Musculoskeletal Imaging

Which Imaging Is Best for a Painful Hip Arthroplasty After Normal Radiographs?

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Which Imaging Is Best for a Painful Hip Arthroplasty After Normal Radiographs?

A 68-year-old patient returns to your clinic six years after a successful total hip arthroplasty (THA), now complaining of new, deep groin pain with weight-bearing. The initial workup is complete: inflammatory markers are normal, ruling out infection, and new radiographs show the implant is stable with no obvious signs of loosening or fracture. The pain persists, and you need to look deeper. This scenario—a symptomatic THA patient with infection excluded and unrevealing radiographs—requires a specific advanced imaging strategy. This article details the clinical workflow for this exact situation, explaining why the American College of Radiology (ACR) rates an MRI of the hip without IV contrast as Usually Appropriate.

Who Fits This Clinical Scenario?

This workflow is designed for a well-defined patient population. It applies specifically to patients with a total hip arthroplasty who present with new or worsening symptoms—such as pain, clicking, or a sense of instability—long after the initial postoperative period. Critically, this guidance is for when infection has been reasonably excluded through clinical evaluation and laboratory testing (e.g., normal C-reactive protein and erythrocyte sedimentation rate). The initial imaging step, plain radiographs, has already been performed and did not reveal a definitive cause for the symptoms.

This pathway is not for:

  • Patients with suspected infection: If there is any clinical or laboratory suspicion for periprosthetic joint infection (fever, warmth, erythema, elevated inflammatory markers), the imaging workup is different. That patient falls under the “infection not excluded” scenario, which prioritizes studies that can evaluate for abscesses or sinus tracts.
  • Patients with acute trauma: A patient who presents with hip pain immediately following a fall or significant injury requires a workup focused on identifying a periprosthetic fracture.
  • Patients with metal-on-metal implants or suspected trunnionosis: These cases have a unique set of concerns related to metal-ion-related adverse local tissue reactions (ALTR) and require a dedicated imaging protocol, often involving specific MRI sequences or specialized CT.

Correctly identifying your patient’s scenario is the crucial first step to ordering the most effective and appropriate imaging study.

What Diagnoses Are You Working Up in This Scenario?

When a patient with a THA develops late-onset pain and infection is ruled out, the differential diagnosis shifts toward mechanical and biological causes of implant failure or soft tissue pathology. Advanced imaging is ordered to investigate these possibilities, which are often invisible on plain radiographs.

The most common cause of late-term THA failure is aseptic loosening. This occurs when the bond between the implant and the bone weakens over time, leading to micromotion and pain. Radiographs can be insensitive to early loosening, and cross-sectional imaging is needed to detect subtle signs like periprosthetic lucency or component migration.

Another key consideration is polyethylene wear and particle disease. The bearing surfaces of the implant wear down over time, shedding microscopic particles. The body’s inflammatory response to these particles can cause osteolysis—the resorption of bone around the implant—which weakens the bone-implant interface and can lead to loosening or even periprosthetic fracture.

Occult periprosthetic fracture is less common but must be considered. A non-displaced fracture line may not be visible on radiographs but can be a significant source of pain. Cross-sectional imaging provides a much more sensitive evaluation of the surrounding bone integrity.

Finally, the source of pain may not be the implant itself but the surrounding soft tissues. Conditions like abductor tendon tears, iliopsoas impingement against the acetabular component, or other forms of soft tissue inflammation can mimic implant-related pain and are best evaluated with imaging that provides high soft-tissue contrast.

Why Is MRI of the Hip Without IV Contrast the Recommended Study?

For the symptomatic post-arthroplasty patient where infection is excluded, the ACR designates MRI of the hip without IV contrast as Usually Appropriate. The primary rationale is its superior ability to evaluate the full spectrum of potential non-infectious pathologies, from bone-implant interface issues to critical soft tissue abnormalities.

Modern MRI protocols incorporate metal artifact reduction sequences (MARS) or similar techniques (e.g., MAVRIC, SEMAC). These specialized sequences are essential, as they minimize the signal distortion caused by the metallic implant, allowing for clear visualization of the adjacent bone and soft tissues. This enables the detection of subtle osteolysis, periprosthetic fluid collections (synovitis), and soft tissue pathologies like gluteal tendinopathy or iliopsoas impingement with high sensitivity.

While MRI is a top choice, it’s important to understand the alternatives and why they may be less suitable for this specific scenario:

  • CT of the hip without IV contrast is also rated Usually Appropriate. It is an excellent alternative, particularly if MRI is contraindicated or unavailable. CT provides superior detail of bone architecture, making it highly effective for quantifying osteolysis, assessing implant position, and detecting subtle fractures. However, it offers significantly less detail of the surrounding soft tissues and involves ionizing radiation (☢☢☢ 1-10 mSv).
  • MRI of the hip without and with IV contrast is rated Usually not appropriate. In this scenario where infection is already excluded, the addition of gadolinium-based contrast agent typically does not add significant diagnostic information. The primary concerns—aseptic loosening, particle disease, and mechanical soft tissue issues—are well-visualized on non-contrast sequences. Adding contrast increases scan time, cost, and introduces the risks associated with gadolinium exposure without a clear benefit.

Ultimately, the choice between MRI and CT may depend on institutional preference, scanner availability, and the specific clinical question. However, for a comprehensive initial evaluation of both bone and soft tissue, non-contrast MRI with MARS is the preferred starting point.

Once you’ve decided on MRI hip without contrast, our protocol guide covers the technique, contrast, and reading principles: MRI Hip Without Contrast.

What’s Next After MRI of the Hip Without Contrast? Downstream Workflow

The results of the MRI will guide the subsequent clinical management. The goal is to move from a non-specific symptom of “hip pain” to a specific diagnosis that can be addressed.

  • If the MRI is positive for aseptic loosening or significant osteolysis: This finding typically warrants a referral back to the orthopedic surgeon. The next step is surgical consultation to discuss the risks and benefits of revision arthroplasty. The imaging helps the surgeon plan the procedure by defining the extent of bone loss and the integrity of the remaining bone stock.
  • If the MRI identifies a clear soft tissue cause (e.g., abductor tendon tear, iliopsoas bursitis): Management may begin with conservative measures such as physical therapy, activity modification, or targeted injections. For severe tears or refractory symptoms, surgical consultation for repair may be necessary.
  • If the MRI is negative or findings are indeterminate: When a high-quality MRI with MARS sequences shows no clear cause for the pain, the hip joint itself may not be the primary pain generator. The next step could be an Image-guided anesthetic injection, a procedure rated as May be appropriate. A successful diagnostic block confirms the hip as the source of pain, even with negative imaging, and may prompt further investigation. If the block provides no relief, the workup should expand to include referred pain sources, most commonly the lumbar spine.

Pitfalls to Avoid (and When to Get Help)

Navigating the workup of a painful THA requires attention to detail to avoid common missteps.

1. Forgetting to specify MARS: Ordering a “routine” hip MRI without specifying metal artifact reduction sequences will likely result in a non-diagnostic study, obscured by artifact. Always include “with MARS” or your institution’s equivalent on the order.
2. Misinterpreting fluid: A small amount of simple fluid in the joint capsule can be a normal finding. Differentiating this from pathologic synovitis or a complex fluid collection indicative of an adverse tissue reaction is key.
3. Anchoring on the hip: If advanced hip imaging is negative, do not stop the workup. Persistent pain in the hip region is frequently referred from the lumbar spine (e.g., radiculopathy) or sacroiliac joint.
4. Ignoring CT’s strengths: While MRI is excellent, do not dismiss CT. If the primary clinical question is the precise quantification of bone loss for pre-operative planning, a non-contrast CT may provide more accurate information than MRI.

If the clinical picture and imaging findings are discordant, or if the diagnosis remains elusive after advanced imaging, consultation with a musculoskeletal radiologist or an orthopedic arthroplasty specialist is the appropriate next step.

Related ACR Topics and Tools

This article focuses on one specific clinical scenario. For a comprehensive overview of all variants related to imaging after total hip arthroplasty, and to understand how this workflow fits into the bigger picture, please see our parent guide.

To explore other clinical scenarios, optimize imaging protocols, or discuss radiation dose with patients, these GigHz tools can help:

Frequently Asked Questions

Why not just order a CT scan, since it is also rated ‘Usually Appropriate’?

A non-contrast CT is an excellent and appropriate choice, particularly for evaluating bone loss (osteolysis) and implant position. However, an MRI with metal artifact reduction sequences (MARS) provides superior evaluation of the surrounding soft tissues, allowing for the simultaneous diagnosis of conditions like abductor tendon tears, bursitis, or iliopsoas impingement, which can also cause hip pain.

Is intravenous contrast ever needed for an MRI in this scenario?

For this specific scenario—where infection has been confidently excluded—IV contrast is rated ‘Usually not appropriate’ by the ACR. It rarely adds diagnostic value for the primary concerns of aseptic loosening, particle disease, or mechanical soft tissue issues. Contrast would only be reconsidered if new clinical information arises that puts infection or a neoplastic process back into the differential diagnosis.

What if my patient has a pacemaker or other contraindication to MRI?

If a patient cannot undergo an MRI, a non-contrast CT of the hip is the best alternative. It is also rated ‘Usually Appropriate’ and is highly effective for assessing the bone-implant interface, component positioning, and identifying occult fractures or osteolysis. Its main limitation is the reduced sensitivity for soft tissue pathology.

What are ‘MARS’ sequences and are they really necessary?

MARS (Metal Artifact Reduction Sequence) and similar techniques are specialized MRI software packages designed to minimize the signal distortion and artifact created by metallic implants. They are absolutely essential for a diagnostic study. A standard MRI of a hip arthroplasty will be severely degraded by artifact, rendering the images uninterpretable for evaluating the tissues immediately surrounding the implant.

My patient’s radiographs look perfect. Why do we need more imaging?

Plain radiographs are crucial for initial assessment but are insensitive to many causes of painful arthroplasty. Early aseptic loosening, polyethylene wear with osteolysis, soft tissue problems like tendinopathy, and even non-displaced periprosthetic fractures can all be invisible on radiographs. Advanced imaging like MRI or CT is required to look beyond the implant’s gross position and assess the subtle biological and mechanical issues at the interface between the implant, bone, and surrounding soft tissues.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026