Association between infrapatellar fat pad ultrasound elasticity and anterior knee pain in patients with knee osteoarthritis

Abstract

This study investigates whether infrapatellar fat pad (IPFP) elasticity is associated with anterior knee pain in patients with knee osteoarthritis (KOA). The IPFP elasticity of 97 patients with KOA (Kellgren and Lawrence [KL] grades of the femorotibial and patellofemoral joints ≥ 2 and ≤ 2, respectively), aged 46-86 years, was evaluated via shear wave speed using ultrasound elastography. The patients were divided into two groups according to the presence or absence of anterior knee pain. Univariate analyses were used to compare patient age, sex, femorotibial KL grade, magnetic resonance imaging findings (Hoffa, effusion synovitis, bone marrow lesion scores, and IPFP size), and IPFP elasticity between the groups. Multivariate logistic regression analyses were subsequently performed using selected explanatory variables. IPFP elasticity was found to be associated with anterior knee pain in the univariate (p = 0.007) and multivariate (odds ratio: 61.12, 95% CI 1.95-1920.66; p = 0.019) analyses. Anterior knee pain is strongly associated with stiffer IPFPs regardless of the femorotibial KL grade, suggesting that ultrasound elastography is useful for the diagnosis of painful IPFP in patients with KOA.

Figure 1

Knee pain map. A knee pain map of the right knee is shown. Patient-reported pain in areas 5 (patella) or 7 (patellar ligament) while walking is categorized as anterior knee pain.

Figure 2

Histological infrapatellar fat pad fibrosis evaluation. (A) The infrapatellar fat pad (IPFP) lesion with the most extensive fibrosis of that in three nonconsecutive slice sections is detected in each sample using a microscope at 40 × magnification (scale bar = 500 µm). (B) The image of the IPFP lesion with the most extensive fibrosis is split into RGB channels. The black area representing the fibrosis is measured and expressed as the percentage. Image calculations are conducted using ImageJ Fiji package.

Figure 3

Association between the percentage of maximal fibrotic lesions and shear wave speed in the infrapatellar fat pad. The correlation between the percentage of maximal fibrosis and the shear wave speed is evaluated using 14 infrapatellar fat pad specimens (correlation coefficient: 0.51; p = 0.062).