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?