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Anatomy, Joint Orientation and Arthrokinematics
Knee
Tibiofemoral Joint
• Femur run in a medial and inferior oblique direction
• Sits on a vertical tibia
Tibiofemoral Joint
• Femoral condyles are convex
• Articular surface of medial femoral and tibial condyle larger
• Poor congruency between the articulating surfaces
Menisci
• Fibro cartilaginous disks• Thicker peripherally • Good blood supply
outer 1/3• Rest Avascular
Menisci
• Roles within the knee– Increase congruency– Distribute weight
bearing across the knee– Act as shock absorbers– Aid lubrication reducing
friction – Add nutrition to articular
cartilage – Aid the locking
mechanism of the knee
Medial Menisci
• Larger than lateral• C Shaped• Larger posteriorly• Anchored to medial
capsule and MCL• Anterior horn connects
with transverse ligament• Lots of ligamentous and
capsular restraints• Limits mobility increasing
injury risk
Lateral Menisci
• More Circular• More Mobile• Medial and lateral
meniscus move posteriorly with flexion
• Medial and lateral meniscus move anteriorly with extension
• If a tear occurs, normal movement is lost, causing locking
Ligaments
• Coronary Ligament– Part of the joint capsule– Connect meniscu to
tibial plateau– Often injured in twisting
injuries
Ligaments
• Transverse Ligament– Connects the anterior
horns of the medial and lateral menisci together
Ligaments
• Meniscofemoral Ligament– Posterior horn of lateral
menisci to medial femoral condyle
– Anterior and Posterior Divisions
Medial Collateral Ligament
• Strong flat ligament• Merges with adductor
magnus fibres• Deep portion attaches to
medial meniscus• Deep portion capsular
thickening• Seperated by pes anserinus
tendons by bursa• Resists valgus force to the
knee and external rotation of the tibia
Lateral Collateral Ligament
• Cord like ligament• Extracapsular• More flexible than MCL• Resists varus stress• Resists tibial external
rotation
Anterior Cruciate Ligament
• Medial tibia to lateral femoral condyle
• 2 bands– Anteromedial
• Taut in knee flexion
– Posterolateral• Taut in knee extension
• Resists anterior translation of tibia on femur and hyperextension of knee
Anterior Cruciate Ligament
• Secondary restraint of varus/valgus motion
• Prevents continued femoral posterior translation during closed chain flexion
• Intracapsular but extrasynovial
• Blood vessels form a periligamentous sheath around the ligament
• Mechanoreceptors found in femoral attachment
Posterior Cruciate Ligament
• Posterior intercondylar area of tibia to medial condyle of femur
• Twice as strong as ACL• 2 Bands– Anterolateral– Posteromedial
• Merges with posterior horn of lateral menisci and meniscofemoral ligament
Posterior Cruciate Ligament
• Restricts posterior translation of tibia on femur and external rotation of tibia
• Secondary restraint of varus/valgus motion
• Intracapsular, but extrasynovial
Posterior Ligaments
• Oblique Popliteal Ligament– Thickening of posterior
capsule– Expansion of
semimembranosus tendon – Passes superior and laterally
to femoral intercondylar line• Arcuate Popliteal Ligament
– Inferior lateral aspect of posterior capsule
– From fibula head to posterior tibial and lateral femoral condyle
Joint Capsule
• Thick ligamentous sheath composed mainly of muscle tendons and their expansions
• Deficient anteriorly due to patella
Bursae
Infrapatella Fat Pad
• Sits between the joint capsule and synovial membrane
• Between Patella Ligament and knee joint
• Can be impinged or damaged in trauma
ArthrokinematicsKnee Extension• Open Chain
– Tibia Glides Anteriorly and Rolls Anteriorly– Tibia external rotation from 20° Flexion to Full Extension
• Closed Chain– Femur Glides Posteriorly and Rolls Anteriorly – Femur Internally rotates on stable Tibia from 20° Flexion to Full Extension
Knee Flexion• Open Chain
– Tibia Glides Posteriorly and Rolls Posteriorly– Tibia internal rotation from Full Extension to 20° Flexion
• Closed Chain– Femur Glides Anteriorly and Rolls Posteriorly– Femur Externally rotates on stable Tibia from Full Extension to 20° Flexion
Arthrokinematics
Extension Flexion
Patellofemoral Joint
• Anterior surface of the femoral condyles
• Posterior surface of the patella
• Divided into medial and lateral facets
• 4-5 mm of articular hyaline cartilage on patella
Ligamentum Patellae (Patellar Tendon)
• Continuation of quadriceps tendon
• Attaches into the tibial tuberosity
Meniscopatellar Fibres
• Fibrous bands running from patella to lateral aspect of medical and lateral menisci
Retinaculum
• Medial and Lateral• Expansions of different
connective tissue• Patellofemoral and
patellotibial ligaments• Vastus Medialis, Vastus
Lateralis, ITB
Patellofemoral Joint Arthrokinematics
• Articulation– Inferior margin of patella articulates with the
femur at approx 10-20° of knee flexion– As knee flexion increases the contact area of the
patella moves proximally– As knee flexion increase the contact area of the
condyles moves posteriorly– Patella does not articular with trochlea of femur
near terminal extension
Patellofemoral Articulations
Patellofemoral Articulations
Patellofemoral Contact Area
• The contact surface of the patellofemoral joint INCREASES with flexion
• @ 30° knee flexion the contact area = 2.0cm²
• @ 90 ° knee flexion the contact area = 6.0cm²
• The larger the contact surface area the more a load can be distributed over a greater area
• E.g which is more painful, a women standing on you in stilettoes or walking boots?