Gluteal Region and Sciatic Nerve: Anatomy and Clinical Injections

Overview

The gluteal region lies posterior to the pelvis, bounded superiorly by the iliac crest and inferiorly by the gluteal fold. It is the most common site for intramuscular (IM) injections, making understanding of its neurovascular anatomy essential for every clinician.

Surface Landmarks

Iliac crest: Forms the upper border
Posterior superior iliac spine (PSIS): Marks the S2 level; dimple of Venus
Greater trochanter: Lateral prominence
Gluteal fold: NOT the inferior border of gluteus maximus (the muscle extends ~7 cm below the fold)
Ischial tuberosity: Palpable in flexion (sitting position); covered by gluteus maximus in standing

Safe Quadrant for IM Injection

Divide the buttock into four quadrants using a vertical line from the PSIS and a horizontal line through the greater trochanter. Inject ONLY into the upper outer (superolateral) quadrant to avoid:

Sciatic nerve (midline, midway between greater trochanter and ischial tuberosity)
Superior and inferior gluteal arteries and nerves

Clinical note: Modern guidelines favor the ventrogluteal site (between iliac crest, ASIS, and greater trochanter) over dorsogluteal due to thinner fat layer and absence of major neurovascular structures.

Muscles of the Gluteal Region

Superficial Group

Gluteus maximus
- Largest muscle in the body
- Innervation: Inferior gluteal nerve (L5, S1, S2)
- Actions: Powerful hip extension, lateral rotation
- Insertion: Gluteal tuberosity of femur + iliotibial tract
- Tested by: Climbing stairs, rising from sitting
Gluteus medius and minimus
- Innervation: Superior gluteal nerve (L4, L5, S1)
- Actions: Hip abduction and medial rotation
- Insertion: Greater trochanter
- Trendelenburg test: When standing on one leg, the opposite hip drops if these muscles are weak (or the superior gluteal nerve is damaged) — indicates lesion of superior gluteal nerve or L5 radiculopathy

Deep Group (lateral rotators)

Piriformis: Key landmark — most structures enter/leave the pelvis through the suprapiriform and infrapiriform foramina
Obturator internus with gemelli (superior and inferior)
Quadratus femoris

Sciatic Nerve

Largest nerve in the body (~2 cm wide at the hip)
Formed from ventral rami of L4-S3
Emerges from the infrapiriform foramen, deep to gluteus maximus
Travels midway between the greater trochanter and ischial tuberosity (vulnerable to misplaced IM injections)
Enters the posterior thigh, dividing (usually) into tibial and common fibular (peroneal) nerves above the popliteal fossa
Sensory supply: Skin of foot and lateral leg (via its branches)
Motor supply: Hamstrings and all muscles below the knee

Superior and Inferior Gluteal Foramina

Suprapiriform Foramen

Superior gluteal artery (branch of internal iliac)
Superior gluteal nerve

Infrapiriform Foramen

Inferior gluteal artery
Inferior gluteal nerve
Sciatic nerve
Posterior femoral cutaneous nerve
Pudendal nerve (briefly — re-enters perineum via lesser sciatic foramen)
Internal pudendal artery

Clinical Correlations

Piriformis Syndrome

Sciatic nerve compression by an inflamed or hypertrophied piriformis
Causes buttock pain radiating down the posterior thigh
FAIR test: Flexion, Adduction, Internal Rotation reproduces symptoms
Common in runners and cyclists

Sciatic Nerve Injury

Common fibular division more vulnerable (more lateral, tighter to fibula)
Foot drop (loss of dorsiflexion and eversion)
Sensory loss over dorsum of foot and lateral leg
Causes: Hip fracture/dislocation, misplaced IM injection, prolonged sitting (Sunday night palsy — though usually peroneal at fibular head)

Trendelenburg Gait

Pelvis drops on the unaffected side when standing on the affected leg
Indicates weakness of contralateral gluteus medius/minimus (or superior gluteal nerve lesion)
"Compensatory" Trendelenburg: patient leans trunk toward affected side to shift center of gravity

Key Takeaway

The gluteal region is a clinical exam favorite. Memorize: safe quadrant for IM injection, structures passing through greater sciatic foramen (above/below piriformis), Trendelenburg sign, and sciatic nerve injury patterns.