A 12-year-old boy presented with pain and a mass on the medial aspect of the right proximal leg. He first noticed symptoms at around 10 years of age. The pain appeared on knee flexion, and was absent when he walked or ran. His height and body weight were 162 cm and 59 kg, respectively. He had no past medical history related to the lesion. There was no history of trauma or injury at the knee. On examination, a non-mobile hard mass was palpable with tenderness at the medical side of the proximal tibia. Swelling was not obvious. Plain radiographs showed a lesion protruding from the bone with continuity to the underlying bone. The size of the lesion was 0.8 cm on a plain radiograph (Fig. ). CT depicted a protuberant bone lesion with continuity to normal bone (Fig. ), but an overlying cartilaginous cap was not obvious. The MRI showed the lesion had continuity to the host bone marrow. There was no obvious inflammation characterized by high signal intensity on a T2 weighted fat-suppression image around the tip of the osteochondroma (Fig. ). For surgical resection, the lesions were approached posterior to the conjoint tendon (Fig. ). While retracting the attachment of the pes anserinus, the lesion was resected using a curved chisel. Histologically, the specimen showed partially sclerotic lamellar bone trabeculae covered by an attenuated hyaline cartilaginous cap undergoing endochondral ossification with fatty marrow, compatible with osteochondroma. There was no evidence of malignancy. Six months after surgery, the symptoms disappeared.
A 13-year-old girl presented with pain and swelling on the medial aspect of the proximal leg, which she had noticed for several years. Her height and body weight were 161 cm and 64 kg, respectively. She had no past medical history related to the lesion. There was no history of trauma or injury. On physical examination, the non-mobile hard lesion was palpable with slight tenderness on the medial side of the proximal tibia. Plain radiographs showed a lesion protruding from the bone with continuity to the underlying bone (Fig. ). The size of the lesion was 2.0 cm on a plain radiograph. MRI depicted a protuberant bone lesion with continuity to normal bone. However, an overlying cartilaginous cap or surrounding inflammation was not apparent (Figs. ). Surgically, the lesions were approached posterior to the conjoint tendon, and resected using a curved chisel (Fig. ). The lesion was composed of lamellar bone trabeculae with fatty marrow and a covering cartilaginous component, compatible with osteochondroma. There was no evidence of malignancy. Six months after surgery, the preoperative symptoms had disappeared.