Human leg
The human leg is the lower limb of the human body, including the thigh, knee, lower leg, ankle, foot, or sometimes even the hip or buttock region. There are thirty bones in each leg. The major bones are the femur, tibia, and adjacent fibula.
The part of the leg between the hip and the knee is called the thigh. The part between the knee and the ankle is called the lower leg, shank, crus, or in anatomy simply the leg. The lower leg includes the shin in the front and the calf at the back.
Legs are used for standing, many forms of human movement, recreation such as dancing, and constitute a significant portion of a person's mass. Evolution has led to the human leg's development into a mechanism specifically adapted for efficient bipedal gait. While the capacity to walk upright is not unique to humans, other primates can only achieve this for short periods and at a great expenditure of energy. In humans, female legs generally have greater hip anteversion and tibiofemoral angles, while male legs have longer femur and tibial lengths.
Structure
In human anatomy, the lower leg or crus is the part of the lower limb that lies between the knee and the ankle. In the lower leg, the calf is the back portion, and the tibia or shinbone together with the smaller fibula make up the shin, the front of the lower leg. Anatomists restrict the term leg to this use, rather than to the entire lower limb. The thigh is between the hip and knee and makes up the rest of the lower limb. The term lower limb or lower extremity is commonly used to describe all of the leg.File:Primatenskelett-drawing.jpg|thumb|upright|Comparison between human and gorilla skeletons.
Evolution has provided the human body with two distinct features: the specialization of the upper limb for visually guided manipulation and the lower limb's development into a mechanism specifically adapted for an efficient bipedal gait. While the capacity to walk upright is not unique to humans, other primates can only achieve this for short periods and at a great expenditure of energy.
The human adaption to bipedalism has also affected the location of the body's center of gravity, the reorganization of internal organs, and the form and biomechanism of the trunk. In humans, the double S-shaped vertebral column acts as a great shock-absorber which shifts the weight from the trunk over the load-bearing surface of the feet. The human legs are exceptionally long and powerful as a result of their exclusive specialization for support and locomotion—in orangutans the leg length is 111% of the trunk; in chimpanzees 128%, and in humans 171%. Many of the leg's muscles are also adapted to bipedalism, most substantially the gluteal muscles, the extensors of the knee joint, and the calf muscles.
Bones
The major bones of the leg are the femur, tibia, and adjacent fibula, which are all long bones. The patella is a sesamoid bone in front of the knee. Most of the leg skeleton has bony prominences and margins that can be palpated, and some serve as anatomical landmarks that define the extent of the leg. These landmarks are the anterior superior iliac spine, the greater trochanter, the superior margin of the medial condyle of tibia, and the medial malleolus. Notable exceptions to palpation are the hip joint, and the neck and body, or shaft of the femur.Usually, the large joints of the lower limb are aligned in a straight line, which represents the mechanical longitudinal axis of the leg, the Mikulicz line. This line stretches from the hip joint, through the knee joint, and down to the center of the ankle. In the tibial shaft, the mechanical and anatomical axes coincide, but in the femoral shaft they diverge 6°, resulting in the femorotibial angle of 174° in a leg with normal axial alignment. A leg is considered straight when, with the feet brought together, both the medial malleoli of the ankle and the medial condyles of the knee are touching. Divergence from the normal femorotibial angle is called genu varum if the center of the knee joint is lateral to the mechanical axis, and genu valgum if it is medial to the mechanical axis. These conditions impose unbalanced loads on the joints and stretching of either the thigh's adductors and abductors.
The angle of inclination formed between the neck and shaft of the femur varies with age—about 150° in the newborn, it gradually decreases to 126–128° in adults, to reach 120° in old age. Pathological changes in this angle result in abnormal posture of the leg: a small angle produces coxa vara and a large angle coxa valga; the latter is usually combined with genu varum, and coxa vara leads genu valgum. Additionally, a line drawn through the femoral neck superimposed on a line drawn through the femoral condyles forms an angle, the torsion angle, which makes it possible for flexion movements of the hip joint to be transposed into rotary movements of the femoral head. Abnormally increased torsion angles result in a limb turned inward and a decreased angle in a limb turned outward; both cases resulting in a reduced range of a person's mobility.
Muscles
Hip
| Movement | Muscles |
| Lateral rotation | •Sartorius •Gluteus maximus •Quadratus femoris •Obturator internus •Gluteus medius and Gluteus minimus •Iliopsoas •Obturator externus •All functional adductors except gracilis* and pectineus •Piriformis |
| Medial rotation | •Gluteus medius and minimus •Tensor fasciae latae* •Adductor magnus •Pectineus |
| Extension | •Gluteus maximus •Gluteus medius and minimus •Adductor magnus •Piriformis •Semimembranosus* •Semitendinosus* •Biceps femoris* |
| Flexion | •Iliopsoas •Tensor fasciae latae* •Pectineus •Adductor longus •Adductor brevis •Gracilis* •Rectus femoris* •Sartorius* |
| Abduction | •Gluteus medius •Tensor fasciae latae* •Gluteus maximus •Gluteus minimus •Piriformis •Obturator internus |
| Adduction | •Adductor magnus •Adductor longus •Adductor brevis •Gluteus maximus •Gracilis •Pectineus •Quadratus femoris •Obturator externus •Semitendinosus* |
| Notes | ♣ Also act on vertebral joints. * Also act on knee joint. |
There are several ways of classifying the muscles of the hip:
- By location or innervation ;
- By development on the basis of their points of insertion ; and
- By function.
The anterior dorsal hip muscles are the iliopsoas, a group of two or three muscles with a shared insertion on the lesser trochanter of the femur. The psoas major originates from the last vertebra and along the lumbar spine to stretch down into the pelvis. The iliacus originates on the iliac fossa on the interior side of the pelvis. The two muscles unite to form the iliopsoas muscle, which is inserted on the lesser trochanter of the femur. The psoas minor, only present in about 50 per cent of subjects, originates above the psoas major to stretch obliquely down to its insertion on the interior side of the major muscle.
The posterior dorsal hip muscles are inserted on or directly below the greater trochanter of the femur. The tensor fasciae latae, stretching from the anterior superior iliac spine down into the iliotibial tract, presses the head of the femur into the acetabulum but also flexes, rotates medially, and abducts to hip joint. The piriformis originates on the anterior pelvic surface of the sacrum, passes through the greater sciatic foramen, and inserts on the posterior aspect of the tip of the greater trochanter. In a standing posture it is a lateral rotator, but it also assists extending the thigh. The gluteus maximus has its origin between the iliac crest and the coccyx, from where one part radiates into the iliotibial tract and the other stretches down to the gluteal tuberosity under the greater trochanter. The gluteus maximus is primarily an extensor and lateral rotator of the hip joint, and it comes into action when climbing stairs or rising from a sitting to a standing posture. Furthermore, the part inserted into the fascia latae abducts and the part inserted into the gluteal tuberosity adducts the hip. The two deep glutei muscles, the gluteus medius and minimus, originate on the lateral side of the pelvis. The medius muscle is shaped like a cap. Its anterior fibers act as a medial rotator and flexor; the posterior fibers as a lateral rotator and extensor; and the entire muscle abducts the hip. The minimus has similar functions and both muscles are inserted onto the greater trochanter.
The ventral hip muscles function as lateral rotators and play an important role in the control of the body's balance. Because they are stronger than the medial rotators, in the normal position of the leg, the apex of the foot is pointing outward to achieve better support. The obturator internus originates on the pelvis on the obturator foramen and its membrane, passes through the lesser sciatic foramen, and is inserted on the trochanteric fossa of the femur. "Bent" over the lesser sciatic notch, which acts as a fulcrum, the muscle forms the strongest lateral rotators of the hip together with the gluteus maximus and quadratus femoris. When sitting with the knees flexed it acts as an abductor. The obturator externus has a parallel course with its origin located on the posterior border of the obturator foramen. It is covered by several muscles and acts as a lateral rotator and a weak adductor. The inferior and superior gemelli muscles represent marginal heads of the obturator internus and assist this muscle. These three muscles form a three-headed muscle known as the triceps coxae. The quadratus femoris originates at the ischial tuberosity and is inserted onto the intertrochanteric crest between the trochanters. This flattened muscle act as a strong lateral rotator and adductor of the thigh.
The adductor muscles of the thigh are innervated by the obturator nerve, with the exception of pectineus which receives fibers from the femoral nerve, and the adductor magnus which receives fibers from the tibial nerve. The gracilis arises from near the pubic symphysis and is unique among the adductors in that it reaches past the knee to attach on the medial side of the shaft of the tibia, thus acting on two joints. It share its distal insertion with the sartorius and semitendinosus, all three muscles forming the pes anserinus. It is the most medial muscle of the adductors, and with the thigh abducted its origin can be clearly seen arching under the skin. With the knee extended, it adducts the thigh and flexes the hip. The pectineus has its origin on the iliopubic eminence laterally to the gracilis and, rectangular in shape, extends obliquely to attach immediately behind the lesser trochanter and down the pectineal line and the proximal part of the Linea aspera on the femur. It is a flexor of the hip joint, and an adductor and a weak medial rotator of the thigh. The adductor brevis originates on the inferior ramus of the pubis below the gracilis and stretches obliquely below the pectineus down to the upper third of the Linea aspera. Except for being an adductor, it is a lateral rotator and weak flexor of the hip joint.
The adductor longus has its origin at superior ramus of the pubis and inserts medially on the middle third of the Linea aspera. Primarily an adductor, it is also responsible for some flexion. The adductor magnus has its origin just behind the longus and lies deep to it. Its wide belly divides into two parts: One is inserted into the Linea aspera and the tendon of the other reaches down to adductor tubercle on the medial side of the femur's distal end where it forms an intermuscular septum that separates the flexors from the extensors. Magnus is a powerful adductor, especially active when crossing legs. Its superior part is a lateral rotator but the inferior part acts as a medial rotator on the flexed leg when rotated outward and also extends the hip joint. The adductor minimus is an incompletely separated subdivision of the adductor magnus. Its origin forms an anterior part of the magnus and distally it is inserted on the Linea aspera above the magnus. It acts to adduct and lateral rotate the femur.