MRI UTE-T2* shows high incidence of cartilage subsurface matrix changes 2 years after ACL reconstruction.

Alteration of deep cartilage matrix has been observed following anterior cruciate ligament (ACL) injury, evidenced by elevated MRI UTE-T2* values measured in small, 2-D cartilage regions of interest. This Level I diagnostic study seeks to more thoroughly evaluate deep cartilage matrix changes to medial tibiofemoral UTE-T2* maps 2 years after ACL reconstruction and examine the relative utilities of 3-D compared to 2-D assessments of cartilage UTE-T2* maps. Thirty-eight ACL-reconstructed and 20 uninjured subjects underwent MRI UTE-T2* mapping. "Small" single mid-sagittal 2-D and larger 3-D "tread mark" regions of interest were manually segmented and found to be correlated in medial cartilage (r > 0.58, p < 0.005). 3-D analyses of UTE-T2* maps showed differences to medial tibial cartilage between ACL-reconstructed and uninjured subjects (p = 0.007) that were not detected by smaller 2-D regions (p > 0.46). Quantitative comparisons show 14/38 (37%) ACL-reconstructed subjects have values >2 standard deviations higher than uninjured controls. Among a subset of ACL-reconstructed subjects with no morphologic MRI evidence of medial tibiofemoral cartilage or meniscal pathology (n = 12), elevated UTE-T2* values in "small" 2-D femoral (p = 0.011), but not larger 3-D tread mark regions of interest (p > 0.13), were observed. These data show the utility of 2-D UTE-T2* assessments of mid-sagittal weight-bearing regions of medial femoral cartilage for identifying subclinical deep cartilage matrix changes 2 years after ACLR. Clinical Significance: Mid-sagittal single slice 2-D UTE-T2* mapping may be an efficient means to assess medial femoral cartilage for subsurface matrix changes early after ACL reconstruction while 3-D assessments provide additional sensitivity to changes in the medial tibial plateau.