INTRODUCTION

Acute leukemia (AL) is the most common cancer in children1. Major therapeutic advances have been made over the past twenty years, as 80% of children with acute lymphoblastic leukemia (ALL), and 60% of those who have acute myeloid leukemia (AML) now recover from their disease 2.
Osteonecrosis (ON) is a long-known complication of leukemia3,4. Local ischemia due to compromised blood flow is the final common pathway in the pathogenesis of ON. Ischemic lesions do not always lead to irreversible bone necrosis if there is a restoration of vascular perfusion 5. Glucocorticoid is one of the most known involved factors for ON, particularly dexamethasone, by a kind of intraosseous compartment syndrome starting with an hyperplasia of marrow fat cell to intra-osseous hypertension causing an impaired blood flow 6,7. An increased exposure to corticosteroids in ALL treatment has led to an increase in ON levels this past decades 8–11.
ON incidence is estimated at 1.5% after treatment with chemotherapy, and between 5 and 10% after allogeneic hematopoietic stem cell transplantation (HSCT) 12,13. It increases to 17.6% when diagnosed on routine imaging 14. In 2013, among the 943 patients already included in the L.E.A (Leucemie Enfants Adolescents) program, a study of 24 patients with ON showed that being over 10 years old at AL diagnosis, the achievement of a stem cell transplant (SCT) and a cumulative high levels corticosteroid favored the onset of ON 12.
Ease of access to MRI for fifteen years has allowed a more precise and earlier diagnosis of ON disorders and opens the possibility of less invasive therapeutic management, limiting the long-term sequelae. In addition, two major works to harmonize the radiological classification, regardless of the injured joint, and to better define ON were carried out in 2015 by Niinimäki et al 15,16 and the Ponte di Legno group 17. In this context, while nearly 4000 patients have been included in the L.E.A program over the last 6 years, we performed a novel study to describe clinical and radiological ON occurring during the treatment of AL in childhood. Our secondary objectives were to explore the risk factors for the onset of ON, to analyze the predictive factors of having multifocal damage and / or severe damage on MRI at diagnosis. In addition, we also evaluated the impact of ON on QoL of patients who reached adulthood.