Regional Differences in Anterior Cruciate Ligament Signal Intensity After Surgical Treatment

Abstract

Background: Magnetic resonance–based measurements of signal intensity have been used to track healing of surgically treated anterior cruciate ligaments (ACLs). However, it is unknown how the signal intensity values in different regions of the ligament or graft change during healing. Hypotheses: (1) Normalized signal intensity of the healing graft or repaired ACL is heterogeneous; (2) temporal changes in normalized signal intensity values differ among the tibial, middle, and femoral regions; and (3) there are no differences in regional normalized signal intensity values 2 years postoperatively among grafts, repaired ACLs, and contralateral native ACLs. Study Design: Cohort study; Level of evidence, 2. Methods: Magnetic resonance imaging scans were analyzed from patients in a trial comparing ACL reconstruction (n = 35) with bridge-enhanced ACL repair (n = 65). The ACLs were segmented from images acquired at 6, 12, and 24 months postoperatively and were partitioned into 3 sections along the longitudinal axis (femoral, middle, and tibial). Linear mixed modeling was used to compare location-specific differences in normalized ligament signal intensity among time points (6, 12, and 24 months) and groups (ACL reconstruction, repair, and contralateral native ACL). Results: For grafts, the middle region had a higher mean normalized signal intensity when compared with the femoral region at all time points ( P < .01) but compared with the tibial region only at 6 months ( P < .01). For repaired ACLs, the middle region had a higher mean normalized signal intensity versus the femoral region at all time points ( P < .01) but versus the tibial region only at 6 and 12 months ( P < .04). From 6 to 24 months, the grafts showed the greatest reduction in normalized signal intensity in the femoral and middle regions (vs tibial regions; P < .01), while there were no regional differences in repaired ACLs. At 2 years after surgery, repaired ACLs had a lower normalized signal intensity in the tibial region as compared with reconstructed grafts and contralateral native ACLs ( P < .01). Conclusion: The results suggest that graft remodeling is location specific. Repaired ACLs were more homogeneous, with lower or comparable normalized signal intensity values at 2 years as compared with the contralateral native ACL and reconstructed grafts.

Quantitative MRI Biomarkers to Predict Risk of Reinjury Within 2 Years After Bridge-Enhanced ACL Restoration

“…These techniques have been shown to identify detailed structural changes in the healing ligament and provide an objective evaluation of ligament maturation and remodeling after surgery. 25,26,49 Our current observations are in agreement with a recent study that focused on signal intensity, indicating an increased risk of hamstring autograft failure in patients with a higher signal intensity ratio at 1 year. 41 The current study used a combination of SI and CSA to measure failure load to predict the risk of revision surgery, which was evaluated in both univariate and multivariable settings.…”

“…5 These previous findings align with those of the current study, as it would be expected that an increase in the healing ACL failure load would lessen the risk of revision surgery. These findings complement previous reports of temporal changes in ACL or graft-normalized SI within 2 years after surgery, corresponding to tissue healing, 25,26 and those associated with high graft SI corresponding to incomplete healing and integration, 18,27,41 as well as graft rupture within 1 year after ACLR. 41…”

“…Preoperative MR images were used to measure the posterior slope of the tibial plateau in the medial compartment (ie, medial posterior tibial slope) as previously described. 25,26 The medial posterior tibial slope was measured in a sagittal slice at the center of the medial plateau as the angle between a line that joined the peak points on the anterior and posterior rims of the plateau and as a line perpendicular to the longitudinal axis of the tibia. Measurements were performed based on established techniques by an experienced member (A.M.K.)…”

“…1,2 To supplement the existing patient-reported, clinical, and functional assessments, noninvasive imaging methods have been developed to evaluate graft maturity and to estimate the structural properties of the surgically treated ACL using quantitative magnetic resonance imaging (qMRI). 6,8,25,26,46,49 Studies have determined that changes in qMRI parameters, such as signal intensity (SI), volume, and cross-sectional area (CSA) of the ligament or graft, can be used to determine the integrity of the healing structures, as these parameters have been shown to reflect the biomechanical and histologic properties of the healing tissues. 4,6,8,54 Despite promising preclinical and clinical evidence on the utility of qMRI for the noninvasive assessment of the healing ACL structural properties and postoperative remodeling, these techniques have not yet become mainstream.…”

Changes in the Cross-Sectional Profile of Treated Anterior Cruciate Ligament Within 2 Years After Surgery

“…; intraexaminer reliability of the segmentation intraclass correlation coefficient >0.9) segmented all the ACLs and grafts ( Figure 1A ) manually using commercial image processing software (Mimics; Materialise). 14 , 15 , 26 A custom MATLAB script (MathWorks) was developed to turn the segmented ligaments ( Figure 1B ) into 3D point clouds ( Figure 1C ). 21 The program used linear regression to approximate the ligament longitudinal axis in the sagittal plane ( Figure 1C ).…”