Quadratus femoris injections under image guidance ensure precise delivery of an injectate into the quadratus femoris muscle and ensure the sciatic nerve is avoided during the procedure. CT and ultrasound can be used, with ultrasound becoming more challenging in those with larger body habitus.
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Indications
therapeutic for ischiofemoral impingement 1
diagnostic injection 2
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 principles of quadratus femoris injections are to:
identify the quadratus femoris muscle and the sciatic nerve with imaging
confirm a correct needle tip position with imaging
administer injectate, usually a corticosteroid and a small amount of local anesthetic
Pre-procedural evaluation
Relevant imaging should be reviewed, and 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
temporary leg weakness
focal fat necrosis/skin discolouration at the injection site
steroid flare
Equipment
skin marker and marking 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. 23-gauge needle
needle gain an adequate position i.e. 22-gauge Quincke needle
sterile gauze
adhesive dressing
Syringe selection
A suggested syringe and injectate selection for a CT-guided injection
10mL mL syringe: 4 mL of local anesthetic i.e. 1% lidocaine
5 mL syringe: 2 mL non-ionic iodinated contrast i.e. iohexol 300
3 mL syringe (Luer lock): 40mg triamcinolone acetonide (40 mg/1 mL) and 1 mL 1% lidocaine
Needle selection
When planning the needle entry point and path, the distance from the skin to the target should be measured and a long enough needle should be selected
quadratus femoris: 22-gauge Quincke needle (standard or longer length)
Technique
CT (lateral approach)
check for allergies
consent
optimize patient positioning by lying them prone on the CT table, with a CT marking grid over the posterolateral thigh
perform planning CT and plan procedure, identifying the sciatic nerve and then measure the distance from the skin to the target
clean skin and draw up appropriate medications
local anesthesia along the proposed needle path
under CT guidance using a posterolateral approach, insert the 22-gauge needle into the appropriate position in the quadratus femoris muscle within the ischiofemoral interval
check the needle tip position with a small amount of iodinated contrast
administer steroid and local anesthetic injectate
remove the needle and apply dressing/band-aid as required
Complications
It is important to correctly identify the sciatic nerve during these procedures to avoid injury, due to its close proximity 3. Using a smaller volume and short-acting local anesthetic will reduce the possibility of a longer-lasting sciatic nerve block after the injection. Steroid flare is a relatively common side effect that will settle. Steroid containing injections should be postponed if there are signs and/or symptoms of local and/or systemic infective. Possible fat necrosis causing skin dimpling and skin discolouration can occur due to the steroid leaking into the surrounding soft tissues 4.