Knee Joint

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Knee Joint

• The knee is primarily a hinge joint allowing
  flexion extension these movements are
  accompanied by gliding rolling in addition to
  rotation about a vertical axis. The knee joint
  is robust but given the complexity of its
  movements which must occur during loading at or
  above body weight its function is often at risk
  particularly when it is hyperextended. Knee
  injuries are consistently the most common cause
  of disabling injuries in the NFL

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Articular surfaces

• The knee consists of three articulations
• 1. Two femorotibial articulations (lateral
  medial) between the lateral medial femoral and
  tibial condyles.
• 2. One intermediate femoropatellar articulation
  between the patella and femur
• The fibula is not involved in the knee joint.

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• The stability of the knee joint depends on
• 1. Strength and actions of surrounding muscles
  and tendons, the most important muscles in
  stabilizing the knee are the quadriceps femoris
  particularly the fibers of the vastus lateralis.
• 2. Ligaments connecting the femur tibia

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Joint Capsule

• The joint capsule consists of an external fibrous
  layer and an internal synovial membrane that
  lines the internal surfaces of the articular
  cavity not covered by articular cartilage.
• The fibrous layer attaches to the femur
  superiorly just proximal to the articular margins
  of the condyles.
• Posteriorly it encloses the condyles the
  intercondylar fossa.
• The fibrous layer has an opening posterior to the
  lateral tibial condyle to allow the popliteus
  tendon to pass out of the joint capsule and
  attach to the tibia.
• Inferiorly the fibrous layer attaches to the
  margins of the articular surface of the tibia
  (tibial plateau).

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• The quadriceps tendon, patella patellar
  ligament are intimately applied to the fibrous
  capsule anteriorly.

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• The synovial membrane lines the internal aspects
  of the fibrous capsule and attaches to the
  periphery of the patella and the edges of the
  cartilaginous menisci.
• The synovial membrane reflects from the posterior
  aspect of the joint anteriorly into the
  intercondylar region, covering the cruciate
  ligaments and the infrapatellar fat pad
  separating them for the articular cavity. This
  creates a median infrapatellar synovial fold, a
  vertical fold of synovial membrane that
  approaches the posterior aspect of the patella
  creating left right femorotibial articular
  cavities.
• Fat filled lateral medial alar folds cover the
  inner surface of the fat pads that occupy the
  space on each side of the patellar ligament
  internal to the fibrous layer.

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• Superior to the patella, the knee cavity extends
  deep to the vastus lateralis as the suprapatellar
  bursae.
• Muscle fibers of the vastus intermedius form the
  articular muscle of the knee which attaches to
  the synovial membrane and retracts the bursa
  during knee extension.

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Ligaments

• The joint capsule is strengthened by 5
  extracapsular (capsular) ligaments
• 1. Patellar ligament The distal part of the
  quadriceps tendon, it passes from the apex and
  margins of the patella to the tibial tuberosity.
  Laterally it receives aponeurotic expansions of
  the vastus lateralis (medial lateral
  retinacula) these are important for maintaining
  the alignment of the patella.
• The collateral ligaments are taut in extension
  but become lax as the knee flexes which allows
  rotation of the knee.
• 2. Fibular (Lateral) collateral ligament Extends
  inferiorly from the lateral epicondyle of the
  femur to the lateral surface of the head of the
  fibula. The tendon of the popliteus passes deep
  to the FCL separating it from the lateral
  meniscus. The FCL splits the tendon of the
  biceps femoris.

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Ligaments

• 3. Tibial (Medial) collateral ligament (TCL)
  extends from the medial epicondyles of the femur
  to the medial condyle and superior medial surface
  of the tibia. The deep fibers of the TCL are
  attached to the medial meniscus.
• 4. Oblique popliteal ligament This is a
  reflected expansion of the tendon of the
  semimembranosus that strengthens the joint
  capsule posteriorly. It arises from the medial
  tibial condyle passes superolaterally to the
  central part of the posterior aspect of the joint
  capsule.
• 5. Arcuate popliteal ligament strengthens the
  capsule posterolateral. It arises from the
  posterior aspect of the fibular head passes
  supero-medially over the popliteal tendon and
  attaches to the posterior surface of the knee
  joint.

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Intra Articular ligaments (cruciate menisci,
popliteus tendon)

• Cruciate ligaments These ligaments join the
  femur to the tibia, cris-crossing within the
  joint but outside the articular cavity. These
  ligaments cross each other obliquely. During
  medial rotation of the tibia on the femur the
  cruciate ligaments wind around each other this
  limits the amount of medial rotation to 10. With
  lateral rotation the ligaments unwind thus
  allowing 60 of lateral rotation when the knee
  is flexed at gt90. The cross over point serves
  as an axis for rotatory movements.

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• 1. Anterior cruciate ligament the weaker of the
  2 ligaments it arises from the anterior
  intercondylar area of the tibia just posterior to
  the attachment of the medial meniscus.
• It extends superiorly posteriorly and laterally
  to the posterior part of the medial side of the
  lateral condyle of the femur.
• The ACL limits the posterior rolling of the
  femoral condyles on the tibial plateau during
  flexion converting it into spin.
• It also prevents posterior displacement of the
  femur on the tibia and hyperextension of the knee
  joint.
• When the joint is flexed at a right angle the
  tibia cannot be pulled anteriorly because it is
  held by the ACL.

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• 2. Posterior cruciate ligament (PCL) the stronger
  of the 2 ligaments, it arises from the posterior
  condylar area of the tibia.
• The PCL passes superiorly and anteriorly on the
  medial side of the ACL to attach to the anterior
  part of the lateral surface of the medial condyle
  of the femur.
• The PCL limits the anterior rolling of the femur
  on the tibial plateau during extension,
  converting it to spin.
• It also prevents anterior displacement of the
  femur on the tibia or posterior displacement of
  the tibia on the femur and helps prevent
  hyperflexion of the knee joint.
• In the weight-bearing flexed knee the PCL is the
  main stabilizing factor for the femur

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• ACL under tension when knee extended
• PCL under tension when knee flexed

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Menisci of the knee

• These are cresentic plates of fibrocartilage on
  the articular surface of the tibia, they serve to
  deepen the joint surface and shock absorption.
• They are thicker at their outer margins and
  taper to thin inner margins.
• The menisci are firmly attached at their ends to
  the intercondylar area of the tibia.
• Their external margins are attached to the
  fibrous joint capsule.
• The coronary ligaments are capsular fibers that
  attach the margins of the menisci to the tibial
  condyles.
• The transverse ligament joins the anterior
  margins of the menisci together.

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• 1. Medial meniscus a C-shaped structure broader
  posteriorly, the anterior horn attaches to the
  anterior intercondylar area anterior to the
  attachment of the ACL. The posterior end
  attaches to the posterior intercondylar area
  anterior to the attachment of the PCL. It is
  firmly adherent to the deep surface of the tibial
  collateral ligament.

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• 2. Lateral meniscus Nearly circular, smaller and
  more mobile than the medial meniscus. The tendon
  of the popliteus separates the lateral meniscus
  from the fibularr collateral ligament. The
  posterior meniscofemoral ligament joins the
  lateral meniscus to the PCL and the medial
  femoral condyle

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• Meniscus tears
• Meniscal repair

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Bursae Around the Knee

• There are at least 12 bursae around the knee
  joint because most tendons run parallel to the
  bones and pull lengthwise across the joint during
  knee movements. The subcutaneous prepatellar and
  infrapatellar bursae are located at the convex
  surface of the joint allowing the skin to be able
  to move freely during knee movements. Four
  bursae communicate with the articular cavity of
  the knee joint suprapatellar bursa (deep to the
  distal quadriceps), popliteus bursa, anserine
  bursa and gastrocnemius bursa.

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Arterial Supply to the Knee 5-62 63B

• The arteries supplying the knee joint are the 10
  vessels that form the perigenicular anastomoses
  around the knee the genicular branches of the
  femoral, popliteal and anterior and posterior
  recurrent branches of the anterior tibial
  recurrent and circumflex fibular arteries. The
  middle genicular branches of the popliteal artery
  penetrate the fibrous layer of the joint capsule
  and supply the cruciate ligaments, synovial
  membrane and peripheral margins of the menisci.

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Innervation of the Knee

• Hiltons law applies the nerves supplying the
  muscles acting on the knee also innervate the
  joint. Articular branches of the femoral nerve
  supply the anterior knee, tibial nerve branches
  go to the posterior knee and the common fibular
  nerve supplies the lateral aspect of the knee.
  The obturator and saphenous nerves also supply
  genicular articular branches.

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Movements of the Knee

• Flexion extension are the main movements of the
  knee, some rotation can occur when the knee is
  flexed. When the leg is extended with the foot on
  the ground the knee passively locks because of
  medial rotation of the femur on the tibia, this
  allows weight bearing without muscular exertion
  by the leg muscles. To unlock the knee the
  popliteus contracts rotating the femur laterally
  5on the tibial plateau allowing flexion to
  occur.

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