From the Guidelines
No, an MRI of the hip is not the appropriate imaging study to evaluate the sacroiliac (SI) joint, and instead, an MRI specifically of the sacroiliac joints should be ordered. This is based on the most recent evidence from the American College of Radiology, which states that MRI of the sacroiliac joints is the next imaging technique of choice in the evaluation of patients with suspected axial spondyloarthritis (axSpA) after radiography is performed 1.
When evaluating the sacroiliac joint, it is essential to use the correct imaging protocol to ensure optimal visualization of the joint. An MRI of the SI joints typically includes dedicated oblique axial and coronal sequences through the SI joints, with fat-suppression techniques to highlight inflammation, such as short tau inversion recovery (STIR) and T1-weighted images 1.
Some key points to consider when ordering an MRI for SI joint assessment include:
- Specify "MRI sacroiliac joints" rather than "MRI hip" to ensure the correct protocol is used and the radiologist focuses their interpretation on the area of clinical concern.
- The use of fat-suppression techniques, such as STIR, can help identify active inflammatory lesions of the sacroiliac joints, including bone marrow edema, capsulitis, synovitis, and enthesitis 1.
- Chronic structural lesions, such as sclerosis, erosions, fat deposition, and ankylosis, can also be detected with MRI, providing important information for diagnosis and treatment planning 1.
By ordering an MRI specifically of the sacroiliac joints, clinicians can ensure that they receive the most accurate and relevant information for diagnosing and managing conditions affecting the SI joint, such as sacroiliitis, ankylosing spondylitis, or other spondyloarthropathies 1.
From the Research
Evaluation of Sacroiliac Joint using MRI of Hip
- The studies 2, 3, 4, 5 suggest that MRI sequences, including T2-weighted multipoint Dixon, STIR, and T2 SPAIR, can be used to evaluate sacroiliac joints for signs of active and chronic sacroiliitis.
- The T2-weighted multipoint Dixon sequence has been shown to be superior to conventional MRI sequences in depicting diagnostic signs of active and chronic sacroiliitis 2, 4.
- Fat-saturated T2-weighted sequences have been found to be superior in showing active bone marrow lesions, which are a hallmark of active sacroiliitis 5.
- However, there is no direct evidence to suggest that an MRI of the hip is specifically ordered to evaluate the sacroiliac joint, as the studies primarily focus on the evaluation of sacroiliac joints using MRI sequences.
Diagnostic Performance of MRI Sequences
- The diagnostic performance of different MRI sequences, including STIR and T2 SPAIR, has been compared in the evaluation of inflammatory sacroiliitis 3.
- The results suggest that T2-weighted SPAIR sequences may be an advantageous option for the evaluation of sacroiliitis due to better signal-to-noise ratios compared to STIR sequences 3.
- The T2-weighted multipoint Dixon sequence has been found to be superior or comparable to conventional MR sequences in the detection of sacroiliitis, except for ankylosis 4.
Clinical Decision-Making
- The decision to order an MRI of the hip should be based on clinical judgment and the presenting symptoms of the patient, rather than being mandated by health care insurers 6.
- A detailed history, thorough physical examination, imaging studies, and diagnostic injections should all be considered in the decision-making process for hip arthroscopy 6.