Epidemiology
Black population
- heterozygote protective from malaria
- AD
Pathogenesis
Abnormal peptide substitution in ß chain of Hb
- HbS
Homozygous 1%
- HbSS
- sickling occurs with relative hypoxia
- trapped in blood vessels
- necrosis & pain
Heterozygous 8%
- sickle cell trait
- Hb SA
- sickling only with extreme hypoxia
NHx
High risk of pneumococcal septicaemic and meningitis
Clinical
1. Vaso-Occlusion
Suffer recurrent crises of abdominal & bone pain
- bone crisis
- finger pain
- can get bone infarcts / medullary or juxtacortical
Treatment
- opioid analgesia
- hydration
2. Anaemia
Sickled cells have shorter T½
3. Osteomyelitis
Bone crises difficult to distinguish from OM
- infarcted bone becomes infected
- Salmonella associated with sickle OM
Chambers et al J Paediatr Orthop 2000
- retrospective review of cases of OM / septic arthritis
- salmonella most common cause of OM
- temp > 38.2, WCC > 15 000
- bone scan and xray not helpful
- blood cultures and tissue biopsy most useful in diagnosis
4. Femoral head AVN
Incidence
- very common in homozygotes (30%)
Progression
Mont et al JBJS Am 2010
- systematic review
- asymptomatic medium to large lesions tend to progress (59%)
- small, medial lesions did not tend to progress (10%)
5. Humeral head AVN
Incidence
- homozygotes (50%)
Operative Management
Issues
Tourniquet
- avoid in homozygous
- beware in heterozygous
Perioperative Management
High risk of crisis peri-operative
- transfuse preoperatively to reduce percentage of HbS
- keep well hydrated and oxygenated
- avoid hypothermia
- avoid post operative anaemia
Femoral Head AVN
Core Decompression
Neumayr et al JBJS Am 2006
- RCT of core decompression v physio in stages I, II and III
- no evidence of improved outcome with core decompression at 3 years
THR
Hernigou et al Clin Orthop Rel Research 2008
- retrospective review 312 THR with average follow up 13 years
- average patient age 32 years
- 3% revision for infection
- 13% revison for aseptic loosening
- 25% incidence of peri-operative medial complications