Eighteen randomized controlled trials including 3,851 patients with knee osteoarthritis were included in this systematic review and meta-analysis comparing intra-articular hyaluronic acid (HA) injections versus placebo. Pooled outcomes of interest included the Visual Analogue Scale (VAS) for pain and the Western Ontario McMaster Osteo-Arthritis Index (WOMAC) subscales for pain, stiffness, and function. At two to four weeks of follow-up, HA injections were associated with reduced WOMAC pain and stiffness compared to placebo, but no difference in VAS at rest, VAS at exercise, or WOMAC function. At five to eight weeks, HA injections resulted in significantly lower VAS at rest, but no differences in other PROMs. These findings suggest that intra-articular HA injections may provide short-term pain relief but do not improve function in knee osteoarthritis.