A novel infrapatellar approach of ultrasound-guided intra-articular injection of the knee from both lateral and medial side: a case series.

Knee osteoarthritis (OA) is common. Ultrasound-guided intra-articular injection (UGIAI) using the superolateral approach is currently the gold standard for treating knee OA, but it is not 100% accurate, especially in patients with no knee effusion. Herein, we present a case series of chronic knee OA treated with a novel infrapatellar approach to UGIAI. Five patients with chronic grade 2-3 knee OA, who had failed on conservative treatments and had no effusion but presented with osteochondral lesions over the femoral condyle, were treated with UGIAI with different injectates using the novel infrapatellar approach. The first patient was initially treated using the traditional superolateral approach, but the injectate was not delivered intra-articularly and became trapped in the pre-femoral fat pad. The trapped injectate was aspirated in the same session due to interference with knee extension, and the injection was repeated using the novel infrapatellar approach. All patients who received the UGIAI using the infrapatellar approach had the injectates successfully delivered intra-articularly, as confirmed with dynamic ultrasound scanning. Their Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain, stiffness, and function scores significantly improved 1 and 4 weeks post-injection. UGIAI of the knee using a novel infrapatellar approach is readily learned and may improve accuracy of UGIAI, even for patients with no effusion.