Background:
Magnetic resonance imaging (MRI) signal intensity (SI) measurements are being
used increasingly in both clinical and research studies to assess the
maturity of anterior cruciate ligament (ACL) grafts in humans. However, SI
in conventional MRI with weighted images is a nonquantitative measure
dependent on hardware and software.
Purpose:
To conduct a systematic review of studies that have used MRI SI as a proxy
for ACL graft maturity and to identify potential confounding factors in
assessing the ACL graft in conventional MRI studies.
Study Design:
Systematic review; Level of evidence, 4.
Methods:
A systematic review was conducted by searching the MEDLINE/PubMed, Scopus,
and Cochrane Library electronic databases according to the PRISMA (Preferred
Reporting Items for Systematic Reviews and Meta-Analyses) guidelines to
identify studies that examined the healing of the intra-articular portion of
the ACL graft by assessing SI on MRIs.
Results:
A total of 34 studies were selected for inclusion in this systematic review.
The MRI acquisition techniques and methods to evaluate the ACL graft SI
differed greatly across the studies. No agreement was found regarding the
time frames of SI changes in MRI reflecting normal healing of the ACL tendon
graft, and the graft SI and clinical outcomes after ACL reconstruction were
found to be poorly correlated.
Conclusion:
The MRI acquisition and evaluation methods used to assess ACL grafts are very
heterogeneous, impeding comparisons of SI between successive scans and
between independent studies. Therefore, quantitative MRI-based biomarkers of
ACL graft healing are greatly needed to guide the appropriate time of
returning to sports after ACL reconstruction.
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