What is the procedure for a CT (computed tomography) arthrogram of the right (RT) knee?

CT Arthrogram of the Right Knee: Procedure and Protocol

A CT arthrogram of the right knee involves injection of contrast material into the knee joint followed by CT imaging to evaluate internal structures, particularly when assessing meniscal tears, articular cartilage damage, and loose bodies. 1

Indications

• Evaluation of internal knee derangement when MRI is contraindicated or unavailable
• Assessment of meniscal and articular cartilage abnormalities
• Detection of loose bodies within the joint
• Evaluation of post-surgical knees where metal hardware limits MRI utility
• Assessment of osteochondral lesions

Procedure Steps

1. Pre-procedure Assessment

   • Review patient history and prior imaging
   • Verify absence of contraindications (active infection, severe contrast allergy)
   • Obtain informed consent

2. Patient Positioning and Preparation

   • Patient lies supine on the CT table
   • The right knee is positioned in slight flexion (10-15 degrees)
   • The area is cleaned with antiseptic solution
   • Sterile draping is applied around the knee

3. Contrast Administration

   • Local anesthetic is administered to the skin and soft tissues
   • A 20-22 gauge needle is inserted into the knee joint using sterile technique
   • Joint fluid may be aspirated if an effusion is present
   • Intra-articular position is confirmed
   • Iodinated contrast material (typically OMNIPAQUE 240,300, or 350) is injected 2
   • Typical volume ranges from 5-15 mL depending on joint capacity

4. CT Imaging Protocol

   • Patient is transferred to CT scanner immediately after injection
   • Thin-slice axial images (≤1 mm) are acquired through the entire knee
   • Multiplanar reformations are created in sagittal and coronal planes
   • 3D reconstructions may be performed if needed

Technical Considerations

• Contrast Selection: Iohexol (OMNIPAQUE) is commonly used, with concentrations of 240-350 mg iodine/mL 2
• Radiation Dose: Protocols are optimized to use the lowest radiation dose necessary while maintaining diagnostic quality 3
• Image Acquisition: Thin-slice acquisition with multiplanar reformations provides optimal visualization of intra-articular structures

Advantages and Limitations

Advantages

• Superior to conventional radiographs for detection and classification of fractures 1
• High specificity (100%) for detecting ligament tears when present 1
• Excellent for evaluating menisci and articular cartilage with reported sensitivities and specificities ranging from 86% to 100% 1
• Better visualization of bony structures compared to MRI
• Can be used when MRI is contraindicated (pacemakers, certain implants)

Limitations

• Involves radiation exposure
• Less sensitive than MRI for bone marrow abnormalities and soft tissue injuries 1
• Invasive procedure with small risk of infection or allergic reaction to contrast

Post-procedure Care

• Patient may experience mild discomfort for 24-48 hours
• Light activity is recommended for 24 hours
• Patient should report signs of infection (increasing pain, redness, swelling, fever)
• Follow-up as clinically indicated

Common Pitfalls to Avoid

• Inadequate joint distension: Insufficient contrast volume can limit visualization of intra-articular structures
• Delayed imaging: Imaging should be performed immediately after contrast injection to prevent contrast resorption
• Improper needle placement: Extraarticular injection will result in non-diagnostic examination
• Overlooking contraindications: Active infection or severe contrast allergy are contraindications

CT arthrography remains a valuable diagnostic tool, particularly when MRI is contraindicated or for specific clinical scenarios requiring detailed evaluation of intra-articular structures with excellent bony detail.