The Knee Joint

Original Author: Oliver Jones
Last Updated: February 16, 2017
Revisions: 31

The knee joint is a bicondylar type synovial joint, which mainly allows for flexion and extension (and a small degree of medial and lateral rotation). It is formed by articulations between the patella, femur and tibia.

In this article, we shall examine the anatomy of the knee joint – its articulating surfaces, ligaments and neurovascular supply.

Fig 1.0 - A broad overview of the bony structures of the knee joint.

Fig 1.0 – A broad overview of the bony structures of the knee joint.


Articulating Surfaces

Fig 1.1 - More detailed view of the bony surfaces. The inferior surface of the femur and superior surface of the tibia is shown.

Fig 1.1 – More detailed view of the bony surfaces. The inferior surface of the femur and superior surface of the tibia is shown.

The knee joint consists of two articulations (see fig. 1.1):

  • Tibiofemoral – The medial and lateral condyles of the femur articulating with the tibia.
  • Patellofemoral – The anterior and distal part of the femur articulating with the patella.

The tibiofemoral joint is the weight-bearing joint of the knee.

The patellofemoral joint allows the tendon of the quadriceps femoris (the main extensor of the knee) to be inserted directly over the knee, increasing the efficiency of the muscle. Both joint surfaces are lined with hyaline cartilage, and enclosed within a single joint cavity.

The patella is formed inside the tendon of the quadriceps femoris; its presence minimises wear and tear on the tendon.


Neurovasculature

The blood supply to the knee joint is through the genicular anastomoses around the knee, which are supplied by the genicular branches of the femoral and popliteal arteries.

The nerve supply, according to Hilton’s law, is by the nerves which supply the muscles which cross the joint. These are the femoral, tibial and common fibular nerves.


Menisci

The medial and lateral menisci are fibrocartilage structures in the knee that serve two functions:

  • To deepen the articular surface of the tibia, thus increasing stability of the joint.
  • To act as shock absorbers.

They are C shaped, and attached at both ends to the intercondylar area of the tibia.

In addition to the intercondylar attachment, the medial meniscus is fixed to the tibial collateral ligament and the joint capsule. Any damage to the tibial collateral ligament results in tearing of the medial meniscus.

The lateral meniscus is smaller and does not have any extra attachments, rendering it fairly mobile.

Fig 1.2 - Posterior view of the knee joint, with the joint capsule removed. Note the close relationship of the tibial collateral ligament, and the medial meniscus

Fig 1.2 – Posterior view of the knee joint, with the joint capsule removed. Note the close relationship of the tibial collateral ligament, and the medial meniscus

Fig 1.3 - The menisci of the knee joint. Superior surface of the tibia

Fig 1.3 – The menisci of the knee joint. Superior surface of the tibia


Bursae

A bursa is synovial fluid filled sac, found between moving structures in a joint – with the aim of reducing wear and tear on those structures. There are four bursae found in the knee joint.

  • Suprapatella bursa – This is an extension of the synovial cavity of the knee, located between the quadriceps femoris and the femur.
  • Prepatella bursa – Found between the apex of the patella and the skin.
  • Infrapatella bursa – Split into deep and superficial. The deep bursa lies between the tibia and the patella ligament. The superficial lies between the patella ligament and the skin.
  • Semimembranosus bursa – Located posteriorly in the knee joint, between the semimembranosus muscle and the medial head of the gastrocnemius.
Fig 1.4 - Sagittal view of the knee joint, showing the major bursae.

Fig 1.4 – Sagittal view of the knee joint, showing the major bursae.


Ligaments

The major ligaments in the knee joint are:

1. Patellar ligament – A continuation of the quadriceps femoris tendon distal to the patella. It attaches to the tibial tuberosity.

2. Collateral ligaments  These are two strap-like ligaments. They act to stabilise the hinge motion of the knee, preventing any medial or lateral movement

  • Tibial (medial) collateral ligament –  A wide and flat ligament, found on the medial side of the joint. Proximally, it attaches to the medial epicondyle of the femur, distally it attaches to the medial surface of the tibia.
  • Fibular (lateral) collateral ligament –  Thinner and rounder than the tibial collateral, this attaches proximally to the lateral epicondyle of the femur, distally it attaches to a depression on the lateral surface of the fibular head.

 3. Cruciate Ligaments These two ligament connect the femur and the tibia. In doing so, they cross each other, hence the term ‘cruciate’ (Latin for like a cross)

  • Anterior cruciate ligament –  attaches at the anterior intercondylar region of the tibia and ascends posteriorly to attach to the femur, in the intercondylar fossa. It prevents anterior dislocation of the tibia onto the femur.
  • Posterior cruciate ligament attaches at the posterior intercondylar region of the tibia, and ascends anteriorly to attach to the femur in the intercondylar fossa. It prevents posterior dislocation of the tibia onto the femur.
Fig 1.5 - The major ligaments of the knee joint.

Fig 1.5 – The major ligaments of the knee joint:Green – patella ligamentRed – collateral ligamentsDark blue – anterior cruciate ligamentLight blue – posterior cruciate ligament


Movements

There are four main movements that the knee joint permits:

  • Extension:  Produced by the quadriceps femoris, which inserts into the tibial tuberosity.
  • Flexion: Produced by the hamstrings, gracilis, sartorius and popliteus.
  • Lateral rotation: Produced by the biceps femoris.
  • Medial rotation: Produced by five muscles; semimembranosus, semitendinosus, gracilis, sartorius and popliteus.

NB: Lateral and medial rotation can only occur when the knee is flexed (if the knee is not flexed, the medial/lateral rotation occurs at the hip joint).

Clinical Relevance: Injury to the Knee Joint

Collateral ligaments

Injury to the collateral ligaments is the most common pathology affecting the knee joint. It is caused by a force being applied to the side of the knee when the foot is placed on the ground.

Damage to the collateral ligaments can be assessed by asking the patient to medially rotate and laterally rotate the leg. Pain on medial rotation indicates damage to the medial ligament, pain on lateral rotation indicates damage to the lateral ligament.

If the tibial collateral ligament is damaged, it is more than likely that the medial meniscus is torn, due to their attachment.

Cruciate ligaments

The anterior cruciate ligament (ACL) can be torn by hyperextension of the knee joint, or by the application of a large force to the back of the knee with the joint partly flexed. To test for this, you can perform an anterior drawer test, where you attempt the pull the tibia forwards, if it moves, the ligament has been torn.

Fig 1.5 - A positive posterior drawer test, signifying damage to the posterior cruciate ligament

Fig 1.5 – A positive posterior drawer test, signifying damage to the posterior cruciate ligament

The most common mechanism of posterior cruciate ligament (PCL) damage is the ‘dashboard injury’. This occurs when the knee is flexed, and a large force is applied to the shins, pushing the tibia posteriorly. This is often seen in car accidents, where the knee hits the dashboard. The posterior cruciate ligament can also be torn by hyperextension of the knee joint, or by damage to the upper part of the tibial tuberosity.

To test for PCL damage, perform the posterior draw test. This is where the clinician holds the knee in flexed position, and pushes the shin posteriorly. If there is movement, the ligament has been torn.

Inflammation of the Bursae

Friction between the skin and the patella cause the prepatella bursa to become inflamed, producing a swelling on the anterior side of the knee. This is known as housemaid’s knee.

Similarly, friction between the skin and tibia can cause the infrapatella bursa to become inflamed, resulting in what is known as clergyman’s knee (typically caused by clergymen kneeling on hard surfaces during prayer).

Unhappy triad

Due to the attachment of the medial collateral ligament to the medial meniscus, damage to the medial collateral can affect this important cartilaginous structure. A lateral force to an extended knee, such as a rugby tackle, can rupture the medial collateral ligament, damaging the medial meniscus in the process. The ACL is also affected, which completes the ‘unhappy triad’.

 

Rate This Article

80

Average Rating:

Quiz

Question 1 / 8
Which of the following is the correct classification of the knee joint?

Quiz

Question 2 / 8
The tendon of which muscle group attaches to the patella?

Quiz

Question 3 / 8
Which type of cartilage are the menisci comprised of?

Quiz

Question 4 / 8
Which ligament of the knee is attached to the medial meniscus?

Quiz

Question 5 / 8
Which of the following correctly describe the attachments of the anterior cruciate?

Quiz

Question 6 / 8
Force applied to the lateral aspect of a fixed knee will most likely damage which ligament?

Quiz

Question 7 / 8
Which movement is the cause of posterior cruciate ligament rupture?

Quiz

Question 8 / 8
Which bursa becomes inflamed to cause Housemaids knee?

Results