Evaluation of Graft Ligamentization by MRI After Anterior Cruciate Ligament Reconstruction

Background: The tendon graft used in anterior cruciate ligament reconstruction (ACLR) undergoes "ligamentization" after implantation, and the reported length of this process varies from 6 to 48 months. Some grafts have ruptured at subsequent follow-up evaluations. Although the progress of graft ligamentization can be followed with postoperative magnetic resonance imaging (MRI) for reassessment, it is not known whether a delay in ligamentization (as reflected by a higher signal of the graft) is associated with an increased chance of subsequent graft rupture.

Hypothesis: Signal intensity of the graft on reassessment MRI (signal-noise quotient [SNQ]) would be associated with the incidence of future graft rupture at subsequent follow-up.

Study design: Case-control study; Level of evidence, 3.

Methods: A total of 565 ACLRs with intact graft on first-time reassessment MRI after surgery were followed for a mean period of 67 months. The rates of 1-year and 2-year follow-up were 99.5% and 84.5%, respectively. The signal intensity of the intact graft on the first-time reassessment MRI was evaluated (1) quantitatively by the SNQ and (2) qualitatively with the modified Ahn classification. Among the 565 ACLRs, 23 additional graft ruptures developed during a time interval of 7 months to 9 years after the surgery.

Results: Higher SNQ was associated with increased chance of subsequent graft rupture (SNQ 7.3 ± 6 for subsequent graft rupture vs 4.4 ± 4 for grafts without subsequent rupture; P = .004, Mann-Whitney U test). The other important confounders that were associated with increased chance of graft rupture were younger age at the time of ACLR (P < .001) and longer follow-up time (P = .002). Multiple linear regression showed that all 3 factors (higher SNQ, younger age, and longer follow-up) were independent predictors of graft rupture (SNQ, P = .03; age, P < .001; follow-up, P = .012). When the reassessment MRI was performed in the second year after ACLR, the odds ratio of future graft rupture of a heterogeneous hyperintense graft when compared with a homogeneous hypointense graft was 12.1 (95% CI = 2.8 to 52.6) P < .001, Fisher exact test).

Conclusion: Higher signal intensity of the intact graft on reassessment MRI (higher SNQ and heterogeneous hyperintense graft) was associated with increased chance of subsequent graft rupture.