Is a CT (Computed Tomography) scan a suitable alternative to an MRI (Magnetic Resonance Imaging) for evaluating the left shoulder in a patient with screws in the joint?

CT as Alternative to MRI for Shoulder Evaluation with Hardware

Yes, CT is an acceptable alternative when MRI cannot be performed due to metallic hardware, though it has significant limitations in evaluating soft tissue pathology. 1

When CT is Appropriate

CT should be reserved for patients with contraindications to MRI or when MRI assessment is limited by artifact from hardware. 1 The ACR guidelines specifically state that noncontrast CT is appropriate when MRI cannot adequately assess the shoulder due to susceptibility artifacts from previously placed proximal humeral hardware. 1

CT's Strengths

• Excellent for bone evaluation: CT provides superior assessment of fracture patterns, glenoid bone loss, and humeral head bone defects (Hill-Sachs lesions) with high spatial resolution 1
• Characterizes complex fractures: CT is the best modality for identifying and characterizing scapular fracture patterns, intra-articular extension, and angulation 1
• Three-dimensional reconstruction: 3D reformatted CT images better visualize fracture displacement and angulation 1

Critical Limitations of CT

CT cannot assess soft tissue structures that are frequently the source of shoulder pain and dysfunction. 1

What CT Misses

• Rotator cuff pathology: CT cannot evaluate rotator cuff tears, which are common in shoulder pain patients, especially older adults 1
• Labral injuries: CT is unable to assess labroligamentous complex injuries (Bankart lesions) without arthrography 1
• Cartilage damage: CT is limited in assessing cartilaginous Hill-Sachs lesions 1
• Capsular and ligament tears: CT cannot evaluate extra-articular soft tissue traumatic pathology 1

Consider CT Arthrography as Upgrade

If soft tissue evaluation is needed and MRI remains contraindicated, CT arthrography is a reasonable alternative. 1

• CT arthrography shows comparable sensitivity to MR arthrography for detecting labral lesions and provides improved visualization of osseous abnormalities like glenoid rim fractures 1
• However, CT arthrography remains inferior to MR arthrography for assessing partial-thickness rotator cuff tears 1
• CT arthrography involves intra-articular contrast injection and radiation exposure 1

Alternative: Ultrasound for Soft Tissues

In specific scenarios with hardware artifacts limiting MRI, ultrasound may be preferred over CT for evaluating rotator cuff pathology. 1

• Ultrasound can assess rotator cuff tears and biceps tendon pathology without radiation 1, 2
• Ultrasound is operator-dependent and limited for intra-articular structures like labral tears 1

Clinical Decision Algorithm

1. If primary concern is bone (fracture, bone loss, hardware loosening): Proceed with noncontrast CT 1

2. If primary concern is soft tissue (rotator cuff, labrum, instability):

   • First attempt: Consider ultrasound for rotator cuff evaluation 1
   • If intra-articular pathology suspected: CT arthrography 1

3. If comprehensive evaluation needed: CT arthrography provides best compromise, though still inferior to MRI for soft tissues 1

Important Caveat

The presence of screws does not automatically preclude MRI. Modern orthopedic hardware is typically MRI-compatible, though it may cause local artifact. 1 Verify with the manufacturer specifications and radiology department whether MRI can be performed safely with reduced artifact sequences before defaulting to CT.