Anterior cruciate ligament (ACL) tears and associated pivot shift are associated with a high prevalence of chondral injury¹, as well as an increase in risk of early osteoarthritis (OA). An early disease model for longitudinal assessment has not been adequately developed. Quantitative magnetic resonance imaging (qMRI), specifically T1ρ and T2 mapping, has shown strong potential in following cartilage degeneration after ACL tears². In this multicenter pilot study, we evaluate correlations between the initial chondral injury sustained over the lateral tibial plateau adjacent to the pivot shift, and matrix depletion in all knee compartments. The study was approved by the local IRBs with informed written consent. Subjects: 63 patients (28±13 yo, 36M) with acute, unilateral ACL tears were recruited within 1 month of their ACL tear at 3 participating locations, with bilateral limbs scanned at baseline, 6 months, and 1 year post-operatively using a 3 Tesla MRI scanner (GE Healthcare) with an 8-channel phased array knee coil (Invivo). Protocols included (1) 2D FSE: TR/TE=5100/33.2 ms, voxel size=0.31x0.33x3.5mm3, echo train length 13; 2) 3D FSE: TR/TE=1500/26.7 ms, voxel size=0.41x0.41x0.5 mm3, echo train length 32 with frequency selective fat saturation; 3) combined T1ρ/T2: voxel size=0.5x0.7x4mm³, TSLs= 0/10/40/80 ms, spin-lock frequency = 500 Hz, magnetization preparation TEs= 0/12.87/ 25.69/51.39ms. Image Evaluation: 2D FSE images were scored according to a modified Noyes grading3 and the area of bone marrow edema (BME) pattern on the lateral tibia and lateral femur. CUBE images were registered to the first T1ρ image (TSL=0) and using a semiautomatic edge based strategy to aid in segmenting regions of interest for T1ρ and T2 analysis: medial femoral (MF), medial tibia (MT), lateral femoral (LF), lateral tibia (LT), patella (P), and trochlea (Tr). T1ρ and T2 values were calculated on a pixel-by-pixel basis using a mono-exponential decay function. Statistical Analysis: A Friedman test was performed to detect differences of baseline Noyes grade across all compartments. Spearman correlations between baseline Noyes grade and BME of the LF and LT were calculated. Additional Spearman correlation coefficients were calculated between T1ρ and T2 values and corresponding Noyes grades of the MF, MT, LF, LT, P and Tr across all time points only for patients who displayed an increase in Noyes score of the LT between baseline and 6 Mo, baseline and 1 yr., or 6 Mo and 1yr. (n=11). Significance was set at p<0.05 (SAS, Cary, NC). Baseline Noyes grade was greatest over the LT. A significant correlation was found between BME and corresponding Noyes grade for the LF (ρ=0.28, p=0.02), but not the LT (ρ=0.17, p=0.2). Significant positive correlations were found between T1ρ or T2 and Noyes grade in the LT, MF and P compartments for the injured knee, and MF and P for the contralateral knee (Table 1). ACL injury demonstrates progressive cartilage loss that is discernable by standardized morphologic MRI, noted over the lateral tibial plateau. The correlation between BME and cartilage injury over the condyle but not the plateau supports the mechanisms of compression over the condyle and shear over the plateau during the pivot shift. QMRI metrics, however, define matrix depletion over areas not affected by the initial pivot shift such as the patella and medial condyle, suggesting an alteration in cartilage homeostasis. The changes on the control side also suggest altered mechanics leading to matrix depletion in the medial and patellofemoral compartments. The LT sustains the greatest initial insult to articular cartilage following an ACL tear. ACL tear subjects with progressive LT changes may have concomitant prolongation of T1ρ and T2 values within the compartment as well as other compartments of the knee, in both the injured and contralateral limbs. The homeostasis of both knees of an individual is affected by an ACL tear.