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Magnetic Resonance Imaging Assessment of Bridge-Enhanced ACL Restoration: An Imaging Atlas of Morphological Features
James A Pruneski1,2, Shankar G Kaushal1, Kirsten Ecklund3
1Department of Orthopedics and Sports Medicine, Boston, Massachusetts, USA.
Background:
The use of bridge-enhanced anterior cruciate ligament (ACL) restoration (BEAR) procedures is on the rise. Yet, there is a paucity of literature describing the radiographic appearance of the ACL after this procedure.
Purpose:
To present the quantitative and qualitative postoperative changes in healing ACLs within the first 24 months after an ACL restoration procedure.
Study Design:
Case series; Level of evidence, 4.
Methods:
A total of 64 patients (64 knees, 19.4 ± 5 years, 57% women) underwent magnetic resonance imaging (MRI) of the knee 6, 12, and 24 months after ACL restoration surgery with an extracellular matrix scaffold as part of a randomized-controlled trial. The ACL sagittal elevation angle and tunnel positions, along with ACL volume, mean cross-sectional area (CSA), length, and normalized signal intensity (SI), were quantified from MRI. Patients were divided into quartiles based on SI at 24 months after surgery for inclusion in the qualitative analysis with an adapted framework for assessing tissue quality. Additional cases were selected for qualitative analysis based on clinical representations. Linear mixed modeling with Tukey post hoc corrections was used to analyze quantitative ACL healing parameters.
Results:
Tunnel positions were anatomic in 26.6% of femurs and 68.8% of tibias. The healing ACL sagittal elevation angle remained stable (<1° change between postoperative time points; P > .1) and was comparable with the contralateral native ACL (<2° difference between contralateral and BEAR at postoperative time points; P > .05) at all time points. The healing ACL volume and CSA decreased over time (P < .01) but remained 20% (volume) and 15% (CSA) larger than the contralateral ACL at 24 months postoperatively (by 341 mm3 volume and 6 mm2 CSA; P < .001). The healing ACL length was constant over time (<1 mm change between postoperative time points; P > .1) and was 5% longer than the contralateral native ACL at final follow-up (by 1.8 mm; P = .027). The ACL SI decreased over time (P < .001) and was 10% less than the contralateral ACL at 24 months (by 0.1 ± 0.3; P = .022). Seven relevant clinical scenarios were highlighted to show a spectrum of healing trajectories after ACL restoration surgery.
Conclusion:
The present study demonstrates that throughout 2 years of serial imaging after an ACL restoration procedure, the healing ACL becomes smaller cross-sectionally and more organized (lower normalized SI). Despite changes in the ACL size and ACL SI, the sagittal orientation remains unchanged and comparable with the contralateral native ACL. In the qualitative analysis, 7 distinct healing trajectories were identified. These data are important for interpreting postoperative imaging after the BEAR procedure, and for identifying that several healing trajectories exist after a restoration procedure. Further studies are warranted to identify patient-specific factors that may influence these trajectories.
Registration:
NCT02664545 (ClinicalTrials.gov identifier).
