What is the recommended protocol for an MRI of the hip?

MRI Hip Protocol Recommendations

The recommended MRI hip protocol depends on the clinical indication: for suspected labral tears or impingement, MR arthrography is the gold standard; for cartilage evaluation, soft tissue pathology, infection, or tumor, MRI without IV contrast is preferred; and for acute trauma with negative radiographs, MRI without contrast is the appropriate next step. 1

Protocol Selection by Clinical Indication

For Suspected Labral Tears and Femoroacetabular Impingement

• MR arthrography receives the highest appropriateness rating (9/9) for detecting labral tears and impingement, as it provides superior contrast separation of intra-articular structures and outlines abnormalities with greater accuracy 1
• Direct MR arthrography involves intra-articular injection of dilute gadolinium solution (1:200 in saline) and has been established as the most reliable technique for diagnosing acetabular labral tears 1
• CT arthrography is an acceptable alternative (rating 7/9) when MRI is contraindicated 1
• Standard MRI without contrast (rating 6/9) can be used but is less sensitive than MR arthrography for labral pathology 1

For Cartilage Evaluation

• Both MRI without IV contrast and MR arthrography receive the highest rating (9/9) for evaluating articular cartilage 1
• High-resolution 3T MRI may improve visualization of the acetabular labrum and hyaline articular cartilage, potentially obviating the need for intra-articular contrast 1
• CT arthrography (rating 8/9) is also highly appropriate for cartilage assessment 1

For Soft Tissue Abnormalities (Tendonitis, Bursitis)

• MRI without IV contrast (rating 9/9) is the primary modality for extra-articular soft tissue pathology 1
• Ultrasound (rating 7/9) is also highly appropriate and can be used for real-time dynamic assessment 1
• IV contrast is rarely needed and does not significantly improve diagnostic accuracy for most soft tissue conditions 1

For Suspected Infection (Septic Arthritis, Osteomyelitis)

• MRI of the pelvis has high sensitivity and specificity for musculoskeletal infection including septic arthritis, osteomyelitis, and pyomyositis 1
• MRI detected osteomyelitis in approximately 50% of children with clinically suspected septic arthritis, and septic arthritis was associated with osteomyelitis in about 70% of cases 1
• Contrast administration does not increase sensitivity or specificity but increases reader confidence and better delineates abscesses 1
• Whole-body MRI may be appropriate when there is suspicion for multifocal osteomyelitis 1

For Acute Trauma with Negative Radiographs

• MRI without IV contrast is the second-line modality (after radiographs) for detecting radiographically occult fractures 1
• At least 90% of proximal femoral fractures are identified on radiographs, so MRI is reserved for cases with negative radiographs but continued clinical suspicion 1
• CT without contrast is less sensitive than MRI but can be used as a problem-solving tool to evaluate occult fractures or better depict fracture morphology 1

For Tumor Evaluation

• MRI without IV contrast should be performed when a tumor is suspected, as it is sensitive for evaluation of bone marrow and soft-tissue extension 1
• Inclusion of the lower thoracic spine and lumbar spine may be performed to identify any abnormality 1

Technical Considerations

Sequence Selection

• Proton density sequences with fat saturation (PDfs) are superior to T1 and T2 sequences for differentiating acetabular from femoral cartilage and the labrum from joint capsule 2
• PDfs sequences allowed differentiation of acetabular from femoral cartilage in 79% of cases versus only 44% for T1 and 40% for T2 sequences 2
• For labral visualization, PDfs sequences identified the labrum in 77% of cases compared to 36% for T1 and 35% for T2 2

Advanced Techniques

• Isotropic three-dimensional (3D) single-acquisition protocols provide submillimeter assessment of bony and labro-cartilaginous structures with superior identification of small labral tears 3
• 3D MRI facilitates reconstruction in arbitrary planes for optimal visualization of structures in their planes of orientation 3
• Radial imaging or radial reconstructions can be used to evaluate the shape of the femoral neck, particularly for femoroacetabular impingement assessment 1, 2

Common Pitfalls to Avoid

• Do not use MRI with and without IV contrast as a routine protocol—it receives lower appropriateness ratings (2-5/9) for most hip indications and adds unnecessary time and cost 1
• Avoid ordering MRI as the initial study for acute trauma—radiographs (AP pelvis with cross-table lateral of affected hip) should always be obtained first 1
• Do not rely on T1 or T2 sequences alone for labral evaluation—they have poor discrimination of intra-articular structures compared to proton density sequences 2
• Be aware that ultrasound has limited utility for intra-articular pathology (rating 1/9 for labral tears) but is excellent for periarticular soft tissue assessment 1