What is involved in a CT (Computed Tomography) shoulder arthrogram?

CT Shoulder Arthrogram Overview

A CT shoulder arthrogram involves intra-articular injection of iodinated contrast material into the glenohumeral joint under imaging guidance (fluoroscopy or CT), followed by CT scanning to evaluate internal joint structures, particularly the labrum, rotator cuff, and cartilage.

Procedure Components

Pre-Procedure Preparation

• Patient positioning: The patient is typically positioned supine with the shoulder in neutral position 1, 2
• Imaging guidance options: The injection can be performed using conventional fluoroscopy, CT fluoroscopy, or conventional CT guidance 3
• Local anesthesia: May or may not be administered prior to injection, though psychological factors, gender, body mass index, and number of needle redirections predict pain levels more than anesthesia use 4

Contrast Injection Technique

• Injection approach: CT-guided intra-articular injection into the glenohumeral joint 5, 3
• Contrast material: Iodinated contrast agent (such as iobitridol 350) is injected, typically diluted in saline solution 5
• Injection volume: Ranges from 10 to 24 mL depending on joint capacity and patient tolerance 5
• Fluoroscopic confirmation: The articular position of the needle is confirmed before contrast injection 2

CT Scanning Protocol

• Imaging parameters: Typically performed at 120-140 kVp with varying mA settings (100-240 mA) 3
• Patient positioning: Helical CT scans obtained in neutral position, as well as internal and external rotation 5
• Slice thickness: Submillimeter multidetector CT technology provides excellent three-plane resolution 2
• Metal artifact reduction: Special protocols can be used when evaluating patients with shoulder arthroplasty 1

Clinical Applications

Primary Indications

• Evaluation after shoulder arthroplasty: CT arthrography is considered superior to MRI or MR arthrography for evaluating the rotator cuff in patients with previous shoulder arthroplasty 1
• Alternative when MRI contraindicated: Useful for patients who cannot undergo MRI or MR arthrography 1
• Labral lesion detection: Provides comparable sensitivity and possibly improved specificity compared to MR arthrography for detecting labral lesions 1
• Glenoid rim fracture visualization: Offers improved visualization of osseous abnormalities such as glenoid rim fractures 1

Diagnostic Capabilities

• Rotator cuff tears: Can evaluate full-thickness rotator cuff tears and assess cuff integrity around implants 1, 2
• Shoulder instability: Addresses Bankart lesions, Hill-Sachs deformities, and labrocapsular structures 2, 6
• Cartilage lesions: Evaluates articular cartilage abnormalities 2
• Anatomical variants: Identifies normal variants and distinguishes them from pathology 6

Limitations and Considerations

Comparative Disadvantages

• Inferior for partial-thickness rotator cuff tears: CT arthrography is inferior to MR arthrography in assessing partial-thickness rotator cuff tears, particularly bursal-sided tears 1
• Limited soft tissue contrast: Cannot assess extra-articular soft tissues as well as MRI 1
• Radiation exposure: Involves ionizing radiation with effective dose of approximately 2.4 mSv for the complete examination 3
• Invasive procedure: Requires intra-articular injection, which carries small risks of infection and discomfort 6, 4

Appropriateness Ratings

• Generally rated 5 out of 9 ("may be appropriate") by the American College of Radiology when MRI or ultrasound cannot be performed 1
• Not typically appropriate as a first-line study for acute shoulder pain or suspected septic arthritis 1
• Rating of 1 out of 9 ("usually not appropriate") for evaluation of shoulder instability in the acute setting 1

Radiation Considerations

The relative radiation level for CT arthrography shoulder is ჽჽ (moderate), with an adult effective dose estimate range of 0.1-1 mSv for the arthrographic injection portion, plus approximately 2.4 mSv for the diagnostic CT examination 1, 3.