Chondroblastoma (benign chondroblastoma) is a relatively common epiphyseal cartilaginous tumor that occurs before the cessation of endochondral ossification. Most cases arise in the epiphyseal centers of long bones, particularly in other epiphyses outside the articular ends, such as the greater trochanter and tuberosity epiphyses. The upper and lower ends of the femur and tibia are common sites, with the incidence near the knee joint accounting for nearly half of all cases. Those occurring in the upper end of the humerus were first reported by Codman and are thus also referred to as Codman tumors.

bubble_chart Pathological Changes

Immature medium-sized polygonal chondroblasts forming visible clusters are densely embedded in the cartilaginous matrix, which contains areas of calcification or even ossification. The entire tumor is scattered with varying amounts of giant cells. The histological presentation can be confused with chondroblastic osteosarcoma or even osteosarcoma. Due to the presence of multinucleated giant cells, it may also be confused with chondromyxoid fibroma or giant cell tumor.

bubble_chart Clinical Manifestations

It is most commonly seen in individuals under 20 years of age, with 90% occurring between 5 and 25 years old. Males are more frequently affected than females. Localized grade I pain may be present, which is intermittent and can radiate to adjacent areas. Often, patients delay seeking medical attention for a long time after symptoms appear. Codman reported a group with delays ranging from 5 to 36 months. The main symptoms are pain and limited shoulder movement, followed by swelling of the proximal humerus and tenderness at the greater tuberosity. The condition is mostly benign. However, some cases may recur after curettage, and malignant transformation or even metastasis can occur. Barnes et al. reported recurrence rates as high as 7–18%, with malignant transformation rates of 3.7–4.5%.

Although primary malignant chondroblastoma is uncommon, it does exist and may arise from spontaneous fleshy tumor-like changes in benign chondroblastoma or secondary to radiation therapy.

Radiographic examination is characteristic, with the tumor confined to the originating epiphysis and rarely penetrating the epiphyseal cartilage to reach the metaphysis. Typically located centrally or eccentrically in the bone end, it appears as an oval or round area of deteriorated disease. A well-defined sclerotic margin is often present. A few eccentric lesions may expand the cortex and exhibit dense bone membrane reactions. The entire tumor shows a membrane-like, loosely scattered distribution of irregular calcifications, resembling a multicameral flocculent pattern, but lacks the distinct trabecular septations seen in giant cell tumors. Unlike giant cell tumors, new bone formation occurs outside the cortical bone directly beneath the tumor, and prolonged cases exhibit more pronounced bone membrane reactions.

The most common sites, in order, are the proximal femur, proximal tibia, distal femur, and proximal humerus.

bubble_chart Treatment Measures

The treatment of benign chondroblastoma primarily involves thorough curettage of the tumor tissue followed by bone grafting. The local recurrence rate post-surgery is approximately 25%. Without bone grafting, the recurrence rate can be as high as 60%. The use of cryotherapy combined with curettage can reduce the recurrence rate. For small tumors with eccentric growth, local tumor resection including surrounding normal bone may be performed. For large and rapidly growing tumors, en bloc resection is recommended. Recurrent tumors or those showing malignant transformation should be considered for segmental resection or amputation. Although the disease is sensitive to radiotherapy, it is not advisable due to the potential for malignant transformation after radiation.