Knee and leg

The knees and legs are two regions of the lower extremities or lower limbs(1). Both of these parts are essential in bearing the upper body’s weight and performing a wide range of movements.

Anatomy of the Knee

The knee is the largest joint in the body(2). It is a complex structure composed of several components, making it vulnerable to a wide range of injuries.

The four main parts of the knee are the bones, cartilages, ligaments, and tendons(3).

Bones of the Knee

Knee joints are made up of three different bones:

  • The patella or kneecap(4)
  • The tibia or shin bone, which is also part of the lower leg(5)
  • The femur or thigh bone, which is part of the upper leg(6)

The patella is a triangular sesamoid bone, meaning it is embedded within the tendon. The patella serves as a protective covering for the knee joint(7).

Additionally, the patella acts as a pulley for the quadriceps femoris muscle to help facilitate movement(8).

Cartilages of the Knee

Underneath the patella is the articular cartilage(9). This cartilage covers the meeting ends of the femur and tibia, as well as the underside of the patella.

The menisci are two wedge-shaped cartilage that act as a cushion and stabilizer for the knee joint. The meniscus is tough and rubbery, allowing it to serve as a shock absorber for the femur and the tibia(10).

Ligaments of the Knee

The knee joint has four kinds of ligaments, each of which performs different functions(11).

The frontal ligaments act as a stabilizer for the patella and patellar ligament, while the medial and lateral ligaments prevent excessive side-to-side movements(12).

The medial and lateral ligaments also serve as a brace or support against sudden and unusual movements(13).

The dorsal ligament ensures the knee does not overextend or bend the wrong way. The cruciate ligaments stop the femur from slipping on the tibia(14).

Tendons of the Knee

Two tendons connect the patella to the front muscles of the upper and lower leg.

The quadriceps tendon attaches the front of the thigh to the kneecap(15). Additionally, the patella is embedded into the quadriceps tendon.

The patellar tendon stretches from the patella down to the tibia or shin bone(16).

Anatomy of the Leg

The leg often refers to the entire lower extremity or lower limb (from the thigh to the foot) when used in daily conversations.

However, in medical or anatomical terms, the leg pertains only to the part of the lower limb stretching from the knee and to the ankle joint(17). This region is otherwise referred to as the lower leg in non-medical terms.

Bones of the Leg

The leg consists of only two long bones. The first is the tibia or shin bone and the second is the fibula.

The tibia is the larger of the two leg bones and serves as the legs’ primary weight-bearing bone(18). This bone is part of the knee and ankle joints and helps enable movement.

The tibia is also known as the second-longest bone in the human body, after the femur or thigh bone.

The fibula is a smaller and thinner bone that runs parallel behind the tibia(19). Unlike the tibia, the fibula does not bear or support body weight.

The primary function of the fibula is to help stabilize ankle joint movements and provide leverage(20). The fibula also serves as a point of attachment for different leg muscles.

Muscles of the Leg

The muscles of the leg are divided into three groups: anterior (front), lateral (side), and posterior (back)(21).

The anterior leg muscles include the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius(22). These muscles are responsible for the flexible movement of the foot at the ankle joint and the toes.

The lateral leg muscles consist only of the fibularis (peroneal) longus and fibularis brevis(23). These muscles surround the foot and also help move the ankle joint.

The posterior leg muscles are composed of seven different muscles that are divided into two categories(24)

  • Superficial muscles: gastrocnemius, soleus, and plantaris
  • Deep layer muscles: popliteus, tibialis posterior, flexor digitorum longus, flexor hallucis longus

Joints of the Leg

The two leg bones are flanked by joints on both ends. The knee joint sits above the leg bones and connects to the thigh or femoral region(25). Meanwhile, the ankle joint is found at the base of the leg.

Common Leg and Knee Injuries

The knee is one of the most easily injured parts of the body(26).

A study showed that knee injuries and lower leg injuries are among the most common lower extremity injuries presented at emergency departments in the US(27).

Results also indicated that fractures were the most common injuries of the lower leg, while sprains or strains were the most common injuries in the knee(28).

Diagnostic imaging modalities, such as X-ray exams, computed tomography (CT) scans, and magnetic resonance (MR) imaging, allow physicians to diagnose knee and leg injuries or illnesses accurately.

Diagnostic imaging also helps track the healing progress, particularly in serious injuries like fractures.

  1. Rad, A. (2020, Oct. 29). Lower extremity anatomy. Kenhub. Retrieved from
  2. American Academy of Orthopaedic Surgeons. (2014, March). Common Knee Injuries. OrthoInfo. Retrieved from–conditions/common-knee-injuries/
  3. Ibid.
  4. Rad, A. (2020, Oct. 29). Leg and knee anatomy. Kenhub. Retrieved from
  5. Ibid.
  6. Crumbie, L. (2020, Nov. 13). Femur. Kenhub. Retrieved from
  7. Ibid.
  8. Rad, A. (2020, Oct. 29). Leg and knee anatomy. Op. cit.
  9. American Academy of Orthopaedic Surgeons. (2014, March). Op. cit.
  10. Ibid.
  11. Rad, A. (2020, Oct. 29). Leg and knee anatomy. Op. cit.
  12. Ibid.
  13. American Academy of Orthopaedic Surgeons. (2014, March). Op. cit.
  14. Rad, A. (2020, Oct. 29). Leg and knee anatomy. Op. cit.
  15. American Academy of Orthopaedic Surgeons. (2014, March). Op. cit.
  16. Ibid.
  17. Rad, A. (2020, Oct. 29). Leg and knee anatomy. Op. cit.
  18. Ibid.
  19. Ibid.
  20. Gupton, M., Munja,l A., & Kang, M. (2020, Jan.) Anatomy, Bony Pelvis and Lower Limb, Fibula. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Retrieved from: 
  21. Rad, A. (2020, Oct. 29). Leg and knee anatomy. Op. cit.
  22. Ibid.
  23. Ibid.
  24. Ibid.
  25. Ibid.
  26. American Academy of Orthopaedic Surgeons. (2014, March). Op. cit.
  27. Lambers, K., Ootes, D., & Ring, D. (2012). Incidence of patients with lower extremity injuries presenting to US emergency departments by anatomic region, disease category, and age. Clinical orthopaedics and related research, 470(1), 284–290.
  28. Ibid.


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Atlas of Knee MRI Anatomy

This webpage presents the anatomical structures found on knee MRI. Magnetic resonance imaging (MRI) is a radiologic procedure that uses a magnetic field and radio waves to develop detailed image cross-sections of the body, including the knee(1).  Medical images from an MRI allow medical professionals to distinguish body tissues, including the meniscus (shock absorbers in …

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Knee radiograph

This webpage presents the anatomical structures found on knee radiograph. Knee Radiograph – AP Knee Radiograph – Lateral What Is a Knee Radiograph? Knee radiographs (X-rays) are used to evaluate fractures and degenerative disorders associated with the knee joints, such as arthritis(1). During knee X-rays, the knee can be examined in an anterior-posterior view (front …

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