Femoral Head Necrosis And Its Relationship With Femoroacetabular Impingement On Radiological Imagings

Purpose: To determine the frequency of femoral head necrosis (FHN) infemoroacetabular impingement (FAI) and the relationship of FHN with FAI. This studyalso determines the prevalence of FHN in FAI subtype based on radiological findings.Materials and methods: Approval from our Institutional Review Board was obtainedprior to this study. Plain film, CT scan and MR imaging examinations of the hip in233patients (116men and117women, range from15-85years, mean age48years) wereperformed in the same institution from March2010to March2011. All patients withunexplained hip joint pain had no surgery, trauma or other diseases involving hips.Diagnosis of FAI was made according to criteria as follows: From X-ray anteroposteriorview images–osseous bump, pistol-grip deformity, femoral head-neck offset <9mm,figure ‘8’ configuration, posterior wall sign together with a lateral centre edge angle>40degrees, extrusion index <25together with a lateral centre edge angle>40degrees. FromCT primary axial images, reconstructed coronal and axial oblique images: ossoeus bump,pistol-grip deformity, femoral head-neck offset <9mm, extrusion index <25together witha lateral centre edge angle>40degrees, increased acetabular depth (>5mm). From MRimages: osseous bump, pistol-grip deformity, femoral head-neck offset <9mm, extrusionindex <25together with a lateral centre edge angle>40degrees.Diagnosis of FHN was made according to findings as follows:From X-ray-Femoralhead lucency, subchondral sclerosis, subchondral collapse (ie, crescent sign) and femoralhead flattening, blurring and poor definition of the bony trabeculae, patchy sclerosis. FromCT: Lucency of femoral head, subchondral fracture, patchy sclerosis, flattening of femoralhead, poor definition of the bony trabeculae. From MRI T1WI findings: Peripheral band of low signal that extends to the subchondral bone plate in the superior portion of the femoralhead outlining a central area of bone marrow; mixed pattern of abnormal signal within thefemoral head; subchondral fracture seen as low signal; flattening of femoral head. T2WIfindings:The double line sign-inner border of the low signal peripheral band demonstrateshigh signal; mixed pattern of abnormal signal within the femoral head; bone marrow edema,joint effusion; subchondral fracture seen as low signal; flattening of femoral head.Results:There were249joints with FAI and217joints without FAI.68FHN jointsfound in all FAI group(27.3%), and35FHN joints found in no FAI group(16.1%).Chisquare test shows a result of P<0.05. FHN was more common in hips with Mixed typeFAI(36.2%).Conclusion: The femoral head necrosis is more common in the hips with FAI than inthose without FAI. Hence FAI may be a predisposing factor for FHN. FHN maybe moreprevalent in mixed type FAI.