Objective: Tumor-induced osteomalacia with the culprit tumor located in the knee joint is rare in clinical practice, and previous literature has only been seen in case reports, which pose great challenges to the clinical diagnosis and treatment of such patients. The purpose is to elucidate clinical characteristics and orthopedic surgical treatment experience of tumor-induced osteomalacia (TIO) with causative tumor located in the knee joint region.
Methods: Clinical data of all consecutive TIO patients with culprit tumors located in the knee joint region was retrospectively analyzed. All patients were surgically treated by an orthopedic bone and soft tissue tumor sub-professional team at Peking Union Medical College Hospital from January 2015 to January 2025. The clinical distribution feature and surgical effects were analyzed, and clinical practice experience was presented.
Results: All nine patients were included in this study. All patients exhibited varying degrees of bone pain and 100% (9/9) of the patients had limited mobility, often accompanied by difficulties in sitting up, walking, and weakness or fatigue. Approximately 44.4% (4/9) of the patients had significantly shorter height after initial symptoms appeared. All patients underwent a total of 10 operations to control the causative tumors in the knee joint region. Culprit tumors were located in the patella (one case), infrapatellar fat pad (three cases), suprapatellar capsule (one case), popliteal fossa (three cases), and the entire knee joint (one case), respectively. There was only one case of skeletal involvement, one case with involvement of bones and soft tissues, and seven cases with soft tissue causative tumors. All the patients had a gradual increase in blood phosphorus levels in the short term after the first orthopedic surgery, after a follow-up of 12 months to 10 years. During the follow-up, no patients experienced recurrence.
Conclusion: The causative tumor for TIO in the knee joint region is hidden and has diverse locations; however, there is no established orthopedic surgical intervention strategy for these rare entities in clinical practice. Due to the unique anatomical location and complex structure of the knee joint, orthopedic surgeons can adopt different surgical approaches to completely remove the causative tumor. For these patients, the prognosis is satisfactory after complete tumor resection, and the condition can be effectively improved. These findings may help to improve the clinical diagnosis and treatment level of orthopedic physicians for this rare entity.
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2025 The Author(s). Orthopaedic Surgery published by Tianjin Hospital and John Wiley & Sons Australia, Ltd.
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