Thigh muscle anatomy: the anterior, medial and posterior compartments

Deep fascia in the thigh separates its muscles into medial, anterior and posterior compartments. The anterior compartment muscles flex the thigh and extend the leg (straighten the knee). The medial compartment muscles adduct the femur at the hip. The posterior compartment muscles flex the leg and extend the thigh. (OpenStax Anatomy and Physiology 2e, 11.6: Appendicular Muscles of the Pelvic Girdle and Lower Limbs.)

The anterior compartment is supplied by the femoral nerve (L2 to L4). Testing the quadriceps is a quick check of this nerve: with the patient lying on their back and the knee slightly bent, they straighten the leg against resistance, and absent contraction suggests femoral nerve damage. (TeachMeAnatomy: Muscles of the Anterior Compartment of the Thigh.)

The medial compartment is supplied mainly by the obturator nerve (L2 to L4). The exception is the hamstring part of adductor magnus, supplied by the tibial part of the sciatic nerve. (TeachMeAnatomy: Muscles of the Medial Compartment of the Thigh.)

The posterior compartment, the hamstrings, is supplied by the sciatic nerve: the tibial part supplies semitendinosus, semimembranosus and the long head of biceps femoris, and the common fibular (peroneal) part supplies the short head of biceps femoris. (TeachMeAnatomy: The Hamstring Muscles.)

The front upper leg muscles are the four parts of quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis and vastus intermedius) and sartorius. Pectineus and the lower end of iliopsoas also lie at the front of the upper thigh. All four parts of quadriceps insert into the patella through the quadriceps tendon, and the patella is anchored to the tibial tuberosity by the patellar ligament. (TeachMeAnatomy: Muscles of the Anterior Compartment of the Thigh.)

OpenStax describes the layout of the quad muscles simply: rectus femoris lies on the front of the thigh, vastus lateralis on the outer side, vastus medialis on the inner side, and vastus intermedius between the two vasti, deep to rectus femoris. Together they extend and stabilise the knee. (OpenStax Anatomy and Physiology 2e, 11.6: Appendicular Muscles of the Pelvic Girdle and Lower Limbs.)

Rectus femoris has a straight head from the anterior inferior iliac spine and a reflected head from the groove just above the acetabulum. It forms the central part of the quadriceps tendon. It is the only quadriceps muscle that crosses both the hip and the knee, so it flexes the hip as well as extending the knee. (University of Washington Musculoskeletal Atlas: Rectus femoris.)

Vastus lateralis (the lateral vastus muscle) arises from the upper intertrochanteric line, the front and lower borders of the greater trochanter, the upper lateral lip of the linea aspera and the gluteal tuberosity. It inserts on the lateral base and border of the patella and forms the lateral patellar retinaculum. Like all the vasti it extends the knee and is supplied by the femoral nerve and, in its case, the lateral circumflex femoral artery. (University of Washington Musculoskeletal Atlas: Vastus lateralis.)

Vastus medialis arises from the lower intertrochanteric line, the spiral line, the medial lip of the linea aspera and the medial supracondylar ridge. It inserts on the medial base and border of the patella and forms the medial patellar retinaculum. (University of Washington Musculoskeletal Atlas: Vastus medialis.)

Vastus intermedius arises from the upper two-thirds of the front and lateral surfaces of the femur and forms the deep part of the quadriceps tendon. (University of Washington Musculoskeletal Atlas: Vastus intermedius.)

The two-joint quadriceps muscle: heads, actions, injuries. Rectus femoris.

Sartorius is a strap-like muscle that runs obliquely across the front of the thigh from the anterior superior iliac spine to the upper medial surface of the tibia. TeachMeAnatomy calls it the longest muscle in the body. It is the most superficial muscle of the anterior compartment and is supplied by the femoral nerve. (TeachMeAnatomy: Muscles of the Anterior Compartment of the Thigh.)

Because it crosses both joints, sartorius flexes and laterally rotates the hip and flexes the knee. (University of Washington Musculoskeletal Atlas: Sartorius.)

OpenStax describes sartorius as a band-like muscle from the anterior superior iliac spine to the medial side of the upper tibia, and notes that it allows us to sit cross-legged. (OpenStax Anatomy and Physiology 2e, 11.6: Appendicular Muscles of the Pelvic Girdle and Lower Limbs.)

The muscles of the inner thigh (the medial compartment) are adductor longus, adductor brevis, adductor magnus, gracilis and obturator externus, with pectineus at the top. Their shared job is adduction: pulling the thigh towards the midline, as when squeezing the knees together. (TeachMeAnatomy: Muscles of the Medial Compartment of the Thigh.)

Adductor longus arises from the front of the body of the pubis, just lateral to the pubic symphysis, and fans out to insert on the middle third of the linea aspera. It adducts and flexes the thigh and is supplied by the anterior division of the obturator nerve. (University of Washington Musculoskeletal Atlas: Adductor longus.)

Adductor brevis lies deep to adductor longus. It arises from the body and inferior ramus of the pubis and inserts on the linea aspera above adductor longus. It adducts the thigh and is supplied by the obturator nerve; its anterior and posterior divisions pass in front of and behind it. (TeachMeAnatomy: Muscles of the Medial Compartment of the Thigh.)

Gracilis is the most superficial and most medial muscle of the group, and it crosses both the hip and the knee. It runs from the body and inferior ramus of the pubis to the medial surface of the tibial shaft, so it adducts the thigh and flexes the knee. (TeachMeAnatomy: Muscles of the Medial Compartment of the Thigh.)

Pectineus arises from the pecten pubis and inserts on the pectineal line of the femur, just below the lesser trochanter. It adducts the thigh and flexes the hip. It is usually supplied by the femoral nerve, sometimes with an extra branch from the obturator nerve, which is why some texts place it in the anterior compartment. (University of Washington Musculoskeletal Atlas: Pectineus.)

OpenStax points out that the adductors do more than adduct: depending on foot position they can rotate the thigh medially or laterally, adductor longus also flexes the thigh, and adductor magnus extends it. (OpenStax Anatomy and Physiology 2e, 11.6: Appendicular Muscles of the Pelvic Girdle and Lower Limbs.)

Adductor magnus has two parts. The adductor part arises from the ischiopubic ramus and inserts along the back of the femur and the linea aspera; it is supplied by the obturator nerve. The hamstring part arises from the ischial tuberosity and inserts on the adductor tubercle of the femur; it is supplied by the sciatic nerve. (Radiopaedia: Adductor magnus muscle.)

The University of Washington atlas calls adductor magnus a powerful adductor of the thigh, whose upper horizontal fibres help flex the thigh and whose vertical fibres help extend it. (University of Washington Musculoskeletal Atlas: Adductor magnus.)

The adductor canal is a tunnel in the middle third of the thigh. Sartorius lies in front of it, vastus medialis to its lateral side and adductor longus and adductor magnus behind it. It carries the femoral artery and vein, the nerve to vastus medialis and the saphenous nerve. It ends at the adductor hiatus, a gap between the adductor and hamstring attachments of adductor magnus. (TeachMeAnatomy: The Adductor Canal.)

After passing through the adductor hiatus into the popliteal fossa behind the knee, the femoral artery and vein are renamed the popliteal artery and vein. (Radiopaedia: Adductor magnus muscle.)

The posterior thigh muscles are the hamstrings: biceps femoris, semitendinosus and semimembranosus. Their tendons border the popliteal fossa, the diamond-shaped space at the back of the knee. (OpenStax Anatomy and Physiology 2e, 11.6: Appendicular Muscles of the Pelvic Girdle and Lower Limbs.)

Biceps femoris lies on the lateral side. Its long head arises from the ischial tuberosity and its short head from the linea aspera of the femur; the two join in a tendon that inserts on the head of the fibula. It flexes the knee, helps extend the hip and rotates the leg laterally when the knee is bent. (TeachMeAnatomy: The Hamstring Muscles.)

Semitendinosus lies medially. It arises from the ischial tuberosity, is largely tendinous in its lower part, and inserts on the medial surface of the tibia. Semimembranosus, flat and broad, lies deep to it. Both flex the knee, extend the hip and rotate the leg medially. (TeachMeAnatomy: The Hamstring Muscles.)

Semimembranosus arises from the upper lateral quadrant of the ischial tuberosity and inserts on the back of the medial tibial condyle. It is supplied by the tibial nerve. (University of Washington Musculoskeletal Atlas: Semimembranosus.)

Automatic page for semimembranosus in the 3D model. Semimembranosus.

The femoral triangle is a hollow at the top of the front of the thigh. Its upper border is the inguinal ligament, its lateral border is sartorius and its medial border is adductor longus. Its floor is formed by iliopsoas, pectineus and adductor longus, and its roof is the fascia lata. (TeachMeAnatomy: The Femoral Triangle.)

From lateral to medial it contains the femoral nerve, femoral artery, femoral vein and the femoral canal with its deep lymph nodes, remembered as NAVEL (nerve, artery, vein, empty space, lymphatics). (TeachMeAnatomy: The Femoral Triangle.)

One muscle from each compartment ends at the same place. The tendons of sartorius (anterior), gracilis (medial) and semitendinosus (posterior) join on the front of the medial tibia, about 4 cm below the tibial plateau, as the pes anserinus ('goose's foot'). A bursa lies between these tendons and the deeper semimembranosus tendon and can become inflamed (pes anserinus bursitis). (Radiopaedia: Pes anserinus.)

Hamstring strains are common in sport. Most studies show more injuries to biceps femoris than to the medial hamstrings. Risk is highest at the end of the swing phase of running, when the hamstrings are maximally lengthened while contracting to slow the leg. A previous hamstring injury is one of the strongest predictors of another, and recurrence rates of 12 to 14% have been reported in soccer players. (Carlson C. The natural history and management of hamstring injuries. Curr Rev Musculoskelet Med. 2008.)

A 'groin strain' is usually an adductor strain. The upper part of the muscle near its pelvic attachment is most often affected, typically in sports with explosive movements or extreme stretching. (TeachMeAnatomy: Muscles of the Medial Compartment of the Thigh.)

Sudden, forceful contraction of the hamstrings can also pull off a piece of the ischial tuberosity (an avulsion fracture), mainly in adolescents whose growth plates are still open. (TeachMeAnatomy: The Hamstring Muscles.)

Adductor brevis

A short adductor in the medial thigh, lying behind pectineus and adductor longus.

Adductor longus

The most anterior adductor muscle; its medial edge forms the medial border of the femoral triangle.

Adductor magnus

The largest adductor, with an adductor part and a hamstring part.

Adductor minimus

The upper, anterior fibres of adductor magnus, sometimes described as a separate part.

Gracilis

A long, thin muscle on the medial side of the thigh.

Long head of biceps femoris

The long, superficial head of biceps femoris, the lateral hamstring.

Pectineus

A flat quadrangular muscle at the top of the medial thigh forming part of the floor of the femoral triangle.

Rectus femoris

The only part of quadriceps femoris that crosses both the hip and knee.

Sartorius

The longest muscle in the body, a strap-like muscle crossing the thigh obliquely.

Semimembranosus

A hamstring muscle on the posteromedial thigh with a long flat tendon of origin.

Semitendinosus

A hamstring muscle with a long cord-like tendon on the posteromedial thigh.

Short head of biceps femoris

The head of biceps femoris that does not cross the hip joint.

Vastus intermedius

The deep quadriceps muscle lying beneath rectus femoris.

Vastus lateralis

The largest quadriceps muscle on the lateral thigh.

Vastus medialis

The medial quadriceps muscle with oblique fibers near the patella.