Knee Joint Complex Flashcards
Medial Angle
175-185 degrees normally
1. Greater than 185 is genu valgum, knock knees, high lateral compressive forces; Increases force on lateral
condyle
2. Less than 175 is genu varum, bow legged, high medial compressive force; Increases force on medial
condyle
3. Abnormal tibiofemoral alignment- as measured by this angle alters compressive and tensile forces at the knee. May lead to frontal plane knee laxity b/c of articular cartilage degeneration (OA).
ACL Tear
High injury rate- most commonly torn in knee flexion
with valgus positioning and tibial rotation in either direction
Commonly torn when ACL wraps around PCL with lateral femoral rotation (open chain: medial tibial rotation)
Commonly torn when ACL wraps around the lateral femoral condyle with medial femoral rotation (open chain: lateral tibial rotation)
Also torn in Knee hyperextension (ACL resists this)
Knee Flexion
Primary: Semimembranosis, Semitendonosis, Biceps Femoris
Secondary: Sartorius, Gracialis, Popliteus, Gastrocnemius
Normal Hyperextension at the knee
5-10 degrees
Genu Recurvatum
More than 10 degrees of hyperextension; pathologic hyperextension of the knee especially seen during
gait which of repeated loading can damage the posterior capsular ligaments
Knee Extension
Primary Muscles: Vastus Lateralis Vastus Medialis Vastus Intermedius Rectus Femoris
Lateral Rotation
Biceps Femoris
Medial Rotation
Semimembranosis, Semitendinosus, Sartorius, Gracilis, Popliteus
Pes anserinus
semitendinosus, gracilis, sartorius
Hamstrings
Prevent Anterior Translation of Tibia; Dynamic Restraint
Popliteus, Patella/Quadriceps
Prevents Posterior Translation of Tibia; Dynamic Restraints
MCL
• Runs from medial aspect of femoral condyle to medial aspect of proximal tibia
• Taut in extension and resists hyperextension
• Resists valgus stress (increasingly so with knee flexion)
• Checks lateral rotation of the tibia
• Back up restraint (when ACL is deficient) in preventing anterior
translation of the tibia
LCL
• Strong cord like
• Runs from lateral femoral condyle to head of fibula
• Taut in extension and resists hyperextension
• Resists varus stress
• Resists lateral rotation of the tibia (most prominently at
35 degrees of flexion)
• Resist combined lateral rotation posterior translation of
the tibia
Genu varum
Increases compressive force on medial
condyle; tension on LCL, compression on MCL
Genu Valgum
Increases compressive force on lateral
condyle; tension on MCL, compression on LCL
ACL
Primary restraint for anterior translation of the tibia
Stability functions
1. Prevents anterior translation of the tibia with respect to the femur
2. Prevents hyperextension
3. Secondary stabilizer (alongside MCL) in
resisting valgus loads
4. Plays a role also in resisting valgus
stress
PCL
Primary restraint to posterior
displacement of tibia
Also helps resist varus and
valgus stresses
Oblique Popliteal Ligament
Joint capsule reinforced by tendinous expansion of the semimembranosus muscle
• Runs from posterior to the tibial medial condyle to central part of the posterior aspect of the joint capsule
• Resists valgus stress in full knee extension
Arcuate Ligament
Runs from fibula head to intercondylar area of the tibia and to the lateral
epicondyle of the femur
• Resists Varus stress in full knee extension
Both Oblique Popliteal Ligament and Arcuate Ligament
• Both are taut in extension and prevent hyperextension
Knee Flexion
0-25 degrees of flexion rolling occurs, after that a combination of rolling and
gliding take place (posterior roll and anterior glide).
ACL and posterior wedge-shaped portions of menisci mediates posterior roll and anterior glide
Knee Extension
PCL and anterior portions of mensici mediates anterior roll and posterior glide
Axial Rotation
Accessible ONLY in knee FLEXION (greatest at 90 degrees of
flexion)
• Range of Motion: 60-70 degrees
• Distinct from screw of mechanism as it accessible but not obligatory
• Due to joint laxity and incongruence
• Center of rotation – medial intercondylar tubercle of the tibia
Resisting knee valgus stress (knee abduction
moment)
muscles of the pes anserinus (semitendinosus, gracilis, sartorius) in flexion
Resisting knee varus stress (knee adduction
moment)
- Iliotibia tract
- Biceps tendon
- Popliteus tendon
Medial/Lateral Rotation is maximized at 90 degrees of knee flexion
True
Screw Home Mechanism
• Referred to as the locking of the knee
• Most evident in last 5° of extension
• Caused mainly by asymmetry in medial and
lateral femoral condyles;
OBLIGATORY, OCCURS PASSIVELY/AUTOMATICALLY AS YOU GO INTO KNEE EXTENSION
At about 30° of flexion, the shorter lateral condyle
completes its rolling and gliding.
As extension continues, the longer medial condyle
continues to roll anteriorly and glide posteriorly. This
causes medial rotation of the femur on tibia about the
fixed lateral condyle
Ligaments (especially the cruciate ligaments- ACL) are
tensioned and may contribute to this obligatory
movement
Unlocking the Knee
• To initiate flexion, the medially rotated
femur must laterally rotate (closed
chain
• To initiate flexion, the laterally rotated
tibia must medially rotate (open chain)
• Assisted via activation of the popliteus
muscle
• Unlocking will still occur in passive
flexion
Voluntary- we can actively do it (VOLITIONAL); DOF we can voluntarily control
Lateral Rotation/Medial Rotation of Knee
Achieved when knee is flexed 90 degrees
Knee Joint Movement:
Axial Rotation
• Accessible only in knee flexion (greatest at 90 degrees of
flexion)
• Range of Motion: 60-70 degrees
• Distinct from screw of mechanism as it accessible but not
obligatory
• Due to joint laxity and incongruence
• Center of rotation – medial intercondylar tubercle of the
tibia
Knee Joint Movement:
Axial Rotation
• Accessible only in knee flexion (greatest at 90 degrees of
flexion)
• Range of Motion: 60-70 degrees
• Distinct from screw of mechanism as it accessible but not
obligatory
• Due to joint laxity and incongruence
• Center of rotation – medial intercondylar tubercle of the
tibia
Medial Rotation
Open chain- Anterior gliding of the lateral femoral condyle on the tibia
Dynamic Restraints to Knee Valgus Stress
Muscle of pes anserinus in Knee flexion
Dynamic Restraints to Knee Varus Stress
Iliotibia Tract
Biceps Tendon
Popliteus Tendon
