1

THE KNEE

Joint Type

• Synovial Hinge Joint– Allows for flexion/extension and

some rotation• Screw-home mechanism

• Articulations– Condyles of femur and tibia

– femur and patella

– Weak mechanically• Needs support from fibrous

capsule, ligaments, and

musculature

2

Bony Structure

Patella• Largest sesamoid bone in body

• Increases the mechanical advantage of the quadriceps mm.

• Articulates with femoral condyles posteriorly

• Supported on lat and med borders by the patellar retinaculum

• Attached proximally by the quadriceps tendon

• Attached distally by the patellar lig.

3

Quadriceps mm.

• Vastus Medialis

• Vastus Lateralis

• Vastus Intermedius

• Rectus Femoris– Common insertion on

tibial tuberosity viapatellar tendon

– Responsible for kneeextension, aid in hipflexion (RF only), andtracking of patella

Hamstrings

• Semitendinosus m.

• Semimembranosus

m.

• Biceps Femoris m.

(long head)

– knee flexion and

hip extension

• Other mm. that aid

in knee flexion:

– Popliteus,

gastrocnemius,

plantaris

4

Pes Anserinus

• Group of 3 muscles withcommon insertion– Superior medial tibia

• Sartorius m.– Flexes, abducts, lat rotates

thigh at hip and flexes kneejoint

• Gracilis– Adducts thigh, flexes and

med rotates leg

• Semitendinosus

• Innervation of all three??

Iliotibial Tract

• IT Band

– Inserts on Gerdy’s

Tubercle (ant. sup.

Tibia)

– Supports lateral side

during flexion and

extension

– Also assisted by

biceps femoris

5

Articular Capsule• Fibrous capsule surrounds

join t and strengthened by

five ligaments :

– Medial (Tibial) Collateral

Lig. (MCL)

– Lateral (Fibular)

Collateral Lig. (LCL)

– Oblique Popliteal Lig.

– Arcuate Popliteal Lig.

– Patellar Ligament

(Tendon)

• Patellar

Retinaculum

– Motions restricted??

Cruciate Ligaments

• Anterior Cruciate Lig. (ACL)

– Ant tibia to lat condyle onpost femur

• Prevents ant translation oftibia on femur and introtation

• Is taut when knee is in fullextension

• Posterior Cruciate Lig. (PCL)

– Post tibia to med condyle onant femur

• Prevents ant translation offemur on tibia and introtation

• Tightens during flexion

6

Ligaments and Bursae

Menisci

• Medial Meniscus– Larger, C-shaped,

attached to MCL

• Lateral Meniscus– Smaller, nearly

circular, popliteustendon preventsattachment to LCL

• Richest bloodsupply around theperimeter

7

Knee Imaging

Blood Supply

• Formed by genicular

anastomoses around

the knee

– Sup/Inf Med/Lat

genicular aa.

– Middle genicular a.

• Fibrous capsule,

cruciate ligaments,

peripheral margins of

menisci, and synovial

membrane

8

Q-Angle & Meniscal Injury

Genu varum Genu valgum

Knee Injuries• ACL Injury

– Foot planted, knee flexion, medial rotation of

femur (lateral rotation of tibia)

9

Knee Injuries• PCL Injury

– “Dashboard impact”

Knee Injuries

• O’Donoghue’s Triad (Unhappy Triad)

– Tear of MCL, meniscus, and ACL

– Caused by lateral blow to a planted foot

10

Overuse & Degenerative

Injuries• Bursitis

• Patellar Tendinitis

• Chondromalacia

Patellae

• Osteoarthritis

Joint Replacement

• Necessary for chronic knee

pain and OA

• Bi or uni-compartmental

• Bi or unilateral

• 95% satisfaction at 15+ years