MSK TBL 16/ILS 10: Knee Joint Anatomic Imaging & Functional Anatomy

knee joint

• formed by femur, tibia, & patella

  • femoral & tibial condyles articulate

  • patella articulates w/ femoral trochlear [patellar] surface

• fibula NOT involved

patella

• largest sesamoid bone

• located within tendon of quadriceps femoris

• articulates w/ femur but NOT tibia

• attaches to tibial tuberosity by continuation of quadriceps = patellar ligament

• function

  • prevent wear & tear on quadriceps tendon

  • increase angle of pull of quads, magnifiying its power

tibia

• weight-bearing, medial bone

• has tibial tuberosity where patellar ligament inserts

• has medial malleolus w/ malleolar groove for tendons of tibialis posterior & flexor digitorum longus muscles

  • another groove, posterolateral to malleolus groove, for tendon of flexor hallucis longus muscle

• provides attchmnt for deltoid ligament of ankle joint

fibula

• little to no weight bearing function

• provides attchment for muscles

• head [apex] provides attchment for fibular collateral ligament of knee joint

knee joint btwn femur & tibia

condylar type of synovial joint

knee joint btwn femur & patella

saddle joint

knee ligaments are taut in

full extension, accompanied by medial rotation of femur on tibia

knee joint stability depends on which muscle

quadriceps

knee joint stabilized laterally by

biceps & gastrocnemius [lateral head] tendons

IT tract

fibular collateral ligaments

knee joint stabilized medially by

sartorius

gracilis

gastrocnemius [medial head]

semitendinosus

semimembranosus

tibial collateral ligament

fibrous joint capsule of knee

• capsule attched to margin of articular surfaces

• has opening posterior to lateral tibial condyle

  • passage of popliteus tendon

median infra-patellar synovial fold

infra-patellar fat pad that divides articular cavity of knee into R. & L. compartments

extracapsular ligaments of knee

• tibial collateral ligament [medial collateral ligament, TCL]

• fibular collateral ligament [lateral collateral ligament, FCL]

• patellar ligament

• oblique popliteal ligament

• arcuate popliteal ligament

TCL

• from medial femoral epicondyle to medial tibial condyle

• injury to this ligament → concomitant damage to medial meniscus

• prevents medial displacement

• taut on extension

FCL

• separated from lateral meniscus & capsule of joint by tendon of popliteus muscle

• from lateral femoral epicondyle to head of fibula

• taut on extension

oblique popliteal ligament

• recurrent expansion of tendon of semimembranosus

• posteriorly attched btwn medial tibial condyle & lateral tibial condyle

• resists hyperextension & lateral rotation

arcuate popliteal ligament

strengthens joint capsule posterolaterally

intracapsular extra-synovial ligaments

• anterior cruciate ligament [ACL]

• posterior cruciate ligament [PCL]

ACL

• from anterior intercondylar region [superior, posterior, & lateral]

  • attach to lateral femoral femoral condyle [posteromedially]

• prevents posterior displacement of femur on tibia

  • prevents hyperextension

• weaker than PCL

• taut during extension

• often injured in conjuction w/ tibial collateral ligament & medial meniscus

  • unhappy triad

PCL

• from posterior intercondylar area of tibia & passes upward, forward, & medially to insert into lateral surface of medial femoral condyle

• stronger than ACL

• prevents backward sliding of tibia on femur

  • limits hyperflexion of knee

• taut during flexion

menisci of knee

• fibrocartilage

• shock absorbers

• attched along their external margins to tibia & fibrous joint capsule [coronary ligaments]

• attached at their ends to intercondylar eminence

• only peripheral 1/3 [red zone] is vascularized

• inner 2/3 avascular

  • central tears heal poorly

medial meniscus

C-shaped [semicircle]

lateral meniscus

nearly circular

transverse ligament of knee

binds anterior horns [ends] of lateral & medial semilunar cartliages [menisci]

anterior bursae of knee joint

• suprapatellar [quadriceps] bursa

• prepatellar bursa

• deep & subcutaneous infrapatellar bursae

posterior bursae of knee

• popliteus bursa

• anserine bursa

• gastrocnemius bursa

• semimembranosus bursa

articularis genus

small muscle that pulls bursa away from joint during extension of knee

bursae that DON’T communicate w/ articular cavity of knee

• prepatellar bursa

  • subcutaneous & anterior to patella

• deep & subcutaneous infrapatellar bursae

  • deep could be aggravated in runners

• semimembranosus bursa

4 bursae that communicate w/ synovial cavity of knee joint

GAPS

1. Suprapatellar [quadriceps] bursa

2. popliteus bursa

3. anserine bursa

4. gastrocnemius bursa

all deep to corresponding tendons of area

Popliteal Region/Fossa Boundaries

fat-filled, diamond-shaped depression posterior to knee joint

• superolateral: biceps femoris long head

• superomedial: semimembranosus

• inferolateral & inferomedial: lateral & medial heads of gastrocnemius

• floor: popliteal surface of femur, posterior knee joint capsule

  • reinforced by oblique popliteal ligament & popliteus muscle

• roof: skin & popliteal fascia

Popliteal region/fossa contents

• popliteal artery & vein

• tibial & common fibular nerves

• small saphenous vein

• genicular branch of obturator nerve

• popliteal lymph nodes

popliteal artery

• begins at adductor hiatus [adductor magnus muscle] as continuation of femoral artery

• terminates at inferior border of popliteus muscle by dividing into anterior & posterior tibial arteries

• deepest structure in popliteal fossa

• popliteal vein is posterior & slightly lateral to artery

  • tibial nerve is posterior & slightly lateral to vein

• gives genicular branches to knee

peripheral artery disease [PAD]

• narrowing of arteries

• popliteal pulse evaluates blood flow to leg

popliteal artery entrapment [PAE]

• muscle hypertrophy or knee trauma

• assess w/ popliteal pulse

blood supply to knee

• genicular branches

  • superior

    • medial

    • lateral

  • Inferior

    • medial

    • lateral

  • middle

• descending genicular artery

• anterior tibial recurrent artery

popliteal vein

• formed by union of anterior & posterior tibial veins at inferior border of popliteus muscle

• terminates at adductur hiatus, where it becomes femoral vein

• tributaries: small saphenous vein

nerve supply of knee joint

• femoral

  • saphenous nerve & nerve to vastus

• obturator

  • via genicular branch

• common fibular [deep & superficial]

  • lateral sural cutaneous nerve arises here

• tibial

  • medial sural cutaneous nerve arises here

popliteal [baker] cyst

• swelling behind knee

  • caused by arthritis, meniscus injury, or herniation or tear of joint capsule

• impairs flexion & extenion of knee

• pain worse when knee extended

“housemaid’s knee”

prepatellar bursitis

“clergyman’s knee”

infrapatellar [superficial] bursitis

fractured distal femur or dislocated knee may injure

popliteal artery

transverse patellar fracture

• from blow to knee or sudden contraction of quadriceps muscle

• proximal fragment of patella pulled superiorly w/ quadriceps tendon

• distal fragment remains w/ patellar ligament

tibial plateau / bumper fracture

• fracture of lateral tibial condyle caused by an automobile bumper

• usually associated w/ common fibular [peroneal] nerve injury

patellofemoral syndrome

“runner’s knee”

• patella tracks improperly [usually laterall] in femoral trochlear groove

• vastus medialis atrophy

• presents as anterior knee pain

chondromalacia patella

• pain in front of knee

• erosion of articular cartilage on posterior surface of patella → bone-on-bone friction

• seen in prior knee trauma, runners, or pple that exercise a lot

genu varum

“bowleg”

• femur abnormally vertical

• small Q angle

• excess weight place on medial aspect of knee joint

• → arthrosis [destruction of knee cartilages] & fibular collateral ligament overstressed

genu valgum

“knock knee/ K legs”

• lateral angulation of leg

• large Q angle

• weight bearing line falls lateral to center of knee

• tibial collateral ligament overstretched

Unhappy triad / O’Donoghue’s triad / terrible triad

1. ACL

2. MCL

3. Medial meniscus

anterior drawer test

tests ACL

Lachman test

• knee slightly bent, examiner stabilizes thigh while pulling shin forward

• tests ACL

posterior drawer test

tests PCL

valgus stress test

• pt supine w/ knees flexed to 30 degrees

• clinician applies valgus stress to knee

• checks for MCL injury

Varus stress test

• pt supine w/ knees flexed to 30 degrees

• clinician applies varus stress to knee

• checks for LCL injury

menisci can get torn during

forceful rotation or twisting

vertical meniscal tear

perpendicular to tibial plateau

horizontal meniscal tear

parallel to tibial plateau, splitting meniscus into upper & lower halves

bucket handle meniscal tear

longitudinal tear where torn portion of meniscus forms handle-shaped fragment

arthroscopy

performed to repair meniscal tear

McMurray test

test for meniscal tears

• pt supine, clinician flexes pts knee & externally rotates foot

• apply valgus stress to knee & extend knee

  • tests medial meniscus

  • (+) test = reproduction of pain & locking

• lateral meniscus tested similarly, except foot rotated internally & varus force applied while extending knee

“LIME”

to name direction of displacement

use orientation of DISTAL bone

what rules out meniscus injury?

if theres no joint line tenderness or effusion, likely not meniscal