Clinical significance of T2*-weighted gradient-echo MRI to monitor graft maturation over one year after anatomic double-bundle anterior cruciate ligament reconstruction: a comparative study with proton density-weighted MRI.

PURPOSE

This study examined the feasibility of T2*-weighted imaging (T2WI) gradient-echo MRI to reflect actual function of the graft after anatomic double-bundle ACL reconstruction. T2WI and proton density-weighted imaging (PDWI) were compared in the assessment of ACL grafts.

METHOD

Sixty-one patients underwent T2WI and PDWI at 3, 6, and 12 months postoperatively. Signal intensity of the anteromedial bundle (AMB) or posterolateral bundle (PLB) graft standardized to the intensity of the PCL was defined as signal intensity ratio (SIR). Correlations between degree of knee instability and SIR were assessed for each bundle, each time point, and each sequence. The diagnostic efficacy of T2WI sequence to detect poorly functioning knee with anteroposterior translation ≥ 4 mm was assessed.

RESULTS

Significant correlations were observed between SIR and KT values for both AMB and PLB at 12 months on T2WI (r=0.39 and 0.53, respectively), but not on PDWI. Notably, 9 of 10 patients with poorly functioning graft showing anteroposterior translation ≥ 4 mm at 12 months formed an isolated group with high T2WI-SIR. Six of the 10 patients displayed an increase in SIR from 6 to 12 months. Defining anteroposterior translation ≥ 4 mm at 12 months as the diagnostic standard for poorly functioning graft, increasing T2*WI-SIR offered 60% sensitivity and > 90% specificity.

CONCLUSIONS

ACL graft intensity on T2WI is more strongly associated with actual function of the graft than that on PDWI. An increasing trend in T2WI-SIR from 6 to 12 months postoperatively represents a possible surrogate indicator for poorly functioning grafts.