Xanthoma typically occurs in the subcutaneous tissues, with rare cases of osseous xanthoma. However, the occurrence of knee joint osteonecrosis combined with xanthoma is even more uncommon. To the best of our knowledge, this is the first reported case. In this article, we describe a 50-year-old female patient who developed xanthoma on the basis of osteonecrosis of the knee joint. The primary clinical symptoms were knee joint pain and limited mobility. Despite conventional treatments for osteonecrosis, there was no significant improvement. Subsequently, she underwent arthroscopic excision of the knee joint xanthoma. Following the procedure, her VAS score decreased from 7 to 2, and knee joint mobility increased from 10-103° to 10-140°. Through our follow-up, the patient did not exhibit symptom recurrence. This case is valuable and provides a feasible therapeutic approach for future clinical applications.