Knee Anatomy

The knee anatomy is a complex hinge joint that flexes, extends, and twists slightly from side to side. It is responsible for weight bearing and movement. The knee consists of bones, meniscus, ligaments, and tendons.

• The knee is the meeting point of the femur (thigh bone) in the upper leg and the tibia (shinbone) in the lower leg.
• The fibula (calf bone), the other bone in the lower leg, is connected to the joint but is not directly affected by the hinge joint action.
• The patella (kneecap), is at the center of the knee.
• The meniscus is sometimes called cartilage, and the knee has two: the medial (inner) and lateral (outer). These crescent-shaped discs are tough and rubbery, and act as a cushion or ‘shock absorber’ between the femur and tibia so that the bones of the knee can move through their range of motion without rubbing against each other.

Four Ligaments of the Knee

Ligaments of the knee act like strong ropes to connect bones to other bones. The stability of the knee joint depends on the following four ligaments.

1. Anterior cruciate ligament (ACL)
2. Posterior cruciate ligament (PCL)
3. Medial collateral ligament (MCL)
4. Lateral collateral ligament (LCL)

Cruciate Ligaments are found inside the knee joint. They cross each other to form an “X” with the anterior cruciate ligament (ACL) in front and the posterior cruciate ligament (PCL) in back. The cruciate ligaments control the back and forth motion of your knee.

Collateral Ligaments are found on the sides of your knee. The medial collateral ligament (MCL) is on the inside and the lateral collateral ligament (LCL) is on the outside. These two ligaments control the sideways motion of the knee and brace it against unusual movement.

Bursae of the Knee

Knee bursae are fluid sacs filled with synovial fluid encompassing the bone joint that will sometimes communicate with the joint cavity. They are found all over the body between muscles and bone and function to reduce friction and act like a cushion which allows for allows everything to move smoothly preventing inflammation.

Two Types of Bursae

1. Communicating
2. Non-communicating Bursae 

Five Main Knee Bursae Based on Location (Total of 14 Knee Bursae)

1. Prepatellar Bursa: Anterior bursae over the kneecap. Inflammation can occur with prolonged kneeling as in trades such as roofers and carpet fitters.
2. Infrapatellar Bursa: Two anterior bursae called deep and superficial infrapatellar bursae underneath the kneecap protecting the patellar tendon
3. Suprapatellar  Bursa: Anterior bursa above the kneecap underneath the quadriceps tendon at the bottom of the thigh preventing friction from the femur.
4. Pes Anserine Bursa: Anterior bursa on the medial (inner side) of the knee two inches below the joint between the medial collateral ligament and tendons of the muscles sartorius, gracilis and semitendinosis. Not uncommonly, runners can develop inflammation of Pes Anserine.
5. Semimembranosus Bursa: is found at the back of the knee between the hamstring muscles (semimembranosus muscle) and the inner calf muscles (medial head of gastrocnemius). A Bakers Cyst is inflammation of the Semimembranosus Bursa that results in a soft mass at the back of the knee, which may occur with arthritis.

Tendons of the Knee

Tendons of the knee are tough bands of tissue which connect muscles to bone and provide stability to the joint.

Muscles of the Knee

Muscles around the knee, while not part of the knee anatomy per se, the hamstrings and quadriceps are the muscles that strengthen the leg and help flex the knee.

• Quadriceps femorus muscle group (rectus femoris, vastus lateralis, vastus medius, and vastus intermedius) crosses the knee via the patella and acts to extend the leg.
• Hamstring muscles (semitendinosus, semimembranosus, and biceps femoris) flex the knee and extend the hip (except for the short head of the biceps femoris).
• Popliteus muscle at the back of the leg unlocks the knee by rotating the femur on the tibia, allowing flexion of the knee.

Learn about the Types and Causes of Common Knee Injuries and Problems

1. Types and causes of Knee Injuries and Problems
2. Knee Anatomy
3. Knee Pain and Injury Symptoms and signs
4. When to Call your Doctor
5. Treatment for Common Knee Injuries and Problems
6. Ice or Heat for An Injury?
7. Meniscus Tear
8. Preventing Knee Injuries
9. Knee Replacement

Our goal at OSMI is to provide our patients quality, cutting-edge orthopedic treatments, both surgical and non-surgical.  If you have questions about knee arthroscopy or surgery, knee joint pain, or physical therapy, please submit an online appointment request or contact our office at 817-529-1900.