Knee Biomechanics Flashcards
femoral medial condyle & its effects
larger & slightly more inferior
- can effect standing posture & loading at the knee
sulcus angle
measured by the highest peaks of the medial and lateral femoral condyle to the deepest part of the trochlear groove
congruency angle
reflects patella position in the trochlear groove and the midpoint of the sulcus angle compared to the lowest portion of the patellar ridge
what does congruency angle inform you of?
if patella is prone to dislocation
distal femoral condyles
A/P convexity
M/L asymmetry
Tibia medial plateau plane
convex in all planes
Tibia lateral plateu planes
frontal - flat to slightly concave
sagittal - flat to slightly convex
fibula
primary association with ankle complex
-attachment site for LCL and bicep femoris
proximal tibial plateau
- two shallow and concave surfaces
- medial section is deeper and has thicker cartilage
anterior capsule (supporting structures of knee)
- quadriceps
- patellar retinacular fibers
lateral capsule (supporting structures of the knee)
- lateral collateral ligament
- lateral patellar retinacular fibers
- iliotibial tract
medial capsule (supporting structures of the knee)
- medial collateral ligament
- medial patellar retinacular fibers
- semimembranosus
- pes anserinus
posterior capsule (supporting structures of the knee)
- oblique popliteal ligamanent
- arcuate ligament
- popliteus
- hamstring muscles
- gastroc
posterolateral capsule (supporting structures of the knee)
- arcuate ligament
- lateral collateral ligament
- popliteus muscle
Patella
generates force to move knee into extension
improve efficiency of movement through flexion
- embedded w/in quadriceps tendon bridging quadricep vis quadricep tendon to the tibial tuberosity via patella tendon
menisci function
- deepen joint to increase contact area & increase stability
- acts as shock absorber & reduce friction
(fill in gap that would otherwise be present during movement)
meniscal ligaments
- meniscotibial ligaments connect tibia and adjacent capsule to meniscus (loose & can pivot during movement(
- transverse ligament connects menisci anteriorly
medial meniscus attachments
firmly attached to joint capsule
- anchored to MCL
- most commonly injured
- allows for slight rotary motion
lateral meniscus attachments
- nearly circular
- smaller and more freely movable than medial meniscus
- covers larger articular surface
load w/o meniscus
w/o menisci, compressive load increases by 3x
Q angle measurements
Line from ASIS to midpoint of patella & line from tibial tubercle
Normal
Male - 5-10 degrees
Femal - 10-15 degrees
Excessive Q angle
Genu Valgus
“knock-kneed gait”
Limited Q angle
Genu Varus
“bow-legged gait”
Normal Knee (tibia)
tibia almost vertical
femur has 5-10 degrees of varus
170-175 lateral angle
Tibial valgus
“knock knees” <165 (lateral)
“bow-legged” >180 (lateral)
If you have increase valgus MCL will….
have more load because we are already in valgus / load lateral aspect of tibia more
what might you expect with significant genu valgus?
more medial compressive stress
lateral tensile stress
What does the “ascending” 1/3 of the lateral tibial plateau represent?
a location for fat pad impingement during knee joint hyperextension
(fat pads reduce friction)
Tibiofemoral joint Flexion & Extension (sagittal plane)
ROM
-5-10 degrees of hyperextension to 130-140 degree of flexion
Tibiofemoral joint Medial & Lateral Rotation (transverse plane)
40-50 degree of rotation (knee at 90 degree flexion)
2:1 ER to IR - full extension
screw home mechanism
10 degrees external rotation (transverse plane) that occurs in full extension; twisting motion of the knee occurs during last 30 degree of extension (sagittal plane)
screw home mechanism occurs due to
- shape of medial femoral condyle
- passive tension of the anterior cruciate ligament
- lateral pull of quadriceps
Patellofemoral joint (transverse plane view - inferior perspective)
- 90 - 135
- 60-90
- 20-60
where the patella sits & follows a lateral facing “open C” track
Medial Collateral Ligament
- resist tibial valgus
- carries valgus stress when knee is flexed
- connected to medial meniscus
Anterior Band of MCL
taut with flexion
Posterior Band of MCL
taut with extension
Lateral Collateral Ligament
- no connections to capsule
- resist adduction and tibial varus
- limits lateral rotation of tibia
ACL (anteromedial and posterolateral band)
anteromedial - 0-20 degrees primary resistance
posterolateral - 20-90 de resistance
function of ACL
prevent forward displacement
- carries 87% of load when anterior translational force is applied
- taut in extension & relaxed in flexion
PCL (anterolateral and posteromedial band)
anterolateral - 50-75% force between 40-120 degree of flexion
posteromedial band- 57% force beyond 120 degree of flexion
-taut during flexion
function of PCL
- prevents forward displacement of femur on tibia
- carries 94% of load in extended knee when posteriorly-directed force applied to tibia
-taut during flexion
Knee ROM depends on
- hip positions due to biarticular muscles
- interaction b/w calf and back of thigh limits flexion
- joint mobility
- pain
open-packed position
25 degree of flexion
close-packed position
full extension + ER
Extension Arthrokinematics
“Fixed” Femur
convex - femur
concave - tibia
concave on convex - roll and slide in same direction
OPEN
Extension Arthrokinematics
“Fixed” Shank
convex - femur
concave - tibia
convex on concave - roll & slide in opposite directions
CLOSED
What happens during flexion (squat)
- with rotation, femoral condyles roll of plateu ass they roll backward
- prevent by sliding forward (ACL taut)
the flexed position increases compressive stress due to
smaller contact area
meniscectomy
taking tissue out (inner - less of healing compacity)
meniscal repair
suturing tissue together (more vascularized -will heel)
OATS (osteochondral autograft transfer system)
shave sites from non-weight bearing –> goes to lab and grow tissue and then put it back in
Anterior Knee Joint muscles (torque)
quadricep
- vastus lateralis
- vastus medialis
- vastus intermedius
- rectus femoris
80% Torque = vastus
20% Torque = RF
Posterior Knee Joint Muscles
- Semimembranosus (medial)
- Semitendinosus
- Sartorius
- Popliteus (lateral)
- Bicep femoris
additional function of bicep femoris
retract posterior horn of meniscus during knee flexion
Lateral Knee joint muscles
bicep femoris
iliotibial band
Load Progression (hardest to easiest)
- single leg + external load
- single leg squat
- 2 down, one up
- single leg assisted
- staggered squat
- body weight squat
External torque =
body or leg weight X EMA
Terminal knee extension
increased EMA x weight of shank = gradually increasing external torque
(more force)
Squat
increased EMA x body weight = gradually decreasing external torque
(less force)
PFJ compressive forces
- deeper squat = requires greater force from the quadricep ( greater external torque on knee)
- decreased angle of QT & PL produces greater joint force between patella and femur
