Summary

The healing process of the reconstructed anterior cruciate ligament (ACL) was evaluated using magnetic resonance imaging-ultrashort echo time T2* mapping. The T2* value of the entire reconstructed ACL at 6 months postoperatively was significantly higher than that of the entire reconstructed ACL at 9 and 12 months and the normal ACL. This indicates that the quality of the reconstructed ACL 6 months

Abstract

Background

The healing process of the reconstructed anterior cruciate ligament (ACL) after anterior cruciate ligament reconstruction (ACLR) is one of the important factors for return to sports.
Magnetic resonance imaging-ultrashort echo time (MRI-UTE) T2* mapping can quantify T2* values in tissues with short T2 relaxation times, such as tendons and ligaments, which cannot be evaluated with conventional MRI. T2* values reflect the amount and arrangement of collagen in the tissue, with lower values in tissues containing dense collagen, and higher values in tissues with sparse collagen.
This study aimed to observe the healing process of the reconstructed ACL after ACLR using MRI-UTE T2* mapping and compare its quality in each healing phase to that of a normal ACL.

Method

Ten patients (10 females; mean ± SD age 18.4 ± 4.3 years) who underwent initial ACLR with autogenous hamstring tendon from 2018–2020 and 12 volunteers (6 males, 6 females; mean ± SD age, 30.8 ± 9.6 years) without any history of knee diseases or surgeries were recruited. Patients who underwent ACLR had MRI-UTE T2* mapping of the operated knee at 6, 9, and 12 months postoperatively, and volunteers underwent MRI-UTE T2* mapping of the right knee joint only once.
T2* values of the reconstructed and normal ACLs were measured at the distal, middle, and proximal sites. The regions of interest of each site were measured at the areas unaffected by artifacts using a 10-mm circle. The mean T2* values measured at the three sites were defined as the T2* values of the entire tissue. The T2* values of the reconstructed ACL at 6, 9, and 12 months postoperatively and the normal ACL were compared using a one-way analysis of variance.

Result
The UTE-T2* values of the reconstructed ACLs were 13.1 ± 1.9 ms, 11.7 ± 1.5 ms, and 11.1 ± 1.3 ms, respectively, at 6, 9, and 12 months postoperatively, and the UTE-T2* value at 6 months postoperatively was significantly higher than those at 9 and 12 months (P < 0.01 vs. 9 months; P < 0.01 vs. 12 months). The UTE-T2* value of the normal ACL was 11.9 ± 2.4 ms, which differed significantly from the value obtained 6 months postoperatively of the reconstructed ACL (P < 0.01).

Conclusion

The T2* value of the entire reconstructed ACL at 6 months postoperatively was significantly higher than that of the entire reconstructed ACL at 9 and 12 months and the normal ACL. This indicates that the quality of the reconstructed ACL 6 months after ACLR did not reach that of the normal ACL.