Editing Human leg (section)

== Structure ==
[[File:Thigh_(PSF).png|thumb|left|Diagram of parts of leg]]
In human anatomy, the lower leg or '''crus''' is the part of the lower limb that lies between the [[knee]] and the [[ankle]].<ref name=Tortora2020>{{Cite book|last1=Tortora|first1=Gerard|last2=Nielsen|first2=Mark |url=https://www.wiley.com/en-us/Principles+of+Human+Anatomy%2C+15th+Edition-p-9781119662860|title=Principles of Human Anatomy|publisher=[[John Wiley & Sons]]|year=2020|isbn=978-1-119-66286-0|page=995|language=en|chapter=27 - Surface Anatomy}}</ref><ref name=Muscolino2016>{{Cite book|last=Muscolino|first=Joseph|url=https://www.elsevier.com/books/the-muscular-system-manual/muscolino/978-0-323-32770-1|title=The Muscular System Manual: The Skeletal Muscles of the Human Body|publisher=[[Elsevier]]|year=2016|isbn=978-0-323-32771-8|page=1|language=en|chapter=1 - Basic Kinesiology Terminology}}</ref> In the lower leg, the [[calf (anatomy)|calf]] is the back portion, and the [[tibia]] or shinbone together with the smaller [[fibula]] make up the [[Tibia#Structure|shin]], the front of the lower leg.<ref name=McDowell2010>{{Cite book|last=McDowell|first=Julie|url=https://www.abc-clio.com/products/a3211c/|title=Encyclopedia of Human Body Systems|publisher=[[ABC-CLIO]]|year=2010|isbn=978-0-313-39176-7|volume=2|page=587|language=en|chapter=11 - The Skeletal System}}</ref> Anatomists restrict the term ''leg'' to this use, rather than to the entire lower limb.<ref name=Patton2015>{{Cite book|last=Patton|first= Kevin|url=https://www.worldcat.org/oclc/928962548|title=Anatomy and Physiology|publisher=[[Elsevier]]|year=2015|isbn=978-0-323-34139-4|page=12|language=en|chapter=1 - Organization of the Body|oclc= 928962548}}</ref> The [[thigh]] is between the [[hip]] and [[knee]] and makes up the rest of the lower limb.<ref name=Muscolino2016/> 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]] [[skeleton]]s. (Gorilla in non-natural stretched posture.)]]
[[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 [[bipedalism|bipedal gait]].<ref name=Striedter2016>{{Cite book|last1=Striedter|first1=Georg|last2=Bullock|first2=Theodore |last3=Preuss|first3=Todd|last4=Rubenstein|first4=John|url=https://www.elsevier.com/books/evolution-of-nervous-systems/kaas/978-0-12-804042-3|title=Evolution of Nervous Systems|publisher=[[Elsevier]]|year=2016|isbn=978-0-128-04096-6|pages=222–226|language=en|chapter=3.12 - Evolved Mechanisms of High-Level Visual Perception in Primates}}</ref> While the capacity to walk upright is not unique to humans, other [[primate]]s can only achieve this for short periods and at a great expenditure of energy.<ref name=Hefti2015>{{Cite book|last=Hefti|first=Fritz|url=https://link.springer.com/book/10.1007/978-3-662-46810-4|title=Pediatric Orthopedics in Practice|publisher=[[Springer Science+Business Media]]|year=2015|isbn=978-3-662-46810-4|edition=2|page=87|language=en|chapter=4 - Spine, trunk|doi=10.1007/978-3-662-46810-4 }}</ref>

The human adaption to bipedalism has also affected the location of the body's [[center of mass|center of gravity]], the reorganization of [[viscus|internal organs]], and the form and [[biomechanics|biomechanism]] of the trunk.<ref name=Soames2018>{{Cite book|last1=Soames|first1=Roger|last2=Palastanga|first2=Nigel|url=https://www.elsevier.com/books/anatomy-and-human-movement/soames/978-0-7020-7226-0|title=Anatomy and Human Movement|publisher=[[Elsevier]]|year=2018|isbn=978-0-702-07259-8|edition=7|pages=220–222|language=en|chapter=3 - Lower limb}}</ref> 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 [[orangutan]]s the leg length is 111% of the trunk; in [[chimpanzee]]s 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 muscle]]s.<ref>''Thieme Atlas of Anatomy'' (2006), p. 360</ref>

=== Bones ===
{{See also|Human skeletal changes due to bipedalism}}
[[File:Human leg bones labeled.svg|thumb|upright|Bones of the leg]]
The major [[bone]]s of the leg are the [[femur]] (thigh bone), [[tibia]] (shin bone), and adjacent [[fibula]], which are all [[long bone]]s. The [[patella]] (kneecap) is a [[sesamoid bone]] (the largest in the body)  in front of the [[knee]]. Most of the leg skeleton has bony prominences and margins that can be [[palpation|palpated]], and some serve as [[anatomical landmark]]s 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]].<ref>''Thieme Atlas of Anatomy'' (2006), p. 361</ref> Notable exceptions to palpation are the [[hip joint]], and the [[femur neck|neck]] and [[body of femur|body, or shaft]] of the femur.

Usually, the large [[joint]]s of the lower limb are aligned in a straight line, which represents the mechanical longitudinal axis of the leg, the [[Jan Mikulicz-Radecki|Mikulicz]] line. This line stretches from the [[hip joint]] (or more precisely the [[femur head|head of the femur]]), through the [[knee joint]] (the [[intercondylar eminence]] of the tibia), and down to the center of the [[ankle]] (the ankle mortise, the fork-like grip between the [[medial malleolus|medial]] and [[lateral malleolus|lateral malleoli]]). In the [[Body of tibia|tibial shaft]], the mechanical and anatomical axes coincide, but in the [[Body of femur|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 (intermalleolar distance exceeds 3&nbsp;cm), and [[genu valgum]] if it is medial to the mechanical axis (intercondylar distance exceeds 5&nbsp;cm). These conditions impose unbalanced loads on the joints and stretching of either the thigh's adductors and abductors.<ref>''Thieme Atlas of Anatomy'' (2006), p. 362</ref>

The angle of inclination formed between the neck and shaft of the femur (collodiaphysial angle) 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.<ref name="Platzer-196">Platzer (2004), p. 196</ref>

=== Muscles ===

==== Hip ====
{{See also|Muscles of the hip}}
{| class="wikitable" style="float:right; margin-left:15px"
|+ Function of hip muscles<ref name="Platzer-244">Platzer (2004), pp. 244–47</ref>
|-
! Movement !! Muscles<br />(in order of importance)
|-
|Lateral<br />rotation
|
•[[Sartorius muscle|Sartorius]]<br>•[[Gluteus maximus]]<br />•[[Quadratus femoris muscle|Quadratus femoris]]<br />•[[Obturator internus muscle|Obturator internus]]<br />•[[Gluteus medius]] and [[Gluteus minimus]]<br />•[[Iliopsoas]]<br />(with [[Psoas major muscle|psoas major]]♣)<br />•[[External obturator muscle|Obturator externus]]<br />•All functional [[Adductor muscles of the hip|adductors]]<br />except [[Gracilis muscle|gracilis]]* and [[Pectineus muscle|pectineus]]<br />•[[Piriformis muscle|Piriformis]]
|-
|Medial<br />rotation
|
•Gluteus medius and<br />minimus (anterior fibers)<br />•Tensor fasciae latae*<br />•[[Adductor magnus muscle|Adductor magnus]]<br />(long medial fibers)<br />•Pectineus (with leg abducted)
|-
| Extension
|
•Gluteus maximus<br />•Gluteus medius and<br />minimus (dorsal fibers)<br />•Adductor magnus<br />•Piriformis<br />•Semimembranosus*<br />•Semitendinosus*<br />•Biceps femoris*<br />(long head)
|-
|Flexion
|
•Iliopsoas<br />(with psoas major♣)<br />•Tensor fasciae latae*<br />•Pectineus<br />•Adductor longus<br />•Adductor brevis<br />•Gracilis*<br />•Rectus femoris*<br />•Sartorius*
|-
| Abduction
|
•Gluteus medius<br />•Tensor fasciae latae*<br />•Gluteus maximus<br />(fibers to fascia lata)<br />•Gluteus minimus<br />•Piriformis<br />•Obturator internus
|-
|Adduction
|
•Adductor magnus<br />(with adductor minimus)<br />•Adductor longus<br />•Adductor brevis<br />•Gluteus maximus (fibers<br />to gluteal tuberosity)<br />•Gracilis<br />•Pectineus<br />•Quadratus femoris<br />•Obturator externus<br />•Semitendinosus*
|-
! Notes || '''♣''' Also act on vertebral joints.<br /> '''*''' Also act on knee joint.
|}

There are several ways of classifying the muscles of the hip:
# By location or innervation (ventral and dorsal divisions of the plexus layer);
# By development on the basis of their points of insertion (a posterior group in two layers and an anterior group); and
# By function (i.e. extensors, flexors, adductors, and abductors).<ref name="Platzer-232">Platzer, (2004), p. 232</ref>

Some hip muscles also act either on the knee joint or on vertebral joints. Additionally, because the areas of origin and insertion of many of these muscles are very extensive, these muscles are often involved in several very different movements. In the hip joint, lateral and medial rotation occur along the axis of the limb; extension (also called dorsiflexion or retroversion) and flexion (anteflexion or anteversion) occur along a transverse axis; and abduction and adduction occur about a [[sagittal]] axis.<ref name="Platzer-244" />

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 muscle|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.<ref>Platzer (2004), p. 234</ref>

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 [[Femur head|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 (and around) 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 [[gluteus minimus|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.<ref>Platzer (2004), p. 236</ref>

[[File:Gray436.png|thumb|left|upright|Muscles of the hip]]
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 [[obturator membrane|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 [[Gemelli muscles|inferior]] and [[Gemelli muscles|superior gemelli muscles]] represent marginal heads of the obturator internus and assist this muscle. These three muscles form a three-headed muscle (tricipital) known as the '''triceps coxae'''.<ref name="Moore">{{cite book |last1=Moore |first1=Keith L. |title=Clinically oriented anatomy |date=2018 |location=Philadelphia |isbn=9781496347213 |page=728 |edition=Eighth}}</ref> 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.<ref>Platzer (2004), p. 238</ref>

[[File:Gray433.png|thumb|left|upright=0.4|Hip adductors]]
The [[Adductor muscles of the hip|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 muscle|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 [[Body of tibia|shaft of the tibia]], thus acting on two joints. It share its distal insertion with the [[Sartorius muscle|sartorius]] and [[Semitendinosus muscle|semitendinosus]], all three muscles forming the [[Pes anserinus (leg)|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 muscle|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 (femur)|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 muscle|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.<ref>Platzer (2004), p. 240</ref>

The [[Adductor longus muscle|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 muscle|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 muscle|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.<ref>Platzer (2004), p. 242</ref>
{{clear|right}}

==== Thigh ====
{| class="wikitable" style="float:right; margin-left:15px"
|+ Function of knee muscles<ref>Platzer (2004), p. 252</ref>
|-
! Movement !! Muscles<br />(in order of<br />importance)
|-
|Extension
|
•[[Quadriceps|Quadriceps femoris]]<br />•[[Tensor fasciae latae muscle|Tensor fasciae latae]]*
|-
|Flexion
|
•[[Semimembranosus muscle|Semimembranosus]]<br />•[[Semitendinosus muscle|Semitendinosus]]<br />•[[Biceps femoris muscle|Biceps femoris]]<br />•[[Gracilis muscle|Gracilis]]<br />•[[Sartorius muscle|Sartorius]]<br />•[[Popliteus muscle|Popliteus]]<br />•[[Gastrocnemius muscle|Gastrocnemius]]
|-
|Medial<br />rotation
|
•Semimembranosus<br />•Semitendinosus<br />•Gracilis<br />•Sartorius<br />•Popliteus
|-
| Lateral<br />rotation
|
•Biceps femoris<br />•Tensor fasciae latae*
|-
|colspan="2"|*Insignificant assistance.
|}
The muscles of the [[thigh]] can be classified into three groups according to their location: anterior and posterior muscles and the adductors (on the medial side). All the adductors except gracilis insert on the femur and act on the hip joint, and so functionally qualify as hip muscles. The majority of the thigh muscles, the "true" thigh muscles, insert on the leg (either the tibia or the fibula) and act primarily on the knee joint. Generally, the extensors lie on anterior of the thigh and flexors lie on the posterior. Even though the sartorius flexes the knee, it is [[Ontogeny|ontogenetically]] considered an extensor since its displacement is secondary.<ref name="Platzer-232" />

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| footer = Anterior and posterior thigh muscles.
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Of the anterior thigh muscles the largest are the four muscles of the [[Quadriceps femoris muscle|quadriceps femoris]]: the central [[Rectus femoris muscle|rectus femoris]], which is surrounded by the three vasti, the [[Vastus intermedius muscle|vastus intermedius]], [[Vastus medialis muscle|medialis]], and [[Vastus lateralis muscle|lateralis]]. Rectus femoris is attached to the pelvis with two tendons, while the vasti are inserted to the femur. All four muscles unite in a common tendon inserted into the [[patella]] from where the [[patellar ligament]] extends it down to the [[tibial tuberosity]]. Fibers from the medial and lateral vasti form two [[Lateral retinaculum|retinacula]] that stretch past the patella on either sides down to the condyles of the tibia. The quadriceps is ''the'' knee extensor, but the rectus femoris additionally flexes the hip joint, and articular muscle of the knee protects the [[articular capsule of the knee joint]] from being nipped during extension. The [[Sartorius muscle|sartorius]] runs superficially and obliquely down on the anterior side of the thigh, from the [[anterior superior iliac spine]] to the [[pes anserinus (leg)|pes anserinus]] on the medial side of the knee, from where it is further extended into the [[crural fascia]]. The sartorius acts as a flexor on both the hip and knee, but, due to its oblique course, also contributes to medial rotation of the leg as one of the pes anserinus muscles (with the knee flexed), and to lateral rotation of the hip joint.<ref>Platzer (2004), p. 248</ref>

There are four posterior thigh muscles. The [[biceps femoris]] has two heads: The long head has its origin on the [[ischial tuberosity]] together with the semitendinosus and acts on two joints. The short head originates from the middle third of the [[linea aspera]] on the shaft of the femur and the [[lateral intermuscular septum of thigh]], and acts on only one joint. These two heads unite to form the biceps which inserts on the [[head of the fibula]]. The biceps flexes the knee joint and rotates the flexed leg laterally—it is the only lateral rotator of the knee and thus has to oppose all medial rotator. Additionally, the long head extends the hip joint. The [[Semitendinosus muscle|semitendinosus]] and the [[Semimembranosus muscle|semimembranosus]] share their origin with the long head of the biceps, and both attaches on the medial side of the proximal head of the tibia together with the gracilis and sartorius to form the pes anserinus. The semitendinosus acts on two joints; extension of the hip, flexion of the knee, and medial rotation of the leg. Distally, the semimembranosus' tendon is divided into three parts referred to as the ''[[pes anserinus profondus]]''. Functionally, the semimembranosus is similar to the semitendinosus, and thus produces extension at the hip joint and flexion and medial rotation at the knee.<ref>Platzer (2004), p. 250</ref> Posteriorly below the knee joint, the [[Popliteus muscle|popliteus]] stretches obliquely from the [[lateral epicondyle of the femur|lateral femoral epicondyle]] down to the posterior surface of the tibia. The [[subpopliteal recess|subpopliteal bursa]] is located deep to the muscle. Popliteus flexes the knee joint and medially rotates the leg.<ref name="Platzer 2004, p 264">Platzer (2004), p. 264</ref>
{{clear}}

==== Lower leg and foot ====
{| class="wikitable" style="float:right; margin-left:15px"
|+ Function of foot muscles<ref name="Platzer-266">Platzer (2004), p. 266</ref>
|-
! Movement !! Muscles<br />(in order of<br />importance)
|-
|Dorsi-<br />flexion
|
•Tibialis anterior<br />•Extensor digitorum<br />longus<br />•Extensor hallucis<br />longus
|-
|Plantar<br />flexion
|
•Triceps surae<br />•[[Fibularis longus|Fibularis (peroneus) longus]]<br />•[[Fibularis brevis|Fibularis (peroneus) brevis]]<br />•Flexor digitorum<br />longus<br />•Tibialis posterior
|-
|[[Eversion (kinesiology)|Eversion]]
|
•Fibularis (peroneus) longus<br />•Fibularis (peroneus) brevis<br />•Extensor digitorum<br />longus<br />•[[Fibularis tertius|Fibularis (peroneus) tertius]]
|-
|Inversion
|
•Triceps surae<br />•Tibialis posterior<br />•Flexor hallucis<br />longus<br />•Flexor digitorum<br />longus<br />•Tibialis anterior
|}
With the [[Popliteus muscle|popliteus]] (see above) as the single exception, all muscles in the leg are attached to the foot and, based on location, can be classified into an anterior and a posterior group separated from each other by the tibia, the fibula, and the [[Interosseous membrane of the leg|interosseous membrane]]. In turn, these two groups can be subdivided into subgroups or layers—the anterior group consists of the extensors and the peroneals, and the posterior group of a superficial and a deep layer. Functionally, the muscles of the leg are either extensors, responsible for the [[dorsiflexion]] of the foot, or flexors, responsible for the [[plantar flexion]]. These muscles can also classified by innervation, muscles supplied by the [[Common fibular nerve|anterior subdivision]] of the plexus and those supplied by the [[Tibial nerve|posterior subdivision]].<ref>Platzer (2004), p. 256</ref> The leg muscles acting on the foot are called the extrinsic foot muscles whilst the foot muscles located ''in'' the foot are called intrinsic.<ref name=Starkey2015>{{Cite book|last1=Starkey|first1=Chad|last2=Brown|first2=Sara|url=https://www.fadavis.com/product/athletic-training-examination-orthopedic-athletic-injuries-starkey-brown-4|title=Examination of Orthopedic & Athletic Injuries|publisher=[[F. A. Davis Company]]|year=2015|isbn=978-0-8036-4503-5|edition=4|page=175|language=en|chapter=8 - Foot and Toe Pathologies}}</ref>

Dorsiflexion (extension) and plantar flexion occur around the transverse axis running through the ankle joint from the tip of the medial malleolus to the tip of the lateral malleolus. Pronation (eversion) and supination (inversion) occur along the oblique axis of the ankle joint.<ref name="Platzer-266" />

===== Extrinsic =====
[[File:Gray437.png|thumb|left|upright=0.55|Anterior muscles]]

Three of the anterior muscles are extensors. From its origin on the lateral surface of the tibia and the interosseus membrane, the three-sided belly of the [[Tibialis anterior muscle|tibialis anterior]] extends down below the [[Superior extensor retinaculum of foot|superior]] and [[Inferior extensor retinaculum of foot|inferior extensor retinacula]] to its insertion on the plantar side of the [[medial cuneiform bone]] and the first [[metatarsal bone]]. In the non-weight-bearing leg, the anterior tibialis dorsal flexes the foot and lifts the medial edge of the foot. In the weight-bearing leg, it pulls the leg towards the foot. The [[Extensor digitorum longus muscle|extensor digitorum longus]] has a wide origin stretching from the lateral condyle of the tibia down along the anterior side of the fibula, and the interosseus membrane. At the ankle, the tendon divides into four that stretch across the foot to the dorsal [[aponeuroses]] of the last phalanges of the four lateral toes. In the non-weight-bearing leg, the muscle extends the digits and dorsiflexes the foot, and in the weight-bearing leg acts similar to the tibialis anterior. The [[Extensor hallucis longus muscle|extensor hallucis longus]] has its origin on the fibula and the interosseus membrane between the two other extensors and is, similarly to the extensor digitorum, is inserted on the last phalanx of big toe ("hallux"). The muscle dorsiflexes the hallux, and acts similar to the tibialis anterior in the weight-bearing leg.<ref>Platzer (2004), p. 258</ref> Two muscles on the lateral side of the leg form the fibular (peroneal) group. The [[fibularis longus|fibularis (peroneus) longus]] and [[fibularis brevis|fibularis (peroneus) brevis]] both have their origins on the fibula, and they both pass behind the [[lateral malleolus]] where their tendons pass under the [[fibular retinacula]]. Under the foot, the fibularis longus stretches from the lateral to the medial side in a groove, thus bracing the [[transverse arch of the foot]]. The fibularis brevis is attached on the lateral side to the tuberosity of the fifth metatarsal. Together, these two [[fibularis muscles]] form the strongest pronators of the foot.<ref>Platzer (2004), p. 260</ref> The fibularis muscles are highly variable, and several variants can occasionally be present.<ref>Chaitow (2000), p. 554</ref>

{{multiple image
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Of the posterior muscles three are in the superficial layer. The major plantar flexors, commonly referred to as the [[triceps surae]], are the [[Soleus muscle|soleus]], which arises on the proximal side of both leg bones, and the [[Gastrocnemius muscle|gastrocnemius]], the two heads of which arises on the distal end of the femur. These muscles unite in a large terminal tendon, the [[Achilles tendon]], which is attached to the posterior tubercle of the [[calcaneus]]. The [[Plantaris muscle|plantaris]] closely follows the lateral head of the gastrocnemius. Its tendon runs between those of the soleus and gastrocnemius and is embedded in the medial end of the calcaneus tendon.<ref>Platzer (2004), p. 262</ref>

In the deep layer, the [[Tibialis posterior muscle|tibialis posterior]] has its origin on the interosseus membrane and the neighbouring bone areas and runs down behind the [[medial malleolus]]. Under the foot it splits into a thick medial part attached to the [[navicular bone]] and a slightly weaker lateral part inserted to the three cuneiform bones. The muscle produces simultaneous plantar flexion and supination in the non-weight-bearing leg, and approximates the heel to the calf of the leg. The [[Flexor hallucis longus muscle|flexor hallucis longus]] arises distally on the fibula and on the interosseus membrane from where its relatively thick muscle belly extends far distally. Its tendon extends beneath the [[flexor retinaculum of foot|flexor retinaculum]] to the sole of the foot and finally attaches on the base of the last phalanx of the hallux. It plantarflexes the hallux and assists in supination. The [[Flexor digitorum longus muscle|flexor digitorum longus]], finally, has its origin on the upper part of the tibia. Its tendon runs to the sole of the foot where it forks into four terminal tendon attached to the last phalanges of the four lateral toes. It crosses the tendon of the tibialis posterior distally on the tibia, and the tendon of the flexor hallucis longus in the sole. Distally to its division, the [[Quadratus plantae muscle|quadratus plantae]] radiates into it and near the middle phalanges its tendons penetrate the tendons of the [[Flexor digitorum brevis muscle|flexor digitorum brevis]]. In the non-weight-bearing leg, it plantar flexes the toes and foot and supinates. In the weight-bearing leg it supports the [[plantar arch]].<ref name="Platzer 2004, p 264" /> (For the [[Popliteus muscle|popliteus]], see above.)

===== Intrinsic =====
The intrinsic muscles of the foot, muscles whose bellies are located in the foot proper, are either dorsal (top) or plantar (sole).
On the dorsal side, two long extrinsic extensor muscles are superficial to the intrinsic muscles, and their tendons form the dorsal aponeurosis of the toes. The short intrinsic extensors and the plantar and dorsal interossei radiates into these aponeuroses. The [[Extensor digitorum brevis muscle|extensor digitorum brevis]] and [[Extensor hallucis brevis muscle|extensor hallucis brevis]] have a common origin on the anterior side of the calcaneus, from where their tendons extend into the dorsal aponeuroses of digits 1–4. They act to dorsiflex these digits.<ref>Platzer (2004), p. 268</ref>

The plantar muscles can be subdivided into three groups associated with three regions: those of the big digit, the little digit, and the region between these two. All these muscles are covered by the thick and dense [[plantar aponeurosis]], which together with two tough septa, form the spaces of the three groups. These muscles and their fatty tissue function as cushions that transmit the weight of the body downward. As a whole, the foot is a functional entity.<ref name="Platzer-270">Platzer (2004), p. 270</ref>

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The [[Abductor hallucis muscle|abductor hallucis]] stretches along the medial edge of the foot, from the calcaneus to the base of the first phalanx of the first digit and the medial sesamoid bone. It is an abductor and a weak flexor, and also helps maintain the arch of the foot. Lateral to the abductor hallucis is the [[Flexor hallucis brevis muscle|flexor hallucis brevis]], which originates from the medial cuneiform bone and from the tendon of the tibialis posterior. The flexor hallucis has a medial and a lateral head inserted laterally to the abductor hallucis. It is an important plantar flexor which comes into prominent use in [[classical ballet]] (i.e. for [[en pointe|pointe work]]).<ref name="Platzer-270" /> The [[Adductor hallucis muscle|adductor hallucis]] has two heads; a stronger oblique head which arises from the cuboid and lateral cuneiform bones and the bases of the second and third metatarsals; and a transverse head which arises from the distal ends of the third-fifth metatarsals. Both heads are inserted on the lateral sesamoid bone of the first digit. The muscle acts as a tensor to the arches of the foot, but can also adduct the first digit and plantar flex its first phalanx.<ref name="Platzer-272">Platzer (2004), p. 272</ref>

The [[Opponens digiti minimi muscle|opponens digiti minimi]] originates from the long plantar ligament and the plantar tendinous sheath of the fibularis (peroneus) longus and is inserted on the fifth metatarsal. When present, it acts to plantar flex the fifth digit and supports the plantar arch. The [[Flexor digiti quinti brevis muscle (foot)|flexor digiti minimi]] arises from the region of base of the fifth metatarsal and is inserted onto the base of the first phalanx of the fifth digit where it is usually merged with the abductor of the first digit. It acts to plantar flex the last digit. The largest and longest muscles of the little toe is the [[Abductor digiti quinti muscle (foot)|abductor digiti minimi]]. Stretching from the lateral process of the calcaneus, with a second attachment on the base of the fifth metatarsal, to the base of the fifth digit's first phalanx, the muscle forms the lateral edge of the sole. Except for supporting the arch, it plantar flexes the little toe and also acts as an abductor.<ref name="Platzer-272" />

The four [[Lumbrical muscle (foot)|lumbricales]] have their origin on the tendons of the flexor digitorum longus, from where they extend to the medial side of the bases of the first phalanx of digits two-five. Except for reinforcing the plantar arch, they contribute to plantar flexion and move the four digits toward the big toe. They are, in contrast to the lumbricales of the hand, rather variable, sometimes absent and sometimes more than four are present. The [[quadratus plantae]] arises with two slips from margins of the plantar surface of the calcaneus and is inserted into the tendon(s) of the flexor digitorum longus, and is known as the "plantar head" of this latter muscle. The three [[Plantar interossei muscles|plantar interossei]] arise with their single heads on the medial side of the third-fifth metatarsals and are inserted on the bases of the first phalanges of these digits. The two heads of the four [[Dorsal interossei muscles (foot)|dorsal interossei]] arise on two adjacent metatarsals and merge in the intermediary spaces. Their distal attachment is on the bases of the proximal phalanges of the second-fourth digits. The interossei are organized with the second digit as a longitudinal axis; the plantars act as adductors and pull digits 3–5 towards the second digit; while the dorsals act as abductors. Additionally, the interossei act as plantar flexors at the [[metatarsophalangeal joint]]s. Lastly, the [[Flexor digitorum brevis muscle|flexor digitorum brevis]] arises from underneath the calcaneus to insert its tendons on the middle phalanges of digit 2–4. Because the tendons of the flexor digitorum longus run between these tendons, the brevis is sometimes called ''perforatus''. The tendons of these two muscles are surrounded by a tendinous sheath. The brevis acts to plantar flex the middle phalanges.<ref>Platzer (2004), p. 274</ref>
{{See also|Table_of_muscles#Leg|l1=Table of muscles}}

=== Flexibility ===
Flexibility can be simply defined as the available [[range of motion]] (ROM) provided by a specific [[joint]] or group of joints.<ref name=alter2004>Alter, M. J. (2004). Science of Flexibility (3rd ed., pp. 1–6). Champaign, IL: Human Kinetics.</ref> For the most part, exercises that increase [[flexibility]] are performed with intentions to boost overall muscle length, reduce the risks of injury and to potentially improve muscular performance in [[physical activity]].<ref name=lowextremity10>Lower Extremity Stretching Home Exercise Program (April 2010). In Aurora Healthcare.</ref> [[Stretching]] muscles after engagement in any physical activity can improve muscular strength, increase flexibility, and reduce [[Acute muscle soreness|muscle soreness]].<ref name=nelson2007>Nelson, A. G., & Kokkonen, J. (2007). Stretching Anatomy. Champaign, IL: Human Kinetics.</ref> If limited movement is present within a joint, the "insufficient extensibility" of the muscle, or muscle group, could be restricting the activity of the affected joint.<ref>Weppler, C. H., & Magnusson, S. P. (March 2010). Increasing Muscle Extensibility: A Matter of Increasing Length or Modifying Sensation. Physical Therapy, 90, 438–49.</ref>

==== Stretching ====
Stretching prior to strenuous physical activity has been thought to increase muscular performance by extending the soft tissue past its attainable length in order to increase range of motion.<ref name=alter2004 /> Many physically active individuals practice these techniques as a "[[warm-up]]" in order to achieve a certain level of muscular preparation for specific exercise movements. When stretching, muscles should feel somewhat uncomfortable but not physically agonizing.
* '''Plantar flexion:''' One of the most popular lower leg muscle stretches is the step standing [[heel]] raises, which mainly involves the [[gastrocnemius]], [[soleus]], and the [[Achilles tendon]].<ref>Roth, E. Step Stretch for the Foot. AZ Central. http://healthyliving.azcentral.com/step-stretch-foot-18206.html {{Webarchive|url=https://web.archive.org/web/20160805005100/http://healthyliving.azcentral.com/step-stretch-foot-18206.html |date=5 August 2016 }}</ref> Standing heel raises allow the individual to activate their [[calf muscle]]s by standing on a step with toes and [[forefoot]], leaving the heel hanging off the step, and [[plantar flexion|plantar flexing]] the [[ankle joint]] by raising the heel. This exercise is easily modified by holding on to a nearby rail for balance and is generally repeated 5–10 times.
* '''Dorsiflexion:''' In order to stretch the [[anterior]] [[leg muscles|muscles of the lower leg]], crossover shin stretches work well.<ref name=shea2013>Shea, K. (12 August 2013). Shin Stretches for Runners. Livestrong. http://www.livestrong.com/article/353394-shin-stretches-for-runners/</ref> This motion will stretch the [[dorsiflexion]] muscles, mainly the [[anterior tibialis]], [[extensor hallucis longus]] and [[extensor digitorum longus]], by slowly causing the muscles to lengthen as body weight is leaned on the ankle joint by using the floor as resistance against the top of the foot.<ref name=shea2013 /> Crossover shin stretches can vary in intensity depending on the amount of body weight applied on the ankle joint as the individual bends at the [[knee]]. This stretch is typically held for 15–30 seconds.
* '''Eversion and inversion:''' Stretching the [[eversion (kinesiology)|eversion]] and [[inversion (kinesiology)|inversion]] muscles allows for better range of motion to the ankle joint.<ref name=lowextremity10 /> Seated ankle elevations and depressions will stretch the [[fibularis muscles|fibularis (peroneus)]] and [[tibialis anterior|tibilalis]] muscles that are associated with these movements as they lengthen. Eversion muscles are stretched when the ankle becomes depressed from the starting position. In like manner, the inversion muscles are stretched when the ankle joint becomes elevated. Throughout this seated stretch, the ankle joint is to remain supported while depressed and elevated with the [[ipsilateral]] (same side) hand in order to sustain the stretch for 10–15 seconds. This stretch will increase overall eversion and inversion muscle group length and provide more flexibility to the ankle joint for larger range of motion during activity.<ref name=alter2004 /><ref name=lowextremity10 />

=== Blood supply ===
{{See also|Superficial femoral artery|Arcuate artery of the foot}}
The arteries of the leg are divided into a series of segments.

In the pelvis area, at the level of the last [[lumbar vertebra]], the [[abdominal aorta]], a continuation the [[descending aorta]], splits into a pair of [[Common iliac artery|common iliac arteries]]. These immediately split into the [[internal iliac artery|internal]] and [[External iliac artery|external iliac arteries]], the latter of which descends along the medial border of the [[Psoas major muscle|psoas major]] to exits the pelvis area through the [[vascular lacuna]] under the [[inguinal ligament]].<ref name="Thieme-Atlas-464">''Thieme Atlas of Anatomy'' (2006), p. 464</ref>

The artery enters the thigh as the [[femoral artery]] which descends the medial side of the thigh to the [[adductor canal]]. The canal passes from the anterior to the posterior side of the limb where the artery leaves through the [[adductor hiatus]] and becomes the [[popliteal artery]].  On the back of the knee the popliteal artery runs through the [[popliteal fossa]] to the [[popliteal muscle]] where it divides into [[Anterior tibial artery|anterior]] and [[Posterior tibial artery|posterior tibial arteries]].<ref name="Thieme-Atlas-464" />

In the lower leg, the anterior tibial enters the extensor compartment near the upper border of the [[interosseus membrane]] to descend between the [[Tibialis anterior muscle|tibialis anterior]] and the [[Extensor hallucis longus muscle|extensor hallucis longus]]. Distal to the [[Superior extensor retinaculum of foot|superior]] and [[Inferior extensor retinaculum of foot|extensor retinacula of the foot]] it becomes the [[dorsalis pedis artery|dorsal artery of the foot]]. The posterior tibial forms a direct continuation of the popliteal artery which enters the flexor compartment of the lower leg to descend behind the [[medial malleolus]] where it divides into the [[Medial plantar artery|medial]] and [[Lateral plantar artery|lateral plantar arteries]], of which the posterior branch gives rise to the [[fibular artery]].<ref name="Thieme-Atlas-464" />

For practical reasons the lower limb is subdivided into somewhat arbitrary regions:<ref name="Platzer-412">Platzer (2004), p. 412</ref> The regions of the hip are all located in the thigh: anteriorly, the subinguinal region is bounded by the inguinal ligament, the sartorius, and the pectineus and forms part of the [[femoral triangle]] which extends distally to the adductor longus. Posteriorly, the gluteal region corresponds to the gluteus maximus. The anterior region of the thigh extends distally from the femoral triangle to the region of the knee and laterally to the tensor fasciae latae. The posterior region ends distally before the popliteal fossa. The anterior and posterior regions of the knee extend from the proximal regions down to the level of the tuberosity of the tibia. In the lower leg the anterior and posterior regions extend down to the malleoli. Behind the malleoli are the lateral and medial retromalleolar regions and behind these is the region of the heel. Finally, the foot is subdivided into a dorsal region superiorly and a plantar region inferiorly.<ref name="Platzer-412" />

=== Veins ===
[[File:Blausen 0609 LegVeins.png|thumb|upright=0.8|[[Vein]]s of the leg]]

The [[vein]]s are subdivided into three systems. The [[deep vein]]s return approximately 85 percent of the blood and the [[superficial vein]]s approximately 15 percent. A series of [[perforator vein]]s interconnect the superficial and deep systems. In the standing posture, the veins of the leg have to handle an exceptional load as they act against gravity when they return the blood to the heart. The [[venous valve]]s assist in maintaining the superficial to deep direction of the [[blood flow]].<ref name="Thieme-Atlas-466">''Thieme Atlas of Anatomy'' (2006), pp. 466–67</ref>

Superficial veins:
* [[Great saphenous vein]]
* [[Small saphenous]]

Deep veins:
* [[Femoral vein]], whose segment is the [[common femoral vein]]
* [[Popliteal vein]]
* [[Anterior tibial vein]]
* [[Posterior tibial vein]]
* [[Fibular vein]]

===Nerve supply===
{{Main|Nerve supply of the human leg}}
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The sensory and motor innervation to the lower limb is supplied by the [[lumbosacral plexus]], which is formed by the [[Ventral ramus of spinal nerve|ventral rami]] of the lumbar and sacral spinal nerves with additional contributions from the [[subcostal nerve]] (T12) and [[coccygeal nerve]] (Co1). Based on distribution and topography, the lumbosacral plexus is subdivided into the [[lumbar plexus]] (T12-L4) and the [[Sacral plexus]] (L5-S4); the latter is often further subdivided into the [[sciatic plexus|sciatic]] and [[Pudendal plexus (nerves)|pudendal plexuses]]:<ref name="Thieme-Atlas-470">''Thieme Atlas of anatomy'' (2006), pp. 470–71</ref>

The lumbar plexus is formed lateral to the [[intervertebral foramina]] by the ventral rami of the first four lumbar spinal nerves (L1-L4), which all pass through [[Psoas major muscle|psoas major]]. The larger branches of the plexus exit the muscle to pass sharply downward to reach the [[abdominal wall]] and the thigh (under the [[inguinal ligament]]); with the exception of the [[obturator nerve]] which pass through the [[lesser pelvis]] to reach the medial part of the thigh through the [[obturator foramen]]. The nerves of the lumbar plexus pass in front of the [[hip joint]] and mainly support the anterior part of the thigh.<ref name="Thieme-Atlas-470" />

The [[iliohypogastric nerve|iliohypogastric]] (T12-L1) and [[ilioinguinal nerve]]s (L1) emerge from the psoas major near the muscle's origin, from where they run laterally downward to pass anteriorly above the [[iliac crest]] between the [[Transversus abdominis muscle|transversus abdominis]] and [[Abdominal internal oblique muscle|abdominal internal oblique]], and then run above the inguinal ligament. Both nerves give off muscular branches to both these muscles. Iliohypogastric supplies sensory branches to the skin of the lateral hip region, and its terminal branch finally pierces the aponeurosis of the [[Abdominal external oblique muscle|abdominal external oblique]] above the inguinal ring to supply sensory branches to the skin there. Ilioinguinalis exits through the inguinal ring and supplies sensory branches to the skin above the [[pubic symphysis]] and the lateral portion of the [[scrotum]].<ref name="Thieme-Atlas-472">''Thieme Atlas of anatomy'' (2006), pp. 472–73</ref>

The [[genitofemoral nerve]] (L1, L2) leaves psoas major below the two former nerves, immediately divides into two branches that descends along the muscle's anterior side. The sensory femoral branch supplies the skin below the inguinal ligament, while the mixed genital branch supplies the skin and muscles around the sex organ. The [[Lateral cutaneous nerve of thigh|lateral femoral cutaneous nerve]] (L2, L3) leaves psoas major laterally below the previous nerve, runs obliquely and laterally downward above the [[Iliacus muscle|iliacus]], exits the pelvic area near the [[anterior superior iliac spine|iliac spine]], and supplies the skin of the anterior thigh.<ref name="Thieme-Atlas-472" />

The [[obturator nerve]] (L2-L4) passes medially behind psoas major to exit the pelvis through the [[obturator canal]], after which it gives off branches to [[Obturator externus muscle|obturator externus]] and divides into two branches passing behind and in front of [[Adductor brevis muscle|adductor brevis]] to supply motor innervation to all the other adductor muscles. The anterior branch also supplies sensory nerves to the skin on a small area on the distal medial aspect of the thigh.<ref name="Thieme-Atlas-474">''Thieme Atlas of anatomy'' (2006), pp. 474–75</ref> The [[femoral nerve]] (L2-L4) is the largest and longest of the nerves of the lumbar plexus. It supplies motor innervation to [[Iliopsoas muscle|iliopsoas]], [[Pectineus muscle|pectineus]], [[Sartorius muscle|sartorius]], and [[Quadriceps muscle|quadriceps]]; and sensory branches to the anterior thigh, medial lower leg, and posterior foot.<ref name="Thieme-Atlas-474" />

The nerves of the sacral plexus pass behind the hip joint to innervate the posterior part of the thigh, most of the lower leg, and the foot.<ref name="Thieme-Atlas-470" /> The [[superior gluteal nerve|superior]] (L4-S1) and [[inferior gluteal nerve]]s (L5-S2) innervate the gluteus muscles and the [[tensor fasciae latae]]. The [[Posterior cutaneous nerve of thigh|posterior femoral cutaneous nerve]] (S1-S3) contributes sensory branches to the skin on the posterior thigh.<ref name="Thieme-Atlas-476">''Thieme Atlas of Anatomy'' (2006), p. 476</ref> The [[sciatic nerve]] (L4-S3), the largest and longest nerve in the human body, leaves the pelvis through the [[greater sciatic foramen]]. In the posterior thigh it first gives off branches to the short head of the [[Biceps femoris muscle|biceps femoris]] and then divides into the [[tibial nerve|tibial]] (L4-S3) and [[common fibular nerve]]s (L4-S2). The fibular nerve continues down on the medial side of biceps femoris, winds around the fibular neck and enters the front of the lower leg. There it divides into a [[Deep fibular nerve|deep]] and a [[Superficial fibular nerve|superficial terminal branch]]. The superficial branch supplies the [[fibularis muscles]] and the deep branch enters the extensor compartment; both branches reaches into the dorsal foot. In the thigh, the tibial nerve gives off branches to [[Semitendinosus muscle|semitendinosus]], [[Semimembranosus muscle|semimembranosus]], [[Adductor magnus muscle|adductor magnus]], and the long head of the biceps femoris. The nerve then runs straight down the back of the leg, through the [[popliteal fossa]] to supply the ankle flexors on the back of the lower leg and then continues down to supply all the muscles in the sole of the foot.<ref name="Thieme-Atlas-480">''Thieme Atlas of Anatomy'' (2006), pp. 480–81</ref> The [[pudendal nerve]] (S2-S4) and [[coccygeal plexus]] (S5-Co)<ref>{{cite book |last=Drake |first=Richard L. |last2=Vogl |first2=A. Wayne |last3=Mitchell |first3=Adam W. M. |last4=Tibbitts |first4=Richard |last5=Richardson |first5=Paul |title=Gray's Atlas of Anatomy |publisher=Churchill Livingstone |date=2014-07-14 |isbn=978-1-4557-4802-0 |page=252}}</ref> supply the muscles of the [[pelvic floor]] and the surrounding skin.<ref name="Thieme-Atlas-482">''Thieme Atlas of Anatomy'' (2006), pp. 482–83</ref>

The [[lumbosacral trunk]] is a communicating branch passing between the sacral and lumbar plexuses containing ventral fibers from L4. The [[coccygeal nerve]], the last spinal nerve, emerges from the [[sacral hiatus]], unites with the ventral rami of the two last sacral nerves, and forms the [[coccygeal plexus]].<ref name="Thieme-Atlas-470" />