Paediatric Imaging

Rickets

metabolic bone disease characterized by disorganized and defective mineralization of bone at the physis. There are many varied causes of rickets. Vitamin D deficient rickets may result from inadequate dietary intake of vitamin D, lack of sun exposure or gastrointestinal conditions which reduce the absorption of vitamin D from the gastrointestinal tract. Rickets may also be seen with any cause of chronic renal disease (renal osteodystrophy). Some forms of rickets are resistant to the usual treatment doses of vitamin D, these are grouped together as vitamin D-resistant rickets. They include primary hypophosphataemia due to defective renal resorption of phosphate, failure of production of 1,25 dihydroxy vitamin D, end-organ insensitivity to 1,25 dihydroxy vitamin D and renal tubular acidosis.

The clinical presentation of rickets is usually with irritability, bone pain and tenderness. Examination may show short stature with swollen wrists and ankles, bowed legs, delayed dentition and prominence of the frontal bones. Examination of the chest may reveal a "rickety rosary" due to enlargement of the costal cartilages (Fig.1).

Radiographs show generalized osteopenia with thinned cortices and ill defined trabeculae, and the epiphyses show delayed ossification. There is broadened lucency in the physeal region with a widened zone of unossified provisional calcification and cupping, fraying and irregularity of the adjacent ossified metaphysis which is often even more osteopenic than other sites (Fig.2). These changes are most marked at the wrists, ankles and knees. Bowing of long bones is characteristic and fractures are frequent. Other radiographic findings include enlargement of the anterior aspect of the ribs at the costochondral junction, coxa vara, basilar invagination of the skull and bilateral acetabula protrusio within the pelvis. Loosers zones occur particularly in vitamin D-resistant rickets and renal osteodystrophy but may be seen in other types of rickets. They appear radiographically as linear lucencies partly traversing a bone; typical sites include the medial aspect of the femoral neck, the pubic rami and the axillary border of the scapula.

Radiographic changes in florid rickets are pathognomonic. In mild cases radiographic diagnosis may be difficult and bone scintigraphy is sometimes helpful. Scintigraphy typically shows patchy increased activity in the shafts of the long bones, ribs and skull.

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Fig.1

Bulbous enlargement of the anterior costochondral junctions forming a "rickety rosary". There is also generalized osteopenia and metaphyseal splaying of the proximal humeri.
Rickets, Fig.1
Rickets, Fig.2 (a)
Rickets, Fig.2 (b)