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Joints and Ligaments

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 - The knee joint is the largest joint in the body.
 - The knee is a synovial
 - hinge type joint.
 - The entire weight-bearing load is transferred 
    through the knee joints.
       When describing the knee, four bones and 
       their articulations should be discussed: 
       the femur, the tibia, the fibula, and the
 - Each articulation surface is covered with hyaline cartilage.
 - The primary articulation of the knee is between the 
   condyles of the femur and tibia.
 - This articulation is separated by the medial and lateral 
   menisci, which serve to deepen the articular surfaces 
   and aid in lubrication  and cushioning of the joint.
       Although not a part of the knee joint, the articulation 
       of the tibia and fibula is significant due to its 
       importance in weight bearing.
 - The patellofemoral joint is a synovial gliding type joint.
 - The patella is a sesamoid bone contained in the tendon of the
       quadriceps muscle. The articulation consists of the 
       underside of the patella and the patellar grove of 
       the femur. The gliding of the patella in the femoral 
       grove allows for increased efficiency of the 
       quadriceps muscle. 
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- Many muscles acting on the thigh have their insertions around 
  the knee. 
- Although not participating in gross knee movements these 
  muscles are significant in the dynamic stabilization of the knee 
- Only the muscles specifically participating in knee flexion, extension, 
  internal, and external rotation are discussed here. 
- The anterior muscles of the knee act primarily as knee extensors.
- The quadriceps femoris muscle is the principle muscle involved in
   knee extension. 
     This muscle can be divided into four distinct parts: 
   1. the rectus femoris
   2. vastus medialis
   3. vastus lateralis
   4. vastus intermedius. 
   - All four parts of this muscle come together to insert on the 
    proximal edge of the patella, which then transfers their action, 
    by way of the patellar tendon, to the tibia. 

The principle muscles involved in knee flexion 
              hamstring muscle group. This group is comprised of:
    1. the biceps femoris
    2. semitendinosus
    3. semimembranosus muscles. 
   - Their insertion occurs on the proximal tibia and head 
     of the fibula. 

 - The biceps femoris muscle has an additional action of 
   externally rotating the tibia. 
 - While the semitendinosus and semimembranosus muscles also 
   have an additional role of internally rotating the tibia. 
 - Other muscles participating in knee flexion and internal 
   rotation are the sartorius, and gracilis muscles.
 - The popliteus muscle also serves to internally rotate the
   knee in a non-weight bearing position. 
 - Additional muscles involved in isolated knee flexion include
    the gastrocnemius and plantaris muscles.

 - Blood is supplied to the knee via the popliteal artery.
 - The popliteal artery originates from the external iliac artery, which
   gives rise to the femoral artery in the proximal thigh.
 - The femoral artery passes posterior to the knee and becomes 
   the popliteal artery. 
 - The knee joint and surrounding musculature is innervated by a 
   number of nerves of the lower limb. Originating from the 
   lumbosacral plexus the femoral and obturator nerves innervate 
   the front and anteromedial sides of the thigh. 
 - The sciatic nerve, which rises from the sacral plexus supplies 
   the posterior thigh and divides above the knee to form the 
   common peroneal and tibial nerves. 

 - Various bursae are located about the knee joint for purposes of 
   decreasing friction over tendons and bones. 
 - The suprapatellar bursa is located between the deep surface of 
   the quadriceps muscle and the distal part of the femur. 
 - This bursa is in communication with the joint capsule of the knee. 
 - The prepatellar bursa is located between the superficial surface 
   of the patella and the skin. 
 - An infrapatellar bursa is located between the patellar ligament 
   and the skin. 
 - The deep infrapatellar bursa is situated between the proximal 
   tibia and the patellar ligament. 

 - Other bursae decrease friction at the attachment sites of the 
   gastrocnemius, gracilis, sartorius, semitendinosus, and 
   semimembranosus muscles. 
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 - Static stabilization of the knee is provided by the ligamentous 
   structures and to a lesser extent the joint capsule surrounding 
   the knee articulations. 
 - The principle stabilizing ligaments of the knee are discussed here. 
 - The anterior portion of the knee joint is stabilized partly by the
   medial and lateral patellar retinacula, which are extensions of the 
   quadriceps femoris muscle 
 - The patellar tendon gives added support to the anterior portion 
   of the knee. 
 - The oblique popliteal ligament and the arcuate popliteal ligament
   stabilize the posterior aspect of the knee. 
 - The oblique popliteal runs from the intercondylar fossa of the 
   femur to the head of the tibia. While the arcuate popliteal rises 
   from the lateral condyle of the femur to attach to the styloid 
   process of the head of the tibia. 
 - The tibial (medial) collateral and the fibular (lateral) collateral 
   ligaments serve to stabilize the medial and lateral aspects of the
   knee joint respectively. 
 - These ligaments also serve to restrain rotation of the knee 
 - The tibial collateral ligament is a broad, flat ligament that runs from
   the medial condyle of the femur to the medial condyle of the tibia. 
 - A deep portion of this ligament blends posteriorly with the joint
   capsule of the knee, which is also attached to the medial meniscus. 
 - The fibular collateral ligament is more rounded and cordlike and 
   extends from the lateral epicondyle of the femur to the lateral 
   aspect of the head of the fibula. 
 - These ligaments are especially important stabilizers of rotational 
   and lateral movement when the knee is in the extended position
 - Two important intra-articular ligaments that provide static support
   to the knee are the anterior (ACL) and posterior (PCL) cruciate
 - Although the ligaments are intra-articular they are not contained
   within the joint capsule of the knee.
 - The ACL extends from the anterior area between the condyles 
   of the tibia in a posterior and lateral direction to a posterior area
   on the medial surface of the lateral condyle of the femur
 - The ACL functions to prevent anterior displacement of the tibia 
   on the femur.
 - The PCL runs from a posterior depression between the condyles 
   of the tibia in an anterior and medial direction to the lateral side 
   of the medial femoral condyle 
 -  The PCL functions to prevent posterior translation of the tibia on 
    the femur.
 -  Additionally both the ACL and PCL serve to reduce rotation of 
    the femur on the tibia. The ligaments are tense in all positions, 
    but increase their tension in the extremes of flexion and 

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 - The principle motions of the knee joint are flexion and extension; 
   however, it does allow for some degree of rotation 
 - The arc of motion of the knee defined by Hoppenfeld (1976) is 
   typically about 0 extension to 135 of flexion. 
 - The amount of internal and external rotation about the knee is 
   approximately 5 to 10 in each direction 
 - It is in extension that the rotational component of the knee joint
   is necessary. 
 - The knee is unable to reach full extension without a small amount
   of external rotation of the tibia on the femur. 
 - This need for external rotation is due to the fact that the medial
   femoral condyle is approximately 1/2-inch longer than the lateral
   femoral condyle 
 - The external rotation of the tibia allows the knee to achieve full 
 - This mechanism is known as the "screw home" mechanism and it
   allows the knee to be held in full extension without undue fatigue 
   of the surrounding musculature  

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