No study to date has evaluated the utility of MRI with metal artifact reduction sequencing (MARS) In the assessment of ACL grafts. MRI assessment of ACL graft integrity following ACL reconstruction is challenging due to magnetic susceptibility artifacts distorting or obscuring the graft and tunnels.
To determine whether MRI with MARS is superior to conventional knee MRI in visualization and diagnostic accuracy for ACL graft rupture.
Retrospective case series.
18 patients, 19 knees (male, 6; female, 12; age, 33 + 11.9 years) who underwent conventional MRI sequence (PD) and two types of MARS MRI (WARP, SEMAC; Siemens) following secondary injury to their ACL reconstructed knee. Six readers with knee MRI experience reviewed sagittal PD, WARP and SEMAC sequences, providing semi-quantitative grades for visualization and diagnostic confidence regarding ACL, PCL, menisci, tibial and femoral tunnel margins, and articular cartilage.
Compared to PD, WARP improved visualization of ACL (mean semi-quantitative score 3.79 vs 3.96, p=0.009), femoral tunnel (3.70 vs 4.01, p=0.001), and tibial tunnels (3.56 vs 3.92, p<0.0001), although at the cost of poorer visualization of femoral articular cartilage (4.70 vs 4.59, p=0.033), tibial articular cartilage (4.70 vs 4.58, p=0.022), medial meniscus (4.75 vs 4.53, p=0.001), and lateral meniscus (4.72 vs 4.56, p=0.026). SEMAC performed similarly to WARP, except that WARP provided significantly better visualization of cartilage and menisci than SEMAC (p<0.00001 each). Diagnostic confidence of ACL integrity was significantly improved over PD for both WARP (1.70 vs 2.17, p = 0.034), and SEMAC (1.70 vs 2.61, p = 0.032). There was no significant difference in diagnostic confidence between WARP and SEMAC (p = 0.071).
There was no significant difference in the interobserver reliability between each sequence. The WARP sequence added 2.84 + 0.69 minutes while SEMAC added 2.95 + 0.40 minutes to the standard knee MRI scan time.
Use of metal artifact reduction sequences (WARP and SEMAC) significantly improved diagnostic accuracy and confidence in detection of ACL graft tears. When the key clinical question is ACL graft integrity, our study supports adding a WARP sequence to the routine knee MRI scan protocol.