Case: A sixty-eight-year-old woman with osteoarthritis in the right knee who had received a single injection of a commercial hyaluronic acid preparation presented with an intraosseous mass that had not appeared in previous imaging studies. Open biopsy and curettage was performed, and a reactive pseudotumor related to viscosupplementation was diagnosed. At the last follow-up fourteen months after surgery, the patient had experienced no recurrence of the lesion.
Conclusion: Viscosupplementation is considered a conservative treatment option for early-stage knee osteoarthritis. To the best of our knowledge, this complication, namely an intraosseous mass, has not been described previously in the literature.