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Lesser sciatic foramen

Image : “Sobo 1909 210” by Dr. Johannes Sobotta. License: Public Domain


Gluteal Region

The gluteal region is the area posterior to the pelvic girdle between the iliac crest and the gluteal fold.

The gluteal region consists of:

  • 2 groups of muscles: the superficial and deep groups
  • Gluteal nerves
  • Gluteal blood vessels
  • Greater sciatic and lesser sciatic foramina
  • Sacrospinous and sacrotuberous ligaments

Gluteal region borders:

  • Superior aspect: iliac crest
  • Medial aspect: medial line
  • Lateral aspect: a line from the anterior superior iliac spine to the greater trochanter
  • Inferior aspect: gluteal fold

Superficial Group of Muscles

The superficial group of muscles consists of the 3 large gluteal muscles, which extend and abduct the hip joint, which stabilizes the knee in extension.posterior to the posterior gluteal line. The gluteus maximus is innervated by the inferior gluteal nerve (S1, S2). The gluteus maximus is the chief extensor of the hip, flexes the hip when a person is sitting down and helps with lateral rotation.

Gluteus Maximus

Gluteus maximus

Image: Gluteus maximus. By Dr. Johannes Sobotta, License: Public Domain

The gluteus maximus is the largest of the 3 gluteal muscles and is responsible for the contour of the buttocks. The gluteus maximus originates from the posterior surface of the sacrum, coccyx, and ilium, then inserts in the iliotibial tract and the gluteal tuberosity of the femur. The gluteus maximus originates However, it is not an important postural muscle, as the gluteus maximus is relaxed when a person is standing and is not used during walking. The gluteus maximus is active during forceful movements, such as running, rising from a sitting position, and climbing.

Gluteus medius

The gluteus medius is a fan-shaped muscle that originates from the posterior surface of the ilium between the anterior and inferior gluteal lines. The gluteus medius is inserted into the lateral aspect of the greater trochanter of the femur. The gluteus medius is situated between the gluteus maximus and gluteus minimus. The superior gluteal nerve (L4, L5, S1) innervates the muscle. The gluteus medius abducts and medially rotates the thigh at the hip joint. The gluteus medius fixes the pelvis during movement and prevents the opposing pelvis from dropping. The gluteus medius plays an important role in maintaining a level pelvis when the contralateral limb is positioned off the ground.

Gluteus minimus

The gluteus minimus is the smallest and deepest of the 3 gluteal muscles. The gluteus minimus originates from the external ilium in between the anterior and posterior lines, then forms a tendon that is inserted into the anterior aspect of the greater trochanter of the femur. The gluteus minimus is innervated by the superior gluteal nerve (L4, L5, S1). Along with the gluteus medius, the gluteus minimus abducts and medially rotates the hip joint, and fixes the pelvis during movement, thereby preventing an opposing pelvic drop.

Tensor fascia lata

The tensor fascia lata is a small muscle that originates from the anterior iliac crest and inserts into the iliotibial tract on the lateral condyle of the tibia. The tensor fascia lata is innervated by the superior gluteal nerve (L4, L5, S1). The tensor fascia lata helps the gluteus medius and gluteus minimus in abducting and medially rotating the thigh during walking. The tensor fascia lata helps with flexion of the hip and stabilization of the knee joint.

Deep Muscles

The deep muscles are a group of small muscles located deep to the gluteus minimus. The deep muscles stabilize and laterally rotate the hip joint.

Piriformis muscles

Image: Piriformis muscles. By Dr. Johannes Sobotta, License: Public Domain

Piriformis

The piriformis originates from the anterior aspect of the sacrum and courses inferolateral via the greater sciatic foramen and finally inserts on the greater trochanter of the femur. The piriformis is innervated by the anterior nerve of S1 to the piriformis and helps to laterally rotate the hip in extension and abduct the hip joint in flexion.

The piriformis is an important landmark because the piriformis divides the gluteal region into superior and inferior parts when the piriformis passes through the greater sciatic foramen. Superior gluteal nerves and vessels emerge superior to the piriformis, whereas the inferior gluteal nerves and vessels lie inferior to the piriformis. The piriformis also helps locate the sciatic nerve, which lies inferior to the piriformis and can be identified as a flat band, 2 cm in width.

Obturator Internus

The obturator internus originates from the ischium and the pubis near the obturator foramen. The obturator internus then runs through the lesser sciatic foramen to insert onto the medial surface of the greater trochanter of the femur. The obturator internus is innervated by the nerve to the obturator internus (S1) and helps to laterally rotate the extended hip and abduct the hip in flexion.

Gemelli

The superior and inferior gemelli are 2 triangular muscles separated by the tendon of the obturator internus. The superior gemellus originates from the ischial spine, and the inferior gemellus originates from the ischial tuberosity. The superior and inferior gemelli insert into the medial surface of the greater trochanter of the femur. The superior and inferior gemelli rotate laterally and abduct the hip joint. The nerve of the obturator internus (S1) innervates the superior gemellus and the nerve to the quadratus femoris (L5, S1) innervates the inferior gemellus.

Quadratus Femoris

The quadratus femoris is a flat muscle situated deep in the gluteal and gemelli muscles. The quadratus femoris originates from the lateral aspect of the ischial tuberosity and inserts on the quadrate tubercle on the intertrochanteric crest. The quadratus femoris is innervated by the nerve to the quadratus femoris (L5, S1) and rotates the hip laterally in the acetabulum.

Gluteal Nerves

There are several nerves in the gluteal region. The sciatic nerve (L4– S3), a branch of the sacral plexus, courses through the greater sciatic foramen deep to the piriformis, then separates into 2 parts (tibial and fibular). The nerve then descends deep to the gluteus maximus into the middle part of the posterior thigh. The other nerves in this region include the superior gluteal nerve (L4, 5, S1), inferior gluteal nerve (L5, S1,2), pudendal nerve, and posterior femoral cutaneous nerve of the thigh (S1-3).

Gluteal Vessels

The gluteal arteries arise from the internal iliac arteries within the pelvis directly or indirectly. Accompanied by the superior gluteal nerve, the superior gluteal artery passes deep to the gluteus maximus muscle and divides into branches that supply the gluteal muscles. The inferior gluteal artery, also a branch of the internal iliac artery, runs deep to the gluteus maximus and medial to the sciatic nerve. The gluteal veins drain into the internal iliac vein.

Greater Sciatic Foramen

The greater sciatic foramen is situated in the posterior aspect of the pelvis and is formed by the sacrospinous and sacrotuberous ligaments. The greater sciatic foramen is wider in women than in men.

The boundaries of the greater sciatic foramen are:

 Boundaries  Foramen
 Anteriorly  Ischial tuberosity
 Posteriorly  Sacrotuberous ligament
 Superiorly  Ischial spine and sacrospinous ligament

The piriformis muscle passes through the foramen and divides the greater sciatic foramen into superior and inferior compartments. The suprapiriformis compartment contains the superior gluteal vessels and nerves, whereas the infrapiriformis compartment contains the inferior gluteal vessels and nerves, pudendal nerve and vessels, sciatic nerve, posterior femoral cutaneous nerve, nerve to the obturator internus, and nerve to the quadratus femoris.

Lesser Sciatic Foramen

The lesser sciatic foramen is formed between the pelvis and the posterior aspect of the thigh by the sacrotuberous and sacrospinous ligaments.

The boundaries of the foramen are:

Boundaries Foramen
Anteriorly Ischial tuberosity
Posteriorly Sacrotuberous ligament
Superiorly Ischial spine and sacrospinous ligament

The lesser sciatic foramen has boundaries formed by the sciatic notch and the 2 ligaments. The obturator internus tendon, pudendal nerves and vessels, and nerve to the obturator internus pass through the lesser sciatic foramen.

Ligaments

The sacrotuberous ligament is part of the biceps femoris muscle and runs from the transverse processes of the lower sacral tubercles, sacrum, and coccyx to the ischial tuberosity. Branches of the inferior gluteal artery, the perforating cutaneous nerve, and branches of the coccygeal plexus pass through the sacrotuberous ligaments.

The sacrospinous ligament is intermingled with the sacrotuberous ligament and runs from the sacrum and coccyx to the ischial spine. The sacrospinous ligament divides the greater sciatic notch into the greater and lesser sciatic foramina, through which several nerves and vessels pass.

Together, the sacrotuberous and sacrospinous ligaments prevent excessive upward tilt of the sacrum and provide pelvic support to the pelvic organs.

Posterior Thigh

The posterior compartment of the thigh consists of three hamstring muscles, nerves, and blood vessels. The hamstring muscles (biceps femoris, semimembranosus, and semitendinosus), with the exception of the short head of the biceps femoris, originate from the ischial tuberosity and insert on the tibia and fibula crossing the hip and knee joints. The hamstring muscles help to extend the hip and flex the knee joint. The hamstring muscles are innervated by the sciatic nerve.

thigh-cross-section-lower-limb-anatomy

Image: Thigh cross section. By Mcstrother, License: CC BY 3.0

The laterally situated biceps femoris has a long head that originates from the ischial tuberosity and a short head, which originates on the linea aspera and lateral supracondylar line of the femur. The two heads converge to form a single tendon that runs down to insert on the lateral surface of the fibular head. The semimembranosus and semitendinosus muscles are situated medially, with the semitendinosus tendon on top of the semimembranous tendon.

The semimembranosus and semitendinosus muscles originate from the ischial tuberosity, but the semimembranosus muscle is inserted on the posterior aspect of the medial femoral and tibial condyles, whereas the semitendinosus muscle inserts on the medial aspect of the proximal tibia posterior to the gracilis muscle. The semimembranosus and semitendinosus muscles are supplied by the tibial division of the sciatic nerve (L5, S1). The semimembranosus and semitendinosus muscles help to extend the hip and flex the knee joint. The semimembranosus muscle also assists in the medial rotation when the knee joint is flexed.

Popliteal Fossa

The popliteal fossa is a diamond-shaped, shallow depression on the posterior aspect of the knee joint. The location of the popliteal fossa corresponds to the posterior aspect of the distal aspect of the femur and the proximal aspect of the tibia. The popliteal fossa contains all the structures related to the neurovascular system that travels from the thigh to the leg.

The roof of the popliteal fossa from superficial to deep is formed by the skin and superficial popliteal fascia (containing the small saphenous vein, lateral and medial sural nerves, terminal branch of the posterior cutaneous nerve of the thigh, and posterior division of the medial cutaneous nerve). The popliteal fascia is continuous with the fascia lata.

The floor of the popliteal fossa is formed by the posterior or popliteal surface of the femur, knee joint capsule, oblique popliteal ligament, and fascia covering the popliteal muscle.

Boundaries of the popliteal fossa are:

 Superomedially  Semimembranous muscle
 Superolaterally  Biceps femoris
 Inferomedially  Medial head of the gastrocnemius
 Inferolaterally  Lateral head of the gastrocnemius

The contents of the popliteal fossa from medial-to-lateral include the following.

The popliteal artery with its branches

The popliteal artery is a continuation of the femoral artery in the leg and lies deep to the other structures in the popliteal fossa. The popliteal artery starts at the hiatus magnus in the thigh and terminates by dividing into the anterior and posterior tibial arteries. The popliteal artery divides into 5 genicular arteries that anastomose to supply the capsule and ligaments of the knee joint.

The popliteal vein with its tributaries

The popliteal vein is formed at the inferior border of the popliteus by the union of the anterior and posterior tibial veins and continues as the femoral vein at the hiatus magnus.

Tibial nerve and the common peroneal nerve

The tibial and common peroneal nerves are branches of the sciatic nerve and lie most superficially in the fossa. The common peroneal nerve runs along the lateral margin of the fossa following the biceps femoris tendon. The common peroneal nerve leaves the popliteal fossa by entering deep to the gastrocnemius. In the popliteal fossa, the common peroneal nerve maintains the nerve supply to the muscles near the popliteal fossa and knee joint.

Other contents of the popliteal fossa are:

  • Genicular branch of the obturator nerve
  • Posterior cutaneous nerve of the thigh
  • Popliteal lymph nodes
  • Popliteal fat pad
  • Small saphenous vein (enters by piercing the popliteal fascia and drains into the popliteal vein)

Clinical Relevance

The popliteal artery can be used to measure blood pressure. The pressure in the popliteal artery is lower than the brachial artery in patients with coarctation of the aorta.

Intramuscular injections can be administered safely in the gluteal region in the superolateral quadrant of the buttock, which is an area devoid of nerves and vessels.

Injury to the superior gluteal nerve following intramuscular injection or other trauma can cause paralysis of the gluteus medius and minimus. This results in a waddling or lurching gait and is demonstrated clinically by a positive Trendelenburg sign. Specifically, when the patient is asked to stand without support on each leg, the pelvis drops on the unsupported leg (e.g., if the left gluteal muscles are paralyzed, then the right pelvis will drop when the patient attempts to stand on the left leg with the right leg unsupported).

Prolapse of the vagina or uterus due to laxity or absence of pelvic ligaments is corrected surgically with a sacrospinous suspension. The sacrospinous ligament is sutured to the vaginal vault or the cervix to restore support to the organs.

A Baker’s cyst is a fluid-filled sac usually associated with arthritis in the knee joint. Fluid develops in the semimembranous bursa leading to inflammation and swelling, but often resolving without treatment. Occasionally, a cyst may rupture, leading to swelling in the posterior aspect of the leg, which resembles deep vein thrombosis.

Abnormal dilatation of the popliteal artery (> 50% of the popliteal artery diameter) can lead to compression of the tibial nerve with diminished plantar flexion and paresthesia of the foot and posterolateral aspect of the leg. Diagnosis of a popliteal artery aneurysm is based on palpation of pulsations in the popliteal fossa or auscultation of a bruit.

Other causes of a popliteal mass include the adventitial cyst of the popliteal artery, deep vein thrombosis, and malignancy.

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