Abstract
This chapter addresses the need for a comprehensive knowledge of lower extremity anatomy in the clinical practice of plastic surgery. Reconstructive surgery related to lower extremity trauma incorporates concepts of soft tissue and bone repair and stabilization combined with the use of local muscles and their inherent blood supply for reconstruction. In aesthetic surgery of the lower extremity, success cannot be achieved without an appreciation of the muscular, fascial, and cutaneous interconnections. Also described are the anatomy of the lower extremity with descriptions of the thigh, leg, and foot. Each section begins with the skeletal foundation and progresses into the fascia, muscles, joints, innervations, and vasculature.
3 Anatomy of the Lower Extremity
3.1 Goals and Objectives
Understand the proper vascular, neural, muscular and bony anatomy of the lower extremity in relation to plastic surgery.
Appreciate that flap surgery is essentially applied anatomy.
Know the anatomy well to maximize flap success and patient safety.
3.2 Introduction
A comprehensive knowledge of lower extremity anatomy is necessary for the clinical practice of plastic surgery. Reconstructive surgery related to lower extremity trauma incorporates concepts of soft tissue and bone repair and stabilization combined with the use of local muscles and their inherent blood supply for reconstruction. In aesthetic surgery of the lower extremity, success cannot be achieved without an appreciation of the muscular, fascial, and cutaneous interconnections. This chapter describes the anatomy of the lower extremity with descriptions of the thigh, leg, and foot. Each section begins with the skeletal foundation and progresses into the fascia, muscles, joints, innervations, and vasculature.
3.3 Anatomy of the Lower Extremity
The main functions of the lower extremity are motion and stabilization of the trunk. It consists of a skeletal structure that interacts through several joints: several thick and potent muscles that assist in several movements and a vascular supply. This is covered with skin and subcutaneous tissue. It can be divided into four regions: gluteal, thigh, leg, and foot.
3.4 Fascia
Similar to the trunk, the gluteal region, thigh, and leg have two layers of fascia: the superficial and deep. Superiorly they come together at the level of the inguinal ligament and inferiorly they give rise to retinacular bands. 1
The superficial fascia encircles the entire lower extremity, including the buttock. It is typically more dense and thicker proximally than in the distal extremity. It is found within the fat of the subcutaneous tissue. It usually gets pierced by nerves and vessels that travel from the deeper structures to the skin.
The deep fascia (also known as fascia lata) is a vascularized fibrous tissue that encircles muscles. It helps separate each region of the lower extremity into different compartments. This does not only serve as pathways for vessel perforators but also improves efficiency by providing attachment areas for muscles. Superiorly, the inguinal ligament serves as the anterior attachment of the deep fascia. Posteriorly, the fascia attaches to the sacrum and coccyx. On the lateral aspect, the fascia joins the iliac crest.
Characteristics of the deep fascia include a lateral band known as the iliotibial band and the saphenous opening. The saphenous opening is an oval defect in the deep fascia that allows the passage of the branches of the femoral artery, the saphenous vein, and lymphatics. It is covered by a portion of superficial fascia that is known as fascia cribrosa. 2
The fascia of the foot is slightly different from the rest of the extremity. The superficial fascia contains minimal adipose tissue. The deep fascia gives rise to the extensor retinacula, the flexor and peroneal retinaculum, and the plantar fascia. There is superior and inferior extensor retinaculum that supports tendons of dorsiflexion that are located on the dorsum of the foot. The flexor retinaculum is on the medial aspect of the ankle and supports the plantar-flexor tendons. The peroneal retinaculum is on the lateral ankle and supports the tendons of the peroneus longus and peroneus brevis. 3
3.5 Skeletal Structure
3.5.1 Bones
Femur
The largest and thickest bone in the human body forms the main support for the thigh: the femur. 2 This bone has a posterior concavity that allows it to support the rest of the body. It has special features that articulate with pelvic bones as well as the leg bones.
The superior aspect of the femur contains four irregular structures 1 :
Femoral head: Found on the medial aspect of the bone, it forms two-thirds of a sphere that articulates with the iliac bone at the level of the acetabulum. 1 It is covered with cartilage.
Neck of the femur: Supports the femoral head and connects it to the femoral shaft. It has an inferolateral angulation that projects slightly anteriorly.
Greater trochanter: It is a 1-cm posterior projection found on the lateral aspect of the femur. The gluteus medius, gluteus maximus, obturator internus, and superior and inferior gemellus muscles insert into it.
Lesser trochanter: A medial projection of the femur, it serves as an insertion point to the psoas major and the iliacus.
The inferior portion of the femur bone contains several important features. The medial and lateral condyles are found on the distal portion. They are two projections on the medial and lateral aspects of the distal femur. The medial condyle is longer than the lateral but less prominent. They are separated anteriorly by a depression known as the patellar surface and posteriorly by a notch known as the intercondylar fossa of the femur. 4 The anterior, posterior, and inferior surfaces of the condyles constitute the articular surface of the distal femur. Immediately superior to the condyles, there is the medial and lateral epicondyles. They serve as attachments for ligaments of the knee joint. Superior to the medial epicondyle, there is also the adductor tubercle which serves as the insertion point of the adductor magnus.
Patella
The patella is a sesamoid, flat triangularly shaped bone that is embedded in the quadriceps femoris muscle and makes part of the knee joint. The anterior surface receives the quadriceps femoris tendon. 5 The posterior surface articulates with the femur and contains cartilage. The inferior portion of the posterior surface contains the infrapatellar fat pad. The patella ultimately allows extension force by amplifying the force exerted by the quadriceps. 6
Tibia
Along with the fibula, the tibia forms the structural base of the leg. It provides support and assists with motion as it serves as the attachment point for several muscles.
The proximal portion of the bone consists of the tibial condyles. They support the articulations to the femur forming the tibiofemoral joint. Similar to the femur, the medial and lateral condyles are separated by the intercondylar area. The cruciate ligaments as well as the menisci attach to this portion of the tibia. The intercondylar area is divided into anterior and posterior parts by the intercondylar eminence; this eminence is formed by projections of the bone called medial and lateral intercondylar tubercles that correspond to a lateral projection of the medial condyle and a medial projection of the lateral condyle. 1 The lateral condyle also contains a facet for the head of the fibula. Immediately below the condyles, there is the tibial tuberosity that serves as attachment for the patellar ligament and continuation of the quadriceps femoris.
The body of the bone is divided into three surfaces: medial, lateral, and posterior. The medial portion can be directly felt and palpated over the skin as it has no attachments (except proximally). The posterior surface has a ridge called “soleal line” that runs from the articular facet for the fibula to the medial border. 2
The inferior extremity appears smaller than the superior aspect of the bone. It has an inferior articular surface that serves as an articular point with the talus bone. The medial surface is palpable and forms the medial malleolus, and continues inferiorly to have another small surface for articulation with the talus bone. The lateral surface forms the fibular notch, which articulates the fibula.
Fibula
This small and thin bone is part of the leg structure. Its function revolves around providing insertion points for musculature rather than support of the body. It also has two extremities and a body.
The fibular head is separated from the body of the bone by the fibular neck. In its medial aspect, we can find a surface that articulates with the lateral condyle of the tibia. We can also find an interosseous membrane that connects the fibula and the tibia. On the inferior extremity, we find the lateral malleolus. It has a medial surface that articulates with the talus bone.
Foot Bones
The skeletal structure of the foot is unique in that it represents a transition of muscle layout from vertical to horizontal. The ankle itself bridges this transition. In order to achieve this, the human foot has 26 bones. 7
The tarsal bones are organized into two rows 8 :
Proximal: made up by the talus and calcaneus.
Distal: includes the cuboid, cuneiforms bones (lateral, intermediate, and medial), and the navicular bones. This last bone is found just proximal to the cuneiforms bones.
The first toe consists of a metatarsal bone followed by a proximal and a distal phalange. Second through fifth toes have also a metatarsal bone followed by a proximal phalange; however, it also has a middle phalange that separates the proximal from the distal phalanges. The joints that are found between the metatarsus and the phalanges are called metatarsophalangeal and those found between phalanges are called interphalangeal.
3.5.2 Joints
Hip Joint
The hip joint serves as the area of transfer of support of the trunk into the lower extremities. The pelvis constitutes a stable and complex skeletal structure which is discussed in Chapter 4.
The upper extremity of the femur contains the head of the femur that articulates with the pelvic acetabulum. It forms a ball-socket joint that enables transfer of load as well as motility. The head of the femur as well as the acetabulum is covered with cartilage that minimizes friction and ensures smooth motion. It also contains a capsule that attaches to the bone just outside the acetabular to the base of the femur neck. It permits a wide range of motion.
There are four ligaments that reinforce this important joint and they are the iliofemoral, ischiofemoral, pubofemoral, and the ligamentum teres. 9 , 10 , 11 Their main function is to strengthen the capsule and prevent excessive motion of the joint leading to injury or dislocation.
Knee Joint
This joint connects the thigh and the leg. It is made of two articulations: the tibiofemoral and the patellofemoral joints. The first joint is formed by the femoral and tibial condyles and it allows for extension and flexion of the leg. The second joint is formed by the femur and the articular surface of the patella which mainly assists the tibiofemoral joint in its functions. 12
The joint is reinforced by several ligaments and tendons that provide stability 1 :
Anterior: We can find the patellar ligament, quadriceps tendon, the medial and lateral patellar retinaculum.
Lateral: Fibular collateral ligament (lateral collateral ligament—LCL).
Medial: Tibial collateral ligament (medial collateral ligament—MCL).
Posterior: Oblique popliteal ligament (posterior ligament), arcuate popliteal ligament, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), meniscofemoral ligaments.
The medial and lateral menisci are also key components in the structure of the knee. They are C-shaped fibrocartilaginous structures that minimize friction in the knee joint. 13 They are attached to the tibia and ultimately help transmit the weight of the trunk into the distal structures of the leg.
Ankle Joint
It serves as the connection between the foot and the leg. The ankle is also a transition point where muscles go from a vertical to horizontal arrangement. It is made of three bones: the tibia, the fibula, and the talus.
The ankle includes three joints: the talocrural joint (ankle proper joint) formed by the distal ends of the fibula and tibia that enclose the upper surface of the talus; the subtalar joint where the talus and the calcaneus bones meet; and the inferior tibiofibular joint where the medial and distal end of the fibula articulates with the lateral side of the tibia. 8
There are four ligaments that reinforce this important joint: the deltoid (medial ankle), calcaneofibular (lateral ankle), anterior, and posterior talofibular ligaments. 1 , 7 , 14 Similar to the knee and hip ligaments, these four ligaments allow movement of the foot—dorsiflexion, plantarflexion, rotation, and inversion—by stabilizing the joint and avoiding dislocations or injury.
3.6 Muscles
3.6.1 Gluteal Region
There are three predominant muscles in the buttock area: gluteus maximus, gluteus medius, and gluteus minimus muscles. These are muscles involved with external rotation and the abduction of the hip. We can also find the Tensor fasciae latae muscle that participates in thigh flexion, medial rotation, and abduction. Other muscles that assist in the movement of the pelvis and the hips include the psoas major and iliacus. 1 , 2
3.6.2 Tensor Fasciae Latae
General: This is a flattened, small, and rectangular muscle that extends from the iliac crest to the knee. The muscle belly is small; however, it has a large aponeurosis.
Insertions and Structure: It arises from the outer lip of the iliac crest. The muscle belly descends inferiorly and posteriorly to fuse with the fascia lata, forming the iliopubic tract. 1 , 2
Blood supply: Derives from the superior gluteal artery and the lateral circumflex femoral artery.
Innervation: Superior gluteal nerve from nerve roots L4, L5, and S1.
Classification : This muscle flap is a Mathes and Nahai type I class, as it has a single dominant pedicle, the ascending branch of the lateral femoral circumflex artery. It has a wide variety of reconstructive options, both as a local flap (defects of the abdomen, groin, ischium, trochanter, sacrum) and a free flap (defects of the head and neck, upper extremity, lower extremity, foot). 15
3.6.3 Gluteus Maximus
General: This is the largest and most superficial of the gluteal muscles. It plays a significant role in the appearance of the buttock and hip.
Insertions and structure: It has a very broad origin, arising from the gluteal zone of the ilium, sacrum, and sacrotuberous ligament and the lumbar fascia. The muscle fibers travel downward and laterally and the fascicles are separated by fibrous septa that join to form an aponeurosis. It inserts into the gluteal tuberosity of the femur and the iliotibial tract.
Blood supply: Main arteries that supply this muscle are the superior and inferior gluteal arteries.
Innervation: The inferior gluteal nerve is responsible for the innervation of this muscle with fibers from L5, S1, and S2.
Classification: This muscle flap is a Mathes and Nahai type III class, as it has two dominant pedicles, the superior and inferior gluteal arteries. It also has two minor pedicles, the first perforator of profunda femoris and two to three intermuscular branches of the lateral femoral circumflex. It has several reconstructive options, both as a local flap (defects of the ischium, trochanter, sacrum) and as a free flap for breast reconstruction. 15
3.6.4 Gluteus Medius
General: It is a triangular-shaped muscle that is deep to the gluteus maximus.
Insertions and structure: Originates in the gluteal surface of the ilium, deep to the gluteus maximus. The muscle fibers converge toward the superior extremity of the femur and form a flat tendon at the level of the greater trochanter.
Blood supply: The superior gluteal artery is responsible for the blood supply to this muscle.
Innervation: Nerve roots from L4, L5, and S1 supply this muscle through the superior gluteal nerve.
3.6.5 Gluteus Minimus
General: It is a triangular-shaped muscle that can be found in the deep and anterior portion of the gluteal region.
Insertions and structure: It originates from the gluteal surface of the ilium, deep to the gluteus medius. The muscle fibers travel toward the upper extremity of the femur and form a tendon that inserts in the greater trochanter.
Blood supply: Similar to the gluteus medius, blood supply derives from the superior gluteal artery.
Innervation: The superior gluteal nerve, with roots from L4, L5, and S1 innervate this muscle.
3.6.6 Psoas Major
General: It is a long and fusiform muscle that can be found in the external iliac fossa of the pelvis and in the posterior trunk, next to vertebral bodies.
Insertions and structure: It originates from vertebral bodies T12 to L5. Muscle fibers travel next to the vertebral column downward. The muscle descends through the internal iliac fossa and it joins the anterior border of the iliac muscle forming the iliopsoas muscle. It ultimately inserts into the lesser trochanter of the femur.
Blood supply: Derived from the lumbar branch of the iliolumbar artery.
Innervation: Anterior branches of L1–L3 nerves (lumbar plexus).
3.6.7 Iliacus
General: It is a triangular-shaped muscle whose apex joins the psoas major in its medial border.
Insertions and structure: It originates from the internal iliac fossa and after forming the iliopsoas muscle, it inserts into the lesser trochanter of the femur.
Blood supply: It has dual blood supply provided by the iliac branch of the iliolumbar artery and the medial femoral circumflex artery.
Innervation: Innervated by the femoral nerve.
Other muscles that are found in the gluteal region but are not described in this book include the obturator internus, pyramidal muscle, gemellus muscles, and obturator externus.
3.6.8 Thigh Muscles
The musculature of the thigh is divided into three distinct compartments that also helps us identify functions for the muscles. The three compartments are as follows:
Anterior fascial compartment: Muscles in this group usually assist in thigh extension. It includes the rectus femoris, vastus lateralis, vastus intermedius, vastus medialis (these four muscles form the quadriceps muscles), sartorius, and pectineus muscles.
Posterior fascial compartment: Involved with flexion of the thigh. It includes the biceps femoris, semimembranosus, and semitendinosus muscles.
Medial fascial compartment: Adduction is the main function of this group of muscles. It includes the gracilis, adductor longus, adductor brevis, and the adductor magnus.
3.7 Anterior Compartment
3.7.1 Rectus Femoris
General: It is the most superficial portion of the quadriceps. It is a fusiform-shaped muscle that is immediately over the vastus intermedius.
Insertions and structure: It originates from two separate heads—the straight head that arises from the anterior inferior iliac spine and the reflected head that arises just above the acetabulum. The four muscles of the quadriceps (rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis) form on their distal portion the quadriceps tendon, in which the patella is found. Just below the patella, the tendon is known as the patellar tendon and continues and inserts into the tibial tuberosity.
Function: Assists in hip flexion as well as knee extension.
Blood supply: Derived from the descending branch of the lateral femoral circumflex artery.
Innervation: The femoral nerve is responsible for the innervation of all the quadriceps muscles.
Classification: This muscle flap is a Mathes and Nahai type II class, as it has a single dominant pedicle, the descending branch of the lateral femoral circumflex artery. It also has two minor pedicles, the ascending branch of the lateral femoral circumflex and the muscular branches of the superficial femoral artery. It has a wide variety of applications, both as a local flap (coverage of the inferior abdomen, groin, ischium, and perineum) and as a functional muscle free flap (facial reanimation and upper extremity reconstruction). 15
3.7.2 Vastus Lateralis
General: It is found just lateral to the vastus intermedius. It is just superior to it and portions of the muscle can cover fibers of the vastus intermedius.
Insertions and structure: It originates from a tendinous structure at the external portion of the linea aspera of the femur: this extends proximally into the greater trochanter. The muscle belly descends to the patella and inserts to the tibial tuberosity as the quadriceps tendon.
Function: The muscle participates in knee extension.
Blood supply: The lateral circumflex femoral artery provides the main blood supply.
Innervation: Performed by the femoral nerve.
Classification: This muscle flap is a Mathes and Nahai type I class, as it has a single dominant pedicle, the descending branch of the lateral femoral circumflex artery. It also has three minor pedicles—the transverse branch of the lateral femoral circumflex, the posterior branches of the profunda femoris artery, and the superficial branch of the lateral superior genicular. It has a wide variety of options, both as a local flap (coverage of the trochanter, knee, groin, ischium, and perineum) and as a reconstructive option for the abdominal wall and acetabular fossa. 15
3.7.3 Vastus Intermedius
General: It is located around the body of the femur, deep to the rectus femoris muscle.
Insertions and structure: It originates from the proximal two-thirds of the anterolateral aspect of the femur. It terminates as a portion of a tendon (quadriceps femoris tendon) that attaches to the tibial tuberosity.
Function: Participates in extension of the knee.
Blood supply: Derived from the femoral artery.
Innervation: Performed by the femoral nerve.
3.7.4 Vastus Medialis
General: This muscle is medial to the vastus intermedius. It can be found partially attached to the muscle.
Insertions and structure: Originates from the medial portion of the femur and inserts into tibial tuberosity via the quadriceps femoris tendon.
Function: It assists in extension of the leg.
Blood supply: Femoral artery is the main blood supply.
Innervation: Similar to the other vastus muscles, it is innervated by the femoral nerve.
Classification: This muscle flap is a Mathes and Nahai type II class, as it has a single dominant pedicle, a branch of the superficial femoral artery. It also has two minor pedicles, branches of the superficial femoral artery and the musculoarticular branches of the descending genicular artery. It can be used as a distally based flap, a functional muscle or as a V-Y advancement flap skin island for coverage of the upper knee. 15
3.7.5 Sartorius
General: It is the longest muscle in the human body and it runs the entire length of the anterior compartment. It is in the superficial portion of the compartment. The proximal portion of the sartorius forms the lateral border of the femoral triangle.
Insertions and structure: It originates from the anterior-superior iliac spine. It runs inferiorly and medially. It travels behind the medial condyle of the femur and forms a tendon that inserts into the medial aspect of the tibia’s body. The ending of the muscle is called “pes anserinus” and it is formed by the sartorius, gracilis, and semitendinosus tendons.
Function: It assists in flexing and lateral rotation of the hip joint.
Blood supply: Derived from the femoral artery.
Innervation: Done by the femoral nerve.
Classification: This muscle flap is a Mathes and Nahai type IV class, as it has a segmental pedicle as the blood supply, six to seven branches of the superficial femoral vessels. It has proven to be useful in covering defects involving the groin, femoral vessels, and the knee. 15
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