This study investigates that normal changes seen on MRI of the ACL graft over first two years after reconstruction. The graft and perigraft tissues were assessed on serial MRI examinations addressing features such as graft size, signal intensity and perfusion. MR changes were compatible with the histological process known as changes in the ACL graft, usually called ‘ligamentization of the graft’ seems to have stabilized by 24 months.
Nine patients (6 males, 3 females, age: 26 ± 13 years) underwent serial MRI examination at 1 (baseline), 3, 6, 12 and 24 months after hamstring graft reconstruction surgery. MR technique: 3T whole-body scanner: proton-density (PD) sagittal, fat-saturated (FS) PD coronal, PD oblique axial along the ACL, FS PD sagittal, post contrast FS T1-weighted oblique axial and dynamic contrast enhanced (DCE) MRI.
Image analysis: Graft signal intensity on PD sequences was compared to that of the posterior cruciate ligament (PCL). Graft cross-sectional area and perigraft reactive tissue were measured on post-contrast oblique axial images. DCE-derived time-intensity curves yielded maximum enhancement (Emax) and enhancement slope (Eslope) of the graft and perigraft reactive tissue.
At baseline, the graft was of uniformly lower signal intensity compared to posterior cruciate ligament (0.76 ± 0.16). Thereafter, relative graft signal intensity almost doubled and was maximum at 3 months. Afterwards, the graft signal intensity reduced progressively to 24 months, to just baseline ratio.
Average graft cross-sectional area (CSA) at baseline was 36.4 ± 3.5 mm2, increasing by 27% to 45.2±3.7 mm2 at 3 months, and thereafter slowly returning to below baseline caliber being 28.7±4.0 mm2 at 24 months.
Average perigraft reactive tissue cross-sectional area at baseline was 123.3±9.6 mm2, increasing by 30% to 166.5±10.0 mm2 at 3 months, and thereafter slowly reducing to 32.0±10.9 mm2 at 24 months only.
Mild graft enhancement has evident at baseline, was greatest at 3 months and then decreased to below baseline levels at 24 months. Up until 9 months after graft reconstruction, the outer half of the graft enhanced more than the inner half of the graft. After that, both the outer and inner halfs of the graft showed a decreasing perfusion trend with the inner half showing slightly higher perfusion parameters than the outer half. Perigraft enhancement was most avid at baseline and thereafter progressively decreased up to 24 months.