Why was a computed tomography (CT) scan of the right pelvis ordered after a negative X-ray in a patient complaining of right hip pain?

From the Guidelines

A CT scan of the right pelvis was ordered after a negative X-ray because CT imaging provides more detailed visualization of bone and soft tissue structures that may not be visible on plain radiographs, as recommended by the most recent guidelines 1. This decision is based on the understanding that X-rays have limited sensitivity for detecting certain fractures, especially those that are non-displaced or in complex anatomical regions like the pelvis and hip. In patients with persistent hip pain despite negative X-rays, a CT scan can reveal occult fractures (particularly in the femoral neck or acetabulum), stress fractures, bone contusions, or early degenerative changes.

Some key points to consider in this decision include:

• The importance of early detection of fractures or other conditions that could explain the patient's symptoms, as delayed diagnosis can lead to complications such as avascular necrosis or fracture displacement that could necessitate more invasive interventions.
• The value of CT scans in evaluating surrounding soft tissues, potentially identifying conditions like muscle tears, hematomas, or bursitis.
• The recommendation from the American College of Radiology that MRI pelvis and affected hip without IV contrast or CT pelvis and hips without IV contrast is usually appropriate as the next imaging study for the evaluation of acute hip pain from a fall or minor trauma with negative radiographs and suspected fracture 1.
• The acknowledgement that while CT has advantages over MRI in terms of speed and use in patients with significant confusion, MRI may be more sensitive for detecting certain fractures and soft-tissue abnormalities, as noted in studies comparing the two modalities 1.

However, given the most recent and highest quality evidence, the use of CT scan after a negative X-ray is supported for its ability to provide detailed visualization of the pelvis and hip, aiding in the diagnosis of occult fractures or other conditions that may not be visible on plain radiographs 1.

From the Research

Reasons for Ordering a CT Scan After a Negative X-Ray

• The attending physician may have ordered a CT scan of the right pelvis after a negative X-ray due to the high clinical suspicion of a pelvic injury, despite the negative X-ray result 2.
• CT scans are more sensitive than X-rays in detecting certain types of pelvic injuries, such as fractures of the posterior pelvic ring 3, 4.
• The patient's complaint of right hip pain may have prompted the physician to order a CT scan to rule out other potential causes of pain, such as osteonecrosis or fractures that may not be visible on X-ray 5.

Limitations of X-Ray and CT Scan

• X-rays may not detect all types of pelvic injuries, particularly those in the posterior pelvic ring 3, 4.
• CT scans may also have limitations, such as missing significant pelvic injuries if a pelvic compression device is in place 2.
• The sensitivity of CT scans in detecting pelvic injuries can be affected by various factors, including the type of scanner used and the quality of the images obtained 3.

Clinical Judgment and Decision-Making

• The attending physician's decision to order a CT scan after a negative X-ray was likely based on their clinical judgment and evaluation of the patient's symptoms and medical history 6.
• The use of CT scans in conjunction with X-rays and clinical examination can help improve the detection and diagnosis of pelvic injuries 3, 6, 4.