Benign bone tumours. Coloured side-view X-ray of multiple tumours (grainy masses) in a patient's knee. The front of the knee is at right. These are chondromas, benign (non-cancerous) tumours that arise from cartilage tissue. They are most common in adolescents and young adults. Chondromas rarely cause symptoms, but may weaken bones making them more prone to fracturing. Treatment is with surgical removal of the tumours.