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Knee One of the more complex joints in the body Supported and maintained entirely by muscles and ligaments with no bony stability Frequently exposed to severe stresses One of the most frequently injured joints Largest joint in the body Not a true hinge joint (modified hinge) because has a rotational component from accessory motion that accompanies flex/exten Rotation from femoral medial condyle being longer than lateral. With extension, articular surface of lateral is used up while some articular surface remains medially. Therefore medial condyle must also glide posteriorly to use all of the surface. This posterior gliding of medial condyle during the last few degrees of weight-bearing extension (closed chain) causes the femur to rotate medially on the tibia. Non weight bearing extension has the tibia rotate laterally on femur. These last few degrees of motion lock the knee in extension and is called the screw-home mechanism. Patella acts to increase the mechanical advantage of the quadriceps and to protect the joint. The Q angle (patellofemoral angle) is the angle between the quads (esp. the rectus femoris) and patellar tendon. Defined as a line from the ASIS to the midpoint of the patella and from the tibial tuberosity to the midpoint of the patella. The angle at the intersection of these lines represents the Q angle. Normal angle=13-18 degrees (greater in females). Q angles greater or lessor than normal can result in dysfunction. Fibula is not part of the knee joint but plays an important role at ankle. Ligaments Cruciate and collateral ligaments are the two main sets of ligaments primary in stabilizing the knee. They are located within the capsule (intracapsular ligaments). These ligaments cross each other between the medial and lateral condyles to the tibia. They are named by their attachment on the tibia. Anterior cruciate attaches to anterior tibia and spans the knee laterally to posterior lateral condyle of femur. Keeps femur from being displaced posteriorly on tibia. Tightens during extension to prevent excessive hyperextension of knee. With partial flexion, keeps tibia from being moved anteriorly. Posterior cruciate attaches to posterior tibia and runs superior and anterior on the medial side of anterior cruciate. Attaches to anterior femur on the medial condyle. Keeps femur from being displaced anteriorly on tibia. Tightens during flexion and is injured less. Cruciates provide stability in the sagittal plane. Collateral ligaments located on the sides of knee. Medial collateral or tibial collateral is a flat broad ligament attaching to medial condyles and tibia. Fibers of medial meniscus are attached to this ligament which contributes to frequent tearing of medial meniscus during excessive stress. On lateral side is lateral collateral or fibular collateral that is round and cordlike attaching to the lateral condyle and down to head of fibula. Protects from medial stresses. Strong and not injured as frequently. Collateral ligaments provide stability in the fontal plane. Medial provides medial stability and prevents excessive motion from a lateral blow. Lateral provides lateral stability and prevents excessive motion from a medial blow. They become tight during extension which adds stability and are slack during flexion. Meniscus (medial and lateral) are two half moon wedge-shaped fibrocartilage disks on the superior surface of tibia for shock absorption. Thicker laterally and proximal surfaces are concave. Act to deepen relatively flat joint surface. Medial (attached to medial collateral) more frequently torn Bursa act to reduce friction. Pes anserine muscle group = sartorius, gracilis and semitendinosus. All have different proximal attachement. All cross the knee posteriorly and medially then join together. Attachment can be altered to increase medial stability of the knee.