Quadratus femoris injection (technique)

Quadratus femoris injections under image guidance ensure precise delivery of an injectate 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.

Indications

• therapeutic for ischiofemoral impingement ¹
• diagnostic injection ²

Contraindications

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 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.