Complex joint subject to stresses of daily and athletic activities.

Subject to degenerative problems with age.

Subject to sports injuries.

The largest joint in the body.

Function involves bending, flexion, and straightening, extension, of the leg, and rotation can also occur within the knee.

Fluid within the joint is in ultrafiltrate of plasma supplemented with hyaluran, which is a linear macromolecule produced by cells lining the joint capsule.

Hyaluronan renders synovial fluid viscous and elastic.

The joint is composed of the distal femur and the proximal end of the tibia, and the front of the knee is covered by the patella (knee cap).

During motion the patella slides in the trochlea, a grove in the distal femur.

The bone surfaces of the knee are covered with articular cartilage, providing lubrication and minimizing friction of the joint.

The menisci are pieces of cartilage which act as shock absorbers.

The medial meniscus sits between the femur and the tibia on the inner part of the knee and the lateral meniscus is present on the outer part of the joint.

The cruciate ligaments, the anterior (ACL) and posterior cruciate ligaments (PCL), provide stability to the knee, by resisting translational and rotational movements.

The primary function of the anterior cruciate ligament (ACL) is to resist anterior displacement of the tibia on the femur when the knee is flexed.

A secondary function of the ACL is to resist varus or valgus rotation of the tibia.

The ACL also resists internal rotation of the tibia.

The main function of the posterior cruciate ligament (PCL) is to allow femoral rollback in flexion and resist posterior translation of the tibia relative to the femur.

The PCL controls external rotation of the tibia with increasing knee flexion.

The median collateral ligament (MCL) on the inner part of the knee connects the femur and the tibia while the lateral collateral ligament (LCL) on the outer part of the knee resist side to side movements of the knee.

The primary function of the medial collateral ligament is to restrain valgus rotation of the knee joint.

A secondary function of the MCL is to control of external rotation.

The lateral collateral ligament restrains varus rotation and resists internal rotation.

The quadriceps tendon and the patellar tendon make up the extensor mechanism of the knee.

Factors to be considered include the duration and degree of symptoms, the location and quality of pain, the findings of swelling, mechanical symptoms, the presence of instability and factors that alleviate or aggravate symptoms.

Movement of the knee joint can be classified as having 6 degrees of freedom: including anterior/posterior, medial/lateral, and inferior/superior) and 3 rotations including flexion/extension, internal/external, and abduction/adduction.

Movements of the knee joint are determined by the shape of the articulating surfaces of the tibia and femur and the orientation of the 4 major ligaments of the knee joint, including the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments as a 4-bar linkage system.

Knee flexion/extension involves a combination of rolling and sliding called femoral rollback.

Patellofemoral joint is characterized as gliding and sliding.

During flexion of the knee, the patella moves distally on the femur.

During knee flexion the attachments of the patellofemoral joint to the quadriceps tendon, ligamentum patellae, and the anterior aspects of the femoral condyles.

The muscles and ligaments of the patellofemoral joint are responsible for producing extension of the knee.

The patella acts as a pulley in transmitting the force developed by the quadriceps muscles to the femur and the patellar ligament.

X-rays imaging permits evaluation of the bony structures of the knee, while soft tissue structures are best evaluated with MRI.

Intraarticular ligaments, menisci, articular cartilage have no ability to heal after injury.

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