Orthopaedic Surgery - Knee Injection

Basics

Knee aspiration and intra-articular injection are commonly performed for both diagnostic and therapeutic purposes.

Aspiration removes fluid from the knee joint, whereas injection introduces medication or another solution into the joint.

Indications for Knee Injection

Injection may be performed for:

Delivery of medication for treatment of knee pain or inflammation

Administration of local anesthetic to facilitate diagnostic examination

Selected diagnostic procedures involving intra-articular fluid administration

Historically, saline load testing was used to evaluate whether a traumatic periarticular wound communicated with the knee joint, although other imaging-based approaches may also be used depending on the clinical setting.

Indications for Knee Aspiration

Arthrocentesis may be indicated for:

Large symptomatic effusion

Large hemarthrosis

Evaluation for septic arthritis

Investigation of inflammatory synovitis or arthritis

Aspiration may also relieve pain and improve motion when a tense effusion is present.

Equipment

Typical equipment includes:

Antiseptic skin-preparation solution

Sterile gloves

Large-bore needle, commonly approximately 18 gauge

20–60 mL syringes

Additional supplies may include:

Sterile drapes, local anesthetic, dressings, specimen containers, and ultrasound equipment when needed.

Technique

Several approaches to the knee joint are possible.

The superolateral approach is particularly reliable for aspiration of a large effusion.

Patient Position

Place the patient supine with the knee fully extended.

The quadriceps should be relaxed to facilitate access to the suprapatellar pouch.

Sterile Preparation

Perform a wide sterile preparation of the knee.

A broad preparation is useful because manipulation of the patella or knee may be required during the procedure.

Superolateral Entry Site

Identify a point approximately:

1 cm proximal to the superior pole of the patella and 1 cm lateral to its lateral border.

This provides access to the suprapatellar pouch.

Needle Insertion

Advance the needle through the:

Skin, subcutaneous tissues, and lateral retinaculum

toward the suprapatellar pouch between the quadriceps tendon and distal femur.

Once the needle enters the joint, apply gentle suction with the syringe.

Aspiration

Withdraw as much joint fluid as required.

The aspirated fluid should be inspected for:

Color, clarity, viscosity, turbidity, and the presence of blood or purulence.

Large Effusions

If the syringe becomes full before the joint has been adequately decompressed, the syringe can be exchanged while the needle remains within the joint.

A clamp or other sterile stabilization method can be used to prevent movement of the needle during syringe exchange.

Aspiration continues until sufficient fluid has been removed.

Completion of Aspiration

After aspiration is complete:

Remove the needle and apply a sterile dressing or adhesive bandage.

When clinically indicated, synovial fluid should be sent promptly for laboratory analysis.

Synovial Fluid Analysis

Depending on the clinical question, studies may include:

Cell count with differential, Gram stain, bacterial culture, crystal analysis, and other targeted tests.

When septic arthritis is suspected, specimens should be obtained before intra-articular corticosteroid administration.

Therapeutic Injection After Aspiration

If an intra-articular medication is to be administered, the aspiration syringe may be exchanged for the medication syringe while maintaining sterile needle position.

The medication should enter the joint with minimal resistance when the needle is correctly positioned.

Marked resistance should prompt reassessment of needle position rather than forceful injection.

Technical Pearls

Wide Sterile Preparation

Preparing a large area allows the examiner to manipulate the patella or reposition the knee without contaminating the sterile field.

Large-Bore Needle

Synovium, fibrin, or clotted blood may obstruct a smaller needle.

An 18-gauge needle is often useful when aspirating thick fluid or hemarthrosis.

Local Anesthesia

Pain at the puncture site can be reduced with:

A small amount of infiltrated lidocaine or a topical vapocoolant such as ethyl chloride.

Ultrasound Guidance

Ultrasound can improve confidence in needle placement and may be especially helpful in:

Obese patients, small or loculated effusions, distorted anatomy, or previously unsuccessful aspiration attempts.

It also allows visualization of the effusion and surrounding soft tissues.

Contraindication: Overlying Cellulitis

A knee should not be aspirated or injected through infected or cellulitic skin because the needle may introduce organisms into the joint.

An alternative entry site or another diagnostic strategy should be used.

Medications

Lidocaine

Lidocaine may be used as a local or intra-articular anesthetic.

Diagnostic anesthetic injection can temporarily decrease pain and permit a more complete knee examination.

Lidocaine may also be combined with corticosteroid to reduce injection discomfort.

Bupivacaine

Bupivacaine provides a longer duration of local anesthesia than lidocaine.

However, concerns exist regarding dose-dependent chondrotoxicity, particularly with prolonged or continuous intra-articular exposure.

For this reason, intra-articular local anesthetics should be used judiciously.

Corticosteroid

Intra-articular corticosteroid may provide temporary relief of inflammatory knee pain.

It is essential to exclude joint infection before administration.

Typical Preparation

A commonly used preparation is triamcinolone acetonide, historically given as approximately:

40 mg, or 1 mL of a 40 mg/mL preparation, depending on the indication and clinical protocol.

It may be combined with a small amount of local anesthetic.

Corticosteroid Adverse Effects

The most common short-term adverse event is a post-injection flare, consisting of temporary worsening of pain and inflammation after the procedure.

Patients should be warned about this possibility.

Other potential complications include:

Skin depigmentation, subcutaneous fat atrophy, transient hyperglycemia, infection, and, with repeated exposure, concern for cartilage effects.

Hyaluronic Acid

Hyaluronic acid injections have been used for symptomatic treatment of mild to moderate knee osteoarthritis.

Potential benefits include:

Reduction in pain, decreased stiffness, and improvement in function in selected patients.

The magnitude and consistency of benefit vary among patients and products.

Administration

Hyaluronic acid may be given as:

A single injection or as a series of injections, depending on the preparation used.

Complications

Potential complications of knee aspiration or injection include:

Pain, bleeding, hemarthrosis, infection, vasovagal reaction, damage to adjacent structures, post-injection flare, and failure to enter the joint.

Sterile technique and careful anatomic localization reduce these risks.

Patient Monitoring

After injection or aspiration, the patient should be instructed to monitor for:

Increasing pain, progressive swelling, erythema, fever, drainage, or inability to bear weight.

These findings may indicate infection or another significant complication and warrant prompt reassessment.

Patients receiving therapeutic injections should also be counseled regarding the expected duration of symptom relief and the need for further evaluation if symptoms persist or recur.