MRI for Hip Labral Tear

What Is a Hip Labral Tear?

The labrum is a ring of tough, flexible cartilage that lines the rim of your hip socket (acetabulum). It deepens the socket by about 20%, helps distribute pressure evenly across the joint, creates a suction seal that stabilises the femoral head, and contains nerve endings that provide proprioception — your sense of where your hip is in space.

A labral tear occurs when this cartilage ring is damaged — torn, frayed, or detached from the bone. It's one of the most common causes of anterior hip pain and mechanical symptoms (clicking, catching, giving way) in active adults.

The true prevalence of hip labral tears is difficult to pin down because many are asymptomatic. MRI studies of volunteers with no hip symptoms have found labral tears in up to 69% of people — a remarkably high incidence of "silent" tears. Clinically significant tears (those causing symptoms) are most common in athletes and active individuals aged 20-50, particularly in sports involving repetitive hip flexion and rotation (football, martial arts, dance, running).

Hip labral tears are strongly associated with femoroacetabular impingement (FAI) — an abnormal shape of the femoral head (cam morphology) or acetabulum (pincer morphology) that causes mechanical damage to the labrum during movement. FAI is present in up to 80-90% of patients with symptomatic labral tears.

Why MRI Is Used for Hip Labral Tears

Clinical examination can suggest a labral tear (positive anterior impingement test, pain with FABER or FADIR manoeuvres), but it can't confirm the diagnosis or characterise the tear. MRI is the imaging modality of choice because:

• Direct labral visualisation: MRI shows the labrum as a distinct triangular structure on cross-sectional images. Tears, detachments, degeneration, and paralabral cysts are all clearly depicted.
• Articular cartilage assessment: MRI simultaneously evaluates the articular cartilage covering the femoral head and acetabulum — cartilage damage often coexists with labral tears and influences treatment decisions.
• FAI morphology: MRI identifies cam and pincer morphology that predisposes to labral damage. The alpha angle (measuring the asphericity of the femoral head-neck junction) is routinely measured.
• MR arthrography superiority: Direct MR arthrography (MRA), where gadolinium-diluted contrast is injected into the hip joint before scanning, remains the gold standard for labral assessment. The injected fluid distends the joint and outlines tears that might be invisible on standard MRI.
• Pre-surgical planning: Before hip arthroscopy, the surgeon needs detailed information about tear location (anterior, superior, posterior), tear type (detachment, intrasubstance, degenerate), associated cartilage damage, and bony morphology.

MRI Sequences Used

• Proton density (PD) fat-saturated — coronal, sagittal, axial oblique: The primary sequences for labral assessment. The labrum appears as a low-signal triangular structure on PD images. Tears appear as linear high signal or disruption of the normal triangular morphology.
• T1-weighted coronal: Excellent for assessing bone morphology, including the femoral head-neck junction (cam lesion) and acetabular depth/coverage (pincer lesion).
• T2-weighted fat-saturated: Shows oedema in the labrum, bone, and surrounding soft tissues. Paralabral cysts (fluid-filled cysts at the labral base, a strong indirect sign of a labral tear) are bright on T2.
• Radial sequences: Thin slices oriented radially around the femoral neck like spokes of a wheel. This allows the labrum to be assessed in cross-section at every clock-face position (12 o'clock to 6 o'clock), significantly improving tear detection compared to standard orthogonal planes.
• 3D isotropic sequences (e.g. 3D DESS, SPACE): Provide thin-slice coverage that can be reformatted in any plane, including the radial orientations described above.
• MR arthrography sequences: If direct MRA is performed, T1-weighted fat-saturated sequences in multiple planes show the injected gadolinium contrast tracking into labral tears. The contrast outlines the labrum beautifully, making tears much easier to see.

What Radiologists Look For

• Labral tear location: Described by clock-face position (with the patient supine, 12 o'clock is superior, 3 o'clock is anterior). Anterior-superior tears (1-3 o'clock) are the most common, particularly in FAI.
• Tear type: Detachment (labrum separated from the acetabular rim), intrasubstance tear (signal abnormality within the labrum without detachment), flap tear, or complex/degenerate tear. The tear type influences whether arthroscopic repair or debridement is more appropriate.
• Labral morphology: Normal (triangular), hypertrophic (enlarged, often compensatory), or absent/hypoplastic.
• Paralabral cysts: Cysts at the base of the labrum strongly suggest an underlying tear, even if the tear itself is difficult to see on standard MRI.
• Articular cartilage: The radiologist grades cartilage damage using modified Outerbridge or similar criteria. Acetabular cartilage delamination (separation from the underlying bone) is a common finding associated with labral tears.
• Alpha angle: Measured on axial oblique images. An angle greater than 55-60° indicates a cam-type morphology of the femoral head-neck junction.
• Lateral centre-edge angle: Measured on coronal images. An angle greater than 40° suggests pincer morphology (overcoverage). Less than 20° indicates hip dysplasia (undercoverage).
• Bone marrow oedema: Oedema in the femoral head or acetabular rim indicates active mechanical stress and supports the clinical significance of identified tears.

How to Prepare for the Scan

• No specific preparation for standard MRI — eat and drink normally.
• If MR arthrography is planned, the injection is performed under fluoroscopic or ultrasound guidance before the MRI. You'll receive local anaesthetic, so the injection itself is briefly uncomfortable but manageable. Allow an extra 20-30 minutes for the injection procedure.
• Wear shorts or tracksuit bottoms without metal zips or buttons.
• Remove all jewellery, belt buckles, and hip piercings.
• If you're taking pain medication, continue as normal — you want to be comfortable enough to lie still for the scan.

What Happens During the Scan

You'll lie on your back with your legs straight and slightly internally rotated (toes pointing inward). A surface coil is placed over the affected hip. The scan takes 30-45 minutes for standard MRI, or up to 60 minutes if MR arthrography is included.

Keeping your hip still is important — the labrum is a small structure, and movement during the scan can blur the fine detail needed for accurate diagnosis. The radiographer may use padding or straps to help.

The scan is painless for standard MRI. After MR arthrography injection, some patients feel a sense of fullness or mild discomfort in the hip during the scan as the joint is distended with fluid — this typically resolves within a few hours.

What MRI Can't Show

• Dynamic impingement: MRI captures the hip in a static position. It can identify the bony morphology that predisposes to impingement but can't show the actual impingement occurring during movement. Dynamic ultrasound or arthroscopic evaluation provides this information.
• Small labral tears on standard MRI: Without arthrography, small labral tears (particularly posterior tears and partial-thickness tears) can be missed. Detection sensitivity of standard MRI ranges from 66-87% depending on the study, compared to over 90% for MR arthrography.
• Pain source confirmation: MRI shows anatomy, not pain. A diagnostic hip injection (local anaesthetic injected into the joint) that relieves pain confirms the hip joint as the pain source — MRI findings need to be correlated with this clinical information.
• Cartilage biochemistry: Standard MRI shows structural cartilage damage but doesn't detect early biochemical cartilage degeneration. Advanced mapping techniques (dGEMRIC, T2 mapping) can assess cartilage composition but aren't routinely available.

Treatment Pathways After Diagnosis

• Physiotherapy: A structured programme focusing on hip stability, core strengthening, and movement modification is the first-line treatment. Many labral tears — particularly degenerative tears in older patients — respond well to physiotherapy without surgery.
• Activity modification: Avoiding activities that provoke impingement (deep squatting, high kicks, sitting cross-legged) while maintaining general fitness.
• Analgesia and anti-inflammatories: Short-term pain management while pursuing physiotherapy. Intra-articular steroid injection can provide temporary relief and serves as a diagnostic tool.
• Hip arthroscopy: Keyhole surgery to repair (reattach) or debride (trim) the torn labrum, combined with reshaping of cam or pincer bone deformities (osteoplasty). Labral repair is preferred over debridement where possible, as it preserves the labrum's function. Recovery typically takes 3-6 months.
• Periacetabular osteotomy (PAO): For young patients with hip dysplasia (undercoverage) and associated labral tears, this bone-realigning surgery repositions the acetabulum to provide better coverage of the femoral head.
• Open surgical hip dislocation: Occasionally needed for complex cases or posterior labral pathology that's difficult to access arthroscopically.

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