Synchronous chondroblastomas in the knee joint: A case report

Abstract

IntroductionA chondroblastoma (CB) is a benign chondroid bone tumor that typically arises in growing children. It frequently occurs in the proximal tibia, femur, and humerus. However, the biological behavior of CBs remains unclear because of their rarity. Herein, we report a rare case of synchronous CBs arising on the bilateral sides of the knee joint, suggesting the etiology of chronological tumorigenesis.Presentation of caseAn 18-year-old Japanese man with a complaint of right knee pain was referred to our hospital. Radiography revealed an expanding osteolytic lesion in the right proximal tibia. A small lesion in the distal femur was detected on magnetic resonance imaging. A biopsy of the tibial lesion revealed a pathological diagnosis of CB. Two-stage curettages were performed in the tibia and femur, and the pathological diagnosis of the femoral lesion was CB. No recurrence had occurred for 5 years in the tibia and a year in the femur with stable ambulation and a full range of motion.DiscussionIn our case, the CBs in the proximal tibia and distal femur co-occurred, suggesting that the seed of the CB emerged before the separation of these two bones. The key point to the generation of CB is that its origin could be initiated during mesenchymal condensation before the separation and differentiation of bones as if continental drifts.ConclusionWe experienced a rare and suggestive case in CB etiology. An experience of synchronous CBs in the consecutive bones was suggestive of CB etiology and careful management.