Abstract / Summary
Suprapatellar fat pad edema is a frequent magnetic resonance imaging (MRI) finding that may be associated with impingement and anterior knee pain, but quantitative assessment of fat pad stiffness has not been well established. This study evaluated suprapatellar fat pad stiffness using shear wave elastography (SWE) in patients with MRI-confirmed edema and in controls without edema. This prospective case-control study included 35 adult patients with MRI-confirmed suprapatellar fat pad edema and 31 controls without edema on MRI performed for unrelated indications. Within 7 days of MRI, a radiologist blinded to group assignment measured SWE stiffness (kPa) at three predefined corner regions of the triangular fat pad (S1, S2, and S3) and over the manually delineated fat pad area in a single longitudinal plane (SA). Groups were compared using the independent-samples t-test or Mann-Whitney U test, with Bonferroni correction for the four parameters. Discrimination between groups was assessed with receiver operating characteristic analysis. Mean fat pad stiffness (SA) was significantly higher in patients with edema than in controls (26.14 ± 8.69 kPa vs. 13.14 ± 3.04 kPa; p < 0.001), and differences at all three corner regions remained significant after Bonferroni correction. The area under the curve was highest for SA (0.949) and S3 (0.916). Stiffness did not differ significantly between patients with and without anterior knee pain, or between mild and advanced edema ( p > 0.05 for all), although these subgroup analyses had limited power. Suprapatellar fat pad edema on MRI was associated with increased SWE stiffness compared with controls without edema. To our knowledge, this is the first SWE study of the suprapatellar fat pad, and it indicates that this frequent imaging finding is accompanied by measurable changes in tissue stiffness. Because the control group was not clinically representative, cutoffs were derived and evaluated in the same cohort, and a single operator performed all measurements without reproducibility assessment, the findings are preliminary. Larger studies with clinically representative comparison groups and standardized, reproducible protocols are needed to establish the clinical value of SWE. Not applicable (observational study; no health care intervention was assigned).