Avascular necrosis of the femoral head in children and adolescents with sickle cell disease presenting with HIP PAIN

Abstract Background: Avascular necrosis is a progressive and potentially debilitating complication of sickle cell disease (SCD). It can affect any joint, but most frequently (in about 75% of cases) it affects the hip joint as avascular necrosis of the femoral head (AVNFH), leading to chronic pain, disability, and reduced quality of life. There is limited literature on pediatric SCD patients with AVNFH. Methods: This is a cross-sectional retrospective cohort study of pediatric and adolescent patients with SCD enrolled in the Sickle Cell Clinical and Intervention Program (SCCRIP, NCT02098863) who presented with hip pain and had at least one hip magnetic resonance imaging MRI between 2007 and 2022. Results: Out of 825 participants with SCD, we identified 104 (12.6%) who had presented with hip pain and had had at least one hip MRI. The median age at the last hip MRI was 15.1 years (range: 2.2–23.6 years), with the majority being male (56.7%) and having the SS/Sβ0 genotype (70.2%). Of the 104 patients, 57 (54.8%) were diagnosed with AVNFH (overall prevalence = 6.9%) and were more likely to be male (73.7% vs. 36.2%, p=0.0001), but did not differ in median age at the last hip MRI (15.4 years vs. 14.9 years, p=0.051) or SCD genotype (p=0.36). Patients with AVNFH had higher white blood cell count (WBC) (9.1x10^3/mm^3 vs. 7.0x10^3/mm^3, p=0.042) and red cell distribution width (RDW) (18.7% vs. 17.3%, p=0.011), and lower mean platelet volume (MPV) (8.7 fL vs. 9.2 fL, p=0.026). However, no differences were found in hemoglobin levels (9.4 g/dL vs. 9.7 g/dL, p=0.29), hemoglobin F (9.6% vs. 8.2%, p=0.39), vitamin D (20.0 vs. 25.5 ng/mL, p=0.097), hydroxyurea use (82.5% vs. 72.3%, p=0.22), or chronic transfusions (35.1% vs. 36.2%, p=0.91). Healthcare utilization and acute SCD complications were more frequent in the AVNFH group, which had higher annual rates of emergency department visits (0.40 vs. 0.23, p=0.025), inpatient admissions (0.47 vs. 0.28, p=0.0052), vaso-occlusive crises (VOCs) (0.65 vs. 0.34, p=0.0074), and acute chest syndrome (ACS) episodes (0.16 vs. 0.06, p=0.021). Among the 57 patients with AVNFH, 33 (57.9%) required surgical intervention: 20 (35%) underwent core decompression (CD) and 13 (22.8%) underwent total hip arthroplasty (THA). The median time from MRI diagnosis to surgery was 6 months for CD and 1 year for THA. Of the 33 patients who underwent CD, 20 (61%) needed the procedure between 3 and 18 months after diagnosis, with one patient requiring THA after 7 years. There was a statistically nonsignificant increase in opioid utilization 1 year after CD with a mean increase of 3.5 morphine milligram equivalents/day (MME/d) (CI: -5.1, 12.1; p=0.41) and a statistically nonsignificant decrease in opioid utilization 1 year after THA of -2.36 MME/d (CI: -20.65, 0.11; p=0.055) Conclusion: AVNFH is more common among males; age appears to be a risk factor, though the small sample size limits conclusions. Patients tend to have higher WBC and RDW levels. MPV was found to be lower in our cohort, contrary to reports in the literature. There were no differences in hemoglobin levels, hemoglobin F, or vitamin D. We found no protective, or risk factors related to hydroxyurea or blood transfusions. There is a notable increase in healthcare utilization, emphasizing the disease's severity. 19% of patients were younger, highlighting the need for genetic sequencing to assess the impact of polymorphisms as additional risk factors. 39% required core decompression within 6 months of radiological diagnosis, and 23% needed THA one year after diagnosis. Studies and screening guidelines using either x-ray or MRI to detect early AVNFH stages often recommend conservative treatments like physical therapy, which some studies suggest can slow or reverse disease progression. Of those who had core decompression, 68% did not require further THA, while 32% needed THA within a year, indicating that core decompression can serve as an intermediate step to delay THA, especially in growing children where THA isn't an option. Core decompression did not significantly reduce opioid use; some patients may experience chronic pain, though 60% had decreased opioid use. Larger prospective studies are needed to better understand risk factors, the role of disease-modifying therapies, and management outcomes.