Exploratory pilot study of infrapatellar fat pad inflammation and treatment response in anterior knee pain: a single-center, ultrasound-guided injection trial in osteoarthritis and non-OA cohorts

Osteoarthritis (OA) is a leading cause of knee pain, and the infrapatellar fat pad (IPFP) may play a role via local inflammation. This exploratory pilot study assessed infrapatellar fat pad (IPFP) inflammation using Doppler ultrasound in patients with knee osteoarthritis (OA) versus anterior knee pain without OA, aiming to evaluate its relationship to pain severity and preliminary treatment response to conservative management versus ultrasound-guided corticosteroid injection. Given the modest sample size (n = 60) and single-center design, findings are presented as preliminary evidence to inform future larger-scale studies. Sixty patients with anterior knee pain were divided into OA and non-OA groups. Each group was randomly assigned to receive either conservative therapy or an ultrasound-guided steroid injection targeting the infrapatellar fat pad. Pain and function were evaluated at baseline and six months using validated clinical scores, while ultrasound was used to assess the fat pad inflammation before and after intervention. Ultrasound identified infrapatellar fat pad inflammation in both OA and non-OA knees, with 100% prevalence in non-OA patients (30/30) and 53.3–73.3% prevalence in OA patients across groups. At six months, corticosteroid injection produced significantly greater pain relief and functional improvement compared to conservative treatment (p = 0.001). In OA patients, WOMAC scores decreased from baseline 41.7 ± 6.17 to 20.1 ± 1.94 (52% improvement, injection group) versus 47.8 ± 1.86 to 25.7 ± 3.74 (46% improvement, conservative group). In non-OA patients, WOMAC scores decreased from 38.5 ± 4.94 to 17.8 ± 1.32 (54% improvement, injection) versus 46.0 ± 3.44 to 22.4 ± 1.55 (51% improvement, conservative). VAS pain reduction was most pronounced in the non-OA injection group (median 8→2, 75% improvement). Ultrasound demonstrated significantly reduced IPFP thickness and vascularity in injected knees, while only minimal changes were observed in conservatively managed groups. Infrapatellar fat pad inflammation is an important contributor to anterior knee pain in both OA and non-OA populations. Doppler ultrasound enables detection and monitoring of IPFP pathology. Ultrasound-guided corticosteroid injection provides superior pain control and functional improvement compared to conservative management, with particularly pronounced benefits in non-OA patients. These findings support further investigation in larger, longer-term studies to establish the clinical utility and durability of this intervention.