Osteonecrosis of Bilateral Distal Femurs in a Pregnant Patient Following Antenatal Betamethasone.

Corticosteroid therapy is a known risk factor for osteonecrosis, more commonly with chronic use and high cumulative dose. Osteonecrosis (avascular necrosis) has been described in pregnancy involving primarily the femoral head. To our knowledge, only rare cases of femoral meta diaphysis or knee osteonecrosis in pregnancy have been documented in the literature. We report a 28-year-old woman with sickle cell trait and beta-thalassemia trait who developed severe bilateral knee pain shortly after corticosteroid therapy. She was 34-weeks pregnant when she presented with the signs of preterm labor and was found to have oligohydramnios and preeclampsia. She was given two intramuscular injections of betamethasone 12 mg one day apart to enhance the fetal lung maturity. Within hours of the second injection, she developed acute and severe bilateral knee pain affecting her mobility and ambulation. Bilateral knee x-rays were unremarkable. Given the severity and persistence of her pain, magnetic resonance imaging (MRI) of bilateral lower extremities was done few days later and showed signs of early osteonecrosis involving bilateral distal femoral meta diaphysis and right lateral femoral condyle. Other than the steroid therapy she had received, no additional extrinsic risk factors for osteonecrosis were identified. Potential intrinsic risk factors were thought to include her combined sickle-beta-thalassemia traits and pregnancy. She was diagnosed with steroid-induced osteonecrosis, given the temporal relationship. Her presentation was unique, because osteonecrosis affected unreported sites during pregnancy, and it started shortly after a brief course of antenatal steroid. She was treated conservatively with analgesics, and outpatient orthopedic follow-up was recommended. She was advised to avoid prolonged weight-bearing and strenuous activities. On a follow-up appointment two months later, she was still complaining of bilateral knee pain with ambulation though it was less severe. She did not return for follow-up thereafter. We suggest the possibility of osteonecrosis in pregnancy involving uncommon sites, such as distal femur and femoral condyle in this case, following one or two doses of systemic steroid. Obstetricians need to consider osteonecrosis when evaluating an unexplained musculoskeletal pain after betamethasone that is used for preterm labors. More studies, including reporting more cases with unusual presentation and prospective studies following pregnant patients receiving steroid therapy, are needed to better understand the causes, associations, management, and clinical course of osteonecrosis in pregnancy.