Working Diagnosis:
Locally aggressive giant cell-rich bone lesion concerning for giant cell tumor

Treatment:
The patient underwent curettage of the distal femoral lesion with phenol application and bone grafting. Final surgical pathology demonstrated chondromyxoid fibroma.
Chondromyxoid fibroma is a rare benign cartilaginous tumor accounting for less than 1 percent of primary bone tumors. Although benign, it can demonstrate locally aggressive radiographic features and may mimic giant cell tumor or other aggressive bone lesions both radiographically and histologically.

Outcome:
The patient tolerated the procedure well and began early mobilization with physical therapy. At 2-week follow-up she was ambulating with crutches with minimal swelling and knee range of motion from 0 to 90 degrees. At 6 weeks she progressed to weight bearing as tolerated with continued therapy while avoiding sprinting and heavy lifting.
Follow-up imaging demonstrated appropriate graft incorporation and healing. She remained on track for gradual return to athletic participation.

Author's Comments:
This case highlights the importance of considering underlying bone pathology in athletes with persistent atraumatic knee pain that does not improve with conservative treatment. Bone lesions may mimic common sports medicine pathology on presentation. Early imaging and multidisciplinary evaluation are important to avoid delayed diagnosis, prevent progression, and facilitate safe return to sport.

Editor's Comments:
Even though chondromyxoid fibroma is a rare and "benign" condition, it may still require surgical consideration due to pain and limitation of activity and sport. Work-up of these possible benign lesions should be evaluated further to ensure that the lesion is not aggressive or malignant. For chondromyxoid fibromas, the mainstay of treatment is surgical curettage and filling the cavity with a bone graft or bone cement. The surgical treatment of this 'benign' lesion will help with pain and get this athlete back to sport.

References:
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2. Nishio J, Shinohara Y, Chijiiwa Y, Aoki M. Chondromyxoid Fibroma: An Updated Review. In Vivo. 2026 Mar-Apr;40(2):692-703. doi: 10.21873/invivo.14231. PMID: 41760307; PMCID: PMC12949887.

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5. National Comprehensive Cancer Network. Bone Cancer (Version 2.2025). Updated September 11, 2025.

6. Easton DF, Pharoah PD, Antoniou AC, et al. Gene-panel sequencing and the prediction of breast-cancer risk. N Engl J Med. 2015;372(23):2243-2257.

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8. Hartmann W, Harder D, Baumhoer D. Giant cell "rich tumors of bone. Surg Pathol Clin. 2021;14(4):695-706.

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