Subtalar joint injection (technique)

Subtalar joint injections are most often performed for osteoarthritis and the posterior subtalar joint is targeted.  Ultrasound, fluoroscopy and CT guidance can be used.

Indications

• osteoarthritis
• diagnostic

Contra-indications

Absolute

• anaphylaxis to contrast/injectates
• active local/ systemic infection 

Relative

• bleeding diathesis
• 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, i.e. 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)
• a metal rod (fluoroscopy)
• CT biopsy grid (CT)
• skin cleaning product
• sterile drape
• sterile field and tray for sharps
• syringe selection i.e. 10mL, 5mL and 3mL
• 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
• 5mL syringe: iodinated contrast
• 3 mL syringe: 40mg 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

Pre-procedure planning should calculate the distance required to reach the pudendal canal, as larger patients will require longer needles.

• Posterior subtalar joint:  25-gauge 40mm 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 needle tip position
• administer steroid containing injectate 
• removed the needle and apply dressing/ band-aid 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
• 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 which 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 steroid leaking into the surrounding soft tissues, and the patient should have consented for this .

Siehe auch:

• Technik Gelenkinjektionen