Gluteal Region and Hip

Deep fascia covering the gluteal muscles; splits to enclose gluteus maximus.

• Thickens laterally to form part of the iliotibial tract attachment.
• Continuous with the fascia lata of the thigh inferiorly and thoracolumbar fascia superiorly.

• Origin: Posterior gluteal line of ilium, posterior sacrum/coccyx, sacrotuberous ligament, thoracolumbar fascia.
• Insertion: Iliotibial tract (upper three-quarters) and gluteal tuberosity of femur (lower quarter).
• Innervation: Inferior gluteal nerve (L5, S1, S2).
• Blood supply: Superior and inferior gluteal arteries.
• Action: Powerful hip extensor (especially from flexion, e.g., climbing stairs, rising from sitting) and lateral rotator; upper fibres assist abduction, lower fibres assist adduction; via the iliotibial tract, stabilises the extended knee.
• Relations: Largest and most superficial gluteal muscle; overlies the sciatic nerve, piriformis, and the other deep gluteal muscles; a common site for intramuscular injection (upper outer quadrant, to avoid the sciatic nerve).

• Origin: External surface of ilium, between anterior and posterior gluteal lines.
• Insertion: Lateral surface of greater trochanter.
• Innervation: Superior gluteal nerve (L4, L5, S1).
• Blood supply: Superior gluteal artery.
• Action: Abducts the hip; anterior fibres medially rotate, posterior fibres laterally rotate; primary pelvic stabiliser in the coronal plane during single-limb stance (prevents contralateral pelvic drop).
• Relations: Deep to gluteus maximus in its posterior part, superficial anteriorly/laterally.

• Origin: External surface of ilium, between anterior and inferior gluteal lines.
• Insertion: Anterior surface of greater trochanter.
• Innervation: Superior gluteal nerve (L4, L5, S1).
• Blood supply: Superior gluteal artery.
• Action: Abducts and medially rotates the hip; assists gluteus medius in pelvic stabilisation.
• Relations: Deepest of the three gluteal muscles.

• Origin: ASIS and adjacent iliac crest.
• Insertion: Iliotibial tract (which continues to the lateral tibial condyle, Gerdy's tubercle).
• Innervation: Superior gluteal nerve (L4, L5, S1).
• Blood supply: Superior gluteal artery, lateral circumflex femoral artery.
• Action: Flexes, abducts, and medially rotates the hip; tenses the iliotibial tract, assisting knee stability in extension.

• Thickened lateral band of the fascia lata, extending from the iliac crest/tensor fasciae latae and gluteus maximus insertion to Gerdy's tubercle on the lateral tibial condyle.
• Functions as a tension-band stabiliser for the hip and knee during stance, particularly resisting knee varus/lateral instability.
• Clinical relevance: Iliotibial band syndrome, friction over the lateral femoral epicondyle during repetitive knee flexion/extension (common in runners).

• Origin: Anterior surface of sacrum.
• Insertion: Superior border of greater trochanter.
• Innervation: Nerve to piriformis (S1, S2).
• Blood supply: Superior and inferior gluteal arteries.
• Action: Lateral rotator of the extended hip; abductor of the flexed hip.
• Relations: Passes through the greater sciatic foramen, dividing it into suprapiriform and infrapiriform parts, the key landmark for structures exiting the pelvis into the gluteal region.

• Origin: Internal surface of the obturator membrane and surrounding hip bone.
• Insertion: Medial surface of greater trochanter (trochanteric fossa), via a tendon that turns sharply around the lesser sciatic notch.
• Innervation: Nerve to obturator internus (L5, S1, S2).
• Blood supply: Internal pudendal artery, obturator artery.
• Action: Lateral rotator of the extended hip; abductor of the flexed hip.
• Relations: Passes through the lesser sciatic foramen, changing direction almost 90° over the ischium (which acts as a pulley).

• Origin: Superior gemellus, ischial spine; inferior gemellus, ischial tuberosity.
• Insertion: Both blend with the obturator internus tendon into the trochanteric fossa.
• Innervation: Superior gemellus, nerve to obturator internus; inferior gemellus, nerve to quadratus femoris.
• Action: Assist obturator internus in lateral rotation.
• Relations: Flank the obturator internus tendon superiorly and inferiorly, forming a "conjoint tendon" complex.

• Origin: Lateral border of ischial tuberosity.
• Insertion: Quadrate tubercle, intertrochanteric crest of femur.
• Innervation: Nerve to quadratus femoris (L4, L5, S1).
• Blood supply: Medial circumflex femoral artery.
• Action: Strong lateral rotator of the hip; minor adductor.
• Relations: Lies just superior to the medial circumflex femoral artery's course toward the femoral neck, relevant to the vascular supply of the femoral head.

Collectively, piriformis, obturator internus, gemelli, and quadratus femoris form the "short lateral rotators" of the hip, deep to gluteus maximus. They are functionally analogous in role (though not embryology) to the rotator cuff of the shoulder in providing dynamic joint stability.

Formed by the greater sciatic notch of the hip bone, converted to a foramen by the sacrospinous ligament; divided by piriformis into structures passing above and below the muscle.

Mnemonic for infrapiriform contents: "Some People Need Pain In Quiet**, Sciatic, Posterior cutaneous nerve of thigh, Nerve to obturator internus, Pudendal nerve, Internal pudendal vessels, Inferior gluteal nerve/vessels, Quadratus femoris nerve". Order varies by source; the key fact is piriformis as the dividing landmark.

• Boundaries: Lesser sciatic notch of the hip bone, converted to a foramen by the sacrospinous ligament (superiorly) and sacrotuberous ligament (inferiorly/laterally).
• Contents: Tendon of obturator internus, nerve to obturator internus, pudendal nerve and internal pudendal vessels (re-entering the pelvis/perineum here after passing through the greater sciatic foramen).

Superior gluteal nerve (L4, L5, S1):

• Exits the pelvis above piriformis, runs between gluteus medius and minimus.
• Motor to gluteus medius, gluteus minimus, tensor fasciae latae.
• Injury (e.g., poorly placed IM injection, hip surgery, posterior hip dislocation) causes a positive Trendelenburg sign: contralateral pelvic drop during single-limb stance on the affected side, due to loss of pelvic stabilisation.

Inferior gluteal nerve (L5, S1, S2):

• Exits the pelvis below piriformis.
• Motor to gluteus maximus only.
• Injury causes weakness of hip extension, most noticeable rising from a seated position or climbing stairs; less functionally devastating than superior gluteal nerve injury for gait stability.

Sciatic nerve (L4–S3):

• Largest nerve in the body; exits below piriformis (in the majority of individuals, anatomical variants exist where part or all of the nerve pierces or passes above piriformis, relevant to piriformis syndrome).
• Descends through the gluteal region midway between the greater trochanter and ischial tuberosity, then into the posterior thigh.
• Composed of two divisions (tibial and common fibular) bound together within a common sheath until it splits, typically at or above the popliteal fossa.
• Full course and branches covered in the Peripheral Nerves section.

Pudendal nerve relationship:

• Exits the pelvis via the greater sciatic foramen (below piriformis), hooks around the ischial spine and sacrospinous ligament, then re-enters the perineum via the lesser sciatic foramen.
• This "figure-of-eight" path around the ischial spine is the anatomical basis for pudendal nerve block (landmark: ischial spine, palpable transvaginally or transperineally) used in labour analgesia and perineal procedures.

• Articular surfaces: Head of femur (nearly a full sphere) and the lunate surface of the acetabulum (horseshoe-shaped, non-articular acetabular fossa centrally).

• Acetabular labrum: Fibrocartilaginous rim deepening the acetabulum, increasing femoral head coverage and joint stability; continuous inferiorly with the transverse acetabular ligament, which bridges the acetabular notch.

• Capsule: Strong and dense (unlike the shoulder), attaches to the acetabular rim proximally and to the intertrochanteric line anteriorly, but only partway down the femoral neck posteriorly (leaving part of the posterior neck extracapsular). This is clinically relevant to fracture classification (intracapsular vs extracapsular femoral neck fractures).

• Iliofemoral ligament ("Y-ligament of Bigelow"): Anterior, strongest ligament in the body; triangular, from the AIIS to the intertrochanteric line; prevents hyperextension of the hip, crucial for standing posture (allows relaxed upright stance with minimal muscular effort).

• Pubofemoral ligament: Anteroinferior, from the pubic part of the acetabular rim to the intertrochanteric line; limits excessive abduction and extension.

• Ischiofemoral ligament: Posterior, from the ischial part of the acetabular rim, spirals to the neck near the greater trochanter; limits internal rotation and adduction (the primary posterior stabiliser).

• Ligament of the head of femur (ligamentum teres): Weak intracapsular ligament, from the acetabular fossa/transverse acetabular ligament to the fovea. It carries a small branch of the obturator artery (acetabular branch) supplying part of the femoral head. It is of variable and generally minor significance in adults, and more important in childhood before the epiphyseal vessels dominate.

• Blood supply: Predominantly the retinacular vessels, branches of the medial circumflex femoral artery (major contributor) and lateral circumflex femoral artery (minor), running along the femoral neck within the capsule/synovial reflections.
• A small contribution from the artery of the ligament of the head of femur (acetabular branch of obturator artery); trochanteric and cruciate anastomoses also contribute.

• Innervation: Femoral nerve, obturator nerve, nerve to quadratus femoris, superior gluteal nerve, multiple contributions (Hilton's law); notably, hip pathology can refer pain to the knee via the obturator nerve's dual innervation of both joints.

• Movements: Flexion/extension, abduction/adduction, medial/lateral rotation, circumduction, second most mobile joint after the shoulder, but with substantially greater inherent bony stability.

• Stability: Relies on a combination of deep bony socket (unlike the shallow glenoid), a strong fibrous capsule, powerful surrounding ligaments (spiral configuration that tightens in extension), the acetabular labrum, and dynamic muscular support. This trades some mobility for much greater inherent stability compared to the shoulder.

Hip dislocation:

• Posterior dislocation is far more common (~90%), typically from a high-energy axial force through a flexed knee/hip (classic "dashboard injury" in a road traffic collision).
• Femoral head displaces posteriorly, at risk of damaging the sciatic nerve and disrupting the posterior retinacular blood supply.
• Limb typically appears shortened, flexed, adducted, and internally rotated.
• Anterior dislocation is rarer, limb appears abducted and externally rotated.

Femoral neck fracture:

• Common in elderly patients with osteoporosis after a low-energy fall; classified as intracapsular (subcapital, transcervical) or extracapsular (intertrochanteric, subtrochanteric).
• Intracapsular, displaced fractures disrupt the retinacular vessels running along the neck, threatening the femoral head's blood supply.
• Classic presentation: shortened and externally rotated limb.

Avascular necrosis:

• Follows disruption of the retinacular blood supply (medial circumflex femoral artery branches), most commonly after displaced intracapsular femoral neck fracture or hip dislocation.
• Femoral head collapse may occur months to years after the initial injury, given the delayed nature of ischaemic bone death and subsequent structural failure.

Trendelenburg sign:

• Tests gluteus medius/minimus function (superior gluteal nerve).
• On single-limb stance on the affected side, the contralateral pelvis drops (rather than being held level or elevated) due to failure of pelvic stabilisation, a positive sign.
• Causes include superior gluteal nerve injury, hip abductor muscle weakness/tear, and chronic hip pathology.

Intramuscular injection safe zone:

• The upper outer quadrant of the buttock, or more precisely the area overlying gluteus medius (ventrogluteal or upper-outer gluteal sites), is used to avoid the sciatic nerve. The nerve runs more medially/inferiorly, deep to gluteus maximus.
• Injecting too low or medial risks direct sciatic nerve injury.