Prevalence and morphological features of acetabular dysplasia with coexisting femoroacetabular impingement-related findings in a Japanese population: a computed tomography-based cross-sectional study

Abstract

The coexistence of acetabular dysplasia (AD) and femoroacetabular impingement (FAI) has not been well discussed. This study was performed to elucidate the prevalence and morphological features of AD with coexisting FAI-related findings in a Japanese population. Computed tomography images were retrospectively evaluated. AD was classified as definite or borderline. The morphological findings that defined cam deformity were an α angle of ≥55°, head–neck offset ratio (HNOR) of <0.13, pistol grip deformity positivity and herniation pit positivity. The morphological findings that defined pincer deformity were acetabular index of ≤0° and a retroverted acetabulum. In total, 128 hips (male, 64; female, 64) were analyzed. The prevalence of coexistence of AD and FAI-related findings was detected in 23.4% of hips (definite AD and FAI, 7.8%; borderline AD and FAI, 15.6%). The percentages of hips with AD containing cam or pincer deformities among all were 54.3% and 4.3%, respectively. The percentage of AD with coexisting cam and that of AD with coexisting combined deformities was significantly higher in men, respectively. On the other hand, the most major morphological feature of FAI detected in hips with AD was a HNOR of <0.13. The coexistence of AD and FAI-related findings was common in a Japanese population, and 65.2% of hips with AD had some FAI-related findings. In discussing and managing AD, we recommend paying attention to the coexistence with FAI-related findings, especially in men and in borderline AD. In such hips, the most notable parameter as a morphological feature of FAI is a reduced HNOR.

A Contemporary Look at the Evaluation and Treatment of Adult Borderline and Frank Hip Dysplasia

“…The presence of concomitant hip dysplasia and femoroacetabular impingement (FAI) is relatively common. 40 Patients with BHD and cam-type FAI are more likely to demonstrate cam impingement in the proximal rather than distal region of the femoral neck. 27 Anderson et al 2 retrospectively reviewed 164 patients with symptomatic acetabular dysplasia who underwent a PAO.…”

Sclerotic lesions of the femoral head–neck junction for diagnosis of femoroacetabular impingement

“…Previous reports have described the presence of a “herniation pit” on computed tomography or magnetic resonance imaging as a feature of FAI patients. 9,19,20 This pit or lesion forms under compressive forces. This phenomenon is very similar to what occurs to the subchondral area of tibia in knee osteoarthritis, which is affected by the compression between the distal femur and the proximal tibia.…”

“…Although some researchers consider labral lesions in AD to be related to instability of hip joint, others have emphasized that there are AD patients who have symptoms of impingement similar to FAI patients. 9…”

Radiographic analysis of subclinical appearances of the hip joint among patients with labral tears

“…The cohort of asymptomatic men ( n = 244) elucidated that the cam-type deformity was related to the herniation pit, labrum tear, and decrease in the cartilage thickness [14]. A cross-sectional Japanese population study revealed that the rate of coexistence of acetabular dysplasia was 23.4% in patients with FAI [9]. On the contrary, owing to the mechanical stress to the labrum, the dysplastic hip is at risk for abnormal thickening of the labrum [15].…”

“…We also analysed the cystic changes in the acetabulum owing to OA and herniation pit, which is defined as a cystic lesion underneath the anterior cortex at the antero-superior femoral head-neck junction with clear demarcation and diameter of > 3 mm using radiographs and mCT (coronal view) [9, 10].…”