Quantitative imaging of anterior cruciate ligament (ACL) graft demonstrates longitudinal compositional changes and relationships with clinical outcomes at 2 years after ACL reconstruction.

T1 ρ and T2 magnetic resonance imaging (MRI) may allow for a noninvasive assessment of ligamentization after anterior cruciate ligament (ACL) reconstruction. We hypothesized that ACL graft T1 ρ and T2 relaxation times would decrease over time, that T1 ρ and T2 relaxation times would be inversely correlated with Knee Osteoarthritis Outcome Scores (KOOS), and that T1 ρ and T2 values would be lower for autograft relative to allograft reconstruction. Thirty-nine patients (age: 30.5 ± 8.2 years) were followed prospectively after ACL reconstruction with hamstring autograft (N = 27) or soft-tissue allograft (N = 12). Magnetic resonance (MR) imaging and KOOS surveys were completed at 6, 12, 24, and 36 months after surgery. ACL graft was segmented to define T1 ρ and T2 relaxation times. Relaxation times were compared between time points with ANOVA tests. Log-transformed autograft and allograft relaxation times were compared with the Student t tests. The relationship between KOOS and relaxation times at 24 months was investigated with Spearman's rank correlation. ACL graft T1 ρ relaxation times were significantly higher at 6 months relative to 12 months (P = .042), 24 months (P < .001), and 36 months (P < .001). ACL graft T2 relaxation times were significantly higher at 6 months relative to 12 months (P = .036), 24 months (P < .001), and 36 months (P < .001). T1 ρ and T2 relaxation times were significantly lower for autograft reconstruction vs allograft reconstruction at 24 months postreconstruction. Two-year KOOS Sports, Pain, and Symptoms were significantly inversely correlated with T1 ρ and T2 relaxation times. T1 ρ and T2 sequences may offer a noninvasive method for monitoring ACL graft maturation that correlates with patient-reported knee function after ACL reconstruction.