How to Read a Hip MRI: A Patient's Guide

Standard MRI Sequences

• T1-weighted images: show bone anatomy and marrow detail, with normal fatty marrow appearing bright
• T2-weighted with fat saturation: highlight fluid, edema, and inflammation as bright signal against dark suppressed fat
• Proton density sequences: excellent for evaluating the labrum, cartilage, and ligamentum teres
• MR arthrogram: injected contrast distends the joint capsule, significantly improving labral tear detection with sensitivity over 90 percent

Labrum on MRI

The normal labrum appears as a dark, triangular structure attached to the acetabular rim on coronal and sagittal images. Labral tears show as bright signal within or at the base of the labrum on T2 or arthrogram images. Tear patterns include detachment from the acetabular rim, intrasubstance degeneration, and flap tears. The anterior-superior labrum is the most commonly affected location. Paralabral cysts, which appear as bright fluid-filled structures adjacent to the labrum, are strong indirect signs of an underlying tear. For treatment options, see our article on labral tear healing without surgery.

Cam and Pincer Morphology

Femoroacetabular impingement morphology is assessed on MRI and may also be visible on X-rays. Cam morphology appears as a bump or asphericity at the femoral head-neck junction, measured by the alpha angle (greater than 55 degrees is abnormal). Pincer morphology shows as excessive acetabular coverage, measured by the lateral center-edge angle. Both types cause abnormal contact during hip motion, leading to labral tears and cartilage damage. For more on FAI and related conditions, see our hip injury types guide.

Cartilage and Bone Assessment

Articular cartilage appears as an intermediate-signal layer covering the femoral head and acetabulum. Cartilage damage shows as thinning, fissuring, or focal defects, often in the anterosuperior acetabulum where impingement forces concentrate. Bone marrow edema appears as bright T2/STIR signal within normally dark bone marrow and may indicate stress fractures, AVN, or transient osteoporosis. AVN specifically shows a characteristic serpiginous (wavy line) pattern of low signal on T1 images demarcating viable from necrotic bone.

Key Takeaways

• MR arthrogram is the most sensitive technique for detecting hip labral tears
• Cam and pincer morphology on MRI helps identify the structural cause of impingement
• Paralabral cysts are strong indirect evidence of an underlying labral tear
• AVN shows a characteristic serpiginous line pattern on T1 images distinguishing it from other bone pathology

Frequently Asked Questions