Knee joint injections under image guidance ensure precise delivery of an injectate into the knee joint. Either fluoroscopy, ultrasound or CT can be used to guide and administer injectates, which may be diagnostic (e.g. anesthetic), "therapeutic" (e.g. anesthetic/steroids, PRP), or for CT or MR arthrograms.
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Images:
Indications
MRI: retear of a repaired meniscus
CT: meniscal tear in those with MRI contraindication
pain, arthropathy i.e. osteoarthritis
diagnostic injection
Contraindications
Absolute
anaphylaxis to contrast/ injectate
active local/ systemic infection
MRI contraindication (MRI)
Relative
non-arthrogram MRI not performed (MRI arthrogram)
recent injection with steroid in same/other body parts (anesthetic arthrogram)
unable to remain still for the procedure
young age (anesthetic arthrogram)
Procedure
The general principles of knee arthrogram injections are to:
cannulate the joint
confirm an intra-articular position with imaging
administer intra-articular injectate: the knee is the largest joint and the injectate volume should reflect this; at least 20 mL is injected in arthrograms, with 40 mL used in some institutions 1
Pre-procedural evaluation
Relevant imaging should be reviewed, and the details of the patient confirmed. The patient should have an opportunity to discuss the risks and benefits and consent obtained.
Risks include:
infection
bleeding
allergy
focal fat necrosis/skin discolouration at the injection site (anesthetic arthrogram)
steroid flare (anesthetic arthrogram)
Equipment
sterile probe cover (ultrasound)
metal rod for marking and short connecting tube (fluoroscopy)
biopsy grid and short connecting tube (CT)
skin marker
skin cleaning product
sterile drape
sterile field and tray for sharps
syringe selection i.e. 10 mL, 5 mL and 20 mL
larger bore drawing up needle
needle to administer local anesthetic i.e. 25-gauge needle
needle to cannulate the joint i.e. 22 or 25-gauge needle
injectants i.e. local anesthetics, iodinated contrast, corticosteroid preparation
sterile gauze
adhesive dressing
Syringe selection
A suggested syringe and injectate selection for a fluoroscopic-guided/CT guided MRI arthrogram injection:
5 mL syringe: 5 mL of local anesthetic, i.e. 1% lidocaine
10 mL syringe: 10 mL non-ionic iodinated contrast, i.e. iohexol 300
20 mL syringe containing: 0.1 mL gadolinium, 9.9 mL 0.9% saline, 5 mL 0.5% ropivacaine, 5 mL OmnipaqueTM 300
A suggested syringe and injectate selection for a fluoroscopic-guided/CT guided CT arthrogram injection:
5 mL syringe: 5 mL of local anesthetic i.e. 1% lidocaine
10 mL syringe: 10 mL non-ionic iodinated contrast i.e. iohexol 300
20 mL syringe containing: 10 mL OmnipaqueTM 300, 5 mL 0.9% saline, 5 mL 0.5% ropivacaine
A suggested syringe and injectate selection for an ultrasound-guided knee anesthetic arthrogram injection:
5 mL syringe: 5 mL of local anesthetic, i.e. 1% lidocaine
5 mL syringe: 40 mg triamcinolone acetonide (40 mg/1 mL) and 4 mL 0.5% ropivacaine
Needle selection
Smaller gauge needles can be less painful but are less stiff and can bend when trying to cannulate a joint. The needle should be long enough to reach the joint.
Knee: 22-gauge Quincke needle or 25-gauge needle
Technique
CT
check for allergies and if on blood thinners
consent
optimize patient positioning, prone on the CT table, placing an overlying biopsy grid and perform planning CT scan
identify needle entry point on planning images, mark the skin
clean skin and draw up appropriate medications
consider local anesthesia along the proposed needle path
under CT guidance insert a needle into the targeted aspect of the joint
confirm an intra-articular needle tip position with a small amount of iodinated contrast via tubing
administer arthrogram injectate
remove the needle and apply dressing/ band-aid as required
Fluoroscopy
Anterior approach
check for allergies and if on blood thinners
consent
optimize patient positioning with the patient supine, knee in slight flexion, aiming for an anterior needle entry with the target knee closest to the practitioner
optimize imaging field to include all of the knee joint, from above the patella to the tibial metaphysis
identify the central aspect of the lateral femoral condyle, 1 cm cranial from the joint line, and using the metal rod, mark the skin at the target entry point 2
clean skin and draw up appropriate medications
consider local anesthesia along the proposed needle path
under fluoroscopic guidance insert a needle parallel to the x-ray beam using an ‘eye of the needle approach’ into the targeted aspect of the joint until the bone is reached
confirm an intra-articular needle tip position with iodinated contrast via tubing and save a post-injection image
administer arthrogram injectate
remove the needle and apply dressing/ band-aid as required
Lateral subpatellar approach
check for allergies and if on blood thinners
consent
optimize patient positioning with the patient supine, leg straight, aiming for a lateral to medial needle entry with the target knee closest to the practitioner
optimize imaging field to include all of the knee joint, from above the patella to the tibial metaphysis
palpate the lateral aspect of the patella and confirm equator of the patella with fluoroscopy 1
using the metal rod mark the skin at the target entry point, 1 cm inferior to the palpable line to allow for the patella depth
clean skin and draw up appropriate medications
consider local anesthesia along the proposed needle path
under fluoroscopic guidance insert a needle, perpendicular to the x-ray beam, into the targeted aspect of the joint, aiming for the needle tip to reach the central point of the patella
confirm an intra-articular needle tip position with iodinated contrast via tubing and save a post-injection image
administer arthrogram injectate
remove the needle and apply dressing/ band-aid as required
Ultrasound
check for allergies and if on blood thinners
consent
optimize patient positioning with the back of the bed at a slight incline, the patient supine, leg straight, aiming for a lateral to medial needle entry with the target knee closest to the practitioner
using the US probe, identify the suprapatellar pouch under the quadriceps tendon in a transverse plane, optimize imaging focus and depth, and mark the targeted lateral skin entry point 3
clean skin and draw up appropriate medications
consider local anesthesia along the proposed needle path
under ultrasound guidance insert the needle in-plane with the probe into the suprapatellar pouch
administer arthrogram injectate under direct visualization
remove the needle and apply dressing/ band-aid as required
Complications
effusion and knee stiffness if a large arthrographic volume is injected, which will resolve over the next 24-hour period and the patient should be reassured this is normal post-procedure
-
serious complications may be rare (<1% in one large series) 5
rapidly progressive osteoarthritis
-
infection causing septic arthritis
steroid-containing injections should be postponed if there are signs and/or symptoms of local and/or systemic infection
possible fat necrosis causing skin dimpling and skin discolouration can occur due to steroid leaking into the surrounding soft tissues 4, but less likely in deeper injections
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