Can a patient with right humerus (upper arm bone) hardware have a Magnetic Resonance Imaging (MRI) of the left hip to evaluate for a piriformis injury or should a Computed Tomography (CT) scan be used instead?

MRI is Appropriate for Evaluating Piriformis Injury in a Patient with Right Humerus Hardware

MRI of the left hip is appropriate for evaluating piriformis injury in a patient with right humerus hardware, as the distant location of the metallic implant will not interfere with image quality.

Rationale for Using MRI for Piriformis Injury

• MRI is the preferred imaging modality for evaluating soft tissue injuries around the hip, including piriformis syndrome, due to its superior soft tissue contrast and ability to detect muscle and nerve abnormalities 1.
• MRI has demonstrated high sensitivity and specificity in detecting muscle and tendon injuries around the hip joint, making it ideal for evaluating piriformis pathology 1.
• The piriformis muscle is best visualized on MRI, which can show muscle enlargement, inflammation, or anatomic variants that may compress the sciatic nerve 2, 3.

Why CT is Not the First Choice

• CT is primarily useful for evaluating bony structures rather than soft tissue injuries and has limited value in diagnosing piriformis syndrome 1.
• While CT may be useful for characterizing fractures or bony abnormalities, it has inferior soft tissue contrast compared to MRI for evaluating muscle pathology 1.
• CT would be indicated primarily if there were concerns about acetabular fractures or intra-articular fragments, which are not typically associated with piriformis syndrome 1.

Metal Hardware Considerations

• The presence of right humerus hardware should not significantly affect imaging of the left hip due to the substantial distance between these anatomical regions 1.
• Metal artifact from distant hardware (right humerus) will not extend to or interfere with imaging of the left hip 1.
• Modern MRI techniques can further reduce any potential metal artifacts when necessary, though this is unlikely to be a concern given the anatomical separation 1.

Diagnostic Approach to Piriformis Syndrome

• Piriformis syndrome is a non-discogenic cause of sciatica resulting from compression of the sciatic nerve by the piriformis muscle 4, 5.
• Clinical symptoms typically include buttock pain, sciatica, and worsening pain with sitting 4.
• MRI can detect specific findings associated with piriformis syndrome, including:
  • Enlargement of the piriformis muscle 2, 3
  • Anterior displacement of the sciatic nerve 2
  • Signal changes within the muscle suggesting inflammation or edema 3

Advanced MRI Techniques for Piriformis Evaluation

• Diffusion tensor imaging (DTI) and tractography can provide additional assessment of sciatic nerve injury in piriformis syndrome by visualizing nerve integrity and quantifying nerve damage 3.
• These advanced MRI techniques can measure fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values to objectively evaluate sciatic nerve compromise 3.

Conclusion for Clinical Practice

• Begin with standard hip radiographs to rule out obvious bony abnormalities 1.
• Proceed with non-contrast MRI of the left hip as the definitive imaging study for suspected piriformis injury 1.
• The right humerus hardware will not interfere with left hip imaging due to the distance between these anatomical regions 1.