The Knee

acl alar folds anterior cruciate ligament bursae collateral ligament femoral condyles femur joint capsule knee knee articular surfaces knee bursae knee extension knee fat pad knee flexion knee joint knee joint capsule knee ligaments lateral collateral ligament lateral meniscus ligaments medial and lateral femoral condyles medial collateral ligament medial meniscus menisci patella pcl posterior cruciate ligament suprapatellar bursa synovial membrane tibia tibial condyles

The Knee Physiotherapy Solihull Simon Evans
  • Largest joint in the human body – formed by 3 articulations between 3 bones - femur, tibia and patella
  • Synovial, bicondylar joint (although sometimes described as 2 condyloid joints between tibia and femur and a sellar joint between patella and femur)
  • Motion permitted about 2 axes
  • Flexion / Extension - sagittal plane, transverse axis and Rotation - transverse plane, longitudinal axis (only possible physiologically when the knee is flexed)

Articular Surfaces

 3 articulations to be described

  • Medial & Lateral tibio-femoral
  • Patello-femoral

The Femur

  • Medial & lateral femoral condyles patellar surface between them (differentiated by 2 faint ridges anteriorly)
  • Covered in hyaline cartilage
  • Note how concavity of patella surface changes from superior to inferior

The Femur

Femoral Condyles 

  • Biconvex - convex in AP and medio-lateral directions - covered in Hyaline Cartilage
  • Note difference in shape - medial condyle being narrower and longer than lateral
  • Also note orientation relative to each other - lines bisecting each condyle would converge anteriorly due to angulation of medial condyle

 Lateral View - Femoral Condyles

  • Note variation in radius of curvature of both condyles
  • Consequently, motion at knee does not occur about a single stationary axis
  • Axis of motion moves posterior as the knee passes into flexion

The Patella

  • Posterior aspect of patella articulates with patellar surface on the femur
  • Divided by a central ridge into the smaller medial and larger lateral facets
  • In flexion central ridge moves into the concave intercondylar groove (most stable position)
  • Covered in a thick layer of hyaline cartilage which is thickest over central ridge

The Tibia

  • Superior aspect of tibial condyles - covered in hyaline cartilage
  • Divided by intercondylar eminence which is deficient of hyaline cartilage
  • Note difference between 2 condyles…
    • Medial - larger, longer and possibly narrower (reflects shape of femoral condyle)
    • Lateral - rounder
    • Lateral View - Tibial Condyles
      • Medial tibial condyle is biconcave (AP and medio-laterally)
      • Lateral tibial condyle is concave medio-laterally but is convex in an antero-posterior direction

    Joint Capsule

    • Simple capsule passing from one articular margin to next
    • Replaced anteriorly by extensor mechanism – capsule blends with patella, tendon & ligament

    Synovial Membrane

    • Most extensive in the body attaching to the articular margins and lines the capsule for the most part
    • However a number of folds and bursae are also present:
      • Suprapatellar Bursa - Extension of synovial membrane under lower part of quadriceps - attached to base of patella and articular margin in femur
      • The Alar Folds - Two folds of synovial membrane  extending from the lower border of the patella into the intercondylar region of the femur
    • Posteriorly the synovial membrane passes into the intercondylar area and around the cruciate ligaments (covering the medial, lateral and anterior surfaces)

    Non Communicating Bursae and Nutritional Fat Pad

    • Prepatella bursa
    • Superficial infrapatella bursa
    • Deep infrapatella bursa
    • Suprapatella bursa
    • Fat Pad


    • There are a number of ligaments around the knee
    • The 4 most important ones are:
    • Medial (Tibial) collateral ligament
    • Lateral (Fibular) collateral ligament
      • (both extra-capsular)
    • Anterior cruciate ligament
    • Posterior cruciate ligament
      • (both intra-capsular but extra-synovial)

    Medial (Tibial) Collateral Ligament

    • Broad flat band of fibrous tissue (approx 10 cm long) 
    • Multilayered - deep part blending with capsule & medial meniscus of knee
    • Note lower part crossed by tendons of sartorius, gracilis and semitendinosus (separated by pes anserine bursa)
    • Limits abduction and lateral rotation

    Lateral (Fibular) Collateral Ligament

    • Shorter rounded cord of fibrous tissue (approx 5 cm long)
    • Stands clear of the joint (no capsular attachment)
    • Limits adduction of tibia

    Anterior Cruciate Ligament

    • Extremely strong stabiliser of the knee
    • Note direction and obliquity of fibres - passing upward, backward and laterally from its tibial attachment
    • Prevents anterior displacement of tibia

    Posterior Cruciate Ligament

    • Larger of two - Crosses ACL 
    • Prevents posterior displacement of tibia
    • Note direction and obliquity of fibres - upward, forward and medially  from its tibial attachment
    • Both the ACL and the PCL are found within the boundaries of the articular capsule (intra-capsular) but outside of synovial membrane (extra-synovial) 

    The Menisci

    • Poor congruency of the femoral and tibial condyles makes joint inherently unstable
    • Congruency and stability is improved by the presence of the 2 Menisci
    • 2 pieces of fibrocartilage - triangular in cross section and semilunar in shape

    Functions of the Menisci

    • Improve congruency between tibia and femur due to shape 
    • Shock absorption - due to tissue type 
    • Weight dissipation - circumferentially - due to collagen orientation
    • Assist with lubrication 

    Medial Meniscus

    Larger of the 2

    •  Semilunar in shape
    • Wider posteriorly than anteriorly 


    • Intercondylar area - anterior to ACL and PCL attachments
    • Peripherally - via the coronary ligament
    • Blends with capsule & medial collateral ligament (Very firmly bound down - less mobile than the lateral)

    Lateral Meniscus

    • Smaller of the 2 
    • 4/5 of a circle in shape 


    • Anterior horn attached to intercondylar eminence posterior to the ACL
    • Peripherally via coronary ligament
    • Posteriorly to intercondylar eminence anterior to medial meniscus
    • Very mobile due to lack of attachment peripherally to collateral of knee - less susceptible to injury 

    Surface Markings of the Knee Joint

    • Can be done by direct palpation of the joint line
    • Or a line perpendicular to the tibia passing through a point midway between the apex of the patella and the tibial tubercle (anterior)
    • Or a line perpendicular to the tibia 1cm above apex of head of fibula (posterior)

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