Joints of the Knee

1. Tibiofemoral
2. Patellofemoral
3. Proximal Tibiofibular

*Not too concerned with distal tibiofibular for this test

How many degrees of freedome are at the knee?

6

Physiologic motions at the knee

Flex, Ext, Rotation

Knee Loose Packed Position

25 degrees flexion

Knee closed packed position

full extension with external rotation of tibia

Knee capsular pattern

Flexion > Extension

Medial Meniscus

Larger and thicker than lateral meniscus

thicker and wider posteriorly

less mobile

Lateral meniscus

smaller and thinner than medial meniscus

More mobile than medial meniscus

When is MCL taut?

Full Extension

What does the MCL resist?

Primary restraint to excessive abduction/valgus and lateral rotation

*greatest at 25-30 degrees flex

LCL

Loose Packed?

Close Packed?

Loose--Flexion

Closed--Extension

What ligament provides primary restraint

to anterior translation of tibia on femur and lateral rotation of tibia in flexion?

ACL

What percentage of forces causing anterior

translation does the ACL absorb?

90%

Common Mechanisms of injury to ACL

• Foot planted and femur vigorously externally rotated (often in conjunction w/ valgus force)
• Hyperextension w/ foot planted

Which is thicker PCL or ACL?

PCL is 50% thicker and has twice the

tensile strength of the ACL

Medical Term for Bow-Legged

Genu Varum

Genu Varum

increased compression forces medial knee and distraction lateral knee

Medical term for Knock-Kneed

Genu Valgum

Genu Valgum

Increased compression forces lateral knee and distraction medial knee

Female Tibiofemoral Alignment

• Wider Pelvis
• Femoral Anteversion
• Genu Valgum
• Increased Flexibility
• Lateral Tibial Torsion
• Narrow Patella Notch

Male Tibiofemoral Alignment

• Narrower Pelvis
• Larger Muscle Mass
• Genu Varum
• Medial Tibial Torsion
• Wider Patellar Notch

Patellofemoral Joint

Loose Packed?

Full extension

Patellofemoral Joint

Closed Packed?

90 degrees flexion

Patellar Motion/Tracking

120-30 flexion?

• Patella is drawn medially into femoral trochlea
• Medial glide and medial tilt of patella

Patellar Motion/Tracking

30-0 flexion?

• Lateral glide and lateral tilt of patella

Patellar Area of Contact

Hint: Picture/Diagram

Restraints to Lateral Glide of Patella

• Medial patellofemoral ligament (60%)
• Lateral Femoral Condyle
• Medial Retinaculum
• Medial VMO

Factors that effect patellar alignment

• Tight lateral structures (TIB, lat. retinaculum)
• Tight gastroc and hamstrings
• Patella alta
• Excessive ankle pronation
• Femoral anteversion (medial femoral torsion)
• VMO insufficiency or VM/VL imbalance
• Increased quad angle (Q-angle)

Insall-Salvati Index

• Optimally 1:1 ratio of length of patellar tendon to length of patella
• Patella alta and baja when correct ratio not present

Patella Alta

Lengthened Patellar Tendon

Patella Baja

Shortened Patellar Tendon

Camel Sign

Patella Alta

May present w/ second hump = infrapetellar fat pad/bursa

Arthrokinematics of closed chain extension

femur rolls anteriorly on tibia then glides posteriorly

Medial rotation of the femur occurs during

Extension OR Flexion?

Extension

*during last 30 degrees movement halts on lateral compartment but continues on longer medial compartment

Screw Home Mechanism

• 5-0 degrees WB knee ext
• rotation is ONLY movement accompanying extension
• tibia externally rotates and femur internally rotates

Arthrokinematics

Closed chain flexion

• Popliteus unlocks joint
• Tibia internally rotates under femur
•  femur rolls post and tibia glides ant
• ACL check any post roll and ant glide of femur

Arthrokinematics

Open Chain Flexion

• Tibia rolls and glides post on femur
• External rotation tibia under femur

Arthrokinematics

Open Chain Extension

• Tibia rolls and glides anteriorly on femur
• Internal rotation of tibia under femur

Is meniscal distortion inevitable?

YES!!

*inner sides of menisci are attached by horns to tibial plateau and move with tibia

BUT

*durin motion, menisci move on tibia with femoral condyles to maintain joint congruence

Result of menisci receiving slip of quad tendon?

Anterior translation of menisci during extension

Medial Meniscus motion during flexion

pulled ~2-5 mm by semimembranosus tendon

Lateral Meniscus motion during flexion

pulled 10-11 mm by popliteus