Medical School · Year 1 · Anatomy Msk · includes a quiz and discussion video

Lecture 10: Lower Limb - Hip and Thigh

Unit 1.3: Human Gross Anatomy I - Musculoskeletal System

Learning Objectives

By the end of this lecture, students will be able to:

1. Describe the bones of the pelvic girdle and their features
2. Identify the features of the femur and their clinical significance
3. Describe the structure and function of the hip joint
4. Identify the muscles of the gluteal region and their actions
5. Describe the anterior, medial, and posterior compartments of the thigh
6. Explain the course and distribution of major nerves in this region

Bones of the Pelvic Girdle

The pelvic girdle transmits the weight of the upper body to the lower limbs and provides attachment for the powerful muscles of the hip and thigh. Each hip bone (os coxae) is formed by the fusion of three bones that meet at the acetabulum.

The Hip Bone

The hip bone develops from three separate bones—the ilium, ischium, and pubis—that fuse during adolescence at the acetabulum, the cup-shaped socket for the hip joint.

The ilium is the largest of the three components and forms the superior part of the hip bone. Its superior border, the iliac crest, extends from the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS). The iliac crest is easily palpable and is a common site for bone marrow biopsy. The ASIS, located at the anterior end of the crest, serves as the attachment for the inguinal ligament and the origin of the sartorius muscle. The anterior inferior iliac spine (AIIS), just below the ASIS, provides the origin for the straight head of the rectus femoris.

Posteriorly, the PSIS marks the level of the S2 vertebra and the midpoint of the sacroiliac joint—a useful clinical landmark. Below the PSIS, the posterior inferior iliac spine (PIIS) lies above the greater sciatic notch, through which the sciatic nerve and piriformis muscle pass. The internal surface of the ilium features the iliac fossa, a smooth concavity that gives origin to the iliacus muscle, and the auricular surface, which articulates with the sacrum at the sacroiliac joint.

The ischium forms the posteroinferior part of the hip bone. The ischial tuberosity is its most prominent feature—a rough projection that bears weight when sitting and provides origin for the hamstring muscles. The ischial spine, located between the greater and lesser sciatic notches, provides attachment for the sacrospinous ligament. The lesser sciatic notch, below the spine, transmits the internal pudendal vessels and pudendal nerve. The ischial ramus extends anteriorly to join the inferior pubic ramus.

The pubis forms the anteromedial part of the hip bone. The pubic body is the broad medial portion that articulates with the opposite pubis at the pubic symphysis, a secondary cartilaginous joint. The pubic tubercle, a small projection on the superior surface, marks the medial attachment of the inguinal ligament. The superior pubic ramus extends laterally to the acetabulum, while the inferior pubic ramus joins the ischial ramus to complete the obturator foramen.

The Acetabulum

The acetabulum is the cup-shaped cavity on the lateral aspect of the hip bone where all three bones meet. It faces laterally, anteriorly, and inferiorly, an orientation that enhances stability.

The articular surface of the acetabulum is the lunate surface, a horseshoe-shaped area covered with hyaline cartilage that articulates with the femoral head. The acetabular fossa is the non-articular central depression that contains a fat pad and the ligament of the head of the femur. The acetabular notch is an inferior gap in the acetabular rim, spanned by the transverse acetabular ligament.

The acetabular labrum is a fibrocartilaginous rim that attaches to the acetabular margin and deepens the socket, increasing femoral head coverage from approximately 40% to over 50%. This significantly enhances joint stability.

<image>Panel A: Lateral view of hip bone with ilium (blue) showing iliac crest, ASIS with inguinal ligament attachment, AIIS, PSIS, and greater sciatic notch; ischium (green) with ischial tuberosity, ischial spine, and lesser sciatic notch. Panel B: Pubis (orange) forming anteromedial part with pubic tubercle, superior and inferior pubic rami, and obturator foramen in lateral view. Panel C: Acetabulum at junction of three bones showing lunate surface (articular), acetabular fossa (central depression), and acetabular notch (inferior gap) with labrum. Panel D: Medial view showing iliac fossa (iliacus origin) and auricular surface (sacroiliac joint) with all features labeled and scale bar included.</image>

The Femur

The femur is the longest and strongest bone in the body. Its unique anatomy reflects its role in weight transmission and its vulnerability to specific injury patterns.

Proximal Femur

The head of the femur is nearly spherical, covered with articular cartilage except for a small central depression called the fovea capitis, which provides attachment for the ligament of the head of the femur (ligamentum teres). The head articulates with the acetabulum in the hip joint.

The neck of the femur connects the head to the shaft. It is oriented at approximately 125 degrees to the shaft (the angle of inclination) and approximately 15 degrees anteriorly (the angle of anteversion). The neck is mostly intracapsular, meaning that fractures through the neck can disrupt the blood supply to the head—a critical clinical consideration.

The greater trochanter is a large, palpable projection on the lateral aspect of the proximal femur. It provides insertion for the gluteus medius and minimus muscles and serves as a landmark for intramuscular injections. The lesser trochanter is a smaller, conical projection on the posteromedial aspect, serving as the insertion for the iliopsoas tendon.

The intertrochanteric line is a ridge on the anterior surface connecting the two trochanters; it marks the anterior attachment of the hip joint capsule. The intertrochanteric crest is a corresponding ridge posteriorly, notable for bearing the quadrate tubercle where the quadratus femoris muscle inserts. The trochanteric fossa is a depression on the medial surface of the greater trochanter, serving as the insertion for the obturator externus muscle.

The Femoral Shaft

The shaft of the femur is slightly bowed anteriorly. Its smooth anterior surface provides origin for the vastus intermedius. Posteriorly, the linea aspera is a prominent vertical ridge that provides attachment for many thigh muscles. The linea aspera has medial and lateral lips that diverge both superiorly and inferiorly.

Superiorly, the lateral lip continues as the gluteal tuberosity (for gluteus maximus attachment), while the medial lip becomes the pectineal line (for pectineus attachment). Inferiorly, the lips diverge to form the medial and lateral supracondylar lines, which continue to the respective condyles.

Distal Femur

The distal femur expands to form the medial and lateral condyles, which articulate with the tibia. The medial condyle is larger and projects more inferiorly, contributing to the valgus angle of the knee. The medial and lateral epicondyles are bony prominences proximal to the condyles that provide attachment for the collateral ligaments of the knee.

The adductor tubercle is located on the superior aspect of the medial epicondyle and serves as the attachment for the adductor magnus muscle's hamstring portion. The intercondylar fossa is the deep notch between the condyles posteriorly, containing the cruciate ligament attachments. The patellar surface is the smooth anterior surface between the condyles that articulates with the patella.

Clinical Significance

Hip fractures are among the most common and consequential injuries in the elderly. Intracapsular (femoral neck) fractures disrupt the retinacular vessels that supply the femoral head, creating a significant risk of avascular necrosis. Extracapsular (intertrochanteric) fractures generally have better prognosis because they do not compromise the head's blood supply.

The angle of inclination varies among individuals. Coxa vara describes an angle less than 120 degrees (more horizontal neck), while coxa valga describes an angle greater than 135 degrees (more vertical neck). These variations affect joint mechanics and may predispose to certain conditions.

<image>Panel A: Proximal femur with spherical head, fovea capitis, neck at 125-degree angle of inclination, greater trochanter (gluteus medius/minimus insertion), lesser trochanter (iliopsoas insertion), and intertrochanteric line and crest. Panel B: Femoral shaft showing anterior smooth surface and posterior linea aspera with medial and lateral lips diverging superiorly to gluteal tuberosity and pectineal line, and inferiorly to supracondylar lines. Panel C: Distal femur with medial condyle (larger), lateral condyle, epicondyles with collateral ligament attachments, adductor tubercle, intercondylar fossa with cruciate attachments, and patellar surface. Panel D: Blood supply diagram showing retinacular vessels along neck with vulnerable zone highlighted, and clinical note showing intracapsular versus extracapsular fracture locations.</image>

The Hip Joint

The hip joint is a ball-and-socket synovial joint designed for stability while permitting a wide range of motion. It must bear the entire weight of the upper body while allowing the movements necessary for locomotion.

Articular Surfaces

The head of the femur, covered by articular cartilage except at the fovea, articulates with the acetabulum's lunate surface. The acetabular labrum, a fibrocartilaginous ring attached to the acetabular margin, deepens the socket and increases stability by covering more than half of the femoral head.

The fit between the femoral head and acetabulum is remarkably congruent, with the cartilage surfaces matching closely throughout the range of motion. This congruence, combined with the deepened socket, makes the hip inherently more stable than the shoulder.

Joint Capsule

The fibrous capsule of the hip joint is thick and strong. It attaches proximally to the acetabular rim and labrum. Distally, the capsule attaches anteriorly to the intertrochanteric line (making the entire anterior neck intracapsular), but posteriorly it attaches to the neck about 1 cm proximal to the intertrochanteric crest (leaving part of the posterior neck and both trochanters extracapsular).

This arrangement has important clinical implications: intracapsular fractures can disrupt blood supply within the capsule, while extracapsular fractures preserve the head's blood supply.

Ligaments

The hip joint is reinforced by three capsular ligaments that spiral around the neck, tightening during extension and loosening during flexion.

The iliofemoral ligament (Y ligament of Bigelow) is the strongest ligament in the body. It originates from the AIIS and the acetabular rim, inserting onto the intertrochanteric line in an inverted Y pattern. Its primary function is to prevent hyperextension, allowing us to stand erect with minimal muscular effort. It also limits external rotation.

The pubofemoral ligament extends from the pubis and obturator crest to the inferior aspect of the femoral neck and intertrochanteric line. It limits excessive abduction and extension.

The ischiofemoral ligament is the weakest of the three capsular ligaments. It runs from the ischial part of the acetabular rim to the posterior neck, spiraling superolaterally. It limits internal rotation and extension.

The ligament of the head of the femur (ligamentum teres) is an intracapsular but extrasynovial structure running from the acetabular fossa to the fovea of the femoral head. It carries a small artery (branch of the obturator artery) that contributes minimally to the head's blood supply in adults. The ligament provides little mechanical stability but may have a role in proprioception.

The transverse acetabular ligament spans the acetabular notch, completing the socket inferiorly and converting the notch into a foramen through which vessels and nerves enter the joint.

Blood Supply

The blood supply to the femoral head is critically important because of the vulnerability to avascular necrosis after fractures.

The principal supply comes from the medial and lateral circumflex femoral arteries (branches of the profunda femoris). The medial circumflex femoral artery gives rise to retinacular arteries that ascend along the neck within the joint capsule—these provide the majority of blood to the femoral head. The artery of the ligament of the head (from the obturator artery) provides only minor supply in adults, though it may be more important in children.

Femoral neck fractures can shear the retinacular vessels, leading to avascular necrosis of the femoral head in a significant proportion of cases.

<image>Panel A: Coronal section showing femoral head articulating with acetabulum including lunate surface and labrum, joint capsule attaching to acetabular rim anteriorly to intertrochanteric line and posteriorly partway up neck. Panel B: Ligaments in anterior view with iliofemoral ligament (inverted Y, strongest ligament in body) and pubofemoral ligament, posterior view with ischiofemoral ligament spiraling across neck. Panel C: Ligament of head of femur from acetabular fossa to fovea with small artery within, and transverse acetabular ligament spanning notch in superior view. Panel D: Blood supply showing medial and lateral circumflex femoral arteries giving retinacular vessels along neck (vulnerable to fracture), artery of ligament of head (minor supply in adults), and clinical inset of femoral neck fracture disrupting retinacular vessels.</image>

Movements at the Hip Joint

The hip joint permits movement in all three planes, though its range is less than that of the shoulder due to the deeper socket and stronger ligamentous restraints.

Flexion brings the anterior thigh toward the trunk. With the knee extended, flexion reaches approximately 90 degrees (limited by hamstring tightness); with the knee flexed, it can exceed 120 degrees. The primary flexors are the iliopsoas, rectus femoris, and sartorius.

Extension returns the thigh from flexion or moves it posterior to the body. Active extension reaches approximately 30 degrees and is primarily performed by the gluteus maximus and hamstrings. Extension is limited by the iliofemoral ligament, which is taut in the standing position.

Abduction moves the thigh away from the midline (approximately 45 degrees) and is performed by the gluteus medius and minimus, assisted by the tensor fasciae latae. Adduction returns the thigh toward and across the midline (approximately 30 degrees), performed by the adductor muscles and gracilis.

External (lateral) rotation turns the anterior thigh laterally (approximately 45 degrees). The deep lateral rotators (piriformis, obturator internus and externus, gemelli, and quadratus femoris) are the primary muscles, assisted by the gluteus maximus. Internal (medial) rotation turns the anterior thigh medially (approximately 35 degrees), primarily performed by the anterior fibers of the gluteus medius and minimus and the tensor fasciae latae.

Gluteal Region Muscles

The gluteal region contains powerful muscles that control hip movement and maintain stability during walking and standing.

Superficial Muscles

The gluteus maximus is the largest muscle in the body and the primary hip extensor. It originates from the posterior ilium (behind the posterior gluteal line), the dorsal surface of the sacrum and coccyx, and the sacrotuberous ligament. Its fibers run obliquely downward and laterally to insert into the iliotibial tract (upper portion) and the gluteal tuberosity of the femur (lower portion).

The gluteus maximus powerfully extends the hip, particularly against resistance (climbing stairs, rising from sitting, running). It also externally rotates the thigh. Through its attachment to the iliotibial tract, it helps stabilize the extended knee. The gluteus maximus is innervated by the inferior gluteal nerve (L5-S2).

The gluteus medius lies deep to the maximus. It originates from the external surface of the ilium between the anterior and posterior gluteal lines and inserts onto the lateral surface of the greater trochanter. Its primary action is hip abduction, but it is more important as a pelvic stabilizer during the stance phase of gait. The anterior fibers also internally rotate the thigh. It is innervated by the superior gluteal nerve (L4-S1).

The gluteus minimus is the smallest of the three gluteal muscles, lying deep to the medius. It originates from the ilium between the anterior and inferior gluteal lines and inserts onto the anterior surface of the greater trochanter. Its actions mirror those of the gluteus medius: abduction and internal rotation, with an important role in pelvic stabilization. It shares innervation with the medius from the superior gluteal nerve.

The tensor fasciae latae originates from the ASIS and anterior iliac crest, inserting into the iliotibial tract. It assists in flexion, abduction, and internal rotation of the hip, and through its attachment to the iliotibial tract, helps maintain knee extension. It is innervated by the superior gluteal nerve.

<image>Panel A: Superficial gluteus maximus (pink-red) with fibers running obliquely from posterior ilium, sacrum, coccyx, and sacrotuberous ligament to iliotibial tract and gluteal tuberosity, innervated by inferior gluteal nerve (L5-S2). Panel B: Gluteus medius (blue) revealed with maximus reflected, originating from external ilium between gluteal lines inserting on lateral greater trochanter, innervated by superior gluteal nerve (L4-S1). Panel C: Gluteus minimus (green) deep to medius, from ilium between anterior and inferior gluteal lines to anterior greater trochanter, and tensor fasciae latae (yellow) from ASIS to iliotibial tract. Panel D: Action diagrams showing hip extension (maximus), abduction (medius/minimus), and pelvic stabilization in single-leg stance with fiber direction arrows.</image>

Deep Lateral Rotators

Six small muscles in the gluteal region produce external rotation of the hip. They can be remembered using the mnemonic "P-GO-GO-Q" (Piriformis, Gemellus superior, Obturator internus, Gemellus inferior, Obturator externus, Quadratus femoris).

The piriformis originates from the anterior surface of the sacrum and passes through the greater sciatic foramen to insert on the upper border of the greater trochanter. It is a key anatomical landmark because structures entering or leaving the pelvis through the greater sciatic foramen are described by their relationship to it. The piriformis externally rotates and assists in abduction of the flexed hip. It is innervated by the nerve to piriformis (S1-S2).

The obturator internus originates from the internal surface of the obturator membrane and surrounding bone. Its tendon makes a sharp turn around the lesser sciatic notch (using it as a pulley) before inserting on the medial surface of the greater trochanter. The superior and inferior gemelli are small muscles that arise from the ischial spine and ischial tuberosity respectively, inserting with the obturator internus tendon and augmenting its action.

The quadratus femoris is a flat, quadrilateral muscle originating from the ischial tuberosity and inserting on the intertrochanteric crest. It is the most inferior of the deep rotators.

The obturator externus originates from the external surface of the obturator membrane and inferior pubic ramus. It passes posteriorly, inferior to the hip joint, to insert in the trochanteric fossa. Unlike the other deep rotators (which are innervated by direct branches from the sacral plexus), the obturator externus is supplied by the obturator nerve.

Piriformis Syndrome

The sciatic nerve typically exits the pelvis through the greater sciatic foramen, passing inferior to the piriformis muscle. In some anatomical variations, part or all of the nerve may pass through or above the piriformis. Piriformis syndrome describes sciatic nerve irritation or compression by the piriformis, causing buttock pain that may radiate down the leg. It can mimic lumbar disc herniation and is sometimes called "wallet sciatica" because sitting on a thick wallet can exacerbate symptoms.

<image>Panel A: Posterior view with gluteus maximus removed showing piriformis (red) exiting greater sciatic foramen as key anatomical landmark, superior gemellus from ischial spine, obturator internus with sharp turn around lesser sciatic notch, and inferior gemellus from ischial tuberosity. Panel B: Quadratus femoris (purple, flat) from ischial tuberosity to intertrochanteric crest, and obturator externus (green) passing deep and posterior from obturator membrane to trochanteric fossa with nerve supply indicated. Panel C: Sciatic nerve (yellow) exiting below piriformis with variations inset showing nerve passing through or above piriformis, greater and lesser sciatic foramina with sacrospinous and sacrotuberous ligaments. Panel D: Piriformis syndrome illustration showing nerve compression and clinical presentation with P-GO-GO-Q mnemonic for muscle arrangement.</image>

Thigh Compartments

The thigh is divided into three compartments by intermuscular septa extending from the fascia lata to the femur. Each compartment has a distinct function and nerve supply.

Anterior Compartment (Hip Flexors and Knee Extensors)

The anterior compartment is innervated by the femoral nerve (L2-L4) and contains the hip flexors and knee extensors.

The iliopsoas is the most powerful hip flexor. It is actually two muscles—the psoas major (originating from the transverse processes and bodies of T12-L5 vertebrae) and the iliacus (originating from the iliac fossa)—that join to form a common tendon inserting on the lesser trochanter. The psoas major is innervated directly by branches of the lumbar plexus (L1-L3), while the iliacus is innervated by the femoral nerve.

The quadriceps femoris is the great extensor of the knee, consisting of four heads that converge on a common tendon inserting onto the tibial tuberosity via the patella and patellar ligament.

The rectus femoris is the only head crossing both the hip and knee joints. It originates by two heads: the straight head from the AIIS and the reflected head from the ilium just above the acetabulum. It flexes the hip and extends the knee.

The vastus lateralis originates from the lateral lip of the linea aspera and the greater trochanter. The vastus medialis originates from the medial lip of the linea aspera; its distal fibers, called the vastus medialis obliquus (VMO), run almost horizontally and are particularly important for patellar tracking. The vastus intermedius originates from the anterior and lateral surfaces of the femoral shaft, lying deep to the rectus femoris. All three vasti extend the knee only.

The sartorius is the longest muscle in the body. It originates from the ASIS and crosses the thigh obliquely to insert onto the medial surface of the proximal tibia as part of the pes anserinus. Its actions reflect its course: it flexes, abducts, and externally rotates the hip, and flexes the knee.

<image>Panel A: Iliopsoas (psoas major in blue from vertebral column, iliacus in purple from iliac fossa) passing deep to inguinal ligament to insert on lesser trochanter, and sartorius (orange) from ASIS crossing obliquely to medial tibia with pes anserinus inset. Panel B: Quadriceps group with rectus femoris (red, two-headed origin from AIIS and acetabular rim), vastus lateralis (green, from lateral linea aspera), and vastus medialis (blue, from medial linea aspera with VMO fibers highlighted). Panel C: Vastus intermedius (yellow, deep to rectus) from anterior femur, all four converging on quadriceps tendon, patella, and patellar ligament to tibial tuberosity. Panel D: Femoral nerve (L2-L4) branches to all muscles labeled with cross-section at mid-thigh showing anterior compartment position.</image>

Medial Compartment (Adductors)

The medial compartment is innervated primarily by the obturator nerve (L2-L4) and contains the adductor muscles. One exception is the hamstring portion of the adductor magnus, which receives tibial nerve innervation.

The pectineus is the most superior adductor, originating from the pecten pubis (pectineal line) and inserting onto the pectineal line of the femur. It adducts and flexes the hip. Although located in the medial compartment, it is usually innervated by the femoral nerve (sometimes with obturator nerve contribution).

The adductor longus is a triangular muscle originating from the body of the pubis. It fans out to insert onto the middle third of the linea aspera. It is the most anterior of the true adductors and is easily palpated in the groin.

The adductor brevis lies deep to the adductor longus. It originates from the body and inferior ramus of the pubis, inserting onto the upper third of the linea aspera. The obturator nerve divides into anterior and posterior divisions by passing anterior and posterior to the adductor brevis.

The adductor magnus is the largest of the adductors and has two functional parts. The adductor portion originates from the inferior pubic ramus and ischial ramus, inserting onto the linea aspera. The hamstring portion originates from the ischial tuberosity and inserts onto the adductor tubercle of the femur via a tendon. Importantly, the hamstring portion is innervated by the tibial division of the sciatic nerve rather than the obturator nerve.

The adductor hiatus is a gap in the insertion of the adductor magnus, located at the junction between the adductor and hamstring portions. The femoral vessels pass through this opening to become the popliteal vessels.

The gracilis is the most superficial muscle of the medial compartment and the only one crossing both the hip and knee joints. It originates from the body and inferior ramus of the pubis and descends along the medial thigh to insert onto the medial tibia as part of the pes anserinus. It adducts the hip and flexes the knee.

<image>Panel A: Superficial medial compartment showing gracilis (light green) from pubis to pes anserinus (only medial thigh muscle crossing knee), pectineus (pink) from pecten pubis to pectineal line, and adductor longus (blue) fanning from pubis to middle linea aspera. Panel B: Deeper layer with adductor brevis (orange) between pectineus and adductor longus, obturator nerve dividing anterior and posterior to it shown in yellow. Panel C: Deepest layer with adductor magnus (purple, largest) showing adductor portion from inferior pubic and ischial rami to linea aspera and hamstring portion from ischial tuberosity to adductor tubercle, adductor hiatus highlighted. Panel D: Nerve supply summary with obturator nerve to most muscles, femoral nerve to pectineus, tibial nerve to hamstring portion of magnus, and femoral artery passing through adductor hiatus to become popliteal.</image>

Posterior Compartment (Hamstrings)

The posterior compartment is innervated by the tibial division of the sciatic nerve (L5-S2), with one exception: the short head of the biceps femoris receives innervation from the common peroneal division. The hamstrings extend the hip and flex the knee.

The biceps femoris has two heads. The long head originates from the ischial tuberosity, sharing a common tendon with the semitendinosus. The short head originates from the lateral lip of the linea aspera. Both heads join to form a common tendon inserting onto the head of the fibula. The biceps femoris flexes the knee and externally rotates the flexed leg.

The semitendinosus originates from the ischial tuberosity. Its name describes its long tendon, which begins approximately halfway down the thigh. It inserts onto the medial surface of the tibia as part of the pes anserinus (along with sartorius and gracilis). The semitendinosus extends the hip, flexes the knee, and internally rotates the flexed leg.

The semimembranosus originates from the ischial tuberosity, lying deep to the semitendinosus and biceps long head at the origin. Its name describes the membranous expansion of its proximal tendon. It inserts onto the posterior aspect of the medial tibial condyle, with expansions forming the oblique popliteal ligament. Its actions mirror those of the semitendinosus.

The Pes Anserinus

The pes anserinus ("goose's foot") is the combined insertion of the sartorius, gracilis, and semitendinosus on the medial surface of the proximal tibia, just below the knee joint. The mnemonic "SGS" or "Say Grace before Supper" helps remember the order (superficial to deep). The pes anserinus bursa lies between this tendinous insertion and the tibia and can become inflamed (pes anserine bursitis) in certain conditions.

Clinical Considerations

Hamstring strains are among the most common sports injuries, particularly affecting sprinters and athletes who perform sudden accelerations or decelerations. The biceps femoris long head is most frequently injured, typically at the musculotendinous junction. The hamstrings' biarticular nature (crossing both hip and knee) contributes to their vulnerability.

Avulsion of the hamstring origin from the ischial tuberosity can occur in adolescents (due to the unfused apophysis) or adults (frank avulsion). This injury typically results from forced hip flexion with the knee extended, as in waterskiing or hurdling.

<image>Panel A: Biceps femoris (lateral) with long head (dark red) from ischial tuberosity and short head (lighter red) from linea aspera converging to insert on fibular head, and semitendinosus (blue) from ischial tuberosity with long tendon to pes anserinus. Panel B: Semimembranosus (green, deep dissection) from ischial tuberosity to posterior medial tibial condyle with oblique popliteal ligament expansion, ischial tuberosity origin highlighted with shared tendon. Panel C: Pes anserinus inset showing medial tibial view with three tendons inserting (sartorius, gracilis, semitendinosus) and "SGS" mnemonic, nerve supply with tibial portion to all except short head biceps (common peroneal). Panel D: Action arrows showing hip extension, knee flexion, and rotation of flexed leg (internal for semis, external for biceps) with hamstring strain site marked at musculotendinous junction.</image>

The Femoral Triangle

The femoral triangle is a fascial compartment in the upper anterior thigh that contains important neurovascular structures entering the lower limb from the abdomen.

Boundaries

The femoral triangle is bounded superiorly by the inguinal ligament, laterally by the medial border of the sartorius muscle, and medially by the lateral border of the adductor longus muscle. The apex points inferiorly where the sartorius crosses over the adductor longus.

The floor is formed by the iliopsoas laterally and the pectineus medially. The roof consists of the fascia lata and the cribriform fascia (a perforated area of fascia through which superficial vessels and lymphatics pass).

Contents

The contents of the femoral triangle, from lateral to medial, are the femoral nerve, femoral artery, femoral vein, and lymphatics. The mnemonic "NAVL" (Nerve, Artery, Vein, Lymphatics) helps remember this lateral-to-medial arrangement.

The femoral nerve is the most lateral structure and lies outside the femoral sheath. It enters the thigh posterior to the inguinal ligament and immediately divides into its branches.

The femoral artery is the continuation of the external iliac artery, beginning as it passes posterior to the inguinal ligament. Its pulse is palpable at the mid-inguinal point, halfway between the ASIS and the pubic symphysis.

The femoral vein lies immediately medial to the artery and receives the great saphenous vein at the saphenofemoral junction.

The Femoral Sheath

The femoral sheath is a funnel-shaped extension of the transversalis fascia (anteriorly) and iliac fascia (posteriorly) that surrounds the femoral vessels and lymphatics—but not the femoral nerve. It has three compartments: the lateral compartment containing the femoral artery, the intermediate compartment containing the femoral vein, and the medial compartment, called the femoral canal.

The femoral canal contains lymphatics and loose connective tissue. Its medial boundary is the lacunar ligament, while its superior opening, the femoral ring, is the site through which femoral hernias can enter the thigh. Femoral hernias are more common in women and carry a significant risk of strangulation because of the rigid ring boundaries.

<image>Panel A: Femoral triangle boundaries in anterior view with inguinal ligament superiorly (ASIS to pubic tubercle), sartorius laterally, adductor longus medially, and floor of iliopsoas and pectineus. Panel B: Contents from lateral to medial with NAVL mnemonic: femoral nerve (yellow, outside sheath), femoral artery (red, pulse at mid-inguinal point), femoral vein (blue, saphenofemoral junction), and femoral canal. Panel C: Femoral sheath as translucent envelope around artery, vein, and canal only with nerve outside sheath emphasized, great saphenous vein joining femoral vein. Panel D: Cross-section showing three sheath compartments (arterial, venous, canal with lymphatics), lacunar ligament at medial border, femoral ring labeled as site of femoral hernia with inguinal hernia comparison.</image>

The Adductor Canal

The adductor (subsartorial) canal is a fascial tunnel in the middle third of the thigh that transmits the femoral vessels from the femoral triangle to the popliteal fossa.

Boundaries and Contents

The canal is bounded anteriorly by the sartorius muscle, laterally by the vastus medialis, and posteriorly by the adductor longus (above) and adductor magnus (below). The canal is covered by the subsartorial (vastoadductor) membrane, a fibrous sheet connecting the adductors to the vastus medialis.

The contents include the femoral artery and vein, the saphenous nerve (a branch of the femoral nerve), and the nerve to the vastus medialis. The canal ends at the adductor hiatus, where the femoral vessels exit the canal to enter the popliteal fossa as the popliteal vessels.

Nerves of the Gluteal Region and Thigh

Several major nerves supply the gluteal region and thigh, each with distinct courses and clinical implications.

Superior Gluteal Nerve

The superior gluteal nerve (L4-S1) is the only nerve exiting the pelvis above the piriformis muscle through the greater sciatic foramen. It travels between the gluteus medius and minimus, innervating both along with the tensor fasciae latae.

Injury to the superior gluteal nerve, as may occur during hip surgery or posterior hip dislocation, results in weakness of hip abduction and a positive Trendelenburg sign. When the patient stands on the affected leg, the pelvis drops on the unsupported side rather than rising, and the patient may compensate by leaning toward the affected side (Trendelenburg gait).

Inferior Gluteal Nerve

The inferior gluteal nerve (L5-S2) exits the pelvis through the greater sciatic foramen, inferior to the piriformis. It innervates only the gluteus maximus. Injury causes weakness of hip extension, making it difficult to rise from a seated position, climb stairs, or run.

Sciatic Nerve

The sciatic nerve (L4-S3) is the largest nerve in the body, formed from the sacral plexus. It exits the pelvis through the greater sciatic foramen, inferior to the piriformis, and descends in the posterior thigh between the greater trochanter and the ischial tuberosity, deep to the gluteus maximus.

The sciatic nerve actually consists of two distinct components bound in a common sheath: the tibial division (medially) and the common peroneal (fibular) division (laterally). These typically separate in the distal thigh or popliteal fossa, though they may divide earlier or even exit separately around the piriformis.

In the thigh, the tibial division supplies the hamstrings (semimembranosus, semitendinosus, and long head of biceps femoris) and the hamstring portion of adductor magnus. The common peroneal division supplies only the short head of the biceps femoris in the thigh. Both divisions continue to supply all muscles below the knee.

Femoral Nerve

The femoral nerve (L2-L4) enters the thigh lateral to the femoral artery, passing posterior to the inguinal ligament. It immediately divides into multiple branches that supply the anterior thigh muscles (sartorius, quadriceps) and provide sensory innervation to the anterior thigh and medial leg (via the saphenous nerve, which continues with the femoral vessels through the adductor canal).

Obturator Nerve

The obturator nerve (L2-L4) enters the thigh through the obturator foramen. It divides into anterior and posterior divisions that pass anterior and posterior to the adductor brevis, respectively. It supplies most of the adductor muscles and provides sensory innervation to the medial thigh. Obturator nerve entrapment can cause groin pain and adductor weakness.

<image>Panel A: Gluteal region posterior view with piriformis as landmark, superior gluteal nerve (green) exiting above piriformis to gluteus medius, minimus, and TFL, inferior gluteal nerve (blue) exiting below piriformis to gluteus maximus. Panel B: Sciatic nerve (yellow) exiting below piriformis descending between greater trochanter and ischial tuberosity with tibial and common peroneal components within common sheath, branches to hamstrings labeled. Panel C: Anterior thigh with femoral nerve (orange) entering lateral to femoral artery branching to sartorius and quadriceps with saphenous nerve distally, and medial thigh with obturator nerve (purple) dividing around adductor brevis. Panel D: Sensory territory map for femoral, obturator, and sciatic nerves, with Trendelenburg sign illustration showing pelvis drop from superior gluteal nerve injury.</image>

Clinical Correlations

Hip Fractures

Hip fractures are common in elderly patients with osteoporosis and represent a major cause of morbidity and mortality. They are classified as intracapsular (femoral neck fractures) or extracapsular (intertrochanteric or subtrochanteric fractures).

Intracapsular fractures carry a significant risk of avascular necrosis because they can disrupt the retinacular vessels supplying the femoral head. Displaced intracapsular fractures in elderly patients are often treated with hip replacement rather than fixation because of this risk.

Extracapsular fractures have better healing potential because the blood supply to the femoral head is preserved. They are typically treated with internal fixation.

Trendelenburg Sign

The Trendelenburg sign tests the function of the hip abductors (gluteus medius and minimus). When the patient stands on one leg, the abductors of the stance limb normally contract to elevate the pelvis on the unsupported side.

A positive Trendelenburg sign occurs when the pelvis drops on the unsupported side during single-leg stance. This indicates weakness of the abductors on the stance side. Causes include superior gluteal nerve injury, hip pathology (arthritis, fracture), or abductor muscle disease.

Posterior Hip Dislocation

Posterior hip dislocation typically results from a dashboard injury—the knee striking the dashboard during a motor vehicle accident, driving the femoral head posteriorly out of the acetabulum. The affected limb is held in flexion, adduction, and internal rotation.

The sciatic nerve is at risk because of its proximity to the posterior acetabulum. Injury can cause weakness of all muscles below the knee and sensory loss in the leg and foot.

Meralgia Paresthetica

Meralgia paresthetica is entrapment of the lateral femoral cutaneous nerve as it passes under or through the inguinal ligament near the ASIS. This sensory nerve supplies the skin of the lateral thigh, and its compression causes numbness, tingling, and burning pain in this distribution. Risk factors include obesity, tight clothing, pregnancy, and diabetes. Treatment is usually conservative.

<image>Panel A: Hip fracture classification with intracapsular fracture at neck (risk of AVN from disrupted blood supply, treated with hip replacement) and extracapsular fracture at intertrochanteric region (better prognosis, treated with internal fixation). Panel B: Trendelenburg sign showing posterior view of patient on single-leg stance with pelvis dropping on unsupported side, weak gluteus medius indicated, normal response comparison shown. Panel C: Posterior hip dislocation with femoral head displaced posteriorly, limb in flexion, adduction, and internal rotation, sciatic nerve stretched over posterior acetabulum at risk. Panel D: Meralgia paresthetica showing lateral femoral cutaneous nerve entrapped at inguinal ligament near ASIS with sensory distribution on lateral thigh shaded.</image>

Summary

The hip joint is a stable ball-and-socket joint formed by the articulation of the femoral head with the acetabulum. The acetabulum is formed by the fusion of the ilium, ischium, and pubis. The joint is reinforced by strong ligaments, with the iliofemoral ligament being the strongest in the body. The blood supply to the femoral head comes primarily from the medial circumflex femoral artery via retinacular vessels—a supply vulnerable to disruption in femoral neck fractures.

The gluteal muscles control hip movement and stability. The gluteus maximus is the primary extensor, while the gluteus medius and minimus are the primary abductors and crucial pelvic stabilizers. Weakness of the abductors produces a positive Trendelenburg sign.

The thigh contains three compartments. The anterior compartment (femoral nerve) contains the hip flexors (iliopsoas) and knee extensors (quadriceps). The medial compartment (obturator nerve) contains the adductors. The posterior compartment (sciatic nerve) contains the hamstrings, which extend the hip and flex the knee.

The femoral triangle is a key anatomical region containing the femoral nerve, artery, and vein (lateral to medial). The sciatic nerve is the largest nerve in the body, with tibial and common peroneal divisions that separate in the thigh or popliteal fossa.

Key Terms

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