bubble_chart Overview

Multiple hereditary osteochondromas have three characteristics: ① hereditary ② bone shortening or deformity ③ high incidence of malignant transformation into peripheral chondrosarcoma.

bubble_chart Clinical Manifestations

The ratio to solitary osteochondroma is 1:10. Due to its multiple nature, symptoms appear earlier than in solitary osteochondroma, generally before the age of 10. Mild cases (especially in females) may remain latent for life. There is a marked predilection for males, with a male-to-female ratio of 2:1.

Nearly two-thirds of cases exhibit hereditary traits. If one parent has hereditary multiple osteochondromas, approximately half of their offspring will inherit the condition, with a higher prevalence among male descendants. In affected families, if a male member is normal, he will not pass the disease to his offspring; conversely, in the same family, even normal females can transmit the disease to their descendants. In other words, in males, the disease and hereditary capability manifest simultaneously, while in females, the disease may remain latent or asymptomatic but can still be passed on.

The condition is generally diffuse and symmetrical, with all bones formed by endochondral ossification being potential sites for osteochondroma. The metaphyses of growing bones are frequently and extensively affected, particularly near the knee, shoulder, hip, wrist, and ankle, though involvement of the elbow is rare and mild. Hereditary multiple osteochondromas are also common in the trunk bones, occurring near secondary or apophyseal ossification centers. In the scapula, they are mainly found near the vertebral border, inferior angle, acromion, glenoid, and coracoid process; in the pelvis, primarily at the iliac crest; in the spine, mostly at the spinous and transverse processes; and in the ribs, commonly at the costochondral junctions or posterior ends. Except for the calcaneus, which has a secondary ossification center, hereditary multiple osteochondromas do not occur in the carpal or tarsal bones, as these bones develop similarly to epiphyses.

Multiple, fairly symmetrical bony outgrowths can be seen and palpated. In more severe cases, the presentation is characteristic, and diagnosis can often be made based on physical examination alone. In the most severe cases, limb shortening may occur, sometimes so pronounced and diffuse as to resemble achondroplasia. However, hereditary multiple osteochondromas lack the features of achondroplasia, and cartilage growth function is normal. In fact, limb shortening is not due to abnormal cartilage growth but rather to the diversion of cartilage's proliferative potential into external branches (osteochondromas), which are not utilized for bone elongation. Because this external dispersion is unevenly distributed around the bone circumference and between the paired bones of the forearm and lower leg, limb shortening is often accompanied by deformities, such as valgus or varus of the knee, ankle, elbow, or wrist. The most typical deformities occur in the forearm and thorax. Since osteochondromas are more common at the wrist than the elbow, with three-fourths of ulnar elongation occurring distally and four-fifths of radial elongation occurring proximally, the ulna is always shorter than the radius, resulting in the radius curving outward and dorsally, ulnar deviation of the hand, and occasionally radial head dislocation.

bubble_chart Prognosis

Like solitary osteochondroma, multiple hereditary osteochondroma also stops growing when body growth ends. However, if an individual case of osteochondroma shows significant growth during adulthood, it is usually a sign of fleshy tumor transformation, with an incidence rate of about 25%. The fleshy tumor transformation in multiple hereditary osteochondroma generally occurs after the age of 15.