Gluteal Region — Comprehensive Study Notes Summary & Study Notes

🍑 Overview & Objectives

These notes cover the gluteal region: surface anatomy, osteology, muscular anatomy, movements at the hip, neurovasculature, foramina contents, safe injection sites, and lymphatic drainage. Key learning goals include identifying bony landmarks, naming gluteal muscles with their attachments/actions/innervation, explaining Trendelenburg gait, and tracing major nerves and vessels through the greater and lesser sciatic foramina.

🦴 Osteology & Surface Anatomy

The hip bones (os coxae) form the pelvic girdle (ilium, ischium, pubis). Important landmarks: iliac crest, ASIS, PSIS, acetabulum, greater trochanter, ischial tuberosity, and ischial spine. The hip joint is a synovial ball-and-socket joint (head of femur in the acetabulum). The proximal femur features the head, neck, greater/lesser trochanters, intertrochanteric line/crest, and linea aspera.

🔀 Movements at the Hip

Muscles that cross the hip produce: flexion/extension, abduction/adduction, and medial/lateral rotation. By definition, a muscle that decreases the joint angle produces flexion and one that increases the angle produces extension. The gluteal musculature is chiefly responsible for extension (gluteus maximus) and abduction/medial rotation (gluteus medius/minimus).

💪 Superficial Gluteal Muscles

• Gluteus maximus: Originates from the iliac crest, dorsal sacrum/coccyx, and sacrotuberous ligament; inserts on the iliotibial tract and gluteal tuberosity of femur. Innervated by the inferior gluteal nerve (L5, S1, S2). Primary action = powerful extension of the thigh and lateral rotation; steadies thigh via IT band.

• Gluteus medius: Originates between the posterior and anterior gluteal lines of ilium; inserts on the greater trochanter. Innervation = superior gluteal nerve (L4, L5, S1). Action = abduction of the femur (especially of the non-weight-bearing limb), medial rotation, and stabilization of the pelvis.

• Gluteus minimus: Lies deep to medius, similar origin more inferior between gluteal lines, inserts on the greater trochanter. Innervation = superior gluteal nerve. Action = abduction and medial rotation, assists pelvic stabilization.

• Tensor fasciae latae (TFL): Originates at the ASIS and anterior iliac crest; inserts into the iliotibial tract (IT band). Innervated by the superior gluteal nerve. Assists with abduction and medial rotation of thigh and tensions the fascia lata.

🔍 Deep Lateral Rotators (Six Small Muscles)

The deep lateral rotators laterally rotate the thigh and help stabilize the hip. They include:

• Piriformis: Origin = anterior sacrum; exits pelvis via the greater sciatic foramen; innervation S1–S2; lateral rotation of thigh.
• Superior gemellus: Origin = ischial spine; works with obturator internus; innervation = nerve to obturator internus.
• Obturator internus: Origin = pelvic surface of obturator membrane; tendon exits via greater sciatic foramen then turns over lesser sciatic region; innervation = nerve to obturator internus.
• Inferior gemellus: Origin = ischial tuberosity; innervation = nerve to quadratus femoris.
• Quadratus femoris: Origin = ischial tuberosity; insertion below intertrochanteric crest; innervation = nerve to quadratus femoris; strong lateral rotator.
• Obturator externus: Lies deep and is largely obscured posteriorly by quadratus femoris; innervation = obturator nerve; lateral rotation.

🚶 Trendelenburg Gait

Trendelenburg gait results from weakness of the gluteus medius and minimus (usually due to injury of the superior gluteal nerve). On the stance leg side, these muscles normally keep the pelvis level. Weakness causes the pelvis to drop toward the non-weight-bearing side, and the patient compensates by leaning the trunk toward the stance leg to maintain the center of gravity. Clinical identification: if the patient lifts the right foot and the right hip drops, the left gluteus medius/minimus are weak.

🧠 Neurovasculature & Innervation

The gluteal region is innervated predominantly by branches of the lumbosacral plexus. Key nerves and roots: femoral (L2–L4), obturator (L2–L4), sciatic (L4–S3), superior gluteal (L4–L5, S1), inferior gluteal (L5, S1, S2), nerve to obturator internus (L5, S1, S2), nerve to quadratus femoris (L4, L5, S1), pudendal (S2–S4), and posterior femoral cutaneous (S1–S3). The sciatic nerve is made of tibial and common fibular divisions and most commonly exits the pelvis inferior to piriformis (≈90%); variations exist.

📤 Contents of the Greater and Lesser Sciatic Foramina

• Greater sciatic foramen transmits numerous structures between pelvis and gluteal region: piriformis, superior gluteal vessels & nerve (above piriformis), inferior gluteal vessels & nerve (below piriformis), sciatic nerve, posterior femoral cutaneous nerve, nerve to obturator internus, internal pudendal vessels and pudendal nerve (these last two leave gluteal region to re-enter pelvis via lesser sciatic foramen).

• Lesser sciatic foramen transmits structures entering/re-entering the perineum and pelvis: tendon of obturator internus, and pudendal nerve and internal pudendal vessels (re-entering to supply perineum).

🩸 Blood Supply

Primary arterial supply to the gluteal region comes from the superior and inferior gluteal arteries, branches of the internal iliac artery. The superior gluteal artery accompanies the superior gluteal nerve and lies between gluteus medius and minimus. The inferior gluteal artery accompanies the inferior gluteal nerve. The internal pudendal artery passes through the gluteal region to reach the perineum.

💉 Intramuscular Injections — Safe Site

The safest site for gluteal intramuscular injection is the superolateral (upper outer) quadrant of the buttock, targeting the gluteus medius. This location minimizes risk to the sciatic nerve and major vessels. Avoid the inferomedial and posteroinferior regions where the sciatic nerve greater likelihood lies.

🧬 Lymphatic Drainage

Lymph from the deep tissues of the buttock follows gluteal vessels to superior and inferior gluteal lymph nodes, then drains to internal, external, and common iliac nodes and ultimately to lateral lumbar (aortic/caval) nodes. Lymph from superficial tissues drains to the superficial inguinal lymph nodes, which also receive lymph from the thigh.

✅ Quick Clinical Pearls

• Piriformis exits via the greater sciatic foramen and is a landmark for superior/inferior gluteal neurovascular bundles.
• Injury to superior gluteal nerve → Trendelenburg sign/gait.
• Superior lateral quadrant = safe IM injection site to avoid sciatic nerve.
• Know the greater vs lesser sciatic foramina contents to understand pathways for nerves/vessels entering/exiting the pelvis.