Arthrography

Arthrography is a radiographic, CT or MR study of a joint after contrast is injected into the joint cavity under fluoroscopic, ultrasound or CT control. A fine needle (22 to 25 gauge) is placed in the joint using sterile technique and local anaesthetic, and the position is confirmed with a small test injection of iodinated contrast.

For conventional or CT arthrography, a water soluble, non-ionic contrast is used (single contrast), sometimes with air (double contrast) to outline cartilage and capsule. The volume is joint dependent: shoulder 10 to 15 mL, hip 5 to 10 mL, knee 20 to 40 mL, wrist 2 to 3 mL in each compartment, elbow 5 to 8 mL, ankle 5 to 8 mL.

For MR arthrography, dilute gadolinium (about 1 in 200 dilution, for example 0.1 mL of gadolinium in 20 mL saline and iodinated contrast mix) is injected, and imaging follows within 30 to 60 minutes. Exercise of the joint after injection spreads the contrast. The effective dose of conventional arthrography is low, about 0.1 to 1 mSv, and CT arthrography adds 1 to 4 mSv.

Arthrography was once the main test for internal derangements of joints. MR imaging and ultrasound have replaced it for most indications. Arthrography with MR or CT is still used when higher accuracy is needed: labral and capsular tears of the shoulder and hip, small ligament tears of the wrist, loose bodies, cartilage lesions, and the post-operative knee or shoulder.

It is also used therapeutically (injection of corticosteroid and local anaesthetic, hydrodilatation for adhesive capsulitis) and diagnostically (aspiration of fluid, confirming the needle position before injection).

Indications. Shoulder: labral tears (superior labrum anterior posterior and Bankart lesions), partial and full thickness rotator cuff tears, adhesive capsulitis (capsular volume), post-operative cuff or labral repair. Hip: acetabular labral tears, femoroacetabular impingement, chondral lesions, and loose bodies.

Wrist: triangular fibrocartilage complex tears, scapholunate and lunotriquetral ligament tears. Knee: meniscal tears in the post-operative knee, osteochondral lesions, and loose bodies (when MR is unsuitable). Elbow: loose bodies, osteochondritis dissecans, and collateral ligaments. Ankle: osteochondral lesions and ligament tears.

Prosthetic joint: loosening (a contrast leak around the prosthesis) and infection (aspiration for culture). Paediatric hip: developmental dysplasia (in the operating room). Joint injection for pain and anaesthetic response. Not in the presence of infection of the joint or skin.

Contraindications and precautions. Infection of the skin or joint at the injection site, or suspected septic arthritis (aspirate only, no contrast). Allergy to iodinated contrast or gadolinium (the intra-articular dose is small, but reactions occur; a different agent or a saline only technique may be used).

Coagulopathy and anticoagulation (joint injection is usually safe in therapeutic anticoagulation with an international normalised ratio under 3, but local rules apply). Pregnancy: avoid, especially for CT arthrography and gadolinium. Previous joint replacement or recent surgery (risk of infection). MR contraindications apply for MR arthrography (pacemakers, aneurysm clips, metal in the eye).

Warn the patient about pain, swelling and a feeling of fullness for 1 to 2 days after injection, and a risk of infection (about 1 in 10 000 to 1 in 50 000), bleeding and allergic reaction.

Preparation and technique. The skin over the joint is cleaned and anaesthetised. The needle is advanced under fluoroscopy or ultrasound into the joint (for example the glenohumeral joint through the rotator interval or anteriorly through the subscapularis, and the hip joint at the femoral neck). The position is checked by a drop of contrast that flows away freely from the needle tip.

Aspirated joint fluid may be sent for tests. The joint is filled, then moved to spread the contrast. Radiographs, CT or MR follow in the right planes: for MR, abduction and external rotation (ABER) views of the shoulder improve labral tear detection. Exercise after injection spreads the contrast, but MR must be done within 1 to 2 hours before the contrast is absorbed.

Normal appearances. The joint cavity fills evenly with a thin layer of contrast outlining the articular cartilage, the capsule, and the synovial recesses; the capsule is smooth with no extravasation.

Shoulder: the joint capsule holds 15 to 30 mL, with the axillary recess, the subscapularis recess, the biceps tendon sheath, and a smooth anterior and posterior labrum with a triangular shape. The labrum is thin and sharply defined, and the glenoid cartilage a thin white line.

Hip: the capsule holds 10 to 15 mL, the labrum appears as a triangular low signal structure around the acetabular rim, and the zona orbicularis surrounds the femoral neck. Wrist: radiocarpal, midcarpal and distal radioulnar compartments do not communicate in a normal wrist in young adults, so contrast stays within the compartment injected.

Knee: the suprapatellar bursa, the menisci and the cruciate ligaments show as filling defects in the contrast.

Interpretation.

• Rotator cuff tears: contrast passes from the glenohumeral joint into the subacromial subdeltoid bursa through a full thickness tear; partial articular surface tears show contrast entering the tendon without crossing it. The size of the tear, the tendon retraction, and fatty atrophy are assessed on MR or CT.
• Labral tears: contrast tracks into a tear in the labrum (a line of contrast under or through the labrum, detachment from the glenoid rim, a paralabral cyst), including superior labrum tears, anterior inferior labral tears (Bankart), and Hill-Sachs lesions of the humeral head.
• Hip labral tears show a line of contrast in the labrum or at the labral chondral junction, and cam and pincer deformities of impingement.
• Adhesive capsulitis: a small joint volume (under 10 mL), loss of the axillary recess, capsular thickening, and pain on filling; hydrodilatation can distend the capsule as treatment.
• Cartilage lesions: contrast fills a fissure or a defect in the cartilage, a delamination at the chondral bone junction, and thinning of the cartilage.
• Loose bodies: filling defects in the contrast within the joint (recesses, posterior knee, olecranon fossa), which may be calcified and are better seen on CT.
• Ligament tears of the wrist: contrast passes through a defect in the scapholunate or lunotriquetral ligament, or the triangular fibrocartilage complex, from one compartment into another (the radiocarpal into the midcarpal, or into the distal radioulnar joint).
• This occurs also with degenerative perforations in older people, so clinical correlation is needed.
• Synovial disease: villonodular synovitis (nodular synovial filling defects), synovial chondromatosis (multiple loose bodies), and synovial cysts (Baker cyst, which fills from the knee joint with contrast, with rupture seen as a leak into the calf).
• Prosthesis loosening: contrast flows along the bone cement or implant bone interface, indicating loosening, and extravasation outside the joint.
• Ankle and elbow: osteochondral fragments, capsular tears, and ligament injuries.
• Paediatric hip: dysplasia (a hypertrophic ligamentum teres, the limbus, and a pulvinar interposed to block reduction) assessed under anaesthesia.
• Extravasation: contrast leaking outside the capsule (a tear of the capsule or a cuff tear), which is also seen when the needle is outside the joint.

Critical values and findings needing immediate action.

• Septic arthritis (fever, hot swollen joint, purulent fluid on aspiration): stop contrast, send fluid for microscopy and culture, start antibiotics and arrange urgent drainage.
• Anaphylaxis to contrast: stop, adrenaline, oxygen, fluids and resuscitation.
• Joint infection after injection (increasing pain, swelling and fever within days): urgent aspiration, culture and orthopaedic review.
• Large full thickness tear with a locked joint (locked knee from a displaced meniscal tear or loose body): orthopaedic referral for urgent arthroscopy.
• Unstable fracture or avascular necrosis found (for example, collapse of the femoral head): orthopaedic referral.
• Suspected tumour or synovial sarcoma: MR, biopsy and oncology referral.

Limitations and artefacts.

• Arthrography is invasive: pain (common, usually mild), temporary swelling, vasovagal reactions, joint infection (very rare), bleeding, nerve injury, allergic reaction to contrast or gadolinium, and radiation exposure. An unexpected extra-articular injection gives false findings.
• Incomplete filling of the joint, inadequate distension, or air bubbles cause false results; air bubbles mimic loose bodies on CT and MR. Contrast spreading outside the joint after a long delay degrades the image.
• Imaging should be done soon after injection (within 30 to 60 minutes for MR), as contrast is absorbed and signal changes; delays reduce quality.
• Normal variants mimic tears: a sublabral foramen or recess, a Buford complex in the shoulder, a synovial recess at the hip labrum, perilabral sulcus, and a central perforation of the triangular fibrocartilage in older people.
• Conventional arthrography shows the surface of structures, so tears within the substance of the cartilage or tendon are missed (MR shows these).
• MR arthrography is preferred to direct MR in selected cases only (labral tears of the shoulder and hip, cartilage in the young patient), and for most cases, indirect MR without injection is accurate enough, avoids injection, and shows more of the joint.
• Gadolinium use in the joint is off label in some settings, and the dose is very small; the local rule applies.
• Contrast injection into the wrong compartment or a communicating wrist compartment affects interpretation.

Special groups.

• Young athletes: shoulder and hip labral tears and instability are the main indication for MR arthrography.
• Older adults: rotator cuff tears are common (30 to 50% in people over 60) and many are asymptomatic, so findings are matched with symptoms.
• Children: sedation or anaesthesia is needed, and MR or ultrasound is preferred; hip arthrography is used in the operating room for dysplasia and for septic arthritis treatment.
• Patients with joint replacement: aspiration to exclude infection is the main use; contrast is injected only if infection is excluded.
• Patients with haemophilia or on anticoagulation: factor cover or temporary change in treatment as directed by the haematologist.
• Pregnancy: avoid.
• Regions: septic arthritis, tuberculous arthritis and delayed presentation of trauma are common; arthrography with plain radiographs and a simple fluoroscope may still be used for labral and cuff tears where MR is unavailable.

Follow up tests.

• MR (with or without arthrography) or CT arthrography.
• Ultrasound of the joint and tendons.
• Plain radiographs.
• Joint aspiration with cell count, crystals, Gram stain and culture.
• Erythrocyte sedimentation rate, C-reactive protein, full blood count, uric acid.
• Rheumatoid factor and anticyclic citrullinated peptide antibodies.
• Tuberculosis tests.
• Arthroscopy for diagnosis and treatment.
• Referral to orthopaedics, sports medicine or rheumatology.