Background/Purpose: Conventional radiography has been the standard imaging tool to diagnose and grade the severity of hip OA. However, radiography cannot visualize the bone marrow, cartilage and articular soft tissues that are relevant for clinical manifestation and structural progression of disease. The Hip Osteoarthritis MRI Scoring System (HOAMS) was recently developed to enable MRI-based whole-organ semiquantitative assessment of the hip. Frequency distribution of OA-associated features in the various anatomical subregions of the hip has not been described before. Further, the diagnostic performance of radiography to detect these abnormalities is unknown. Our aim was to describe the frequency of MRI-detected features of hip OA (cartilage damage, subchondral cysts, osteophytes and attrition) in various subregions of the hip joint and to evaluate the diagnostic performance of radiography for detection of these features using MRI as the reference.

Methods: 52 consecutive patients with chronic hip pain (mean age ±SD 63.5±9.5 years; 54% women) without inflammatory arthritis or recent trauma were imaged by 1.5T MRI. Of these, 44 subjects (85%) underwent weight-bearing antero-posterior pelvic radiography. For MRI assessment, the hip joint was subdivided into the following subregions (modified HOAMS system): latero-superior, centro-medial, anterior and posterior. According to HOAMS, cartilage was graded 0 to 4 based on extent (depth and area) of surface damage. Subchondral cysts and osteophytes were graded 0-3 and 0-4, respectively based on size. Bone attrition was noted as absent or present in the latero-superior subregion only. Presence of radiographic joint space narrowing (JSN) was compared to MRI-assessed cartilage damage. Sensitivity and specificity of radiography for diagnosing each feature (presence or absence) were calculated using MRI as the reference standard, and the AUC was calculated from the ROC curve for each feature.

Results: 21 of 44 subjects had radiographic OA. Frequency of diffuse cartilage damage (for n=44) (HOAMS grade 3-4) in the latero-superior, centro-medial, anterior and posterior subregions was 58%, 58%, 35% and 33%, respectively. Frequency of subchondral cysts (grade≥1) and osteophytes (grade≥1) was 31% and 64% in the latero-superior, 12% and 77% in the centro-medial, 27% and 15% in the anterior, 8% and 35% in the posterior subregions, respectively. Frequency of bone attrition in the latero-superior subregion was 17%. Sensitivity, specificity and AUC of radiography to detect MRI assessed cartilage damage were 64%, 88% and 0.76 for JSN, 84%, 71% and 0.78 for osteophytes, 44%, 89% and 0.67 for subchondral cyst, and 78%, 86% and 0.82 for attrition.

Conclusion: In this cohort of subjects with hip pain diffuse cartilage damage and osteophytes were more frequent in the latero-superior and centro-medial subregions, while subchondral cysts were more frequent in the latero-superior and anterior subregions. Radiography offers acceptable diagnostic performance for attrition, diffuse cartilage damage (in the form of joint space narrowing) and osteophytes, but shows low sensitivity in detecting acetabular subchondral cysts a finding explained by the projectional drawbacks of radiography.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/frequency-of-mri-detected-hip-osteoarthritis-features-in-persons-with-chronic-hip-pain-and-the-diagnostic-performance-of-radiography-using-mri-as-the-reference/