Hip anatomy

Right hip bone

The ilium, ischium and pubis meet in the acetabulum (triradiate cartilage, which closes at the end of adolescence) and bound the obturator foramen. Coverage of the femoral head is measured with the lateral center-edge angle of Wiberg (normal above 25°, dysplasia below 20°); overcoverage or acetabular retroversion (crossover sign) indicates pincer-type femoroacetabular impingement. The apophyses (anterior iliac spines, ischial tuberosity) are typical sites of avulsion in adolescents.

Right proximal femur

Head, neck, greater and lesser trochanters, joined anteriorly by the intertrochanteric line and posteriorly by the intertrochanteric crest. Neck-shaft angle of about 125–130° and femoral neck anteversion of about 10–15°. Asphericity of the head-neck junction (cam deformity, increased alpha angle) causes cam-type femoroacetabular impingement; femoral neck fractures are intracapsular and may compromise the blood supply of the head (Garden classification).

Sacrum

Five fused vertebrae; the auricular surfaces articulate with the ilium (sacroiliac joints) and the sacral foramina transmit the rami of the sacral nerves. On MRI, subchondral bone marrow edema of the sacroiliac joints is the main sign of active sacroiliitis; in osteoporosis, insufficiency fractures may form an H shape (Honda sign) on bone scintigraphy or CT.

Femoral head cartilage

It covers the femoral head except for the fovea, where the ligament of the head of the femur attaches; it is thickest in the anterosuperior weight-bearing zone. In osteoarthritis, joint space narrowing is typically superolateral; MRI and MR arthrography assess thinning, fissures and focal defects.

Acetabular cartilage

It covers the horseshoe-shaped lunate surface of the acetabulum and is thickest at the roof, the weight-bearing zone; the acetabular fossa and notch lack cartilage and contain the fatty pulvinar and the ligament of the head of the femur. In cam-type femoroacetabular impingement the anterosuperior cartilage may separate from the bone (delamination), often with a tear of the adjacent labrum.

Acetabular labrum

Fibrocartilaginous ring with a triangular cross-section on the acetabular rim, continuous inferiorly with the transverse ligament. Tears are mainly anterosuperior (femoroacetabular impingement, dysplasia); on MR arthrography they must be distinguished from sublabral sulci and may be associated with paralabral cysts.

Origin

Bony rim of the acetabulum.

Insertion

Ring open inferiorly, completed by the transverse ligament across the acetabular notch.

Function

Deepens the acetabulum, distributes load and maintains negative intra-articular pressure (seal effect).

Iliofemoral ligament

Inverted Y-shaped ligament (of Bigelow), the strongest in the body: the superolateral and medial bands diverge toward the intertrochanteric line. It is taut in the upright position and allows standing with minimal muscle effort. On MRI it appears as a thickening of the anterior capsule.

Origin

Anterior inferior iliac spine and adjacent acetabular rim.

Insertion

Intertrochanteric line: upper part (superolateral band) and lower part (medial band).

Function

Limits extension and external rotation; the superolateral band also limits adduction.

Pubofemoral ligament

Triangular anteroinferior reinforcement of the capsule that blends with the medial band of the iliofemoral ligament. Between the two ligaments the capsule is thinner: here the iliopectineal bursa, beneath the iliopsoas tendon, may communicate with the joint.

Origin

Iliopubic eminence, superior pubic ramus and obturator crest.

Insertion

Inferior capsule and lower part of the intertrochanteric line, together with the medial band of the iliofemoral ligament.

Function

Limits abduction and extension; helps limit external rotation.

Ischiofemoral ligament

Posterior reinforcement, thinner than the anterior ligaments, spiraling from the ischium upward and laterally over the neck; some fibers continue into the zona orbicularis. It slackens in flexion: posterior dislocation typically occurs with the hip flexed and adducted (dashboard injury).

Origin

Body of the ischium, behind and below the acetabular rim.

Insertion

Upper surface of the femoral neck, near the base of the greater trochanter, and zona orbicularis.

Function

Limits internal rotation, adduction and extension.

Transverse acetabular ligament

Strong fibrous bridge across the acetabular notch, continuous with the labrum at both ends; the vessels to the ligament of the head of the femur pass beneath it. On MR arthrography its junction with the labrum may mimic a tear.

Origin

Anterior end of the acetabular notch.

Insertion

Posterior end of the acetabular notch.

Function

Completes the acetabular ring and the labrum inferiorly; contributes to the stability of the head.

Ligament of the head of the femur

Flattened intra-articular band, covered by synovium, from the acetabular notch to the fovea. It carries the artery of the ligamentum teres (acetabular branch of the obturator artery), important for the head in children, minor in adults. Its tears, seen on MR arthrography and arthroscopy, cause pain and instability in athletes.

Origin

Margins of the acetabular notch and transverse ligament.

Insertion

Fovea of the head of the femur.

Function

Becomes taut in flexion, adduction and external rotation; contributes to joint stability and proprioception.

Joint capsule

Strong fibrous sleeve from the acetabular rim to the femoral neck: anteriorly it encloses the whole neck, posteriorly it leaves the lateral part of the neck extracapsular. It is reinforced by the iliofemoral, pubofemoral and ischiofemoral ligaments and by deep circular fibers (zona orbicularis). The retinacular vessels of the head run along the neck beneath the synovium. Ultrasound assesses effusion in the anterior recess along the neck, compared with the opposite side.

Origin

Acetabular rim, outside the labrum, and transverse ligament.

Insertion

Intertrochanteric line anteriorly; femoral neck about 1 cm above the intertrochanteric crest posteriorly.

Function

Contains the synovium and synovial fluid; with the ligaments it mainly limits extension and extreme rotation.

Subgluteus medius bursa

Between the lateral part of the gluteus medius tendon and the upper part of the lateral facet of the greater trochanter; normally a potential space. One of the peritrochanteric bursae: on ultrasound and MRI its distension usually accompanies gluteus medius tendinopathy or tears, in greater trochanteric pain syndrome.

Subgluteus minimus bursa

Between the gluteus minimus tendon and the joint capsule, medial and superior to its insertion on the anterior facet of the greater trochanter; normally a potential space. It is the smallest of the peritrochanteric bursae and the least often distended, usually together with gluteus minimus tendinopathy.

Trochanteric bursa (subgluteus maximus)

The largest of the peritrochanteric bursae: between the lateral and posterior facets of the greater trochanter, with the gluteus medius tendon, and the iliotibial tract and gluteus maximus, which glide over it; normally a potential space. On ultrasound and MRI, fluid distension is part of greater trochanteric pain syndrome, which however more often results from tendinopathy or tears of the gluteus medius and minimus: isolated bursitis is rare.

Iliopsoas bursa (iliopectineal)

The largest bursa in the body: between the iliopsoas tendon and the anterior capsule, over the iliopectineal eminence and in front of the femoral head, lateral to the femoral vessels. In about 15% of adults it communicates with the joint through the thin area between the iliofemoral and pubofemoral ligaments, so it distends with joint effusion (osteoarthritis, rheumatoid arthritis). On ultrasound and MRI the distended bursa is a tubular collection along the tendon, which can compress the femoral vein or nerve.

Ischiogluteal bursa

Between the ischial tuberosity, superficial to the origin of the hamstrings, and the gluteus maximus, which covers it when standing and moves away from it when sitting; normally a potential space. Bursitis from prolonged sitting causes low buttock pain; on MRI it is a collection superficial to the tuberosity, to be distinguished from proximal hamstring tendinopathy or avulsion and from the nearby sciatic nerve.

Gluteus maximus

The most superficial and largest muscle of the gluteal region: it covers the deep rotators and the sciatic nerve. Between its tendon and the greater trochanter lies the trochanteric bursa, a site of bursitis in greater trochanteric pain syndrome. Inferior gluteal nerve (L5–S2).

Origin

Gluteal surface of the ilium behind the posterior gluteal line, posterior surface of the sacrum and coccyx, sacrotuberous ligament and thoracolumbar fascia.

Insertion

Iliotibial tract (superficial fibers, the majority) and gluteal tuberosity of the femur (deep fibers).

Function

Extension and external rotation of the hip; the upper fibers assist abduction, the lower fibers adduction. Through the iliotibial tract it stabilizes the extended knee.

Gluteus medius

Fan-shaped belly superficial to the gluteus minimus, covered posteriorly by the gluteus maximus. The anterior and lateral fibers converge onto a flattened tendon at the lateral facet, the posterior fibers onto a thicker tendon at the superoposterior facet. With the gluteus minimus it forms the “rotator cuff of the hip”: tendinopathy and tears, assessed with ultrasound and MRI, are the main cause of greater trochanteric pain syndrome. Superior gluteal nerve (L4–S1).

Origin

Gluteal surface of the ilium between the iliac crest and the anterior and posterior gluteal lines; gluteal fascia.

Insertion

Lateral and superoposterior facets of the greater trochanter.

Function

Hip abduction and stabilization of the pelvis in single-leg stance. Anterior fibres: assist hip flexion and internal rotation. Posterior fibres: assist hip extension and external rotation.

Gluteus minimus

The deepest gluteal muscle, covered by the gluteus medius. Its fibers converge onto an aponeurosis and a flattened tendon directed to the anterior facet of the greater trochanter. Its tears often accompany those of the gluteus medius in greater trochanteric pain syndrome. Superior gluteal nerve (L4–S1).

Origin

Gluteal surface of the ilium between the anterior and inferior gluteal lines.

Insertion

Anterior facet of the greater trochanter; deep fibers to the joint capsule.

Function

Abduction and internal rotation of the hip; stabilizes the femoral head in the acetabulum.

Tensor fasciae latae

Enclosed between two layers of the fascia lata, on the anterolateral aspect of the hip. The interval between the tensor and the sartorius is used for the direct anterior approach to the hip, where the lateral femoral cutaneous nerve is at risk. Superior gluteal nerve (L4–S1).

Origin

Anterior superior iliac spine and anterior part of the outer lip of the iliac crest.

Insertion

Iliotibial tract, in the proximal third of the thigh.

Function

Flexion, abduction and internal rotation of the hip; tenses the fascia lata and, through the iliotibial tract, stabilizes the extended knee.

Piriformis

It leaves the pelvis through the greater sciatic foramen, which it divides into a suprapiriform passage (superior gluteal vessels and nerve) and an infrapiriform passage (sciatic nerve, inferior gluteal vessels and nerve, pudendal nerve, posterior femoral cutaneous nerve). In a minority of cases the sciatic nerve, or its fibular component, passes through the muscle: a variant considered in piriformis syndrome, which remains a diagnosis of exclusion. Nerve to piriformis (S1–S2).

Origin

Pelvic surface of the sacrum, between the anterior sacral foramina (S2–S4), and margin of the greater sciatic notch.

Insertion

Superior border of the greater trochanter.

Function

External rotation of the extended hip and abduction of the flexed hip.

Obturator internus

It leaves the pelvis through the lesser sciatic foramen, turning almost at a right angle around the lesser sciatic notch, where a bursa allows it to glide. With the two gemelli it forms the triceps coxae. Its fascia, in the lateral wall of the ischioanal fossa, contains the pudendal (Alcock) canal. Nerve to obturator internus (L5–S2).

Origin

Internal surface of the obturator membrane and bony margins of the obturator foramen.

Insertion

Medial surface of the greater trochanter, above the trochanteric fossa, together with the gemelli.

Function

External rotation of the extended hip and abduction of the flexed hip; stabilizes the femoral head in the acetabulum.

Obturator externus

It passes below and behind the femoral neck before reaching the trochanteric fossa. The deep branch of the medial circumflex femoral artery runs behind its tendon: preserving the tendon protects the blood supply of the head in posterior approaches and in surgical hip dislocation. Obturator nerve, posterior branch (L3–L4).

Origin

External surface of the obturator membrane and bony margins of the obturator foramen (pubic and ischial rami).

Insertion

Trochanteric fossa of the femur.

Function

External rotation of the hip; stabilizes the femoral head.

Superior gemellus

Small muscle that runs along the upper border of the obturator internus tendon to the greater trochanter; with it and the inferior gemellus it forms the triceps coxae. Nerve to obturator internus (L5–S2).

Origin

External surface of the ischial spine.

Insertion

Tendon of the obturator internus and medial surface of the greater trochanter.

Function

External rotation of the extended hip; stabilizes the femoral head.

Inferior gemellus

Small muscle that runs along the lower border of the obturator internus tendon to the greater trochanter, above the quadratus femoris. Nerve to quadratus femoris (L4–S1).

Origin

Upper border of the ischial tuberosity.

Insertion

Tendon of the obturator internus and medial surface of the greater trochanter.

Function

External rotation of the extended hip; stabilizes the femoral head.

Quadratus femoris

Quadrilateral muscle between the ischial tuberosity and the proximal femur, below the inferior gemellus. In ischiofemoral impingement, narrowing of the space between the ischium and the lesser trochanter compresses the muscle, which shows edema and sometimes atrophy or tearing on MRI. Nerve to quadratus femoris (L4–S1).

Origin

Lateral border of the ischial tuberosity.

Insertion

Quadrate tubercle of the intertrochanteric crest.

Function

External rotation of the hip; assists adduction.

Iliacus

It fills the iliac fossa and joins the psoas major to form the iliopsoas, which passes under the inguinal ligament (muscular lacuna) in front of the joint capsule. An iliacus hematoma (anticoagulant therapy, hemophilia) may compress the femoral nerve, which runs in the groove between the two muscles. Femoral nerve (L2–L3).

Origin

Upper two thirds of the iliac fossa, inner lip of the iliac crest, ala of the sacrum and anterior sacroiliac ligaments.

Insertion

Lesser trochanter, with the iliopsoas tendon, and the femur just below it.

Function

Hip flexion; with the femur fixed, anterior tilt of the pelvis and flexion of the trunk.

Psoas major

The lumbar plexus forms within the muscle: the femoral nerve emerges from its lateral border, the obturator nerve from its medial border, the genitofemoral nerve from its anterior surface. Between the iliopsoas tendon and the capsule lies the iliopectineal bursa, which may communicate with the joint; snapping of the tendon over the iliopectineal eminence is internal snapping hip, shown with dynamic ultrasound. An abscess from spondylodiscitis may track along the muscle sheath down to the groin. Anterior rami of the lumbar nerves (L1–L3).

Origin

Lateral surface of the T12–L5 vertebral bodies and intervening discs; lumbar transverse processes.

Insertion

Lesser trochanter, with the iliacus (iliopsoas tendon).

Function

Hip flexion; lateral flexion of the lumbar spine and lumbopelvic stabilization.

Rectus femoris

The only biarticular head of the quadriceps. The tendons of its two heads join and continue into a central aponeurosis within the belly. It is the most frequently injured quadriceps head in sport (myotendinous junction, aponeurosis of the reflected head); in adolescents the anterior inferior iliac spine may avulse. Femoral nerve (L2–L4).

Origin

Direct head from the anterior inferior iliac spine; reflected (indirect) head from the supra-acetabular groove and the joint capsule.

Insertion

Base of the patella through the quadriceps tendon; tibial tuberosity through the patellar ligament.

Function

Hip flexion and knee extension.

Sartorius

The longest muscle in the body, strap-like, crossing the thigh obliquely. It forms the lateral border of the femoral triangle and, further down, the roof of the adductor canal. In adolescents, traction may avulse the anterior superior iliac spine. Femoral nerve (L2–L3).

Origin

Anterior superior iliac spine.

Insertion

Medial surface of the proximal tibia, at the pes anserinus.

Function

Flexion, abduction and external rotation of the hip; knee flexion.

Vastus intermedius

Deep to the rectus femoris, it covers the anterior and lateral femoral shaft. It is the usual site of anterior thigh contusions, which may progress to myositis ossificans. Femoral nerve (L2–L4).

Origin

Proximal two thirds of the anterior and lateral surfaces of the femoral shaft.

Insertion

Patella via the quadriceps tendon and tibial tuberosity via the patellar ligament.

Function

Knee extension.

Vastus lateralis

The largest head of the quadriceps, on the lateral side of the thigh, deep to the iliotibial tract. It is a usual site for muscle biopsy. Femoral nerve (L2–L4).

Origin

Greater trochanter, gluteal tuberosity and lateral lip of the linea aspera.

Insertion

Patella via the quadriceps tendon and tibial tuberosity via the patellar ligament.

Function

Knee extension.

Vastus medialis

It lies medial to the vastus intermedius and forms the anterolateral wall of the adductor canal. Its distal oblique fibers (vastus medialis obliquus) resist lateral displacement of the patella. Femoral nerve (L2–L4).

Origin

Intertrochanteric line and medial lip of the linea aspera.

Insertion

Patella via the quadriceps tendon and tibial tuberosity via the patellar ligament.

Function

Knee extension and contribution to medial patellar stabilization.

Pectineus

Quadrilateral muscle in the floor of the femoral triangle, between the iliopsoas laterally and the adductor longus medially; the femoral vessels run in front of it. Femoral nerve (L2–L3), sometimes with a contribution from the obturator nerve.

Origin

Pecten pubis, between the iliopectineal eminence and the pubic tubercle.

Insertion

Pectineal line of the femur, from the lesser trochanter to the linea aspera.

Function

Adduction and flexion of the hip.

Adductor brevis

It separates the two branches of the obturator nerve: the anterior branch passes in front of it, the posterior branch behind. It is covered by the pectineus and adductor longus and lies on the adductor magnus. Obturator nerve (L2–L4).

Origin

Body and inferior ramus of the pubis.

Insertion

Pectineal line and proximal part of the linea aspera.

Function

Hip adduction; assists flexion.

Adductor longus

The most anterior of the adductors; its medial border bounds the femoral triangle. It is the most frequently injured adductor in sports with changes of direction; its pubic enthesis, continuous with the rectus abdominis aponeurosis (rectus abdominis–adductor aponeurosis), is the typical site of athletic pubalgia on MRI. Obturator nerve, anterior branch (L2–L4).

Origin

Body of the pubis, below the pubic tubercle.

Insertion

Middle third of the medial lip of the linea aspera.

Function

Adduction and flexion of the hip.

Adductor magnus

The largest adductor, with two parts: the adductor part, supplied by the obturator nerve (posterior branch, L2–L4), and the hamstring part, supplied by the tibial component of the sciatic nerve (L4). Between the two distal insertions, the adductor hiatus transmits the femoral vessels to the popliteal fossa.

Origin

Ischiopubic ramus (adductor part) and ischial tuberosity (hamstring part).

Insertion

Gluteal tuberosity, linea aspera and medial supracondylar line (adductor part); adductor tubercle of the femur (hamstring part).

Function

Hip adduction; the hamstring part assists extension.

Gracilis

The most superficial and medial adductor, the only biarticular muscle of the group. Its distal tendon forms the pes anserinus with the sartorius and semitendinosus and is used as a graft in anterior cruciate ligament reconstruction. Obturator nerve, anterior branch (L2–L3).

Origin

Body and inferior ramus of the pubis.

Insertion

Medial surface of the proximal tibia, at the pes anserinus.

Function

Hip adduction; flexion and internal rotation of the knee.

Semitendinosus

Its long, thin distal tendon is used as a graft in anterior cruciate ligament reconstruction. In proximal hamstring avulsions, MRI defines how many tendons are involved and how far they are retracted, which guides the decision for surgery. Tibial component of the sciatic nerve (L5–S2).

Origin

Inferomedial facet of the ischial tuberosity, through a conjoint tendon with the long head of the biceps femoris.

Insertion

Medial surface of the proximal tibia, at the pes anserinus.

Function

Hip extension; flexion and internal rotation of the knee.

Semimembranosus

Its broad, flat proximal tendon arises anterior and lateral to the conjoint tendon of the semitendinosus and biceps and descends medially beneath it; its muscle belly begins lower than those of the other hamstrings. Tibial component of the sciatic nerve (L5–S2).

Origin

Superolateral facet of the ischial tuberosity.

Insertion

Posteromedial surface of the medial tibial condyle; expansions to the oblique popliteal ligament.

Function

Hip extension; flexion and internal rotation of the knee.

Biceps femoris – long head

It is the hamstring most often injured in sprinting, especially at the proximal myotendinous junction. The sciatic nerve runs just lateral to its ischial origin and should be assessed on MRI in avulsions and hematomas. Tibial component of the sciatic nerve (L5–S2).

Origin

Inferomedial facet of the ischial tuberosity, through a conjoint tendon with the semitendinosus; sacrotuberous ligament.

Insertion

Head of the fibula, with the short head.

Function

Hip extension; flexion and external rotation of the knee.

Iliotibial tract

Lateral thickening of the fascia lata, stretched from the iliac crest to the proximal tibia. Snapping over the greater trochanter is external snapping hip; friction over the lateral femoral epicondyle causes iliotibial band syndrome, typical of runners.

Origin

Iliac tubercle on the outer lip of the iliac crest; the tensor fasciae latae and gluteus maximus insert into it.

Insertion

Gerdy tubercle of the tibia; expansions to the patella and, through the lateral intermuscular septum, to the linea aspera.

Function

Lateral stabilization of the hip and of the extended knee; transmits the pull of the tensor fasciae latae and gluteus maximus.

External iliac artery

From the bifurcation of the common iliac artery, in front of the sacroiliac joint, it follows the medial border of the psoas major to the inguinal ligament, where it continues as the femoral artery. Relation: the external iliac vein lies medial and posterior.

Femoral artery

Continues the external iliac artery below the inguinal ligament, midway between the anterior superior iliac spine and the symphysis; in the femoral triangle it lies lateral to the vein and medial to the nerve, then descends under the sartorius toward the adductor canal. Landmark for vascular access and groin ultrasound.

Deep femoral artery

Arises from the posterolateral side of the femoral artery about 4 cm below the inguinal ligament; it descends close to the femur, behind the adductor longus and in front of the pectineus, adductor brevis and adductor magnus. Gives off the circumflex and perforating arteries.

Medial circumflex femoral artery

Runs backward between the iliopsoas and pectineus, then between the obturator externus and adductor brevis; the deep branch ascends above the quadratus femoris toward the trochanteric fossa and the posterior neck. It is the main source of the retinacular vessels of the head: relevant in femoral neck fractures and avascular necrosis.

Lateral circumflex femoral artery

Runs laterally in front of the iliopsoas, behind the sartorius and rectus femoris; the ascending branch rises lateral to the neck, under the tensor fasciae latae, toward the gluteus minimus. It also gives off the transverse and descending branches; the descending branch is the pedicle of the anterolateral thigh flap.

Internal iliac artery

Descends into the lesser pelvis in front of the sacroiliac joint and, at the upper margin of the greater sciatic notch, divides into a posterior trunk (superior gluteal) and an anterior trunk (obturator, inferior gluteal). The anterior trunk also gives off the visceral branches and the internal pudendal artery.

Obturator artery

From the anterior trunk of the internal iliac artery it follows the lateral pelvic wall, below the obturator nerve, and leaves through the obturator canal. A common variant (corona mortis) connects it with the epigastric vessels over the superior pubic ramus: it is at risk in fractures and surgical approaches to the pubis.

Superior gluteal artery

Largest branch of the internal iliac artery: it leaves the greater sciatic foramen above the piriformis and divides between the gluteus maximus and medius (superficial branch) and between the gluteus medius and minimus (deep branch). Exposed in fractures through the sciatic notch.

Inferior gluteal artery

From the anterior trunk it leaves below the piriformis, medial to the sciatic nerve, and descends between the greater trochanter and the ischial tuberosity on the deep surface of the gluteus maximus, which it supplies.

External iliac vein

Continues the femoral vein from the inguinal ligament and ascends medial to and slightly behind the artery of the same name, until it joins the internal iliac vein to form the common iliac vein.

Femoral vein

In the femoral triangle it is the most medial structure (nerve, artery, vein from lateral to medial) and gradually slips behind the artery toward the adductor canal. Compressible with the probe: the basis of ultrasound for deep vein thrombosis.

Deep femoral vein

Companion of the deep femoral artery, in front of it; it joins the femoral vein a few centimeters below the inguinal ligament (the common femoral vein is the segment above the confluence).

Medial circumflex femoral vein

Accompanies the artery between the iliopsoas, pectineus and obturator externus to the posterior trochanteric region and drains into the femoral vein.

Lateral circumflex femoral vein

Accompanies the artery under the sartorius and rectus femoris and drains into the femoral vein, sometimes into the deep femoral vein.

Internal iliac vein

Receives the gluteal, obturator and pelvic veins; it runs posteromedial to the artery and joins the external iliac vein in front of the sacroiliac joint.

Obturator vein

Accompanies the artery through the obturator canal and along the lateral pelvic wall to the internal iliac vein.

Superior gluteal vein

Companion of the superior gluteal artery through the suprapiriform foramen, between the gluteus medius and minimus; in adults often paired.

Inferior gluteal vein

Companion of the inferior gluteal artery from the gluteus maximus to the infrapiriform foramen, medial to the sciatic nerve.

Femoral nerve

Mixed (L2–L4): descends in the groove between the psoas major and iliacus, under the iliac fascia, and passes under the inguinal ligament lateral to the artery, outside the femoral sheath; it divides shortly below. Supplies the iliacus, pectineus, sartorius and quadriceps; sensation of the anterior thigh and, through the saphenous nerve, of the medial leg. It may be compressed by an iliopsoas hematoma or injured in anterior approaches to the hip.

Obturator nerve

Mixed (L2–L4): emerges from the medial border of the psoas major, descends on the lateral pelvic wall above the obturator vessels and leaves through the obturator canal; the anterior branch passes in front of the adductor brevis, the posterior branch behind it. Supplies the adductors and the skin of the medial thigh; hip pain can be referred to the knee.

Lateral femoral cutaneous nerve

Sensory (L2–L3): from the lateral border of the psoas major it crosses the iliacus obliquely, passes under the inguinal ligament about 1 cm medial to the anterior superior iliac spine and descends in front of the sartorius into the fascia lata. Compression at this point causes meralgia paresthetica.

Sciatic nerve

Mixed (L4–S3), the largest nerve: it leaves the greater sciatic foramen below the piriformis, descends between the greater trochanter and the ischial tuberosity behind the gemelli, obturator internus and quadratus femoris, covered by the gluteus maximus, then behind the adductor magnus and under the long head of the biceps. Supplies the hamstrings and, through the tibial and common fibular nerves, the leg and foot. At risk in posterior dislocation and in the posterior approach to the hip.

Superior gluteal nerve

Motor (L4–S1): leaves above the piriformis with the superior gluteal vessels and runs between the gluteus medius and minimus to the tensor fasciae latae, which it supplies together with these two muscles. Injury (lateral approaches, injections) weakens the abductors: Trendelenburg sign.

Inferior gluteal nerve

Motor (L5–S2): leaves below the piriformis, superficial to the sciatic nerve, and enters the deep surface of the gluteus maximus, the only muscle it supplies.

Posterior femoral cutaneous nerve

Sensory (S1–S3): leaves below the piriformis, medial to and behind the sciatic nerve, descends under the gluteus maximus and then under the fascia, on the hamstrings, toward the skin of the posterior thigh and popliteal fossa. It gives off the inferior cluneal nerves and perineal branches.

Nerve to quadratus femoris

Motor with articular branches (L4–S1): leaves below the piriformis in front of the sciatic nerve and descends on the ischium, deep to the gemelli and the obturator internus tendon, to the quadratus femoris and inferior gemellus. Contributes to the innervation of the posterior capsule.

Nerve to obturator internus

Motor (L5–S2): leaves below the piriformis, crosses the ischial spine lateral to the internal pudendal vessels and re-enters through the lesser sciatic foramen to the pelvic surface of the obturator internus; gives a branch to the superior gemellus.