knee joint

Arthrology

BONES
Femur

·      condyles are eccentrically curved

·      anterior portion is segment of oval

·      posterior portion is segment of sphere

·      project behind femoral shaft

·      anterior groove for patella

·      called trochlea

·      posterior notch

·      called intercondylar notch

·      shape of condyles different

·      medial is narrower, longer and more curved

·      long axis of condyles different

·      lateral is sagittal

·      medial is 22o to sagittal

TIbia

·      condyles (plateaus) are two flat surfaces

·      separated by intercondylar eminence

·      menisci and cruciates attach anterior and posterior to eminence

·      posterior lip of lateral condyle rounded

·      medial plateau flat

·      lateral plateau domed

Patella

·      triangular-shaped sesamoid

·      vertical ridge divides surface into

·      small medial facet

·      larger lateral facet

·      another vertical ridge divides medial facet into two

·      patella moves 7-8 cm wrt femur during flexion-extension

·      contact varies with position of knee

·      full extension - distal portion of lateral facet with lateral condyle

·      full flexion - proximal portions of both facets with both condyles

capsule
Femur

·      attached at articular margin

·      except in two places

·      posteriorly attached to intercondylar ridge at lower limit of popliteal surface

·      laterally encloses pit and groove for politeus tendon

Tibia

·      attached at articular margin

·      except in two places

·      posteriorly attached to ridge between condyles at lower end of groove for PCL

·      laterally prolonged over politeus tendon to styloid process on head of fibula as arcuate popliteal ligament

Folds

·      invaginated anteriorly by fat pad

·      called median infrapatellar fold

·      capsule above patella deficient

·      perforates when infant walks

·      communicates with suprapatellar bursa

·      three defects in capsule

·      superiorly where communicates with suprapatellar bursa

·      laterally allowing popliteus tendon to enter

·      anteriorly where margins attached to patella

Synovium

·      attachments do not coincide with capsule

·      because of intra-articular structures

Femur

·      lines intercondylar notch

·      separated from capsule on lateral condyle by attachment of popliteus

Tibia

·      reflected forward by ACL and PCL

·      anterior fold called infrapatellar fold (ligamentum mucosae)

·      alar fold extends medially and laterally from it

Bursae

·      communicates with

·      suprapatellar bursa

·      popliteus bursa

·      gastrocnemius bursae

·      semimembranosus bursa via medial gastrocnemius bursa

Bursae

Suprapatellar

Popliteus

Semimembranosus

Gastrocnemius

blood and nerve supply
Blood

·      supplied from anastomoses around knee

·      chief contributors are 5 genicular branches of popliteal artery

·      middle genicular supplies cruciate ligament

Nerve

·      femoral

·      from branch to vastus medialis

·      sciatic

·      genicular branches from tibial and common peroneal

·      obturator

·      twig from posterior division

·      cruciates supplied by branches of tibial nerve

Cruciate ligaments

·      connect tibia and femur

·      named from tibial origins

·      intra-capsular (intra-articular) but extrasynovial

·      herniated into joint from behind

·      carry layer of synovium in that covers anterior and lateral surfaces but leaves posterior surface uncovered

anterior cruciate ligament
Form

·      38 mm long and 10 mm wide

·      consists of

·      small anteromedial band

·      large posterolateral band

Attachments

·      femoral attachment is on posterior part of medial surface of lateral condyle

·      4 mm anterior to posterior edge of femur

·      extends for 23 mm

·      forms segment of circle

·      tibial attachment is in pit adjacent to lateral edge of medial condyle

·      15 mm posterior to anterior edge of tibia

·      extends for 30 mm

·      anteromedial band

·      attached most superiorly on femur

·      attached most anteromedially on tibia

·      tense in flexion

·      posterolateral band

·      attached most inferiorly on femur

·      attached most posterolaterally on tibia

·      tense in extension

Blood supply

·      from posterior vessels entering intercondylar notch near femoral attachment

·      from anterior vessels in soft tissue and synovium near fat pat

Function

·      as strong as MCL

·      half as strong as PCL

·      minimal tension at 45o flexion

·      maximal tension at 90o flexion

·      primary anterior stabiliser

·      prevents anterior translation of tibia on femur

·      provides 85% of resistance

·      primarily anteromedial bundle

·      prevents hyperextension of knee

·      primarily posterolateral bundle

posterior cruciate ligament
Form

·      38 mm long and 13 mm wide

·      consists of

·      large anterior bundle

·      small posterior bundle

Attachments

·      femoral attachment is to posterior part of lateral surface of medial condyle

·      forms segment of circle

·      tibial attachment is to depression behind and below intra-articular portion of tibia

·      extra-articular

·      more vertically orientated than ACL

Function

·      is axis around which rotation of knee occurs

·      guides screw-home mechanism

·      primary posterior stabiliser

·      prevents posterior translation of tibia on femur

·      provides 90% of resistance

·      prevents femur slipping forward while knee flexed going down stairs or down hill

·      prevents hyperextension of knee

·      secondary restraint when ACL absent

Menisci

form

·      crescent-shaped

·      triangular in cross-section

·      cover 1/2 to 2/3 of articular surface of tibial plateau

·      outer edges attached to

·      inner surface of knee joint capsule (except where popliteus interposed laterally)

·      tibia by coronary ligament

·      anterior and posterior horns attach to tibia in front of and behind intercondylar eminence (MAL LMP)

·      inner edges concave, thin and unattached

·      inferior surface flat

·      superior surface concave

·      largely avascular

·      except for outer 10-30%

·      supply from geniculate vessels via premeniscal plexus in capsule

·      also some supply from bone at capsular attachments and attachments of horns

Medial

·      3.5 cm long

·      comma-shaped

·      posterior horn wider than anterior

·      horns enclose lateral meniscus

·      posterior horn attached firmly to semimembranosus via extension

·      transverse ligament passes between anterior horns of medial and lateral menisci

Lateral

·      compared with medial

·      thicker

·      wider

·      smaller in diameter

·      more mobile

·      covers more of tibial plateau

·      anterior horn attached to ACL

·      posterior horn attached to

1.   PCL

2.   medial condyle of femur

·      via meniscofemoral ligaments

·      of Humphrey (anterior to PCL)

·      of Wisburg (posterior to PCL)

3.   popliteus via extension

·      tendon of popliteus separates posterolateral periphery of meniscus from joint capsule and deep tibial collateral ligament

·      enveloped in synovial membrane

·      forms oblique groove on meniscus

·      less prone to injury, esp. during rotation

·      follows femur more closely due to meniscofemoral ligaments

·      popliteus draws posterior horn back