summary Sickle cell disease is a common genetic disorder of abnormal hemoglobin synthesis that causes affected blood cells to become "sickle shaped" with an inability to pass through blood vessels efficiently. Patients present with severe bone pain, acute hand swelling, and osteonecrosis. Diagnosis is made with hemoglobin electrophoresis. Treatment is medical management with hydroxyurea for sickle cell crises and monitoring for developing of osteonecrosis and osteomyelitis. Epidemiology Incidence approximately 2 million Americans carry the sickle cell gene 1 in 12 African Americans Etiology Two forms sickle cell anemia sickle cell anemia involves the presence of two abnormal hemoglobin S alleles more severe form sickle cell trait sickle cell trait involves a single copy of the abnormal hemoglobin gene usually asymptomatic increased risk of sudden-death with exertion due to collapse responds early to oxygen, rest, hydration more common Pathophysiology under low oxygen conditions the affected blood cells become "sickle shaped" and are unable to pass through vessels efficiently Orthopaedic manifestations sickle cell crisis (see below) osteomyelitis septic arthritis osteonecrosis of femoral and humeral heads bone infarcts growth retardation / skeletal immaturity dactylitis (acute hand / foot swelling) Imaging General Radiographs recommended AP and lateral standard of involved area findings bone infarcts common biconcave "fishtale" vertebrae MRI recommended for differentiating bone infarction from osteomyelitis obtain gadolinium enhanced T1 sequences which will identify infection Bone Scan helps differentiate infarct from infection Studies General Labs serum CBC, ESR, CRP may be elevated in both osteomyelitis and sickle cell crisis joint aspiration and culture may be necessary to determine if diagnosis is osteomyelitis or sickle cell crisis Sickle Cell Crisis Presentation severe bone pain usually begins near age 2-3 years caused by substance P may lead to bone infarcts Treatment nonoperative hydroxyurea provides pain relief during bone crisis Osteomyelitis Introduction often in diaphysis organism increased incidence of salmonella (may spread from gallbladder infection) staph aureus and salmonella are the most common organisms causing osteomyelits in children with sickle cell disease, although unclear which is more common salmonella osteomyelitis occurs most commonly in children with sickle cell disease Imaging radionuclide bone scan and radionuclide bone marrow scan can differentiate bone infarct from osteomyelitis osteomyelitis: normal marrow uptake, abnormal bone scan infarct: decreased marrow uptake, abnormal bone scan Evaluation aspirate and culture to differentiate from a bone infarct Septic arthritis Sickle cell patients are susceptible to infection due to hyposplenia sluggish circulation decreased opsonization of bacteria Presentation bone pain fever Labs elevated CRP and ESR Studies aspirate joint and culture to identify organism Treatment irrigation & debridement consider preoperative oxygenation and exchange transfusion prior to surgery Avascular Necrosis of Femoral Head Osteonecrosis of the femoral head can be bilateral in sickle cell disease Presentation hip pain with weight bearing screening with hemoglobin to hematocrit ratio is the strongest predictor for osteonecrosis Treatment Nonoperative partial weight bearing and range of motion indications initial treatment Operative total hip arthroplasty indications failed non operative intractable pain outcomes results of total joint arthroplasty are poor due to ongoing remodeling of bone