Approach Considerations
The best approach to a knee injection is the path of least obstruction and maximal access to the synovial cavity, which could be superolateral, superomedial, or anteromedial/anterolateral.
Plain radiography is recommended for better assessment of the bony anatomy of the individual knee joint. The knee injection site can be selected according to the patient’s bony anatomy and can be marked with the tip of a retracted ballpoint pen before sterile preparation (see Periprocedural Care, Patient Preparation).
The superolateral approach into the suprapatellar pouch might provide a better and more reliable route of entry into the knee joint than the superomedial or anteromedial/anterolateral approaches. [9, 8]
Lockman also reported the concept of the triangle with reasonable accuracy, in which one line is drawn from the apex of the patella (the apex of the triangle) to the lateral pole of the patella and another line is drawn from the apex to the medial upper pole of the patella, resulting in an inverted triangle. [20] The base of the triangle forms the upper border of the patella. The lateral line of the triangle is then marked at the midpoint, where the needle can be inserted and directed intra-articularly into the knee joint.
Injection Into Knee
Superolateral approach
For the superolateral approach, the patient lies supine with the knee almost fully or fully extended with a thin pad support underneath the knee to facilitate relaxation. The clinician’s thumb is used to gently rock then stabilize the patella while the needle is inserted underneath the supralateral surface of the patella, aimed toward the center of the patella, and then directed slightly posteriorly and inferomedially into the knee joint.
Superomedial approach
For the superomedial approach, the patient lies supine with the knee almost fully or fully extended with a thin pad support underneath the knee to facilitate relaxation. The clinician’s thumb is used to gently rock and then stabilize the patella while the needle is inserted underneath the supramedial surface of the patella, aimed toward the center of the patella, and then directed slightly posteriorly and inferolaterally into the knee joint.
Anterolateral and anteromedial approaches
For the anterolateral and anteromedial approaches, the patient can sit or lie supine with the knee flexed 90° to afford better exposure of the intra-articular surface and thus facilitate ease of needle entry into the joint space.
The sterile needle is inserted either lateral to the patellar tendon (for the anterolateral approach) or medial to the tendon (for the anteromedial approach), approximately 1 cm above the tibial plateau, and directed 15-45° from the anterior knee surface vertical midline toward the intra-articular joint space. [20, 9, 8] (See the images below.)
Anteromedial approach to intra-articular knee joint injection with patient in sitting position and knee flexed 90 degrees (ThePainSource.com)
Anteromedial approach to intra-articular knee joint injection with patient in sitting position and knee flexed 90 degrees (ThePainSource.com)
Postprocedural Care
The postprocedural protocol includes a comparison of preinjection and postinjection pain levels with specific knee examinations and palpation. The effect of lidocaine should be immediate, whereas steroids usually take effect within 1-2 days.
According to an American College of Rheumatology survey, 71% of rheumatologists ask patients to decrease weightbearing, often for 48 hours post injection.
Postinjection flare, characterized by localized pain, may occur within several hours of an intra-articular knee joint steroid injection. It usually resolves within 48 hours. If a flare occurs, the patient should be instructed to ice the area and take nonsteroidal anti-inflammatory drugs (NSAIDs). Rest is also recommended.
Overall, no major safety issues were detected within the constraints of a trial designed by the Cochrane study. [10]
Complications
Noninfectious
Tendon rupture and nerve atrophy or necrosis are common complications of joint injections; however, they are uncommon with knee injections. Both result from steroid injections. Other complications, such as skin atrophy, vitiligo, and dystrophic calcification around the joint capsule, may occur but are very uncommon.
Another noninfectious complication of joint injections is steroid toxicity, which manifests as osteoporosis, menstrual irregularity, ecchymoses, and/or accelerated cataract formation. All of these are related to the systemic absorption of steroids. Other systemic metabolic effects of steroids that have been reported include suppression of the hypothalamic-pituitary axis and an increase in blood glucose levels, both of which are self-limited. A rare but clinically significant complication is osteonecrosis, which occurs in 0.1-3% of cases.
Of the above complications, impaired blood glucose control has the most practical significance, particularly in patients with diabetes.
A 2017 study of 119 patients with knee osteoarthritis found that 2 years of quarterly triamcinolone injections led to to increased cartilage loss as compared with intra-articular saline injections. [16]
Infectious
Of the infectious complications of joint injections, iatrogenic septic arthritis is the most feared. This complication occurs in 1 per 2000-15,000 injections. If septic arthritis is suspected, it must first be distinguished from a postinjection flare, which usually lasts hours rather than days; thus, if a flare persists for longer than 48 hours or begins after 48 hours post injection, an infectious cause should be suspected. If iatrogenic septic arthritis is suspected, immediate repeat arthrocentesis should be performed, along with immediate institution of an antibiotic regimen.
As an initial treatment, repeated arthrocentesis is equal to surgery. When repeated arthrocentesis is performed as an initial treatment and effusion volume fails to decrease substantially over the first 48-72 hours, arthrotomy or arthroscopy should be performed.
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Sterile glove
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Sterile 25-Gauge x 1.5-inch needle
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Anteromedial approach to intra-articular knee joint injection with patient in sitting position and knee flexed 90 degrees (ThePainSource.com)
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Anteromedial approach to intra-articular knee joint injection with patient in sitting position and knee flexed 90 degrees (ThePainSource.com)
Tables
Agent |
Relative Anti-inflammatory Potency |
Relative Mineralocorticoid Potency |
Solubility |
Hydrocortisone |
1 |
2-3 |
High |
Prednisolone |
4 |
1 |
Medium |
Methylprednisolone |
5 |
0 |
Medium |
Triamcinolone |
5 |
0 |
Medium |
Betamethasone |
20-30 |
0 |
Low |
Dexamethasone |
20-30 |
0 |
Low |
