Shear wave elastography reveals elevated infrapatellar fat pad stiffness in patients with early osteoarthritis symptoms after ACL reconstruction

Objective

The infrapatellar fat pad (IPFP) plays an important role in knee biomechanics and inflammation, particularly following anterior cruciate ligament reconstruction (ACLR). This study investigated whether IPFP stiffness, measured with shear wave elastography, is associated with early symptoms of osteoarthritis (OA) in individuals within one year after ACLR.

Design

In this cross-sectional study, 24 participants underwent bilateral IPFP stiffness assessments using shear wave elastography. Participants were positioned supine with 20° knee flexion. The stiffness limb symmetry index (LSI) was calculated to normalize stiffness between the ACLR and contralateral limbs. Early OA symptoms were defined as scores ≤85 % on at least two of four subscales of the Knee Injury and Osteoarthritis Outcome Score (KOOS). Independent t-tests were used to evaluate group differences in IPFP stiffness LSI, and receiver operating characteristic curve analysis determined the optimal LSI threshold for discriminating between groups.

Results

Eleven participants (46 %) showed early OA symptoms. Participants with early OA symptoms exhibited a significantly higher IPFP stiffness LSI compared to those without symptoms (49.2 ± 48.7 % vs. -17.3 ± 34.4 %, p < 0.001). An optimal stiffness LSI threshold of 7.1 % was identified, achieving 90.9 % sensitivity, 92.3 % specificity, and an area under the curve of 0.94.

Conclusions

Shear wave elastography shows potential as a non-invasive tool for detecting early IPFP stiffness changes associated with OA symptoms post-ACLR. These findings suggest that IPFP stiffness may be an early marker for OA risk, warranting further longitudinal studies to evaluate its progression and to further examine the clinical utility of shear wave elastography.