Background/Purpose: Linear or punctate hypointensities are commonly seen on gradient echo (GRE) sequences in the tibiofemoral joint (TFJ) space of osteoarthritic joints. These magnetic susceptibility artifacts (SAs) are thought to represent vacuum phenomenon, a common radiologic finding in OA joints and vertebral disks. They appear adjacent to the cartilage or menisci and cartilage assessment may be impaired due to signal loss or be misinterpreted as a lesion. Aim was to assess the frequency of SAs in the TFJ space on dual-echo steady state (DESS, a GRE sequence very sensitive to magnetic susceptibility) and on intermediate-weighted (IW) fat-suppressed (fs) sequence, and assess associations with intraarticular calcifications and joint space narrowing (JSN) on X-ray (XR), and with MRI-detected meniscal damage in the TFJ.

Methods: 346 knees of 177 subjects aged 35-65 with knee pain were included. 3T MRI was performed at baseline and at 6-month follow-up (f/u). Baseline anteroposterior knee XR were read for JSN according to the OARSI atlas and linear/punctate calcifications within the TFJ were recorded as present or absent. The WORMS system was used to assess meniscal damage on MRI, and the presence of any damage (grade ≥1) was recorded at baseline. Linear/punctate hypointensities representing SAs in the TFJ space were assessed on coronal DESS and IW fs sequences. Readings were done blinded and in a random order. XR, DESS and IW images were each read on separate reading sessions >2 weeks apart. κ statistics were applied to assess concordance between findings on the baseline DESS and IW fs or XR.

Results: Subjects had a mean age of 52 (SD±6) years, BMI of 29±4, and 95 (54%) were men. Baseline Kellgren-Lawrence (KL) grades (for worst knee) were: KL 0- 37 (21%) knees; KL 1- 14 (8%) knees; KL 2- 26 (15%) knees; KL 3- 81 (46%) knees; KL 4- 19 (11%). On XR, 44 (13%) and 9 (3%) knees had medial and lateral JSN, respectively; and 7 (2%) and 14 (4%) knees had calcifications in the medial and lateral TFJ space, respectively. On MRI, 126 (36%) knees had medial and 31 (9%) knees had lateral meniscal damage. In the medial TFJ, 13 and 4 knees showed SAs at baseline on DESS and IW fs, respectively. On DESS, 6 of 13 knees had persistent SA at f/u and 6 knees had incident SA at f/u. In the lateral TFJ, 5 and 1 knees showed SAs at baseline on DESS and IW fs, respectively. On DESS, 2 of 5 knees had persistent SAs at f/u and 1 new SA was noted at f/u. In the medial TFJ, compared to knees without SAs on DESS, knees with SAs were more likely to have medial meniscal damage (9/13, 69% vs. 117/333, 35%, p=0.017) and medial JSN (5/13, 38%, vs. 39/333, 60%, p=0.016). Agreement on presence/absence of SAs between DESS and IW was κ=0.46 (95%CI 0.17-0.75) and that between SAs on DESS and calcifications on XR was κ=0.18 (-0.06 – 0.42) in the medial TFJ. We could not calculate p-values or κ in the lateral TFJ due to a very small number of SAs.

Conclusion: SAs on GRE sequence in the TFJ were seen in <5% of knees in this cohort. SAs are more frequently seen in knees with medial meniscal tears and medial JSN, which suggests an association with more advanced OA-related joint damage. SAs on MRI rarely correspond to XR-detected calcifications and commonly show longitudinal changes, which support the theory that these represent vacuum phenomenon.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/frequency-and-fluctuation-of-susceptibility-artifacts-in-the-tibio-femoral-joint-space-in-painful-knees-on-3t-mri-and-association-with-meniscal-tears-radiographic-joint-space-narrowing-and-calcificat/