Learning Objectives

• Describe movements related to the knee joint
• Functions of ligaments in various movements of knee joint
• Mechanism of locking and unlocking of the knee joint
• Illustrate genicular anastomosis and justify its clinical significance
• Enlist the commonly injured ligaments of knee joint
• Correlate the effects of injury of each ligament with its topographic anatomy

Movements of the knee joint

●Flexion – limited by compression against the thigh; produced by Hamstrings & short head of Biceps

●Extension produced by Quadriceps Femoris

●Medial Rotation; produced by Sartorius, Gracilus, Semitendinosus.

●Lateral Rotation; produced by Biceps Femoris

Functions of ligaments in various movements

●Anterior cruciate ligament (ACL). Controls rotation and forward movement of the tibia.

●Posterior cruciate ligament (PCL). This ligament controls backward movement of the tibia.

●Medial collateral ligament (MCL). This ligament gives stability to the inner knee and prevents excessive varus movement.

●Lateral collateral ligament (LCL). This ligament gives stability to the outer knee and prevents excessive valgus movement.

Mechanism of Locking & Unlocking

●Knee is locked in the extended position with the major ligaments taut & femur medially rotated on the tibia

●As the knee joint assumes the position of full extension, medial rotation of femur results in a twisting and tightening of all the major ligaments of the joint, and the knee becomes mechanically rigid; the cartilaginous menisci are compressed like between the femoral and tibial condyles.

●Before flexion of the knee joint can occur, it is essential that the major ligaments be untwisted and slackened to permit movements between the joint surfaces. Unlocking is accomplished by the popliteus, which laterally rotates the femur on the tibia. Once again, the menisci have to adapt their shape to the changing contour of the femoral condyles. The attachment of the popliteus to the lateral meniscus results in that structure being pulled backward also.

Genicular Anastomosis

●Compensates for narrowing of popliteal artery during prolonged flexion of the knee

●Formed by the five genicular branches of popliteal artery

Important Relations

Important Relations

Anteriorly: The prepatellar bursa

Posteriorly: The popliteal vessels; tibial and common peroneal nerves; lymph nodes; and the muscles that form the boundaries of the popliteal fossa (semimembranosus, semitendinosus, biceps femoris) , the two heads of the gastrocnemius, and plantaris

Medially: Sartorius, gracilis, and semitendinosus muscles

Laterally: Biceps femoris and common peroneal nerve

Clinicals

Ligamentous Injury of the Knee Joint

●Medial collateral ligament, lateral collateral ligament, the ACL, and the PCL—are commonly injured in the knee. Sprains or tears occur depending on the degree of force applied

Medial collateral ligament

●Forced abduction of the tibia on the femur can result in partial tearing

● Meniscal tears result in localized tenderness on the joint line, whereas sprains of the medial collateral ligament result in tenderness over the femoral or tibial attachments of the ligament

Lateral Collateral Ligament

●Forced adduction of the tibia on the femur.

Cruciate Ligaments

●Injury to the cruciate ligaments can occur when excessive force is applied to the knee joint.

●Tears of the ACL are common( haemarthrosis, swollen joint)

●Tibia can be pulled excessively forward on the femur

Meniscal Injury of the Knee Joint

●Injuries of the menisci are common. The medial meniscus is damaged much more frequently than the lateral, this is because of its strong attachment to the medial collateral ligament of the knee joint, which restricts its mobility.

●The injury occurs when the femur is rotated on the tibia, or the tibia is rotated on the femur, with the knee joint partially flexed and taking the weight of the body.

●When the torn part of the meniscus becomes wedged between the articular surfaces, further movement is impossible, and the joint is said to “lock.”

Baker’s cyst

●A Baker’s cyst, also called a popliteal cyst, is a fluid-filled swelling that develops at the back of the knee

●It’s caused when the tissue behind the knee joint becomes swollen and inflamed. The swelling and inflammation can cause: pain in the knee and calf, a build-up of fluid around the knee