Avascular necrosis of the hip in children with sickle cell disease and high Hb F: magnetic resonance imaging findings and influence of alpha-thalassemia trait

Avascular necrosis (AVN) of the hip is a common cause of morbidity in sickle cell disease (SCD). Its prevalence increases with age and predisposing factors include coexistent alpha-thalassemia trait, frequent vaso-occlusive crisis and a high hematocrit (Hct). SCD is relatively mild among Kuwaiti patients because of their elevated Hb F levels, but a subset exists with severe recurrent vaso-occlusive crises. We carried out a prospective magnetic resonance imaging (MRI) study of the hip in a group of patients being followed in the Pediatric Hematology clinics of Al-Mubarak and Al-Amiri Hospitals. The association of AVN with age, frequency of hospitalization, alpha-thal trait, steady-state Hb, Hct, Hb F, WBC and platelet counts was investigated. MRI was carried out with a 1.5-tesla GE unit with a super-conducting magnet. Thirty patients (19 males, 11 females) (23 SS and 7 SbetaThal) were studied. Their ages ranged from 6 to 17 years, with a mean of 9.8 +/- 3.5 years, and Hb F from 11 to 35% with a mean of 22.8 +/- 5.7%. Among the SS patients, 11 (47.8%) had coexistent alpha-thal trait (-3.7-kb deletion). A total of 8 (26.7%) patients (6 SS and 2 SbetaThal) had varying degrees of osteonecrosis of the hip. Four (36.4%) of the 11 SS patients with alpha-thal trait and 2 (16.7%) of those without alpha-thal trait had osteonecrosis. This difference is, however, not statistically significant (chi(2) = 0.3, p = 0.5). While there was also no significant difference in the mean age and hematological parameters (Hb, Hct, Hb F, WBC, platelets), the SS patients with osteonecrosis had a significantly higher number of hospitalizations for vaso-occlusive crisis in the preceding 3 years than those without osteonecrosis.