Background: Mild-to-moderate knee osteoarthritis (KOA) can be successfully treated using intra-articular hyaluronic acid (IA-HA). The medial infrapatellar (MIP) approach and lateral infrapatellar (LIP) approach are two of the most used techniques for performing IA-HA, but it is still not clear which one is preferable. Objectives: The study aims to find the best knee injection technique between MIP and LIP approaches. Methods: In total, 161 patients were enrolled, divided into two groups (MIP or LIP). Each technique was performed once a week for three weeks. Patients were evaluated using the Numeric Rating Scale (NRS), Knee Injury and Osteoarthritis Outcome Score (KOOS) and Roles and Maudsley Score (RMS) at T0 (before the first injection), T1 (one week after the third injection) and T2 (six months after). Results: NRS, KOOS and RMS showed a statistically significant improvement in both groups at all the detection times, without significant differences. No differences were detected between the groups in terms of systemic effect effusions, while the MIP group presented a mildly higher number of bruises in comparison with the LIP group (p = 0.034). Conclusions: Both the IA-HA techniques are equally effective in measured outcomes. The MIP approach seems to produce some local and transient side effects. So, the choice of the LIP or MIP approach depends on the operator's skill and experience.
Keywords: hyaluronic acid; intra-articular hyaluronic acid; knee osteoarthritis; lateral infrapatellar approach; medial infrapatellar approach; rehabilitation.