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 population¹
• 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 life²
• The number of multiple osteochondromas varies from two to hundreds
• 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,³ 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:
  • 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 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
• Fetal alcohol syndrome
• Turner syndrome: associated with exostoses of tibia
• Tuberous sclerosis: association with exostosis of long bones
• Radiation-induced osteochondromas
• 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.⁴
• 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.

Surgical

• 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
• Neurologica - compression of spinal cord,⁵ 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 osteochondromas⁶
• Internal injuries or obstruction have been reported, causing e.g. 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.