Diclofenac etalhyaluronate combines the sustained-release properties of diclofenac with the therapeutic benefits of hyaluronic acid, providing extended analgesic effects for osteoarthritis management. This study investigated the effects of diclofenac etalhyaluronate and subsequent osteoarthritic changes in rat models of advanced and end-stage osteoarthritis. Monosodium iodoacetate (0.5 or 2.0 mg) was injected directly into the right hip joint of rats (n = 8 rats/group) using a posterior approach to induce osteoarthritis. Four weeks after monosodium iodoacetate administration, diclofenac etalhyaluronate (0.25 mg/25 µL) or 25 µL saline was administered in the same way. Pain behavior, number of microglia in the dorsal horn of the spinal cord, radiological features on microcomputed tomography, and histology of the hip joint were evaluated. Administration of diclofenac etalhyaluronate increased the pain threshold and reduced the number of microglia in the dorsal horn of the spinal cord in both models. However, radiological and histological examinations did not detect significant arthritic changes in either group that received diclofenac etalhyaluronate. Intra-articular administration, therefore, contributes to pain relief and improvement of central sensitization in advanced and end-stage osteoarthritis of the hip without subsequent progression of osteoarthritis. These findings highlight the potential of intra-articular administration of diclofenac etalhyaluronate as a conservative treatment option for advanced and end-stage hip osteoarthritis, particularly for patients who may be unsuitable for surgery or have limited response to oral nonsteroidal anti-inflammatory drugs.