Lower Limb



Lower Limb



1 Introduction


As with the upper limb in Chapter 7, this chapter approaches our study of the lower limb by organizing its anatomical structures into functional compartments. The thigh and leg each are organized into three functional compartments, with their respective muscles and neurovascular bundles. The lower limb subserves the following important functions and features:



Be sure to review the movements of the lower limb as described in Chapter 1 (see Fig. 1-3). Note the terms dorsiflexion (extension) and plantarflexion (flexion), and inversion (supination) and eversion (pronation), which are unique to the movements of the ankle.



2 Surface Anatomy


The components of the lower limb include the gluteal region, thigh, leg, and foot. The key surface landmarks include the following (Fig. 6-1):




• Inguinal ligament: the folded, inferior edge of the external abdominal oblique aponeurosis that separates the abdominal region from the thigh (Poupart’s ligament).


• Greater trochanter: the point of the hip and attachment site for several gluteal muscles.


• Quadriceps femoris: the muscle mass of the anterior thigh, composed of four muscles—rectus femoris and three vastus muscles—that extend the leg at the knee.


• Patella: the kneecap; largest sesamoid bone in the body.


• Popliteal fossa: the region posterior to the knee.


• Gastrocnemius muscles: the muscle mass that forms the calf.


• Calcaneal (Achilles) tendon: the prominent tendon of several calf muscles.


• Small saphenous vein: drains blood from the lateral dorsal venous arch and posterior leg (calf) into the popliteal vein posterior to the knee.


• Great saphenous vein: drains blood from the medial dorsal venous arch, leg, and thigh into the femoral vein just inferior to the inguinal ligament.


Superficial veins drain blood toward the heart and communicate with deep veins that parallel the arteries of the lower limb. When vigorous muscle contraction compresses the deep veins, venous blood is shunted into superficial veins and returned to the heart. All these veins have valves to aid in the venous return to the heart.


Corresponding cutaneous nerves are terminal sensory branches of major lower limb nerves that arise from lumbar (L1-L4) and sacral (L4-S4) plexuses (Fig. 6-2). Note that the gluteal region has superior, middle, and inferior cluneal nerves, and the thigh has posterior, lateral, anterior, and medial cutaneous nerves. The leg has lateral sural, superficial fibular, saphenous, and sural cutaneous nerves (named from the lateral leg to the posterior leg). The sural nerve on the posterior leg parallels the small saphenous vein, and the saphenous nerve (terminal portion of the femoral nerve) parallels the great saphenous vein from the medial ankle to the level of the knee.





3 Hip


Bones and Joints of the Pelvic Girdle and Hip


The pelvic girdle is the attachment point of the lower limb to the body’s trunk and axial skeleton. The pectoral girdle is its counterpart for the attachment of the upper limb. The sacro-iliac ligaments (posterior, anterior, and interosseous) are among the strongest ligaments in the body and support its entire weight, almost pulling the sacrum into the pelvis. Note that the pelvis (sacrum and coxal bones) in anatomical position is tilted forward such that the pubic symphysis and the anterior superior iliac spines lie in the same vertical plane, placing great stress on the sacro-iliac joints and ligaments (see Figs. 5-3 and 6-3). In fact, the body’s center of gravity when standing upright lies just anterior to the S2 vertebra of the fused sacrum.



The bones of the pelvis include the following (Fig. 6-3 and Table 6-1):




Additionally, the proximal femur (thigh bone) articulates with the pelvis at the acetabulum (see Fig. 6-3 and Table 6-1).


The hip joint is a classic ball-and-socket synovial joint that affords great stability, provided by both its bony anatomy and its strong ligaments (Fig. 6-4 and Table 6-2). As with most large joints, there is a rich vascular anastomosis around the hip joint, contributing a blood supply not only to the hip but also to the associated muscles (Fig. 6-5 and Table 6-3).






The other features of the pelvic girdle and its stabilizing lumbosacral and sacro-iliac joints are illustrated and summarized in Chapter 5.






Nerve Plexuses


Several nerve plexuses exist within the pelvis and send branches to somatic structures (skin and skeletal muscle) of the pelvis and lower limb. The lumbar plexus is composed of the ventral rami of spinal nerves L1-L4, which give rise to two large nerves, the femoral and obturator nerves, and several smaller branches (Fig. 6-6). The femoral nerve (L2-L4) innervates muscles of the anterior thigh, whereas the obturator nerve (L2-L4) innervates muscles of the medial thigh.



The sacral plexus is composed of the ventral rami of spinal nerves L4-S4. Its major branches are summarized in Figure 6-7 and Table 6-4. The small coccygeal plexus has contributions from S4-Co1 and gives rise to small anococcygeal branches that innervate the coccygeus muscle and skin of the anal triangle (see Chapter 5). Often the lumbar and sacral plexuses are simply referred to as the lumbosacral plexus.






4 Gluteal Region


Muscles


The muscles of the gluteal (buttock) region are arranged into superficial and deep groups, as follows (Fig. 6-8 and Table 6-5):



TABLE 6-5


Gluteal Muscles



























































MUSCLE PROXIMAL ATTACHMENT (ORIGIN) DISTAL ATTACHMENT (INSERTION) INNERVATION MAIN ACTIONS
Gluteus maximus Ilium posterior to posterior gluteal line, dorsal surface of sacrum and coccyx, and sacrotuberous ligament Most fibers end in iliotibial tract that inserts into lateral condyle of tibia; some fibers insert on gluteal tuberosity of femur Inferior gluteal nerve (L5-S2) Extends flexed thigh at the hip and assists in its lateral rotation; abducts and assists in raising trunk from flexed position
Gluteus medius Lateral surface of ilium Lateral surface of greater trochanter of femur Superior gluteal nerve (L4-S1) Abducts and medially rotates thigh at hip; steadies pelvis on limb when opposite limb is raised
Gluteus minimus Lateral surface of ilium Anterior surface of greater trochanter of femur Superior gluteal nerve (L4-S1) Abducts and medially rotates thigh at hip; steadies pelvis on limb when opposite limb is raised
Tensor fasciae latae Anterior superior iliac spine and anterior iliac crest Iliotibial tract that attaches to lateral condyle of tibia Superior gluteal nerve (L4-L5) Abducts, medially rotates, and flexes thigh at hip; helps to keep knee extended
Piriformis Anterior surface of sacrum and sacrotuberous ligament Superior border of greater trochanter of femur Branches of ventral rami (L5-S2) Laterally rotates extended thigh at hip and abducts flexed thigh at hip; steadies femoral head in acetabulum
Obturator internus Pelvic surface of obturator membrane and surrounding bones Medial surface of greater trochanter of femur Nerve to obturator internus (L5-S2) Laterally rotates extended thigh at hip and abducts flexed thigh at hip; steadies femoral head in acetabulum
Gemelli, superior and inferior Superior: ischial spine
Inferior: ischial tuberosity
Medial surface of greater trochanter of femur Superior gemellus: same nerve supply as obturator internus
Inferior gemellus: same nerve supply as quadratus femoris
Laterally rotate extended thigh at the hip and abducts flexed thigh at the hip; steady femoral head in acetabulum
Quadratus femoris Lateral border of ischial tuberosity Quadrate tubercle on intertrochanteric crest of femur Nerve to quadratus femoris (L4-S1) Laterally rotates thigh at hip; steadies femoral head in acetabulum


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The gluteus maximus muscle is one of the strongest muscles in the body in absolute terms and is a powerful extensor of the thigh at the hip (Fig. 6-8). It is especially important in extending the hip when rising from a squatting or sitting position, and when climbing stairs. The gluteus maximus also stabilizes and laterally rotates the hip joint. The gluteus medius and gluteus minimus muscles are primarily abductors and medial rotators of the thigh at the hip, steadying the pelvis over the lower limb when the opposite lower limb is raised off the ground (see Fig. 6-34).


The tensor fasciae latae muscle abducts, medially rotates, and stabilizes the extended knee. The deep fascia of the thigh (fascia lata) is especially thickened laterally and is known as the iliotibial tract. Both the tensor fasciae latae and most of the gluteus maximus muscles insert into this tract and help stabilize the hip and knee extension when standing. People may shift their weight from one lower limb to the other and stabilize the limb they are standing on by placing tension on this iliotibial tract.



Neurovascular Structures


The nerves innervating the gluteal muscles arise from the sacral plexus (see Figs. 6-7 and 6-8 and Tables 6-4 and 6-5) and gain access to the gluteal region largely by passing through the greater sciatic foramen. The blood supply to this region is via the superior and inferior gluteal arteries, which are branches of the internal iliac artery in the pelvis (see also Fig. 5-13 and Table 5-6) and also gain access to the gluteal region via the greater sciatic foramen. These neurovascular elements pass in the plane deep to the gluteus medius muscle (superior gluteal neurovascular bundle) or deep to the gluteus maximus muscle (inferior gluteal neurovascular structures). Also passing through the gluteal region is the largest nerve in the body, the sciatic nerve (L4-S3), which exits the greater sciatic foramen, passes through or more often inferior to the piriformis muscle, and enters the posterior thigh passing deep to the long head of the biceps femoris muscle (see Fig. 6-8).


The internal pudendal artery and pudendal nerve (a somatic nerve, S2-S4) pass out of the greater sciatic foramen, wrap around the sacrospinous ligament, and reenter the lesser sciatic foramen to gain access to the pudendal (Alcock’s) canal (see Figs. 5-22 and 6-8). The pudendal nerve innervates the skeletal muscle and skin of the perineum (see Table 6-4). The internal pudendal artery is the major blood supply to the perineum and external genitalia.





5 Thigh


The thigh is the region of the lower limb between the hip and knee. As you learn the anatomical arrangement of the thigh and leg, organize your study around the functional muscular compartments. The thigh is divided into three muscular compartments: an anterior (extensor) compartment, a medial (adductor) compartment, and a posterior (flexor) compartment by intermuscular septae.



Bones


The femur, the longest bone in the body, is the bone of the thigh. It is slightly bowed anteriorly and runs slightly diagonally, lateral to medial, from the hip to the knee (Fig. 6-9 and Table 6-6). Proximally the femur articulates with the pelvis, and distally it articulates with the tibia and the patella (kneecap), which is the largest sesamoid bone in the body. The proximal femur is supplied with blood from the medial and lateral femoral circumflex branches of the deep femoral artery (see Fig. 6-13), an acetabular branch of the obturator artery, and by anastomotic branches of the inferior gluteal artery. The shaft and distal femur is supplied by femoral nutrient arteries and by anastomotic branches of the popliteal artery, the distal continuation of the femoral artery posterior to the knee.






Anterior Compartment Thigh Muscles, Vessels, and Nerves


Muscles of the anterior compartment exhibit the following characteristics (Figs. 6-10 and 6-11 and Table 6-7):



TABLE 6-7


Anterior Compartment Thigh Muscles























































MUSCLE PROXIMAL ATTACHMENT (ORIGIN) DISTAL ATTACHMENT (INSERTION) INNERVATION MAIN ACTIONS
Psoas major (iliopsoas) Sides of T12-L5 vertebrae and discs between them; transverse processes of all lumbar vertebrae Lesser trochanter of femur Ventral rami of lumbar nerves (L1-L3) Acts jointly with iliacus in flexing thigh at hip joint and in stabilizing hip joint
Iliacus (iliopsoas) Iliac crest, iliac fossa, ala of sacrum, and anterior sacro-iliac ligaments Tendon of psoas major, lesser trochanter, and femur Femoral nerve (L2-L3) Acts jointly with psoas major in flexing thigh at hip joint and in stabilizing hip joint
Sartorius Anterior superior iliac spine and superior part of notch inferior to it Superior part of medial surface of tibia Femoral nerve (L2-L3) Flexes, abducts, and laterally rotates thigh at hip joint; flexes knee joint
Quadriceps Femoris
Rectus femoris Anterior inferior iliac spine and ilium superior to acetabulum Base of patella and by patellar ligament to tibial tuberosity Femoral nerve (L2-L4) Extends leg at knee joint; also steadies hip joint and helps iliopsoas to flex thigh at hip
Vastus lateralis Greater trochanter and lateral lip of linea aspera of femur Base of patella and by patellar ligament to tibial tuberosity Femoral nerve (L2-L4) Extends leg at knee joint
Vastus medialis Intertrochanteric line and medial lip of linea aspera of femur Base of patella and by patellar ligament to tibial tuberosity Femoral nerve (L2-L4) Extends leg at knee joint
Vastus intermedius Anterior and lateral surfaces of femoral shaft Base of patella and by patellar ligament to tibial tuberosity Femoral nerve (L2-L4) Extends leg at knee joint


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Additionally, the psoas major and iliacus muscles (which form the iliopsoas) pass from the posterior abdominal wall to the anterior thigh by passing deep to the inguinal ligament to insert on the lesser trochanter of the femur. These muscles act jointly as powerful flexors of the thigh at the hip joint (Table 6-7; see also Fig. 4-32).



Medial Compartment Thigh Muscles, Vessels, and Nerves


Muscles of the medial compartment exhibit the following characteristics (see Figs. 6-10 and 6-11 and Table 6-8):




The pectineus muscle, while residing in the medial compartment, is largely innervated by the femoral nerve, although it also may receive a branch from the obturator nerve. The adductor magnus, being an exceptionally large and powerful muscle, also receives some innervation via the tibial portion of the sciatic nerve, which runs in the posterior compartment of the thigh.



Posterior Compartment Thigh Muscles, Vessels, and Nerves


Muscles of the posterior compartment exhibit the following characteristics (Fig. 6-12 and Table 6-9; see Fig. 6-8):







Femoral Triangle


The femoral triangle is located on the anterosuperior aspect of the thigh and is bound by the following structures (see Fig. 6-10):



Inferiorly, a fascial sleeve extends from the apex of the femoral triangle and is continuous with the adductor (Hunter’s) canal; the femoral vessels course through this canal and become the popliteal vessels posterior to the knee. The femoral triangle contains the femoral nerve and vessels as they pass beneath the inguinal ligament and gain access to the anterior thigh (see Fig. 6-10). Within this triangle is a fascial sleeve called the femoral sheath, a continuation of transversalis fascia and iliac fascia of the abdomen, that contains the femoral artery and vein and medially the lymphatics. Laterally the femoral nerve lies within the femoral triangle but outside this femoral sheath. The most medial portion of the femoral sheath is called the femoral canal and contains the lymphatics that drain through the femoral ring and into the external iliac lymph nodes. The femoral canal and ring are a weak point and the site for femoral hernias. The femoral ring is narrow, and consequently, femoral hernias may be difficult to reduce and may be prone to strangulation.




Femoral Artery


The femoral artery supplies the tissues of the thigh and then descends into the adductor canal to gain access to the popliteal fossa (Fig. 6-13 and Table 6-10). The superomedial aspect of the thigh also is supplied by the obturator artery. These vessels form anastomoses around the hip and, in the case of the femoral-popliteal artery, around the knee as well (see Fig. 6-13).






Clinical Focus 6-11   Femoral Pulse and Vascular Access


The femoral pulse is felt at about the midpoint of the inguinal ligament. The femoral artery at this point lies directly over or just medial to the femoral head, just lateral to the femoral vein and about a finger’s breadth medial to the femoral nerve (see Figs. 6-10 and 6-13). The femoral artery and vein may be used to gain access to major vessels of the limbs, abdominopelvic cavity, and thorax (e.g., catheter threaded through femoral artery and into aorta for coronary artery angiography and angioplasty). Similarly, the larger veins of the inferior vena cava and the right side of the heart and pulmonary veins may be accessed through the femoral vein.


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Thigh in Cross Section


Cross sections of the thigh show the three compartments and their respective muscles and neurovascular elements (Fig. 6-14). Lateral, medial, and posterior intermuscular septae divide the thigh into the following three sections:




Refer to the muscle tables to note several exceptions to these general divisions. However, learning the primary action and general innervation of the muscles by functional compartments will help you organize your study. Also, note that the large sciatic nerve usually begins to separate into its two component nerves—the tibial nerve and the common fibular nerve—in the thigh, although this separation may occur proximally in the gluteal region in some cases.


Jun 16, 2016 | Posted by in ANATOMY | Comments Off on Lower Limb
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