Leg and knee anatomy

Author: Adrian RadBSc (Hons) • Reviewer: Nicola McLarenMSc
Last reviewed: August 022023
Reading time: 18 minutes

Kneelegand foot (overview)

How many times have a layman’s language and anatomy ever matched? Almost never. For exampletake a look at the leg. When your non-health science friends talk about the ‘leg’they mean the entire lower extremity. Howeverin the world of anatomythe ‘leg’ strictly means the portion between the knee and the ankle joints. It is composed of several structures:

Tibia
Fibula
Leg muscles

In this pagewe will take a look at all of the above as well as the anatomy of the knee.

Key facts about the leg and knee
Bones of the leg	Tibia: the largest and most medial leg boneforming both the knee and ankle joints. It facilitates weight-bearing and movement Fibula: the thinnest and most lateral leg boneforming only the ankle joint. It mainly facilitates movement. Mnemonic: FibuLA is LAteral
Knee joint	Bones: tibiafibulapatella Articulations: tibiofemoralpatellofemoral Menisci: lateralmedial Ligaments: frontalmedial/lateraldorsalcruciateanterolateral Bursae: suprapatellarprepatellarinfrapatellar
Muscles of the leg	Anterior group: tibialis anteriorextensor hallucis longusextensor digitorum longusfibularis tertius Lateral group: fibularis longusfibularis brevis Posterior group: - Superficial layer: gastrocnemiussoleusplantaris - Deep layer: popliteustibialis posteriorflexor digitorum longusflexor hallucis longus

Contents

Tibia and fibula
Knee joint
1. Bones and soft tissues
2. Muscles
Muscles of the leg
Sources
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Related videos

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Tibia and fibula

The tibia and fibula are two long bones that run parallel to each otherforming the scaffold of the leg and providing attachment points for many muscles. The tibiacommonly known as the ‘shin bone’is the largest and most medial of the two. You can palpate its anterior border when you run your finger down the anterior aspect of your leg. You can also certainly feel it when you hit it against a surface by accident. The tibia is the weight-bearing bone of the leg and is directly involved in the formation of both the knee and ankle joints. Thereforeit facilitates movement.

The fibula is smallerthinnerand laterally positioned compared to the tibia. As a resultit doesn’t play any crucial role in weight bearing. Howeverthe fibula function is more nuanced - it plays a secondary role in the articulation of the ankle jointfacilitating its movementand provides the proximal attachment point for a number of muscles. The fibula also articulates with the tibia in two locations: slightly distal to the knee (superior tibiofibular joint) and just superior to the ankle (inferior tibiofibular joint). These joints are surrounded and reinforced by strong ligamentswhich also prevent excessive and potentially damaging movements. Here’s a diagram with the tibia bone labelledas well as the fibulashowcasing all their surface landmarks.

They look quite complicated and daunting at a first glanceright? Actuallyif you learn them systematicallythey are easier than you think. Complete the study unit below to master the anatomy of the tibia and fibula.

Knee joint

Bones and soft tissues

The main parts of the knee joint are the femurtibiapatellaand supporting ligaments. The condyles of the femur and of the tibia come in close proximity to form the main structure of the joint. The patellacommonly known as the ‘kneecap’is a sesamoid bone that sits within the tendon of the quadriceps femoris. It serves a protective function for the knee and facilitates movement by acting as a pulley for the quadriceps femoris muscle.

The knee joint is quite a complex structure. In factit actually consists of two separate joints housed within one single joint capsule:

Tibiofemoral joint (medial and lateral articulations); between the corresponding femoral and tibial condyles
Patellofemoral joint; situated between the patella and the femur

Since the knee joint must strike the perfect balance between strength for weight bearing and flexibility for movement purposesit is reinforced by various soft tissue structures. The joint is surrounded by several fat pads and bursaewhich are synovial fluid-filled sacs that reduce the friction caused by the tendons and muscles as they move against bony areas. The joint contains two shock-absorbers (menisci)which also function to improve congruency at the knee.

In additionthe knee joint is strengthened by various ligamentssuch as the patellar ligamenttibial and fibular collateral ligamentsoblique popliteal ligament and anterolateral ligement. Inside the jointthere are additional reinforcing ligamentssuch as the transverse ligamenttogether with the anterior (ACL) and posterior (PCL) cruciate ligaments. These intracapsular knee ligaments prevent dislocation of the jointbut can be commonly injured amongst professional athletes.

Key facts about the knee joint
Articulations	Tibiofemoral (lateral and medial condyles of the femur + tibial plateaus of the tibia) Patellofemoral (patellar surface of the femur + posterior surface of the patella)
Menisci	Mediallateral
Ligaments	Frontal ligaments - they stabilize the patella: patellar ligament (extension of the quadriceps femoris muscle)retinaculum (of the vastus medialis and lateralis) Medial/lateral ligaments - prevent excessive sideways movement: medial (tibial) collateral ligamentlateral (fibular) collateral ligament Dorsal - they prevent overextension of the knee: oblique popliteal ligamentarcuate popliteal ligament Cruciate - they prevent the slippage of the femur on the tibia: anterior cruciate ligament (ACL)posterior cruciate ligament (PCL)
Joint capsule	Fibrous capsule with the inner synovial membrane; popliteus muscle penetrates the lateral side of the capsule
Bursae	Suprapatellarprepatellarinfrapatellar

Here’s a labelled knee diagram to see how everything fits together:

Anatomy of the knee (anterior and posterior views)

If you want to learn more about the anatomy of the knee jointincluding its complex range of motion (flexionextensionrotationand the knee’s terminal locking mechanism)simply take a look at the following resources!

Muscles

The knee joint itself is moved by several musclesthe majority of which are part of the anterior compartment of the thigh. These include the sartorius and the four muscles of the quadriceps femoris (rectus femorisvastus medialisintermediusand lateralis)all of which extend the leg at the knee joint. They receive innervation via the femoral nerve (the neurovasculature of the lower extremity can be a daunting taskbut we're here to help you out!)

Key facts about the anterior thigh muscles
Sartorius	*Origins: Anterior superior iliac spine (ASIS) Insertions: Medial surface of proximal tibia (via Pes anserinus) Innervation: Femoral nerve (L2-L3) Functions*: Thigh flexionabductionand external rotation at the hip joint; leg flexion and internal rotation at the knee joint
Quadriceps femoris	*Origins: Anterior inferior iliac spine and superior margin of acetabulum (rectus femoris)intertrochanteric line of femur (vastus medialis)linea aspera of femur and greater trochanter of femur (vastus lateralis)anterior surface of femoral shaft (vastus intermedius) Insertions: Tibial tuberosity (via patellar ligament)medial and lateral femoral condyles (vastus medialis and lateralis) Innervation: Femoral nerve (L2-L4) Functions*: Thigh flexion at the hip joint and leg extension at the knee joint (rectus femoris)leg extension at the knee joint (vastus medialislateralisand intermedius)

The antagonistic muscles of the knee joints are called the hamstrings. They are also part of the thighbut they are located in the posterior compartment. These muscles include the biceps femoris semitendinosusand semimembranosus musclesall of which flex the leg at the knee joint. They receive their innervation via the sciatic nerve.

Key facts about the posterior thigh muscles
Semimembranosus	*Origins: (superolateral impression of) Ischial tuberosity Insertions: Medial condyle of tibia Innervation: Tibial division of sciatic nerve (L5-S2) Functions*: Thigh extension and internal rotation at hip joint; leg flexion and internal rotation at knee joint; pelvis stabilization
Semitendinosus	*Origins: (posteromedial impression of) Ischial tuberosity Insertions: Proximal end of tibia below medial condyle of tibia (via pes anserinus) Innervation: Tibial division of sciatic nerve (L5-S2) Functions*: Thigh extension and internal rotation at hip joint; leg flexion and internal rotation at knee joint; pelvis stabilization
Biceps femoris	*Origins: Ischial tuberosity (long head)linea aspera of femur (lateral lip)lateral supracondylar line of femur (short head) Insertions: Head of fibula Innervation: Tibial division of sciatic nerve (long head) and common fibular division of sciatic nerve (short head) Functions*: Thigh extension and external rotation at hip joint; Leg flexion and external rotation at knee joint

One other specific musclecalled the gracilishelps with flexion of the knee joint but also with its internal rotation. This muscle is part of the medial compartment of the thigh and receives innervation via the obturator nerve.

Muscles of the leg

Now that we have covered the proximal articulation of the leglet’s move further and take a look at the muscles that move the more distal articulation (the ankleor talocruraljoint). The leg is divided into three major anatomical compartmentseach one containing a specific group of muscles:

anterior group
lateral group
posterior group

Here’s a leg muscles diagram to give you an overview:

As the name suggeststhe anterior leg muscles are located along the anterior aspect of the leg. There are four muscles in this compartment: tibialis anterior extensor hallucis longus extensor digitorum longusand fibularis tertius. They receive their innervation via the deep fibular nerve. Their principal functions are dorsiflexion inversionand eversion of the foot at the ankle joint. Some are also responsible for toe (hallux) extension.

Key facts about anterior leg muscles
Tibialis anterior	*Origins: Lateral surface of tibiaInterosseous membrane Insertions: Medial cuneiform boneBase of metatarsal bone 1 Innervation: Deep fibular nerve (L4L5) Functions*: Foot dorsiflexion at the talocrural joint; foot inversion at the subtalar joint; Supports medial longitudinal arch of foot
Extensor hallucis longus	*Origins: (Middle third of ) Medial surface of fibulaInterosseous membrane Insertions: Base of distal phalanx of great toe Innervation: Deep fibular nerve (L5S1) Functions*: Toe extension at the metatarsophalangeal and interphalangeal joints; foot dorsiflexion at the talocrural joint
Extensor digitorum longus	*Origins: (Proximal half of) Medial surface of fibulaLateral tibial condyle, Insertions: Distal and middle phalanges of digits 2-5 Innervation: Deep fibular nerve (L5S1) Functions*: Toe extension at the metatarsophalangeal and interphalangeal joints 2-5; foot dorsiflexion at the talocrural joint; foot inversion at the subtalar joint
Fibularis tertius	Origins: (Distal third of) Medial surface of fibula Insertions: Dorsal surface of base of metatarsal bone 5 Innervation: Deep fibular nerve (L5S1) Functions: Foot dorsiflexion at the talocrural joint; foot eversion at the subtalar joint
Mnemonic	Tiny Elegant Fire Extinguishers (stands for: Tibialis anteriorExtensor hallucis longusFibularis (peroneus) tertiusExtensor digitorum longus)

The lateral compartment of the leg is the smallest of them allcontaining only two muscles: fibularis (peroneal) longus and fibularis brevis. Due to their slightly complicated trajectory as they wrap-around the foottheir actions might not be that obvious. These muscles plantar flex and evert the foot by moving the ankle joint. They receive their innervation via the superficial fibular nerve.

Key facts about the lateral compartment of the leg
Fibularis longus	*Origins: Head of fibulasuperior two-thirds of lateral surface of fibulaintermuscular septa Insertions: Medial cuneiform bonemetatarsal bone 1 Innervation: Superficial fibular nerve (L5S1) Functions*: Foot plantar flexion at the talocrural joint; foot eversion at the subtalar joint; supports longitudinal and transverse arches of foot
Fibularis brevis	*Origins: Distal 2/3 of lateral surface of fibula Insertions: Tuberosity of metatarsal bone 5 Innervation: Superficial fibular nerve (L5S1) Functions*: Foot plantar flexion at the talocrural joint; foot eversion at the subtalar joint
Mnemonic	Fly Long Superficial Fly Boy (stands for: Fibularis LongusSuperficial fibular nerve (innervation for both)Fibularis Brevis

Last but not leastlet’s move to the posterior compartment of the legwhich is the largest one. There are seven muscles in totalseparated into two layers. The superficial muscles are the gastrocnemius soleus (together forming the triceps surae) and plantaris.

Key facts about the superficial muscles of the posterior compartment of the leg
Gastrocnemius	Origins: Lateral head: Posterolateral surface of lateral femoral condyle; Medial head: Posterior surface of medial femoral condylePopliteal surface of femoral shaft Insertion: Posterior surface of calcaneus (via calcaneal tendon) *Innervation:* Tibial nerve (S1S2) Functions: Foot plantar flexion at the talocrural joint and knee flexion at the knee joint
Soleus	Origins: Soleal lineMedial border of tibiaHead of fibulaPosterior border of fibula Insertion: Posterior surface of calcaneus (via calcaneal tendon) Innervation: Tibial nerve (S1S2) Functions: Foot plantar flexion at the talocrural joint
Plantaris	Origins: Lateral supracondylar line of femurOblique popliteal ligament of knee Insertion: Posterior surface of calcaneus (via calcaneal tendon) Innervation: Tibial nerve (S1S2) Functions: Foot plantar flexion at the talocrural joint and knee flexion at the knee joint (weak)

The deep layer consists of many morenamely the popliteus tibialis posterior flexor digitorum longusand flexor hallucis longus. As the name suggestsall these muscles run along the posterior aspect of the legproducing plantar flexion of the ankle joint. Some of them also help with foot inversion and toe flexion around the metatarsophalangeal joints. They receive innervation via the tibial nerve.

Key facts about the deep muscles of the posterior compartment of the leg
Popliteus	*Origins: Lateral femoral condyleposterior horn of lateral meniscus of knee joint Insertions: Posterior surface of proximal tibia Innervation: Tibial nerve (L5-S2) Functions*: Unlocks knee joint; knee joint stabilization
Tibialis posterior	*Origins: Posterior surface of tibiaposterior surface of fibulaInterosseous membrane Insertions: Tuberosity of navicular boneall cuneiform bonesbases of metatarsal bones 2-4 (cuboid bone) Innervation: Tibial nerve (L4L5) Functions*: Foot plantar flexion at the talocrural joint; foot inversion at the subtalar joint; Supports medial longitudinal arch of foot
Flexor digitorum longus	*Origins: Posterior surface of tibia (inferior to soleal line) Insertions: Bases of distal phalanges of digits 2-5 Innervation: Tibial nerve (S1S2) Functions*: Toe flexion at the metatarsophalangeal and interphalangeal joints 2-5; foot plantar flexion at the talocrural joint; foot inversion at the subtalar joint
Flexor hallucis longus	*Origins: (Distal 2/3 of) Posterior surface of fibulaInterosseous membrane Insertions: Base of distal phalanx of great toe Innervation: Tibial nerve (S2S3) Functions*: Toe flexion at the metatarsophalangeal and interphalangeal joint 1; foot plantar flexion at the talocrural joint; foot inversion at the subtalar joint

The gastrocnemius and plantaris muscles deserve a special mention. Due to their origins from the femurthey are also important players in flexing the leg around the knee joint. In order to retain these musclesit’s important for you to consistently revise them.

Test your knowledge on the main muscles of the lower limb with this integrated quiz.

In order to remember all muscles that belong to the posterior leg compartment you can use the following mnemonic;

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Superficial group:

Gastrocnemius
Plantaris
Soleus

Deep group:

Tibialis posterior
Flexor hallucis longus
Popliteus
Flexor digitorum longus

You can start by taking a look at the following study unit:

Learn more about the leg and knee anatomy by taking our special quizcustomized to focus on bonesmusclesnerves and vessels of this region!

Sources

All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.

Articlereview and layout:

Adrian Rad
Nicola McLaren

Illustrators:

Kneelegand foot (overview)- Liene Znotina
Anatomy of the kneetibiaand fibula - Liene Znotina
Anatomy of the knee joint (sagittal view) - Paul Kim
Anatomy of the knee (anterior and posterior views) - Liene Znotina
Muscles of the knee and leg (anterior and posterior views) - Liene Znotina

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Leg and knee anatomy

Tibia and fibula

Knee joint

Bones and soft tissues

Muscles

Muscles of the leg

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