Osteochondroma is a bony abnormality that occurs on the surface of bone and is covered with cartilage, also known as an exophytic wart. The cause of osteochondroma is unknown, and some investigators believe that osteochondroma is a true mass, while others believe that it is a developmental epiphyseal growth defect. Osteochondromas can be solitary, called isolated osteochondromas, or multiple, called multiple hereditary osteochondromatosis. Age of onset: Osteochondromas are mostly seen in children and adolescents, and 70% to 80% of them occur under the age of 20, with the age of onset between 5 and 20 years old, and more males than females. Site: Osteochondroma mostly occurs in long tubular bones, 30% in femur, 20% in humerus, 17% in tibia, 10% in short tubular bones of hands and feet, 5% in iliac bone, 4% in scapula, 2% in vertebrae, and rarely in ulna and radius of upper limbs; the incidence of lower limbs is significantly higher than that of upper limbs, and the ratio is 2:1; osteochondroma occurs in the epiphysis of tubular bones, such as distal femur, proximal tibia and humerus. It is rare that it occurs in the diaphysis and epiphysis of the bone. Clinical manifestations: Isolated osteochondromas with a single occurrence are often asymptomatic and are most often seen as an incidental, painless, bone-connected bulging mass. Sometimes the lump rubs against the surface tissue, causing bursitis and mild pain; a few lumps compress adjacent nerves, blood vessels, and tendons, causing corresponding symptoms. The mass grows slowly as the body grows taller, and when the development stops (epiphysis closes), the mass stops growing and the mass stops growing. During development, some hereditary osteochondromatosis multiforme may cause bone and joint deformities in the corresponding areas. In adulthood, if the mass grows rapidly and becomes painful, it is a sign of malignancy. The incidence of malignant transformation of osteochondroma into chondrosarcoma is 1% in single cases, while the incidence of malignant transformation is higher in multiple cases, about 5% to 10%. It is one of the few bone tumors that can be diagnosed by X-ray alone. It is similar to multiple tumors and is characterized by a protrusion from the bone surface outward, with the bone cortex and trabeculae at the base continuous with those of the host bone and the cartilage cap at the tip. In the former, the base is wide and the tumor is triangular or pestle-shaped into the soft tissue, and the cartilage cap at the tip is not visible or shows uneven calcification and ossification; in the latter, the base is narrow and the tumor is large, and the tumor has more cartilage components and shows a cauliflower shape with uneven density on X-ray. Osteochondromas often occur at the attachment points of tendons or ligaments in the epiphysis and grow away from the joint by the pull of muscles or ligaments. The epiphysis widens due to failure of canalization, which is more pronounced in multiple hereditary osteochondromas. In malignant osteochondroma, the tumor is blurred with poorly defined borders and may have extensive calcification or ossification shadows. Pathological examination: In childhood, the histological features of osteochondroma are obvious. The cartilage cap on its surface is composed of columnar arrangement of chondrocytes, under which are mast cell layer, matrix calcification layer and primitive bone trabeculae, which resembles the process of cartilage osteogenesis in epiphysis. The cartilage cap calcifies or ossifies to varying degrees by adulthood. Treatment I. Follow-up observation: For single, asymptomatic and small tumors, observation is feasible without surgery. The indications or surgical guidelines for osteochondroma requiring surgery are as follows: 1) Tumor causes pain and discomfort due to joint activities; 2) Tumor is relatively large and affects aesthetics; 3) Tumor compresses adjacent blood vessels and nerves causing corresponding symptoms and signs; 4) Tumor growth causes deformity of host bone or adjacent bone; 5) Tumor surface is cauliflower-shaped with more calcification or ossification shadow, especially if the tumor occurs in the pelvis or scapula. The tumor surface is cauliflower-like with more calcification or ossification shadow, especially if the tumor occurs in the pelvis or scapula, because its malignant rate is relatively high, the treatment should be active and preventive early resection. For patients with multiple hereditary osteochondromas, treatment is more difficult because the tumor has a higher chance of malignancy and often leads to developmental deformities of bones and joints, so it is advisable to selectively operate in stages to remove the tumor and correct the deformity. The principle of osteochondroma surgery is to remove the whole tumor by flush with the host bone and with a small part of normal bone, especially the cartilage cap on the surface of the tumor should not remain, and if there is bursa formation, it should also be removed together. In children, the operation should not damage the epiphysis, so as not to cause deformity of bone development. If the osteochondroma has become malignant, it should be treated as chondrosarcoma and be extensively excised.