Diaphyseal Aclasis

Synonym: hereditary multiple exostoses

An inherited autosomal dominant disorder in which multiple osteochondromas are seen throughout the skeleton.¹ The long bones of arms and legs are most commonly affected. It is associated with short stature and asymmetrical growth at the knees and ankles, which may lead to deformities.

• Affects 0.9-2 individuals per 100,000 population.¹
• More frequently found in whites than in other races.

Risk factors

• Inheritance is autosomal dominant, with near-complete penetrance.
• It is genetically heterogeneous and has been associated with mutations in at least 3 different genes called EXT genes.¹

• Usually presents during the first decade of life.²
• The number of multiple osteochondromas varies from two to hundreds. The number of osteochondromas may vary significantly within and between families, with the mean number of locations being about 15-18.³
• Bones may be broad and badly modelled.
• Most of the osteochondromas are located at the periphery of the most rapidly growing ends of long bones,⁴ but they also often involve the medial borders of the scapulae, ribs and iliac crests.
• Osteochondromas tend to grow while the growth plates are open, but growth ceases with skeletal maturity.
• Most of the osteochondromas are painless, and the main concern is often cosmetic. Pain may follow trauma to surrounding soft tissues or may be due to malignant transformation.
• Impaired body growth, both symmetrical and asymmetrical, is common and results in:⁵
  • Short stature
  • Limb-length discrepancies
  • Valgus deformities of the knee and ankle
  • Asymmetry of the pectoral and pelvic girdles
  • Bowing of the radius with ulnar deviation of the wrist
  • Shortening of the metacarpals and finger phalanges
  • Subluxation of the radial head
  • Symptoms of peripheral nerve compression

• Dysplasia epiphysealis hemimelica (Trevor 's disease): osteochondromas arise in the epiphyses and involve the joint.
• Multiple epiphyseal dysplasia: autosomal dominant; irregular epiphyseal ossification with intracapsular or periarticular chondromas of the knees and ankles.
• Enchondromatosis (Ollier's disease): intra-osseous benign cartilaginous tumours.⁶
• Fetal alcohol syndrome.
• Turner's syndrome: associated with exostoses of tibia.
• Tuberous sclerosis: associated with exostoses of long bones.
• Radiation-induced osteochondroma.
• Trauma: fractures.

• Plain X-ray - may be the only imaging study required.
• CT scan - useful in the assessment of osteochondromas in the pelvis, shoulder or spine.
• Ultrasound - useful in the assessment of complications associated with osteochondromas, e.g. thrombosis, aneurysm and bursitis.
• MRI scan - useful in the assessment of malignant transformation, and for evaluating compression of the spinal cord, nerve roots and peripheral nerves.⁷
• Arteriography - for demonstrating vascular occlusion, and aneurysm and pseudoaneurysm formation.

Diaphyseal aclasis is associated with other genetic syndromes, such as Langer-Giedion syndrome, trichorhinophalangeal syndrome and DEFECT 11 syndrome.

• Individual osteochondromas may grow large enough to require surgery.
• Surgical treatment for limb-length discrepancy.
• Corrective osteotomy for valgus deformity at the knee.
• Supramalleolar osteotomy of the tibia for severe valgus ankle deformity.
• Surgery for deformities of the forearm.
• Urgent surgery may be required for vascular ischaemia.
• Most associated chondrosarcomas can be treated with wide excision.

• Entrapment of tendons.
• Fractures.
• Bony deformities.
• May interfere with normal childbirth and lead to a higher rate of Caesarean deliveries.
• Neurological - compression of spinal cord,⁸ nerve roots and peripheral nerves.
• Vascular injuries - arterial or venous thrombosis; aneurysms and false aneurysms may occur.
• Bursa formation - bursae may become inflamed and painful.
• Malignant transformation - estimated to occur in 1-25% of osteochondromas.⁹
• Internal injuries or obstruction have been reported, e.g. causing dysphagia, haemothorax, and both urinary and intestinal obstruction.

• The prognosis is dependent on the development of complications.
• Spontaneous resolution of osteochondromas during childhood and puberty is rare but has been described.