How to perform a knee joint injection
Source
Surgeon:
Joonas Rautavaara (rheumatologist)
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Summary
Focus: Safe knee joint puncture for synovial fluid aspiration and/or local therapeutic injection.
Key elements: Supine positioning with the knee extended, superior lateral patellar landmarking, synovial fluid aspiration, sample analysis when indicated, and intra-articular injection against low resistance.
Indications and Clinical Context
Step-by-Step Technique
Preparations and patient positioning
The patient is in a supine position with knee extended and the skin of the legs exposed.
Select the equipment:
syringes
needle: blue 23G, green 21G or pink 18G
any medicinal agent to be injected, according to the indication
For large joints, preferably
Methylprednisolone 40 mg/ml, for example 80 mg (2 ml) or
Triamcinolone 20 mg/ml, for example 20 mg (1 ml)
Dilution of glucocorticoids with saline, or with local anesthetic is advisable when injecting into large joints as dilution has been found to reduce the tendency to pain after the injection. A diluted glucocorticoid is also distributed more evenly in the joint.
For the knee joint, the dilution ratio for glucocorticoids can be 1:2-4, for example. Fixed combinations of glucocorticoid with an anesthetic can also be used.
Landmarks and injection site
Palpate the superior lateral edge of the patella. A good injection site is about 0.5 cm below it in the AP direction.
Mark the injection site.
Clean the skin area.
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Injection
Advance from the marked injection site through the skin with the needle horizontally.
Aspiration of the synovial fluid is best done at a depth of approximately 2 cm.
Synovial fluid analysis
The turbidity and color of the synovial fluid can be assessed visually. Fairly clear synovial fluid with visible graduation scale is a sign of no pronounced infection. Cloudy synovial fluid is caused by large number of white blood cells making the graduation scale invisible.
In unexplained fluid accumulation, take a specimen if possible.
Cell count + crystal analysis and bacterial culture to be ordered
If antibiotic therapy has already been started and there is strong suspicion of septic arthritis, bacterial nucleic acid detection to be ordered
If Lyme disease-induced arthropathy is suspected, Borrelia nucleic acid detection to be ordered
You can also take a swab sample for bacterial culture if the synovial fluid yield is small.
Injecting the medicinal agent if indicated
After evacuation of the knee joint you can use the same needle for the intra-articular injection as indicated up to the point of low resistance.
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Piftalls and Complications
Pitfalls
Wrong injection site
Before intra-articular injection of the medicinal agent make sure the needle is in the synovial cavity or synovial recess by synovial fluid aspiration.
Challenges with sample aspiration
If the synovial capsule is thickened, the villous synovial proliferations/synovial debris may block the needle during aspiration of synovial fluid. The stronger the aspiration and the larger the syringe, the greater the risk. Try changing to a smaller syringe. Try clearing the blocked needle tip by injecting a small quantity of fluid into the joint and then re-aspirate.
If sample aspiration is unsuccessful when acute gout is suspected, try saline or heparin irrigation. After injecting 1 ml of fluid try aspirating again. This will also yield a sample for bacterial analysis.
Storage of the synovial fluid sample
A synovial fluid sample should be analyzed promptly after taking the sample. Synovial fluid containing blood will rapidly coagulate. There may be cell degradation in the sample after just an hour. Crystals, on the other hand, are inorganic salts and are better preserved and so their analysis can be made the next day.
Injecting too frequently
In case of acute inflammation, intra-articular injections can be given at 1-month intervals for the first 3 months. Afterwards, if needed, 3 months apart.
There is no strong evidence of adverse effects of glucocorticoids on the joint, although frequent injections may cause unwanted systemic effects.
Complications
Infection
Intra-articular infection after a joint injection is very rare, the incidence being 1:2000-1:100 000, most commonly 1:10 000. Nevertheless, maintain aseptic technique while doing the procedure.
Joint pain
Joint pain during 24 hours post-injection is an adverse effect occurring in up to 10% of cases, particularly with glucocorticoid injections. It may result from a local tissue injury caused by the needle alone but is usually due to an irritation reaction to the crystalline glucocorticoid or hyaluronate. The joint may be painful, perhaps even feel warm, for about 24 hours, but these symptoms ease spontaneously. The symptoms can be alleviated by analgesics or cold treatment.
Hemarthrosis
Intra-articular hemorrhage is a very rare complication of a joint injection. Antithrombotic treatment or anticoagulant medication is not a contraindication for intra-articular injection as the risk is very small, about 0-2%, even in patients using these medicines. In patients on anticoagulants, however, the smallest possible needle is recommended for joint injection.
Local skin atrophy or hypopigmentation
Local skin atrophy occurs in about 1% of the patients after intra-articular injection of glucocorticoids. Typically, atrophy at the injection area develops at 1-4 months post-injection. In addition to atrophy, there may be hypopigmentation around the injection area. Atrophy and hypopigmentation are caused by subcutaneous glucocorticoid accumulation, potentially due to extracapsular injection or extracapsular seepage of the glucocorticoid via the puncture canal.
Tendon tear
Tendon tears during intra-articular injections are very rare and are often due to unintentional injection of glucocorticoid into the adjacent tendon rather than the joint itself. To avoid tendon injuries, glucocorticoids should always be injected against low resistance.
Pericapsular calcium deposit
Pericapsular calcification, or calcium deposits around the joint capsule of the target joint is a very common adverse effect, occurring after intra-articular injections in up to 10% of cases. Pericapsular calcium deposits are usually asymptomatic and harmless. In most cases, calcium is spontaneously absorbed from the synovial capsule but in some patients X-ray images may show even permanent calcifications, particularly in small joints such as the PIP and the DIP joints of the fingers.
Compromise of diabetes management
Following intra-articular injections, some of the glucocorticoid dose will be absorbed into the systemic bloodstream and in diabetic patients, for example, blood sugar level might be elevated for a few days post-injection. The risk is highest for short-acting agents or when multiple injections are given together. Patients with diabetes should be advised to step up their blood sugar monitoring post-injection, and if necessary to adjust their diabetes medication doses temporarily.
Aftercare
General guidelines
The puncture site should be covered by an adhesive patch and kept dry and clean for 24 hours to minimize the risk of infection.
For a better therapeutic effect, avoid stress of the punctured joint for 24-48 hours and avoid heavy strain for one week.
Glucocorticoids are more absorbed into the bloodstream, particularly from large weight-bearing joints, if the joint is stressed.
FAQ
What is the goal of knee joint injection or puncture?
The goal is safe knee joint puncture for synovial fluid aspiration and/or to administer a local therapeutic injection.
Where is the injection site for knee joint injection?
A good injection site is about 0.5 cm below the superior lateral edge of the patella in the AP direction.
What can be ordered from synovial fluid analysis in unexplained fluid accumulation?
Cell count, crystal analysis, and bacterial culture can be ordered. If antibiotic therapy has already been started and there is strong suspicion of septic arthritis, bacterial nucleic acid detection can be ordered. If Lyme disease-induced arthropathy is suspected, Borrelia nucleic acid detection can be ordered.
What aftercare is recommended after knee joint injection?
The puncture site should be covered by an adhesive patch and kept dry and clean for 24 hours. Stress of the punctured joint should be avoided for 24-48 hours, and heavy strain should be avoided for one week.
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