; sex, 33% female, 67% male; days since injury = 50 ± 52). A transverse suprapatellar ultrasound assessment imaged the femoral cartilage in participants' injured knees before a clinical arthroscopy. A custom program automatically separated a manual cartilage segmentation into standardized medial and lateral femoral regions and calculated mean thickness (i.e., cross-sectional area/length of cartilage-bone interface), mean echo intensity and echo-intensity heterogeneity. An orthopedic surgeon assessed arthroscopic cartilage damage in the medial and lateral femoral condyles using the Outerbridge grading system (cartilage damage = Outerbridge ≥ 1). Separate logistic regressions for medial and lateral femoral cartilage were used to determine the association between each ultrasound metric and arthroscopic cartilage damage. In medial femoral cartilage, for every 1 standard deviation decrease in echo-intensity mean and heterogeneity, there is, respectively, a 91% (adjusted odds ratio, 0.09; 95% confidence interval, 0.01-0.69) and 97% (adjusted odds ratio, 0.03; 95% confidence interval, 0.002-0.50) increase in the odds of having arthroscopic cartilage damage. Lateral cartilage ultrasound metrics are not associated with lateral arthroscopic cartilage damage. This study provides preliminary evidence that femoral cartilage ultrasound echo intensity is a non-invasive measure associated with medial femoral cartilage health after anterior cruciate ligament injury.

Keywords: Arthroscopy; Cartilage thickness; Knee; Outerbridge; Ultrasonography.

Fig. 1

Standardized femoral cartilage segmentation. First, a single reader manually segmented the total cartilage cross-sectional area and marked the lowest point of the intercondylar notch (yellow diamond; a). Next, a custom program automatically separated the manual segmentation into standardized cartilage regions (i.e., medial, intercondylar, lateral; b). Last, the custom program calculated the mean cartilage thickness by dividing the regional cartilage cross-sectional area (b) by the regional cartilage length (c).