bubble_chart Overview

Diaphyseal aclasis is a developmental disorder of cartilage. It manifests as multiple exostoses and metaphyseal deformities, hence it is also known as metaphyseal aclasis. Jaffe named it hereditary multiple exostoses, and it is also referred to as osteochondromatosis.

bubble_chart Etiology

It is a congenital developmental deformity, inherited as an autosomal dominant trait. 65-75% of patients have a family history, indicating heredity. The cause of the disease is unknown, possibly due to: ① Dysplasia of the bone membrane, thinner bone cortex, and incomplete bone membrane, which cannot effectively restrict bone growth outward. ② Insufficient osteoclast activity, resulting in poor bone remodeling. This explains the broad, trumpet-shaped metaphysis. ③ Defective development of the cartilage membrane, leading to excessive cartilage growth, which then transforms into bone. Since all displaced cartilage has a tendency to become malignant, this explains the frequent tendency of exostoses to undergo malignant transformation.

The disease manifests in childhood or adolescence, with a higher incidence in males than females, approximately 3:1.

bubble_chart Pathological Changes

This disease originates from the ossification of cartilage and is surrounded by a bone membrane, particularly in areas of active bone growth, such as the distal femur, proximal tibia, and distal ulna. Additionally, it can be observed in the clavicle, ilium, scapula, and vertebral bodies, but rarely in the skull. It is uncommon in the bones of the hands and feet, which distinguishes it from chondrodysplasia. The metaphysis of the affected bone is enlarged and poorly shaped, starting from the joint and extending almost parallel on both sides until it abruptly narrows at the junction with the diaphysis, often described as trumpet-shaped. There are protrusions of varying sizes at the metaphysis, known as osteochondromas. Initially, the osteochondroma is composed of cartilage, but its base gradually becomes replaced by bone tissue. As the skeleton grows, the osteochondroma gradually moves towards the center, so the duration of its existence can be estimated by the distance from the osteochondroma to the epiphyseal line.

Microscopically, the cortical bone of the osteochondroma shows a normal lamellar structure and Haversian systems. The trabeculae of the cancellous bone are normal, and the medullary cavity contains fat and has hematopoietic function. The cartilage covering it is called the cartilage cap, with immature, sparse, and dispersed cells on its surface. The cells are more mature at the junction with the cancellous bone. The growth of the osteochondroma depends on the proliferation of the cartilage cap.

bubble_chart Clinical Manifestations

In severe cases of the disease, the patient may have a short stature, limbs of unequal length, and varying degrees of curvature in the affected bones. Near the epiphysis of long bones, there are hard, irregularly shaped, immovable masses known as osteochondromas, which cause grade I pain. Sometimes, due to friction, a bursa may form nearby, which can be accompanied by inflammation. If tendons or nerves are compressed, corresponding symptoms may arise. Osteochondromas can also fracture, but they usually heal quickly. If osteochondromas in the vertebral body grow into the spinal canal, they can cause paraplegia. Sometimes, conditions such as genu varum may also be present.

X-ray findings: The characteristic features include a broad metaphysis with poor modeling, a short diaphysis, and multiple exostoses. The metaphysis takes on a "trumpet" shape. The ulna is shortened, the radius is curved, and there may be partial dislocation of the radial head, which sometimes needs to be differentiated from Madelung deformity. Osteochondromas protrude outward from the metaphysis, often in a direction away from the joint, varying in size, number, and shape: conical, mushroom-shaped, cauliflower-shaped, etc. The cancellous bone structure is consistent with that of the parent bone, and the cartilage cap is not visible on imaging, so the actual size of the mass is larger than what is seen on X-ray. In the forearm and lower leg, osteochondromas can cause compressive absorption of adjacent bones.

bubble_chart Diagnosis

The diagnosis of this disease is not difficult, characterized by hereditary familial traits and the presence of multiple osteochondromas. The characteristic manifestation is the poor metaphyseal modeling presenting a flared shape. It is often confused with chondrodysplasia (Ollier's disease), which primarily manifests as intraosseous lesions, commonly seen in the finger bones, and can be distinguished by its non-hereditary nature.

bubble_chart Treatment Measures

Deformities of the metaphysis do not require treatment. If the osteochondroma is large and affects appearance, or impairs joint movement and compresses tendons or nerves, surgical removal should be performed.

bubble_chart Prognosis

After the cessation of growth in the "mother bone," warts generally do not continue to grow. If the growth rate of the osteochondroma suddenly increases or if it continues to grow after stopping, there is a possibility of malignant transformation, with an incidence rate of 2-10%. On X-ray images, if the tumor shows unclear boundaries, bone destruction, and irregular spots, malignancy should be suspected. Osteochondromas around the hip joint and scapula are prone to malignant transformation and should be given extra attention. If malignant transformation occurs, it should be treated according to the principles of osteosarcoma. The degree of malignancy is relatively low, and metastasis occurs later, resulting in a better prognosis.