The bursae of the knee

Knee

The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...

are the fluid sacs and synovial pockets that surround and sometimes communicate with the joint cavity. Thin-walled and filled with synovial fluid

Synovial fluid

Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...

, they represent the weak point of the joint, but also produce enlargements to the joint space. They can be grouped into either communicating and non-communicating bursae or, as below, after location.

Frontal

In front there are five bursae:

1. the suprapatellar bursa or recess between the anterior surface of the lower part of the femur and the deep surface of the quadriceps femoris. It allows for movement of the quadriceps tendon over the distal end of the femur
2. the prepatellar bursa
   Prepatellar bursa
   The prepatellar bursa is a frontal bursa of the knee joint. It is a superficial bursa with a thin synovial lining located between the skin and the patella.-Pathology:...
   
   between the patella and the skin
   Skin
   -Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
   
   , results in "housemaid's knee" when inflamed. It allows movement of the skin over the underlying patella.
3. the deep infrapatellar bursa between the upper part of the tibia and the patellar ligament. It allows for movement of the patellar ligament over the tibia.
4. the subcutaneous [or superficial] infrapatellar bursa between the patellar ligament and skin.
5. the pretibial bursa between the tibial tuberosity and the skin. It allows for movement of the skin over the tibial tuberosity.

Lateral

Laterally there are four bursæ:

1. the lateral gastrocnemius [subtendinous] bursa between the lateral head of the gastrocnemius
   Gastrocnemius muscle
   In humans, the gastrocnemius muscle is a very powerful superficial pennate muscle that is in the back part of the lower leg. It runs from its two heads just above the knee to the heel, and is involved in standing, walking, running and jumping. Along with the soleus muscle it forms the calf muscle...
   
    and the joint capsule
2. the fibular bursa between the lateral (fibular) collateral ligament and the tendon of the biceps femoris
   Biceps femoris muscle
   The biceps femoris is a muscle of the posterior thigh. As its name implies, it has two parts, one of which forms part of the hamstrings muscle group.-Origin and insertion:It has two heads of origin;...
   
   
3. the fibulopopliteal bursa between the fibular collateral ligament and the tendon of the popliteus
   Popliteus muscle
   The popliteus muscle in the leg is used to unlock the knee during walking/running by laterally rotating the femur on the tibia during a closed chain movement ....
   
   
4. and the subpopliteal recess (or bursa) between the tendon of the popliteus and the lateral condyle of the femur

Medial

Medially, there are five bursae:

1. the medial gastrocnemius [subtendinous] bursa between the medial head of the gastrocnemius
   Gastrocnemius muscle
   In humans, the gastrocnemius muscle is a very powerful superficial pennate muscle that is in the back part of the lower leg. It runs from its two heads just above the knee to the heel, and is involved in standing, walking, running and jumping. Along with the soleus muscle it forms the calf muscle...
   
    and the joint capsule
2. the anserine bursa between the medial (tibial) collateral ligament
   Medial collateral ligament
   The medial collateral ligament of the knee is one of the four major ligaments of the knee. It is on the medial side of the knee joint in humans and other primates. It is also known as the tibial collateral ligament, or abbreviated as the MCL.- Structure :It is a broad, flat, membranous band,...
   
    and the tendons of the sartorius
   Sartorius muscle
   The Sartorius muscle – the longest muscle in the human body – is a long thin muscle that runs down the length of the thigh. Its upper portion forms the lateral border of the femoral triangle.-Origin and insertion:...
   
   , gracilis
   Gracilis muscle
   The gracilis is the most superficial muscle on the medial side of the thigh. It is thin and flattened, broad above, narrow and tapering below.-Origin and insertion:...
   
   , and semitendinosus
   Semitendinosus muscle
   The semitendinosus is a muscle in the back of the thigh; it is one of the hamstrings.-Structure:The semitendinosus, remarkable for the great length of its tendon of insertion, is situated at the posterior and medial aspect of the thigh ....
   
    (i.e. the pes anserinus
   Pes anserinus
   Pes anserinus is the anatomic term used to describe two different structures:* Pes anserinus * Pes anserinus...
   
   )
3. the bursa semimembranosa between the medial collateral ligament and the tendon of the semimembranosus
   Semimembranosus muscle
   The semimembranosus is a muscle in the back of the thigh. It is the most medial of the three hamstring muscles.-Structure:The semimembranosus, so called from its membranous tendon of origin, is situated at the back and medial side of the thigh....
   
   
4. there is one between the tendon of the semimembranosus and the head of the tibia
5. and occasionally there is a bursa between the tendons of the semimembranosus and semitendinosus

External links

• Image at nlm.nih.gov