Working Diagnosis:
Chondroblastoma

Treatment:
He initially completed a course of physical therapy for his knee joint motion limitations. Because of his persistent symptoms of pain and effusion, our orthopedic tumor service recommended a CT-guided biopsy to confirm the diagnosis of chondroblastoma followed by radiofrequency ablation. Subsequent radiographs and MRI studies post procedure showed a decrease in the size of the tumor with less perilesional edema. Case Photo #7 , Case Photo #8 He also reported improvement in his pain and range of motion of the knee.

Outcome:
Following the radiofrequency ablation, the athlete had improvement in his pain. He was kept non-weight bearing for 4 weeks and then completed a course of physical therapy. He returned back to running, playing, and riding his bike without any discomfort two months post operatively. He did not resume soccer because of COVID.

Author's Comments:
The athlete initially presented with pain, negative radiographs, and a persistent effusion. Because of the persistent effusion and antalgic gait, advanced imaging was performed looking for internal derangement. Instead, a tumor was found. Most common malignant tumors presenting in the distal femur include osteosarcoma and Ewing sarcoma. Fortunately for our patient, he had a benign chondroblastoma which accounts for only 1% of all bone tumors. Chondroblastomas occur in the distal femur, proximal tibia, and humerus at the epiphysis. Most common presenting symptom is pain. Local recurrence is 10% within the first 3 years. Because of this, all cases should be monitored with a full history, physical exam and radiographs. Malignant chondroblastomas are rare but have a poor prognosis and may occur years after the original lesion.

Editor's Comments:
This clinical case highlights the importance of urgency with assessment of joint pain and swelling in the pediatric population, as some conditions (e.g. malignancies, septic arthritis) may have potentially serious consequences. Fortunately, in this case, the patient had a favorable outcome.

Chondroblastomas, as mentioned by the author, are very rare. If left untreated, these benign tumors do not undergo spontaneous regression, but malignant transformation is rare. Treatment is often surgical consisting of curettage with or without bone grafting, en bloc resection, or rarely amputation. Adjunctive treatment such as cryotherapy, chemical cauterization with phenol may also be used to reduce risk of recurrence. This case was unique in that minimally-invasive radiofrequency ablation was performed, which has been shown in cases of femoral head chondroblastomas to have a lower risk of epiphyseal plate and articular damage while maintaining good functional outcome without bone deformity or tumor recurrence.

In terms of prognosis, outcomes are very favorable, but if the tumor involved the articular surface or physis, there may be resultant arthritis or growth disturbance, respectively.

Limaiem F, Tafti D, Rawla P. Chondroblastoma. [Updated 2022 Apr 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK536947/

Petsas T, Megas P, Papathanassiou Z. Radiofrequency ablation of two femoral head chondroblastomas. Eur J Radiol. 2007 Jul;63(1):63-7. doi: 10.1016/j.ejrad.2007.03.024. Epub 2007 May 4. PMID: 17482405.

References:
Damron TA. Chondroblastoma.In: eMedicine 2020. Available at: http://www.emedicine.medscape.com/article/1254949. Accessed April 26, 2021.

Limaiem F, Tafti D, Rawla P. Chondroblastoma. In: StatPearls. Treasure Island (FL):StatPearls Publishing; 2021

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