EEI 10/14b Knee Biomechanics I Flashcards
what are the two unique joints of the knee?
- Tibiofemoral joint
2. Patellofemoral joint
what is the importance of the tibiofemoral joint?
the knee is often the symptom, but it isn’t always the issue
- Largest synovial joint
- connects the two longest lever arms in the body
- major support in both static and dynamic situations
- major weight bearing joint
why is the knee joint commonly injured?
- there is a lot of sagittal plane motion, but less in transverse and frontal
- getting too much rotation with the two longest lever arms
- hip, ankle and foot have lots of motion in frontal and transverse planes and the knee is directly related to those joints
what are the two major articulations of the knee?
- medial femoral condyle-medial tibial plateau
2. lateral femoral condyle-lateral tibial plateau
anatomy of the femur
- 2 femoral condyles
- medial
- lateral - intercondylar fossa/notch
- troclear groove
what are the important aspects of the femoral condyles?
- slight convexity in frontal plane
- lots of convexity in the sagittal plane
- medial projects more distally than lateral (2/3”)
what does the intercondylar fossa/notch of the femur attach to?
cruciate ligaments attach to the intercondylar fossa/notch
what does the trochlear groove of the femur do during early flexion?
engages patella during early flexion
Tibia important aspects
- Tibial Condyles
2. Intercondylar tubercules
how do the condyles of the tibia look in different planes?
- frontal - slightly concave
- sagittal:
- medial>slightly concave
- lateral>slightly convex - A/P: medial is larger than lateral
what are key features about the intercondylar tubercules?
- 2 bony spines
2. ligament attachments
how can you tell the difference between right and left menisci?
look for the C shaped medial meniscus from the transverse/top
function of the meniscus?
- enhance TF congruency
- distribution of forces (primary compressive loads)
- friction/shear reduction
- provide joint stability
- assist in lubrication of the joint
how does the meniscus distribute forces?
- increases contact area
- absorb 40-60% of normal load (shock absorber)
- implication of losing meniscus = OA
how does the meniscus provide secondary stability?
- restraint
- A/P
- Combined valgus and rotation
- use lachman’s and pivot shift as tests to check meniscus function
what are the implications of increased stress of meniscus?
- If the contact area decreases with a mensicectomy, then the stress on the articular cartilage increases tremendously
- Long-term consequences of this are OA after 20 years
what kind of attachments do the MCL have to medial meniscus
dense tissue, less mobile
what kind of attachments do the LCL have to Lateral meniscus
more flexible
why do people think that the medial mensicus has a higher risk for injury?
medial is more restricted due to greater ligamentous/capsular restraints
how do the menisci deform and slide with tibiofemoral movement in WB and NWB?
- Knee extension: deform & slide anteriorly
- Knee flexion: deform & slide posteriorly
- *WB: both move and deform, lateral moves more (in general, more deformation in WB)
- *NWB: both move and deform, again lateral moves more (less deformation in NWB)
during knee flexion what kind of compression of the menisci?
- not pure compression
- get active contraction of semimembranosis (medial) and popliteus (lateral) that assists with posterior glide
how are meniscal tears caused?***
- twisting/pivoting on loaded limb
- more common with medial
- local synovitis
- bucket handle tears (acute), part of meniscus flips up and the knee is locked > springy end feel, won’t be able to gain any range of motion
how do menisci get nutrition?
- blood supply by age:
1. infancy: 100% meniscus
2. WB to age 50: diminishes to outer periphery 25-33%
3. age 50: only the periphery - capillaries are only on the periphery
- aided cyclic loading
what is the problem with immobilization and the meniscus?
since it is aided by cyclic loading, NWB is problematic because meniscus can’t get nutrients
what is the impact of not getting repair/removal surgery of the meniscus for chronic mensical tears where motion is not limited
with patients who have non-locking symptoms, having surgery has no difference between doing rehab or just getting a scope input into the knee
what are the main functions of articular cartilage
- Decreases friction (6x more slippery than ice)
- Withstands compression (shock absorber)
- Resists wear
what are different kinds of injuries of articular cartilage
- acute traumatic lesion to femur
- conservative approach: microfractures
- another approach: host procedures, issues with WB, difficulties with scaffoling - degenerative lesions
- multiple causes (aging)
- peripheral tissues affected
- OA
normal alignment of the femur and tibia
- slight genu valgus
- approx 170-175 degrees valgus is normal
- males have a greater angle than females, thus females have more genu valgum (knock knee)
what are the angles for excessive genu valgum and genu varum?
- genu valgum <=165 degrees
- genu varum >= 180 degrees
mechanical axis (LBA) of femur and tibia
- from femoral head to knee center
- from knee center to ankle center
- varies with alignment
- Varus, LBA moves medially
what are implications of the LBA moving medially?
- varus causes the movement of the LBA medially
- this causes increased wear on the medial cartilage because of increased compression
varus moment in bilateral stance
ADDUCTION moment
valgus moment in bilateral stance
ABDUCTION moment
what are implications of LBA moving laterally?
- genu valgum affects knee in addition to ankle and hip
- posterior tibialis has excessive pronation
- hip goes into adduction, there could be weakness that contributes to the issue
during single limb stance, what compartment bears the most weight?
- the medial compartment bears the greatest weight = 2.25 x BW
- lateral compartment 0.91 x BW
- in frontal plane, getting external adduction (varus moment) so we see a lot of the motion going medially
- there is a greater moment/torque for a person who is naturally in genu varus because the moment arm is longer and he/she automatically goes into varus torque during single leg stand in walking
how does one reduce adduction moments?
- Surgical (amount of reduction depends on level of anatomic realignment)
- Osteotomy (High tibial OR Distal femoral): opening a bone and creating a wedge to correct alignment, good for isolated medial compartment OA
- TKA and correction of alignment - Conservative standpoint with PT
- Lateral wedging (5-12% reduction of ADD moment)
- Valgus bracing (8-12% reduction of ADD moment)
- Gait modification (5-40% reduction of ADD moment) - Additional things:
strengthening quads and stretching
what does knee OA result from?
- mechanical and biological events that disrupt the coupling between synthesis and degradation of:
- Articular cartilage chondrocytes
- Subchondral bone
- Risk Factors:
Genetic
Developmental
Traumatic
Intrinsic
what are the changes in cartilage, subchondral bone, and osteophytes with knee OA?
Cartilage: fibrillation, ulceration and loss less space
Subchondral bone loss
Osteophytes increase
what is the change in gait pattern with knee OA?
- stiffened gait pattern
- knee stiffened in mid stance
- lasts even up to 2-5 years even after ACL surgery
major classifications of osteokinematics
- Flexion/extension
- Internal/external rotation
- Abduction/adduction (valgus/varus)
- medial/lateral
- superior/inferior
- anterior/posterior
creating a relationship between adduction and abduction
adduction (varus) /abduction (valgus)
-relationship of the distal segment relative to the midline of the proximal segment
femur internally rotating, yields what tibial rotation?
tibia rotates externally
during flexion/extension what motion do we get of the knee?
- roll and slide/glide
- horizontal line through the femoral epicondyles
what are the primary reasons why we get roll and glide of tibia and femur?
cruciate ligaments
arthokinematics of the knee
Weight Bearing
1. flexion: posterior roll, anterior glide
2. extension: anterior roll, posterior glide
Non-Weight Bearing
1. flexion: roll and glide posterior
2. extension: roll and glide anterior
range of motion is depicted as:
hyperextension - neutral - flexion
ROM of knee during different activities
Flexion/Extension
Passive ROM: 20-0-160°
Gait: 0-70°
Stairs/sitting: 0-90°+
**Position of the hip impacts the ROM because of the rectus femoris of quad and the hamstrings
adduction/abduction ROM
- Axes of motion
Adduction: medial femoral condyle
Abduction: lateral femoral condyle - In full extension, 8° total available ROM
In 20° flexion, 13° total (increases because full extension is closed pack and 20degrees is open pack so there is some joint play)
why is there small available ROM in extension vs at 90degrees?
full extension is closed pack so there is less motion and 20degrees is open pack so there is some joint play
***screw home mechanism yields
- Tibia externally rotates during last 20 of extension (open chain)
- Femur internally rotates on the tibia during the last 20 degrees of extension
- *****Main reasons for screw home mechanism
- Bony meniscus (a/p length of medial condyle is longer than that of the lateral)
- Ligament restrictions (ACL/PCL)
- Slight lateral pull (of ligaments on quad)
significance of unlocking the knee
-internally rotate the tibia on the femur during early flexion (NWB)
Caused by popliteus muscle
significance of closed pack position and the knee
Full extension creates maximal:
- Bony congruency - tibial tubercles lodged in intercondylar notch
- Ligamentous tautness
significance of loose pack position and the knee
25° of knee flexion
- Minimal bony congruence
- Ligaments lax
- Minimal intra-articular pressure
- Relevance to injury: safer to land in a more open pack position where ligaments aren’t as taught
tibiofemoral joint stability
- Joint Capsule
Retinacula - really dense, during TKA yields a lot of loss of ROM
Synovial Lining
2. 4 Main Knee Joint Ligaments Anterior Cruciate Posterior Cruciate Medial Collateral Lateral Collateral
define the cruciate ligaments
- intra-articular, but extra-synovial (within joint, but have a lining between ligament and fluid)
- poor blood supply
- named according to tibial attachment
ACL/PCL travels:
ACL: anterior aspect of the tibia, posteriorly and laterally
PCL: posterior aspect of the tibia, travels anteriorly and medially
how many bands does the ACL have?
2 bundles
sometimes do double bundle reconstruction to increase stability and get more rotational motion
ACL Primary job
- Primary restraint to anterior translation of the tibia on the femur
- Accepts 75-86% of load with anterior directed force on tibia - Primary restraint to hyperextension
ACL secondary restraints**
- Assists with resistance to INTERNAL ROTATION of the tibia on the femur
- Assists with resisting varus and valgus forces
KT-1000
allows to measure translation of tibia on femur
completed at 30 degrees
normal translation is about 5-8mm
stress/strain of acl
normal: strain = 2-4%
tear: strain = 6-8%
can you do open chain exercises post ACL reconstruction?
yes
the more extension, the more anterior translation, the more strain, so people worry that it would be too much strain
BUT, it is actually know that the strain won’t have negative implications. Gradually increase degree of knee extension
ACL strain during different close chain vs open chain activities
- in close chain, with a 30lb weight and squat, the hamstrings have a big impact and strain is reduced on the ACL
- in open chain, with a 10lb weight the strain is around the same, this is because the exercise is isolated to the quad
prevelance of ACL injuries
- 20% of all knee injuries
- 70% are non contact injuries
- there are gender biases towards women:
1. structural
2. biomechanical
3. neuromuscular
why is it more common to see ACL tear in females than males?
- Smaller in length, cross-sectional area, and volume
- Less stiff and fails at lower loads
- Area occupied by collagen fiber is lower
ACL Biomechanical differences in females vs males
-Higher knee valgus angles and moments
-Decreased Hip flexion angles and knee flexion stiffness during cutting
-Greater hip adduction
-Trunk adaptations
-Hip transverse and
frontal plane angles
influence knee valgus
moments
define lower extremity valgus
Combined: Knee ABD, hip ADD/IR, anterior translation of tibia, ankle eversion.
ACL neuromuscular difference in female vs male
-Weaker hip and knee strength (earlier quad activation strength)
-Muscle activation pattern differences in both anticipated and unanticipated maneuvers
(females activate glutes slower than males)
what is the significance of the PCL
- Runs from superior-anterior-medial (femur) to inferior-posterior-lateral (tibia)
- Compared to the ACL:
1. Shorter
2. Less oblique
3. Greater CSA (120-150%) - blends with posterior capsule
do you see PCL or ACL tears more often?
ACL!
PCL is shorter, broader, and has a greater CSA so it is stronger
-provides posterior translation of the tibia
-it’s job lends it to be injured less
what is a main cause of a PCL tear?
- fall and hit your tibial tubercule on the floor, occurs when your ankle is plantar flexed and pushes it posteriorly (when knee hits the ground in a fall)
- –if you land with your foot dorsiflexed, it’s a patellar contusion
how many bands does the PCL have?
2
one is tight in flexion and the other is tight in extension
primary restraints of the PCL
Restricts posterior translation of the tibia on the femur
- In full flexion – taut, absorbs 93% of posteriorly directed loads
- Maximum excursion occurs at 75-90°
- Bands
- Anterolateral: tight in flexion
- Posteromedial: taut in extension - Non-weight bearing flexion: PCL opposes posterior pull of knee flexors
what do you limit after PCL reconstruction?
limit hamstring curls for 3-4 months b/c pull tibia posteriorly and messes with PCL
PCL secondary restraints
- assists with resistance to external rotation of the tibia on the femur
- assists with resistance of varus and valgus forces
MCL Attachments
High and low attachments
above the medial condyle of the femur and below the medial surface of the shaft of the tibia
-800N force to failure
Layers of the MCL
3 layers
- superficial (pes anserinus)
- Middle (superficial MCL)
- Deep (deep MCL)
blends in with superficial fascia all the way to the pes anserinus and attaches to the medial meniscus
MCL on knee extension and flexion
- taut upon full knee extension: helps resist hyperextension
- during extension: superficial vertical fibers relaxed and deep oblique fibers taut
- during flexion: superficial vertical fibers are tight and deep oblique fibers relaxed
MORE INJURY IN EXTENSION where ligament is tighter
difference between MCL and LCL
MCL is broader and not as distinct as LCL
MCL is strong
MCL is attached to medial meniscus that has less mobility, thus it is prone to injury
primary job of MCL
- resist valgus forces -> limits external rotation of the tibia (gapping medially, compressing laterally)
- resist anterior translation of the tibia on the femur
25 degree knee flexion impact on MCL
open pack position
-MCL contributes 78% valgus stress
thus, at open pack position, valgus is more because there are less stability forces keeping the knee congruent
5 degree of knee flexion impact on MCL
closed pack position
-MCL contributes to 57% of valgus stress
thus, at close pack position, valgus is less because there are other stability forces keeping the knee congruent
LCL attachments
attaches from the anterior styloid of the fibula to the posterior femoral condyle
tolerates 392 N of force to failure (half the force of MCL)
really cordlike
why is LCL injury less common than MCL?
LCL requires varus force mechanism for tear and varus forces are less common to generate than valgus forces
MCL injury caused by valgus stress
LCL injury caused by varus stress
primary job of the LCL
resist varus forces and resist hyper-extension
IT band function
- anterolateral support to the knee
1. in knee extension: IT band is anterior to knee axis
2. in knee flexion: IT band is posterior to knee axis
IT band attachments
TFL all the way to insert in gerdy’s turbercule and to the patella via the lateral patellafemoral ligament
Posterior capsule function
Resists hyper-extension
PCL blends with it
with a lot of hyperextension, what is the issue?
posterior capsule laxity (>5 degrees) - genu recurvatum
-injuries are not common
Posterolateral corner function**
resists varus stress, external rotation, and posterior translation
a lot of variability
how do you test the posterolateral corner function?
dial test
30 degrees degrees knee flexion and maximal external rotation
if one leg goes a lot further than 30 degrees there is an issue with the posterolateral corner because there is laxity
posterolateral corner major stabilizers
- LCL (FCL)
- Popliteo-fibular ligament
- Popliteus muscle and tendon
- tendon unlocks the knee
- structural stability
5 major components of the posteromedial corner?
a lot of different structures on the inside of the knee that helps check motion other than the MCL
- posterior horn of the medial meniscus
- posterior oblique ligament
- semimembranosus
- posteromedial joint capsule
- oblique popliteal ligament
overall, what’s the main significance of the posterolateral and posteromedial corners of the knee?
in addition to stability in varus and valgus, they provide a lot of rotary stability
Muscles of the TF joint
- generally considered flexors and extensors
- ALL have moment arms capable of generating frontal and transverse plane moments
Knee flexors
- hamstrings (semimembranosus - attaches to medial meniscus, semitendinosus - part of the pes anserinus, biceps femoris). cross the hip joint and extend it and flex the knee joint
- gastroc
- popliteus
- gracilis
- plantaris (often absent)
pes anserine
say grace before tea
sartorius most anteriorly
gracilis
semitendinosis last one
all attach medially on the tibia as one converged tendon
quad weakness
loss of eccentric control during gait
- less knee flexion during weight acceptance
- less force attenuation - greater TF compressive forces
- linked to early onset of OA and second ACL injury
compensations for quad weakness
at the hip and the ankle
