××，男，５岁，因左膝关节内侧疼痛２月余，当地医院诊断骨肿瘤转我院。查体：跛行，左膝主动伸直受限，被动伸直膝内后侧疼痛，股骨内髁内后侧摸到不明显的硬物，边缘不清，表面不光滑，明显压痛。右侧膝关节在相同部位触摸到相同硬物，无症状，关节活动正常。化验：Ａ... ××, male, 5 years old, due to medial left knee pain more than two months, the local hospital diagnosed with bone tumor transferred to our hospital. Physical examination: limping, limitation of active extension of the left knee, passive knee extension of the posterior side of the knee, and unobtrusive hard objects in the posterior side of the femoral condyle. The border is unclear, the surface is not smooth, and tenderness is evident. The right knee had the same hard object on the same site and was asymptomatic with normal joint activity. Test: A...