Knee Joint

• The knee joint is a synovial joint which is very complex and is primarily a hinge joint.
• Enlarged femoral condyles articulate on enlarged tibial condyles.
• The tibia bone bears most of the body weight and is the medial bone.
• The fibula is the lateral bone and serves as the attachment for knee joint structures and does not articulate with femur or patella and not apart of the knee joint.
• The patella is a sesamoid bone embedded in quadriceps and patellar tendon. It is similar to a pulley. Creates improved angle of pull resulting in greater mechanical advantage in knee extension.
• The menisci forms cushions between bones.
• Medial meniscus forms a receptacle for medial femoral condyle. Larger and more open. Up to 50% of the load on medial side of knee.
• The lateral meniscus receives the lateral femoral condyle. Close C configuration. Up to 80% on lateral side of the knee.
• Menisci tears occurs due to significant compression and shear forces during knee rotation while flexion or extending during quick directional changes in running.
• If the menisci are removed, forces are no longer distributed over a wide area of tibia.\
• Lateral collateral ligament -> infrequently injured.
• Medial collateral ligament -> maintains medial stability by resisting valgus forces or preventing knee joint abduction.
• The synovial cavity supplies the knee joint with synovial fluid. Lies under the patella and between the surfaces of the tibia and femur. It is called the capsule of the knee.
• Infrapatellar fat pad is located posterior to the patellar tendon. It is an anatomical variant that may be irritated or inflamed with injuries or overuse of the knee.
• The bursae absorbs shock and reduce friction.
• The Q angle is the center line of pull for entire quadriceps which runs from the anterior superior iliac spine to the center of the patella. Higher Q angles predispose people to a variety of potential knee problems.
• Closed chain (weight bearing) -> flexion -> femur rolls posteriorly on tibia, laterally rotates and abducts.
• Closed chain -> flexion (kicking) -> tibia rolls anteriorly on femur, medially rotates and adducts.
• As the knee approaches full extension, the tibia must externally rotate approximately 10 degrees to achieve proper alignment of tibial and femoral condyles.
• Knee flexors include biceps femoris, semimembranosus, semitendinosus, sartorius, gracilis, popliteus, and gastrocnemius.
• Knee extensors include rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis. Contraction reduce strain on MCL. Works with PCL to prevent posterior displacement.
• Knee external rotation includes biceps femoris.
• Knee internal rotators include semitendinosus, semimembranosus, and popliteus (hamstrings).
• Quadricep muscles are vital in jumping. Eccentric contraction during decelerating actions. Functions as decelerators when speed needs to be decreased to change direction/when the body need to be stopped when coming down from a jump.
• Hamstring muscles are originate at the ischial tuberosity of the pelvic bone.
• Popliteus -> flexion of the knee and internal rotation of the knee as it flexes.
• Two joint muscles are most effective when either the origin or the insertion is stabilized to prevent movement in the direction of them muscle when it contracts.
• Sartorius muscle -> example of two joint muscle -> total length increases as it becomes more effective at flexing the knee when the pelvis is rotated posteriorly and stabilized by the abdominal muscles.
• Biceps Femoris -> flexion of the knee, extension of the hip, posterior pelvic rotation, external rotation of the knee, and external rotation of the hip. Inserts on the lateral tibial condyle and head of the fibula.

  
• Semitendinosus -> flexion of the knee, extension of the hip, posterior pelvic rotation, internal rotation of the hip, internal rotation of the knee. Inserts on the anteromedial side of the tibia.

  
• Semimembranosus -> flexion of the knee, extension of the hip, posterior pelvic rotation, internal rotation of the hip, internal rotation of the knee. Inserts on the posteromedial side of the tibia.

  
• Vastus Medialis -> extension of the knee. Uniarticular.

  
• Vastus Intermedius -> extension of the knee. Uniarticular.

  
• Vastus lateralis -> extension of the knee. Uniarticular.

  
• Rectus femoris -> flexion of hip, extension of knee, and anterior pelvic rotation. Biarticulation.

  
• The knee consists of the tibiofibular joint, patellofemoral joint, and tibiofemoral joint.

  
• Anterior cruciate ligament -> elongated 7% from extension to 90 degrees flexion.

  
• Posterior cruciate ligament -> disrupted by hyperextension or violent quadriceps contraction, which pulls tibia forward on femur. Not often injured. Injured due to direct contact with an opponent force.