Rickets

Rickets essentially refers to osteomalacia in the paediatric population that occurs prior to fusion of the growth plate.

Demographics and clinical presentation

Rickets is seen in a number of distinct populations which include ⁴:

1. premature infants (especially if on parenteral nutrition)
2. unbalanced infant nutrition
   • protracted exclusive breast feeding
   • non-vitamin D supplemented formula fed infants
   • vegetarian diets
3. maternal vitamin D deficiency
4. lack of sun exposure
   • dark skin in sun-poor countries
   • lack of out door time
   • clothing that eliminates sun exposure

The onset and presentation of rickets depends on the aetiology and degree of deficiency. Typically in severe cases rickets becomes apparent in the second year of life.

Presentation is usually with skeletal changes (see below) and bone pain.

Pathology

Results from abnormality or deficiency in one or more of ¹:

• 1,25 di-hydroxy vitamin D
• calcium
• phosphorus
• alkaline phosphatase
• body pH

As a result of this imbalance the ratio of mineralised to non-mineralised osteoid is abnormal (with an excess of non-mineralised osteoid present) and bone strength is reduced.

Radiographic features

In the growing skeleton the deficiency of normal mineralisation is most evident at growth plates where there is an excess on non-mineralised osteoid resulting in growth plate widening. With increasing severity and abnormal biomechanics the metaphysis flares out and appears frayed.

It is not surprising that these features are most prominent at the growth plates where growth is greatest:

• knee : distal femur, proximal tibia
• wrist : especially the ulna¹
• anterior rib ends : rachitic rosary

It is important to remember that even bones that appear mineralised are weak, and result in bowing, most commonly seen in the lower limbs once the child is walking. The legs bow outwards with variable deformity of the hips (both coxa vara and coxa valga are seen ¹). The lower ribs may also be drawn inwards inferiorly by the attachment of the diaphragm (Harrison's sulcus).

Treatment and prognosis

Treatment requires correction of the metabolic imbalance. Only rarely is orthopaedic surgical intervention required to correct skeletal deformities.

Differential diagnosis

The differential for leg bowing in children includes ²:

• developmental or congenital bowing
• Blount disease
• osteogenesis imperfecta
• many others that are not usually a consideration (see leg bowing in children).

The differential for widening of the growth plate includes :

• scurvy
• delayed maturation due to illness
• endocrine disturbances
  • growth hormone excess
  • hyperparathyroidism
  • hypothyroidism

The differential for flaring of the metaphysis includes:

• anaemia(s)
• fibrous dysplasia
• storage diseases
• chronic lead poisoning
• bone dysplasias