Sickle Cell Bone Complications
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Direct answer
Sickle cell bone complications arise when deoxygenated haemoglobin S polymerises and sickles red cells, which block small intraosseous vessels and cause infarction, osteonecrosis or infection. The three favourites for examiners are dactylitis in infants, avascular necrosis of the femoral head and Salmonella osteomyelitis. Dactylitis and avascular necrosis come from vaso-occlusion, while osteomyelitis adds a bacterial complication.
What you must remember
- Mechanism: deoxygenated HbS polymerises, sickling red cells that occlude small bone vessels and cause infarction in the marrow and cortex.
- Dactylitis: painful swelling of the hands and feet in infants and toddlers, usually under three years, and often the first sign of the disease.
- Avascular necrosis: the femoral head is the commonest site and the humeral head the next; MRI detects it earliest, while plain X-rays change late.
- Salmonella osteomyelitis: the classic organism in sickle cell disease, although Staphylococcus aureus remains a common cause overall.
- Infarction versus infection: both cause bone pain and may cause fever, and blood cultures, MRI and bone aspiration are needed to separate them.
- Marrow changes: marrow expansion produces H-shaped or fish-mouth vertebrae, seen on lateral spine radiographs.
- Chronic leg ulcers: around the ankles, a recognised complication of the haemoglobinopathy that heals slowly.
- Management principle: hydration, analgesia and transfusion for crises, antibiotics only for proven infection, core decompression for early femoral head necrosis and arthroplasty for advanced collapse.
Five complications compared by setting and test
Sickle cell bone problems differ in age of onset, mechanism and the investigation that confirms them, so examiners test the pairing of age with imaging. Each row links a complication to the setting in which it appears and the test that settles the diagnosis.
| Complication | Typical setting | Key feature | Best confirming test |
|---|---|---|---|
| Dactylitis | Infants and toddlers | Painful swollen hands and feet | Clinical; X-ray if doubt |
| Femoral head avascular necrosis | Adolescents and adults | Groin or hip pain, limp | MRI |
| Salmonella osteomyelitis | Children, often febrile | Bone pain, fever, long bone involvement | Blood cultures and MRI |
| Bone infarct | Any age during crisis | Deep bone pain, no infection | MRI |
| H-shaped vertebrae | Children and adults | Fish-mouth endplate changes | Lateral spine X-ray |
Dactylitis is a clinical diagnosis in young children, while femoral head necrosis calls for MRI rather than waiting for plain films. Salmonella osteomyelitis should be suspected whenever fever accompanies bone pain in a child with sickle cell disease.
Where the exam tries to catch you
Students usually lose marks by mixing infarction with infection and by relying on plain films for early disease.
- Trap: treating dactylitis as septic arthritis or osteomyelitis and planning surgery. Correct: dactylitis is a vaso-occlusive event that usually settles with hydration, analgesia and supportive care, although infection must still be excluded.
- Trap: trusting a normal X-ray to rule out avascular necrosis of the femoral head. Correct: MRI shows marrow oedema and early necrosis before radiographic collapse, so it is the test for persistent hip pain.
- Trap: assuming every febrile bone pain is a sickle crisis. Correct: Salmonella and Staphylococcus osteomyelitis must be excluded with cultures and MRI, because infection needs antibiotics and drainage.
Frequently asked questions
Why is the femoral head the commonest site of avascular necrosis in sickle cell disease?
The femoral head is the commonest site of avascular necrosis in sickle cell disease because its blood supply is end-arterial and vulnerable to occlusion by sickled cells. The humeral head is the next most common site.
How does dactylitis in sickle cell disease present?
Dactylitis in sickle cell disease presents as painful, swollen hands and feet in infants and toddlers, often as the first sign of the disease. It results from infarction of the small bones and usually settles with hydration, analgesia and supportive care.
Which organism causes osteomyelitis most characteristically in sickle cell disease?
Salmonella species are the classic cause of osteomyelitis in sickle cell disease, while Staphylococcus aureus is the commonest cause in the general population. Bone infarction can mimic infection, so cultures and MRI are needed before the diagnosis is settled.
Which imaging detects early avascular necrosis in a sickle cell hip?
MRI detects avascular necrosis of the femoral head earlier than plain radiographs, showing marrow oedema before any collapse or sclerosis appears. Radiographs stay normal for a period, so MRI is preferred when a patient with sickle cell disease has persistent hip pain.
What are H-shaped vertebrae in sickle cell disease?
H-shaped or fish-mouth vertebrae in sickle cell disease are vertebral bodies with central depression of the endplates, caused by marrow expansion and infarction. They are seen on lateral spine radiographs and reflect the marrow changes of the disease.