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Ultrasound · Hip

Piriformis Injection

hippiriformissciatic nervedeep gluteal pain

Treats

  • Piriformis syndrome with sciatic irritation
  • Deep gluteal pain / non-spinal sciatica

Contraindications

  • Active local skin infection at entry site (absolute)
  • Known allergy to local anesthetic, steroid, or antiseptic prep
  • Therapeutic anticoagulation — review case-by-case (deep gluteal injection)
  • Uncontrolled diabetes (relative)
  • Beaton-Anson sciatic variant with sciatic nerve or its peroneal division passing through the piriformis belly (relative — abandon intramuscular injection, use peri-fascial only)
  • Active sciatic neuropathy from another cause (relative — re-evaluate diagnosis)

Pre-procedure checklist

  • Confirm patient identity (two identifiers)
  • Confirm procedure, side, and site — mark with patient awake
  • Review allergies and anticoagulation
  • Confirm informed consent
  • Pre-scan: identify piriformis (confirm sacral attachment to distinguish from gemelli/obturator internus); identify sciatic nerve completely; check for Beaton-Anson variant (~15-20%); Doppler inferior gluteal vessels
  • Time-out immediately before needle entry

Positioning

  • Prone with neutral pelvis; pillow under iliac crests to improve visualization
Positioning

Probe

  • Curvilinear probe (2-5 MHz) for depth; low-frequency linear in thin patients
Probe

Landmarking — find the view

  • Probe over PSIS → slide inferior to see sacrum medially and PIIS laterally
  • Continue distally until ilium disappears (greater sciatic notch)
  • Identify piriformis deep to gluteus maximus, coursing sacrum → greater trochanter
  • Internally/externally rotate hip to confirm piriformis motion
  • Identify sciatic nerve deep/inferior to piriformis along its full length before injection
  • Confirm muscle is piriformis by tracing fibers MEDIALLY to the lateral sacrum (only piriformis attaches there — gemelli/obturator internus do not)

The correct ultrasound view

  • Gluteus maximus superficial; fusiform piriformis belly oblique with clear sacral attachment; sciatic nerve deep (honeycomb)
The correct ultrasound view

Needle corridor

  • Medial → lateral so the needle terminates lateral to the sciatic nerve and lateral to the inferior gluteal vessels. Between gluteus maximus (above) and piriformis (below); avoid sciatic nerve.
Needle corridor

Avoid

  • Sciatic nerve (always identify before injection — in Beaton-Anson variants the nerve passes through the muscle)
  • Inferior gluteal artery/vein
  • Inferior gluteal nerve (L5, S1, S2 — exits through greater sciatic foramen below piriformis and innervates gluteus maximus; injury causes gluteus maximus weakness)
  • Posterior femoral cutaneous nerve (runs with inferior gluteal vessels)
  • Pudendal NV bundle (if advancing medially toward ischial spine)

Steps

  1. 1Advance in-plane (medial → lateral) under real-time US.
  2. 2Stop at piriformis belly or perifascial plane lateral to the sciatic nerve; aspirate gently.
  3. 3Test inject a small bolus; then inject anesthetic ± steroid or botulinum toxin as indicated.
  4. 4STOP IMMEDIATELY if the patient reports electric, shooting, or paresthetic sensations down the leg — this indicates intraneural or perineural sciatic placement. Withdraw 1-2 mm and reposition.

Tips

  • Map vessels with Doppler; if sciatic nerve not clearly visualized along its full course, do not inject.
  • If color Doppler shows a vessel in the planned path, abandon and re-plan.
  • Limit corticosteroid to ≤ 3 per site per year.

Resident pearls

  • Beaton-Anson variants: In ~15-20% of patients the sciatic nerve or its peroneal division courses THROUGH the piriformis belly. Before any intramuscular injection, scan the entire piriformis and trace the sciatic nerve continuously — if the nerve passes through the muscle, abandon intramuscular injection and use a peri-fascial approach only.
  • The most common identification error is confusing piriformis with the superior/inferior gemellus or obturator internus immediately caudal. All four look similar. The piriformis is the ONLY one whose fibers clearly attach to the lateral sacrum — always trace medially to confirm.
  • Confirm the piriformis muscle by having the patient internally/externally rotate the hip.
  • Approach medial-to-lateral so the needle terminates lateral to the sciatic and lateral to the inferior gluteal vessels.

Supplies

  • 10 mL Syringe
  • 22G 3.5" Spinal Needle
  • 18G Drawing Needle
  • 1% Lidocaine (5-10 mL)
  • Triamcinolone 40 mg OR Dexamethasone 4-10 mg
  • If using botulinum toxin: onabotulinumtoxin A 100 U typical (range 50-200 U). Dosing is product-specific and NOT interchangeable between brands (Botox ≠ Dysport ≠ Xeomin) — confirm product, dilution, and dose with attending before drawing up.
  • Alcohol Swabs (vial tops)
  • Betadine/Chloraprep
  • Sterile Gloves
  • Sterile 4x4 Gauze Pads
  • Sterile Towels & Drapes
  • Adhesive Bandage (Band-Aid)
  • Washcloth/Towel (gel cleanup)
  • Needle Disposal Safety Cap
  • Sterile probe cover & gel

Post-procedure

  • Apply a clean dressing; remove after 24 hours.
  • Local anesthetic relief for 1-4 hours; steroid begins 24-72 hours.
  • Steroid 'flare' in 2–10% — manage with ice and acetaminophen.
  • Rest 24-48 hours; resume normal activity as tolerated thereafter.
  • Return immediately for: spreading redness, swelling, fever, disproportionate pain, OR new leg weakness, foot drop, or worsening sciatica.
  • Diabetics: expect 50-100 mg/dL glucose rise for 3-5 days.
  • Maximum 3 injections per site per year.