Scurvy is a disease caused due to deficiency of Vitamin C. It is characterised by bleeding gums, pseudoparalysis and bony changes.
Pathophysiological basis of radiologic finding of scurvy
The pathophysiological changes seen in scurvy are the result of depression of normal cellular activity such that the ability of supporting tissue to produce & maintain intracellular substance is markedly impaired.There is suppression of osteoblasts, however resorption continues & osteoporosis result.
At the growth plate, though cartilage proliferation is decreased mineralization is unimpaired & hence zone of provisional calcification appears wide & dense. Such changes around epiphyseal ossification center gives appearance of a thin ring of increased density. Vascular invasion in zone of provisional calcification with suppression of osteoblastic activity results in decreased density in the zone of primary & secondary spongiosa. The zone of provisional calcification extends beyond the margins of metaphysis resulting in periosteal elevation & marginal spur formation. Periosteum might be elevated due to subperiosteal hemorrhage (due to increased capillary fragility). All these above changes are most pronounced in region of active endochondral bone growth.
Radiological Signs Associated with ScurvyWhite line of Frankl: It is a dense band at the growing metaphyseal end involving the provisional zone of calcification.
Wimberger's ring: Small epiphysis surrounded by a sharp, sclerotic rim
Trummerfeld zone of lucency: It is a transverse band of radiolucency beneath the dense zone of provisional calcification
Pelkan's spur: The marginal spur formation is called Pelkan's spur
Corner sign: Suggestive of subphyseal infarctions, subperiosteal hemorrhage
Figure 1: Scurvy
Which bones are involved?Changes of scurvy are best seen involving:
- Distal end of femur ( medial side ).
- Proximal & distal ends of tibia & fibula
- Distal end of Radius & ulna
- Proximal end of humerus
- Sternal ends of Ribs
Why Vitamin C deficiency causes bone changes?Vitamin C deficiency leads to a defect in the formation of bone matrix as it is necessary for formation of hydroxyproline, which is vital for collagen. About 90% of matrix of mature bone is collagen & hence a lack of collagen will have severe effect on bone formation. In childhood, this gives rise to scurvy & the adult counterpart is osteoporosis.
Radiological picture in scurvy following treatmentWith onset of healing, the cortex becomes thicker & spongiosa is more clearly defined. The transverse band of diminished density in metaphysis regains its normal density & disappears as terminal spongiosa & cortex become completely mineralized. As growth proceeds, the thickened provisional zone of calcification is buried within the shaft as a "Transverse line". When a subperiosteal hematoma is present, raised periosteum begins to layer the periphery of hematoma with a new shell of subperiosteal bone. Concurrent with resorption of hematoma, this new layer of bone thickens & shrinks down onto the shaft to become the new cortex. Residue of this cortical thickening may persist for years. Central inset of rarefaction may also persist for years in epiphyseal centres.
Co-existent Rickets & ScurvyMultiple deficiencies may modify Roentgen appearance of skeletal response. Difference in time of onset of individual deficiencies as well as periods of remission & relapse may also affect classical description.When scurvy & Rickets both are present, scurvy features predominate because of diminished osteoblastic activity. The consequent low alkaline phosphatase levels contrast with high levels in rickets that are associated with excessive osteoid production.
Other diseases causing Wimberger's signIn congenital syphilis, there are erosions involving upper medial surfaces of tibia. This is also known as Wimberger's sign.
Scurvy LineLucent transverse band between sclerotic provisional zone & heavier spongiosa deeper in shaft is called as scurvy line.