Knee Biomechanics Flashcards
1
Q
What type of joint is the knee?
A
a modified ginglymus joint
2
Q
What bones are all involved in the knee?
A
femur, tibia and patella
3
Q
Is the knee part of the OKC or CKC?
A
it is part of the closed kinetic chain system
4
Q
What are the movements provided by the knee?
A
flexion and extension
5
Q
What are the two separate types of joints in the knee?
A
- Tibiofemoral joint
- Patellofemoral joint
6
Q
Describe the tibiofemoral joint? What does it articulate with and what is between each surface?
A
- proximal tibia articulates with the distal femur
- meniscus is between the two surfaces
7
Q
Describes what articulates with the patellofemoral joint?
A
articulation of the posterior surface of the patella and the trochlear surface of the anterior femur
8
Q
Describe the Q-angle? What is the alignment and the landmarks?
A
- alignment at the patellofemoral joint
- landmarks: line connecting the ASIS to the midpoint of the patella, and a line to the tibial tuberosity
9
Q
What portion of the knee has increased pressure with a smaller Q-angle?
A
medial knee pressure is increased
10
Q
What portion of the knee has increased pressure with a larger Q-angle?
A
Lateral knee pressure is increased
11
Q
What is genu valgum?
A
knocked kneed
12
Q
Where is the increase compression for knee with genu valgum? How much can genu valgum ambulation increase compression forces?
A
- increase compression in lateral compartment of knee (increased chance of OA)
- by 2.5-3.0 multiplied by your body weight
- causes mechanical breakdown of components in lateral compartment
13
Q
What knee angle is excessive for genu valgum?
A
greater than 190 degrees is excessive
14
Q
What angle is normal for genu valgum?
A
5-10 degrees is normal
15
Q
What is genu varum?
A
bow legged
16
Q
What is the knee angle for genu varus?
A
knee angle less than 170 degrees
17
Q
Where is the increase compression for knee with genu varum?
A
increased compression in medial compartment of knee
18
Q
What can “theoretically” predispose genu varum?
A
- coxa vara femoral neck-shaft (angle less than 125 degrees)
- weaken hip muscle, particularly the hip abductors (glute med)
19
Q
What is Genu recuvatum? Describe its position?
A
- extension beyond +10 of neutral
- area of condyles in contact during end range extension is decreased, resulting in increased compressive forces secondary to smaller area
20
Q
What are the functions of the proximal tibiofibular joint?
A
- dissipation of torsional stresses applied at the ankle
- dissipation of lateral tibial bending movements
- tensile weight bearing
21
Q
Where does movement occur for the proximal tibiofibular joint?
A
at the ankle
22
Q
What type of joint is the tibiofemoral joint?
A
double condyloid synovial joint
23
Q
How many degrees of freedom does the tibiofemoral joint have?
A
3 degrees of freedom
- flex/extend
- IR/ER
- Abd/Add
24
Q
Extension-Tibia on femur: open chain
A
anterior roll anterior glide
25
Flexion-Tibia on femur: open chain
posterior roll posterior glide
26
Extension-femur on tibia: closed chain
anterior roll posterior glide
27
Flexion-femur on tibia: closed chain
posterior roll anterior glide
28
When does the screw-home mechanism occur and why does it occur?
- occurs in the final 20-30 degrees of knee extension
| - due to the shape and size of the medial condyle
29
What does the ACL all resist against?
- resists against knee extension
- helps prevent hyperextension (recurvatum)
- excessive tibial anterior slide
- excessive femoral posterior slide
- excessive axial rotation, varus and valgus forces
30
Where does the ACL attach?
to the anterior tibia and runs in a posterior, lateral and proximal direction attaching to the lateral femoral condyle
31
Describe the chain of events for extension (the screw-home) when foot is planted with knee flexed?
- The ACL becomes tight
- ACL tightness restricts movement of the lateral femoral condyle
- the medial condyle is not restricted so it keeps moving
- causes tibial ER, femoral IR
- this locks the knee at full extension
32
What does the popliteus do during flexion of the knee?
unlocks the knee and causes the tibia to medially rotate
33
What is the closed packed position for tibiofemoral joint?
full extension with ER
34
What is open packed position for tibiofemoral joint?
25-30 degrees of knee flexion
35
What is the capsular pattern for tibiofemoral joint?
flexion > extension
36
What is the importance of the patellofemoral joint?
- increases angle of insertion for the quads
| - increases the torque producing capability for the quads
37
Arthrokinematics for patella moving on femur
patella slides along fixed intercondylar groove
38
Arthrokinematics for femur moving on patella
intercondylar groove slides along fixed patella
39
What are the gliding motions of the patellofemoral joint?
- flexion/extension (superior and inferior glides)
- medial and lateral glides
- medial and lateral tilts
- medial and lateral rotation
- anterior and posterior tilts
40
What is patella alta?
high-riding patella
41
What is patella baja?
low-riding patella
42
What kind of joint is the poximal tibiofibular joint? and describe the shapes of articulations
- plane synovial joint
| - fibula is slightly convex, tibia is slightly concave
43
How many degrees of freedom does the proximal tibiofibular joint have?
- 3 DOF (gliding motions)
- anterior/posterior
- superior/inferior
- rotation
44
What is the closed packed position for the proximal tibiofibular joint?
full ankle dorsiflexion
45
What is the open packed position for the proximal tibiofibular joint?
0 degrees plantar flexion
46
What is the capsular pattern for the proximal tibiofibular joint?
pain with biceps femoris muscle contraction
47
What causes lateral patellar tracking?
- ITB
- bowstringing
- lateral patellar retinacular fibers
48
What causes medial patellar tracking?
- VMO
- raised lateral facet
- medial patellar retinacular fibers
49
What can a valgus external force cause on the knee to patella and knee itself?
- causes ER of the femur and IR of tibia
- increases tension at QT and PT and increases bowstringing force
- it results in increased lateral displacement of patella
50
What are the 3 bands of the ACL?
anteromedial, intermedial, and posterolateral
51
In knee extension, which bands are tight/slack for ACL?
- anteromedial band is slack
| - posterolateral band is tight
52
In knee flexion, which bands are tight/slack for ACL?
- anteromedial band is tight
| - posterolateral band is slack
53
How do you injure the ACL? besides cutting it off with a saw
- large valgus force with foot planted
- large axial rotation force applied with foot planted
- combination of previous 2
- severe hyperextension
54
Where does the PCL attach?
posterior tibia and runs in a proximal, medial and anterior direction attaching to the medial femoral condyle
55
What does the PCL resist against? When is it most effective (flex/extend)?
- excessive tibial posterior slide
- excessive femoral anterior slide
- excessive femoral axial rotation, varus and valgus forces
- most effective in flexion
56
How do you injure the PCL?
- falling on fully flexed knee with proximal tibia striking first
- force posterior translation of tibia
- worse with increasing flexion
- rotation, varus, and/or valgus force applied with foot planted
- severe hyperextension with gapping to posterior side
57
Where does the superficial MCL attach?
-proximally to the medial femoral epicondyle and distally at the shaft of the tibia and tibial condyle
58
Where does the deep portion MCL attach?
attachment to the medial meniscus and blends with the knee joint capsule
59
What is the function of the MCL?
- resist valgus force
- resist knee extension
- reinforce medial capsule
- prevent ER of the leg with the knee extended
60
How do you injure the MCL
- valgus producing force with foot planted
| - severe hyperextension
61
Where does the LCL attach?
runs from the lateral epicondyle of the femur to the head of the fibula
-DOES NOT attach to the meniscus
62
What is the function of the LCL?
- resist varus force
- resist knee extension
- prevent ER of the leg with knee extended
- reinforce lateral capsule
- reinforce posterior-lateral capsule
63
How do you injure the LCL?
- varus producing force with foot planted
| - severe hyperextension
64
What all reinforces the joint capsule anteriorly ?
- muscle-tendinous: quads
| - connective tissue: patellar tendon and patellar retinacular fibers
65
What does the joint capsule encompass?
both compartments of the tibiofemoral joint and the patellofemoral joint
66
What all reinforces the joint capsule laterally ?
- Connective tissue: LCL, lateral retinaculum, IT band
| - muscular tendinous: biceps femoris, popliteus, gastrocnemius
67
What all reinforces the joint capsule posteriorly?
- connective tissue: oblique popliteal ligament and arcuate complex
- muscular-teninous: gastrocnemius and hamstring group
68
What all reinforces the joint capsule posterior-laterally ?
Connective tissue: arcuate complex and LCL
| muscular-tendinous: popliteus
69
What all reinforces the joint capsule medially?
- connective tissue: retinaculum, MCL, posterior-medial capsule, and posterior oblique ligament
- muscular-teninous: pes anserine
70
What are the functions of the meniscus?
- deepen the surface of the tibia
- makes a concavity atop the tibial plateau
- shock absorbers
71
What is the meniscus and where are the located?
- fibrocartilaginous discs
| - located directly between the femoral condyles and the tibial plateau
72
Describe the medial meniscus?
- larger and more C-shaped
| - has anterior and posterior horns
73
What attaches to the medial meniscus?
- MCL and medial capsule
| - posteriorly attaches to the semimembranosus
74
Is the medial or lateral meniscus injured more frequently and why?
-medial injured more frequently because of firm attachment of the tibia and decrease mobility
75
Describe the lateral meniscus and its function?
- more circular shaped
- loosely attached to the tibia
- absorbs more of the stress
76
Is the medial or lateral meniscus more mobile?
lateral and less susceptible to injury
77
What does the lateral meniscus attach to?
posteriorly attaches to the popliteus
78
What happens to the menisci during knee extension?
-move anteriorly with the tibia
79
What happens to the menisci during knee flexion?
-move posterior with the tibia
80
How do you injure the meniscus?
- axial rotation, values force most common MOI
| - injury can be correlated with early onset OA
81
What percent of ACL tears are associated with meniscal injury?
50%
82
What is the function of bursae?
reduces friction between moving structures
83
Where is the infra patellar fat pad and what is its function?
- between the patellar tendon and the tibia (very sensitive)
| - helps reduce friction in the knee
84
What is active insufficiency?
- extreme shortened muscle results in decreased motor recruitment
- must shorten over both joint
85
What is passive insufficiency?
-tightened/lengthened muscles causes decreased muscle contraction
86
Describe the length tension relationship?
-muscles at full contraction or extension lose contractile capabilities
