Summary

This study aimed to compare the maturation of hamstring tendons (HT) and quadriceps tendons (QT) used in anterior cruciate ligament (ACL) reconstruction using MRI-Ultra Short Echo Time (UTE) T2* mapping; at all postoperative time points, the UTE-T2* values in the QT group were lower than those in the HT group, concluding that QT is not inferior to HT in terms of graft maturation.

Abstract

Introduction

MRI-Ultra Short Echo Time (UTE) T2* mapping is a highly accurate MRI imaging technique for quantifying the tissue state of tendons and ligaments. Tissues with high collagen content and well-organized alignment have lower T2* values, which is useful for evaluating maturation. In anterior cruciate ligament (ACL) reconstruction, the quadriceps tendon (QT) has recently gained attention as a graft material. The clinical outcomes of QT graft were comparable to hamstring tendon (HT) and bone tendon bone, but the differences in their maturation processes remain unclear. This study aimed to evaluate the differences in maturation of HT and QT after ACL reconstruction using MRI-UTE T2* mapping. We hypothesize that QT is not inferior to HT regarding the maturation and that their maturation processes are comparable.

Methods

We selected patients who underwent primary ACL reconstruction using either HT or QT. Among them, we included patients who were available for direct follow-up until 12 months postoperatively and who underwent MRI examinations at 6, 9, and 12 months postoperatively, allowing for evaluation using MRI-UTE T2* mapping. The study included 10 patients in each group: the HT group (10 female, mean age 18.4 ± 4.3 years) and QT group (6 male and 4 female, mean age 18.8 ± 11.6 years). ACL reconstruction was performed by a single orthopedic surgeon. The patients underwent postoperative rehabilitation using a standardized program. UTE T2* mapping images were obtained using a 1.5-T MRI scanner. A 5–10 mm2 region of interest, free from artifacts, was selected.
Measurements were taken at three sites in the intra-articular region of the reconstructed ACL based on the method reported by Okuda et al. (proximal, middle, and distal) and at one site each in the intraosseous regions of the tibia and femur. Each site was measured three times, and the average of these three measurements was defined as the UTE T2* value for each region. The intra-articular and intraosseous UTE-T2* values of the HT and QT groups were compared at 6, 9, and 12 months postoperatively using the Mann-Whitney U test. The significance level was set at 0.05.

Results

In the QT group, the UTE-T2* values in the intraosseous region of the femur at 6, 9, and 12 months postoperatively were significantly lower compared to the HT group. (at 6 months, HT: 11.5 ± 2.4, QT: 7.4 ± 0.6, p<0.01, at 9 months, HT: 11.0 ± 1.7, QT: 7.2 ± 0.9, p<0.01 and at 12 months, HT: 11.1±1.5, QT: 7.0±0.8, p<0.01). In the intra-articular and intraosseous regions of the tibia, there was no significant difference between the two groups.

Discussion And Conclusion

At all postoperative time points, the UTE-T2* values in the QT group were lower than those in the HT group. This indicates that the maturation process differs between QT and HT, which is a new finding obtained from this study. In conclusion, it was demonstrated that in terms of graft maturation, QT is not inferior to HT.