Subtalar joint injections are most often performed for osteoarthritis with injection into the posterior subtalar joint. Ultrasound, fluoroscopy and CT guidance can be used.
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Indications
diagnostic
Contraindications
Absolute
anaphylaxis to contrast/injectates
active local/systemic infection
Relative
recent injection with steroid in same/other body parts
unable to remain still for the procedure
young age
Procedure
The general principle of a (posterior) subtalar joint injection is to:
cannulate the joint
confirm an intra-articular position with imaging
administer intra-articular injectate, usually a corticosteroid and a small amount of longer acting local anesthetic, e.g. ropivacaine
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
failure of the procedure to relieve pain
Equipment
skin marker
ultrasound machine and sterile probe cover (ultrasound)
metal rod (fluoroscopy)
CT biopsy grid (CT)
skin cleaning product
sterile drape
sterile field and tray for sharps
syringe selection i.e. 10 mL, 5 mL and 3 mL
larger bore drawing up needle
needle to administer local anesthetic i.e. 30-gauge needle
needle to cannulate pudendal canal i.e. 25-gauge needle
sterile gauze
adhesive dressing
Syringe selection
Luer lock syringes are best used as severely arthritic posterior subtalar joints can be difficult to inject.
A suggested syringe and injectate selection for fluoroscopic or CT-guided subtalar joint injection:
10 mL syringe: 5 mL of local anesthetic i.e. 1% lidocaine
5 mL syringe: iodinated contrast
3 mL syringe: 40 mg triamcinolone acetonide (40 mg/1 mL) and 1 mL 0.5% ropivacaine
A suggested syringe and injectate selection for ultrasound-guided (posterior) subtalar joint injection -
10 mL syringe: 5 mL of local anesthetic i.e. 1% lidocaine
3 mL syringe: 40mg triamcinolone acetonide (40 mg/1 mL) and 1 mL 0.5% ropivacaine
Needle selection
Preprocedure planning should calculate the distance required to reach the pudendal canal, as larger patients will require longer needles.
Posterior subtalar joint: 25-gauge 40 mm needle
Technique
CT
check for allergies and if on blood thinners
consent
position patient by lying on their side, with the targeted side facing up
place CT biopsy grid
perform planning CT, and identify posterior subtalar joint and access whilst avoiding the peroneal tendons
mark skin at the entry site
clean skin and draw up appropriate medications
give local anesthesia along the proposed needle path
under CT guidance, pass the needle into the posterior subtalar joint
inject a small amount of iodinated contrast to confirm the needle tip position
administer steroid containing injectate
removed the needle and apply dressing as required
pain diary to be given
Fluoroscopy
check for allergies and if on blood thinners
consent
position patient by lying on their side, with the targeted side facing up
optimize positioning and C-arm, getting the best view of the posterior subtalar joint 1
using the metal rod mark skin at the entry site
clean skin and draw up appropriate medications
give local anesthesia along the proposed needle path
under fluoroscopic guidance, pass the needle into the posterior subtalar joint
inject a small amount of iodinated contrast to confirm needle tip position and save an image
administer steroid containing injectate
removed the needle and apply dressing/ band-aid as required
pain diary to be given
Complications
Steroid flare is a relatively common side effect that will settle after 1-2 days. The most serious complication is an 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 steroids leaking into the surrounding soft tissues, and the patient should have consented to this 2.