Residency · Residency · Interventional Radiology

Musculoskeletal Interventions: Joint Injections and Aspirations

Introduction

Image-guided musculoskeletal interventions are an expanding area of interventional radiology practice. Joint injections and aspirations performed under fluoroscopic, ultrasound, or CT guidance offer precise needle placement, improved diagnostic accuracy, and enhanced therapeutic outcomes compared to blind landmark-based techniques.

Imaging Modalities for Guidance

Fluoroscopy

Traditional modality for joint injections; provides excellent bony landmark visualization. Arthrography with iodinated contrast confirms intra-articular needle placement. Limitations: ionizing radiation, limited soft tissue visualization.

Ultrasound

Increasingly preferred for superficial joints and periarticular structures. Real-time visualization of the needle, soft tissues, tendons, and effusions. No ionizing radiation; portable; lower cost. Limited utility for deep joints (e.g., hip in obese patients) or complex bony anatomy.

CT Guidance

Reserved for deep or difficult-to-access structures (e.g., sacroiliac joint, facet joints, hip in obese patients). Superior spatial resolution but higher radiation dose and procedural time.

Joint Aspiration

Indications

Suspected septic arthritis: urgent aspiration for Gram stain, culture, cell count, and crystal analysis. Symptomatic effusion: therapeutic drainage for pain relief and improved mobility. Crystal arthropathy workup: identification of monosodium urate (gout) or calcium pyrophosphate (pseudogout) crystals. Hemarthrosis: evaluation after trauma or in patients on anticoagulation.

Technique

Sterile preparation of the skin overlying the joint. Image-guided needle placement (18-22 gauge depending on joint size and fluid viscosity). Aspirate as much fluid as possible; send for: Cell count and differential. Gram stain and culture (aerobic and anaerobic). Crystal analysis under polarized light microscopy. Glucose and protein if infection is suspected.

Interpretation of Synovial Fluid

Therapeutic Joint Injections

Corticosteroid Injections

Indications: osteoarthritis, inflammatory arthritis, adhesive capsulitis, bursitis, tendinopathy. Common agents: triamcinolone acetonide (40 mg for large joints, 20 mg for small joints) or betamethasone. Mixed with local anesthetic (1% lidocaine or 0.25% bupivacaine) for immediate pain relief. Duration of relief: typically 4-12 weeks; may be repeated but limit to 3-4 injections per joint per year. Potential complications: post-injection flare (1-2%), skin atrophy, tendon weakening, transient hyperglycemia in diabetics.

Hyaluronic Acid (Viscosupplementation)

FDA-approved for knee osteoarthritis. Series of 3-5 weekly injections or single high-molecular-weight injection. Mechanism: restores viscoelastic properties of synovial fluid. Efficacy debated; may provide 6 months of symptom improvement in select patients.

Platelet-Rich Plasma (PRP)

Autologous concentrated platelets containing growth factors. Emerging evidence for tendinopathy, early osteoarthritis, and ligament injuries. Not yet covered by most insurance; limited high-quality evidence.

Specific Joint Techniques

Shoulder

Glenohumeral joint: posterior or anterior approach under US or fluoroscopy. Subacromial-subdeltoid bursa: lateral approach under US; for impingement syndrome. Acromioclavicular joint: direct superior approach; small joint volume (1-2 mL).

Hip

Fluoroscopic or US-guided anterior approach targeting the femoral head-neck junction. Confirm intra-articular position with contrast injection under fluoroscopy. Avoid the femoral neurovascular bundle (lateral to medial: nerve, artery, vein).

Knee

Suprapatellar or lateral parapatellar approach under US guidance. Large joint allows 5-10 mL injection volume. Easily accessible for aspiration of even small effusions under US.

Sacroiliac Joint

CT or fluoroscopic guidance; target the inferior third of the synovial portion of the joint. Small joint capacity (1-2 mL); avoid overfilling. Used for diagnosis and treatment of sacroiliitis.

Spine Interventions

Facet Joint Injections

Indications: facet-mediated axial back or neck pain. Fluoroscopic or CT guidance targeting the facet joint space or medial branch nerves. Diagnostic blocks with local anesthetic help confirm the pain source before radiofrequency ablation.

Epidural Steroid Injections

Interlaminar, transforaminal, or caudal approaches. Fluoroscopic guidance with contrast injection to confirm epidural spread. Treat radiculopathy from disc herniation or spinal stenosis.

Complications

Infection: rare (less than 0.1%); strict sterile technique essential. Bleeding: usually minor; caution in anticoagulated patients. Post-injection flare: transient worsening of pain for 24-48 hours. Tendon rupture: associated with repeated peritendinous corticosteroid injections. Vasovagal reaction: most common systemic complication. Nerve injury: rare; more relevant in spine procedures.

Key Clinical Pearls

When septic arthritis is suspected, aspiration should not be delayed for imaging; even bedside aspiration is appropriate in emergencies, with image-guided aspiration for deep joints like the hip. Image guidance significantly improves accuracy of needle placement compared to blind techniques, particularly for the hip, shoulder, and small joints. Avoid corticosteroid injection within 3 months of planned joint replacement surgery due to increased infection risk. Always confirm intra-articular needle position with contrast or US visualization before injecting therapeutic agents.

References

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For the intern

When called at 3am about a joint issue, your priority is suspected septic arthritis—this needs immediate aspiration for Gram stain, culture, and cell count (white blood cell [WBC] count greater than 50,000/mm3 with polymorphonuclear neutrophils [PMN] greater than 75% suggests infection). Even bedside aspiration is appropriate for accessible joints like the knee; image-guided aspiration can wait until morning for deep joints like the hip unless the patient is septic. Therapeutic injections for osteoarthritis or chronic pain are never urgent and should be scheduled electively. If a patient develops severe pain, swelling, or fever within days of a recent joint injection, think infection and aspirate urgently. Post-injection flare (mild pain for 24-48 hours) is common and managed with ice and analgesics—not an emergency.

Common pitfalls

• Missing septic arthritis: A cloudy, purulent joint effusion requires immediate aspiration and broad-spectrum antibiotics. Don't wait for imaging or radiology availability for superficial joints.
• Injecting corticosteroids into infected joints: Always aspirate and analyze fluid before injecting therapeutics if any concern for infection exists. Steroids worsen septic arthritis.
• Forgetting anticoagulation status: While minor bleeding is usually manageable, check international normalized ratio (INR) and platelet count before deep joint procedures. Most therapeutic anticoagulation can continue for simple aspirations.
• Overfilling small joints: The acromioclavicular and sacroiliac joints hold only 1-2 mL. Excessive volume causes capsular rupture and poor outcomes.

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