Lecture 8 - Biomechanics of the Knee (part 1) Flashcards
What are the 2 joints of the knee?
tibiofemoral and patellofemoral
What 3 bones comprises the knee?
- femur (distal) (medial + lateral condyle)
- tibia (proximal)
- patella
Which condyles of the femur articular with the tibia?
the medial and lateral condyles
Which condyle is bigger?
the medial condyle
What surface articulates with the patella?
the patellar surface
What surface prevents lateral patella dislocation?
the patellar surface
What kind of slope does the tibial plateau have?
posterior
What kind of area does the medial tibial plateau have?
large
What kind of shape is the medial tibial plateau?
concave but relatively flat
What kind of shape is the lateral tibial plateau?
concave in medial-lateral direction, flatter than medial plateau
Which bone is the largest sesamoid?
the patella
What are the 3 functions of the patella?
- Protects quadriceps from excessive friction
during knee flexion - Increases angle of application of quadriceps
- Increases moment arm of the quadriceps tendon
What would happen if the patella was removed?
can reduce the quadriceps moment arm by 33-70% with the knee extended and the moment generated by the muscle may be reduced up to 40%
Which 3 bones demonstrate trabecular bone organization?
distal femur, proximal tibia, and patella
Which cartilage is the thickest in the body?
articular cartilage
The articular cartilage helps improve congruity between which 2 joints’ articulating surfaces?
the patellofemoral and tibiofemoral joints
What does the articular cartilage increase?
area of contact
What are the 4 noncontractile supporting structures?
- Articularcapsule
- Collateralligaments
- Cruciateligaments
- Accessoryligaments
What are the 4 articular structures of the knee?
- trabecular bone
- articular cartilage
- menisci
- noncontractile supporting structures
What shape of the fibrocartilage discs?
wedged
Where are fibrocartilage discs located?
between the femur and tibia
What blood supply is found in the fibrocartilage disks?
peripheral blood supply
What are the 3 functions of the menisci?
- Enhancejointlubrication
- Protect underlying articular cartilage
- Increase contact area between tibia and femur (~doubles the surface contact area) and thus decreases stress
What are the 2 collateral ligaments?
medial and lateral
What does the MCL stabilize against?
valgus directed
(abductor) force
Which collateral ligament is most commonly injured?
MCL
What does the LCL stabilize against?
varus directed (adductor) force
What are the 2 cruciate ligaments?
anterior and posterior
What does the ACL resist?
anterior glide of tibia
What does the ACL limit?
extension ROM with menisci
What kind of stabilization does the ACL have?
frontal and transverse plane stabilization
What does the PCL resist?
posterior glide of tibia, rotation, varus and valgus
What stabilization does the PCL have?
frontal and transverse plane stabilization
What rotation does the PCL limit?
lateral tibial rotation with LCL
What are the 2 flexors of the knee?
hamstrings and popliteus
What are the 3 medial rotators of the knee?
sartorius, gracilis, pes anserinus
What are the 4 extensors of the knee?
rectus femoris, vestus intermedius/lateralis/medialis
What is the lateral rotator of the knee?
tensor fasciae latae
What is the alignment of the knee joint affected by?
- Foot, ankle, and hip alignment
- Muscle imbalances
- Abnormal loads on joint
What are the 2 frontal plane alignments of the knee joint?
varus and valgrus
What is the saggital plane alignment of the knee joint?
180 degrees
What is the transverse plane alignment of the knee joint?
0 degrees
What is varus sometimes referred to?
bow leg
Where is the line found in varus cases?
between proximal and distal joints passes medial to the center of the knee
Where does varus increase force across?
the medial tibiofemoral compartment
Where is the line found in valgus cases?
between proximal and distal joints and passes lateral to the center of the knee
Where does valgus increase fore across?
lateral tibiofemoral compartment
What is valgus sometimes referred to?
knock-knee
Where is the mechanical axis found?
femoral head to ankle
Where is the anatomical axis found?
femoral head to knee
What are the 2 axes of the lower limb?
mechanical and anatomical axis
What knee alignment can newborns/young children exhibit?
genu varum
What is genu varum?
varus alignment that goes away by 3-4 years of age
What is genu recurvatum?
knee hyperextension
What does genu recurvatum result from?
muscle imbalances at the ankle or knee
What does genu recurvatum apply increased stress to?
ACL and posterior knee structures
Which two structures are aligned so tranverse axes of proximal tibia and distal femur are parallel in knee extension?
tibial plateaus and femoral condyles
What is knee OA equal to?
5 degrees tibial version
How many lines make up the Q-angle?
2
Where is line 1 of the Q-angle?
ASIS to patella center
Where is line 2 of the Q-angle?
tibial tubercle to patella center
Increased Q angle is considered a risk factor for…
- Patellofemoral pain (PFP)
- Patellar subluxation and dislocation
- Knee OA
- Overuse injuries, etc.
What increases with the Q angle?
the lateral pull of quadriceps on patella
What is the stability of the lateral pull of quadriceps on patella enhanced by?
- lateral femoral condyle
- medial extensor retinaculum
- vastus medialis
How many degrees of freedom does the knee have?
6
What plane is the normal ROM of the knee?
saggital
What does ROM change with?
age
What is uncommon with ROM?
hyperextension ROM
What are the 2 kinetic chains?
closed and open
What does movement of one joint cause in a closed chain?
causes the other joints in the chain to move in a predictable manner
What is an example of a closed chain?
rising from a chair or doing a push up
What does movement of one joint cause in an open chain?
it is independent of other joints in the chain
What is an example of an open chain?
swing phase of gait or bicep curls
In a closed chain, the segment furthest from the body is ___.
fixed/stationary
In an open chain, the segment furthest from the body is ___ and ___ fixed to an object.
free, not
What does moment arm of the trunk weight increase with?
increasing knee flexion
What makes pure rolling motion of the tibiofemoral joint possible?
the more articular surface on the femoral side of the knee joint
What is pure rolling?
every point of contact on one surface has a unique point of contact on other surface
What does the relative motion between the tibia and femur depend on?
which parts are in contact
What two surface shapes directly impact the relative motion of the tibiofemoral joint?
the femoral and tibial articular surface shapes
What surfaces contribute to 3-D movement of the femur and tibia during knee flexion and extension?
tibiofemoral joint surfaces
What does the tibiofemoral motion not adhere strictly to?
the concave-convex rule
When a convex joint surface is moving, roll and glide occurs in the ___ direction; when a concave joint surface is moving, the roll and glide occurs in the ___ direction.
opposite, same
When is the rate of rotation the greatest?
at the end of extension between 30 degrees of flexion and complete extension
During flexion, as the femur rolls into ___, it rotates ___ with respect to the tibia.
flexion, laterally
The femur rotates ___ as it rolls into extension.
medially
Contact between the femur and tibia migrates…
- Posteriorly on the tibia during flexion
- Anteriorly on the tibia during extension
Posterior translation of the femur on the tibia during ___.
flexion
Anterior translation of the femur on the tibia during ___.
extension
What does the patellofemoral motion depend on?
knee position
In extension, the patella is ___.
moveable
Translation of the patella during knee flexion is ___ cm distal glide with knee flexion.
5-7
What action does the patella do during knee flexion?
rotates and tilts laterally until at least 90 degrees of knee flexion
What happens during contact ACL injuries?
- Footplanted
- Femur driven posterior
- Rotation
What happens during non-contact ACL injuries?
- Landing, deceleration, pivoting/cutting
- Knee/hip in extension+valgus
- Quadriceps overload