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

T1ρ 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 T1ρ and T2 relaxation times would decrease over time, that T1ρ and T2 relaxation times would be inversely correlated with Knee Osteoarthritis Outcome Scores (KOOS), and that T1ρ 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 T1ρ 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 T1ρ 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). T1ρ 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 T1ρ and T2 relaxation times. T1ρ and T2 sequences may offer a noninvasive method for monitoring ACL graft maturation that correlates with patient‐reported knee function after ACL reconstruction.