Knee Flashcards
What is the purpose of the patella at the knee joint
increases mechanical advantages of patellar tendon
What are the articulation s at the knee joint
-tibiofemoral (medial and lateral): they have mensci
-patellofemoral: patella sits in a groove
-tibiofibular joint proximal: below the femur and therefore is somewhat separate
How does the knee function in limb length
has a lot to do with how long the limb is
-elongate the limb= extend it
-shorten the limb = flex it
How does the knee function in mobility of the foot
-by changing the knee, the foot will change trajectory
-some rotation at both the knee and the foot
how does the knee function in stability:
can lock in the closed pack position (extension)
Conversation of momentum
-as we step and the foot leaves the ground the whole limb comes with it
-swing the femur forward and the tibia and fibula will come with
how does the knee function in Transmitting loads
-weight shifts, and ground reaction forces
what are force couples at the knee
-through the thigh muscles and calf muscles that work like a force couple
how does the knee sustain high foces
-two long sticks with a joint in the middle allow it to sustain forces
Tibiofemoral joint (femoral surface)
-two condyles on the femur
-medial side is longer anterior to posterior therefore causing some rotation
-between the condyles is an intecondylar notch that contains the ACL and the PCL
-epicondyles: muscle attachments
Tibiofemoral joint (tibial suface)
concave
-fits with femur and has an intercondylar eminence where the ACL/PCL attach
Patella articular surfaces
medial facet:
- odd facet: comes into play with more flexion
lateral facet:
vertical ridge is in the intercondylar groove
Alignment and weight-bearing: anatomical axis
directed inferiorly and medially
-not a straight line = have a little bit go valgus (gene valgum)
Alignment and weight-bearing: angle between tibia and femur
170-175
-genu valgum
-BOS is closer together it gives more stability when switching weight
Alignment and weight-bearing: mechanical axis
from head of femur to talus
-3º from vertical axis
Abnormal genu valgum
“knock knees”
-has coxa varum
-excessive pronation at the feet
-angle is <165º
Abnormal genu valgum
“knock knees”
-has coxa varum
-excessive pronation at the feet
-angle is <165º
Abnormal genu varum
“bow legged”
-has coxa valgum
-angle is> 180º
What is the normal Q angle for males versus females
Males: 13-15º
Females: 15-18º
-females have more flare, and a higher angle that causes more instability at the knee
-affects the line of pull by the quads
What is the Q angle
the angle between the lines
1. mid patella to tibial tuberosity
2. mid patella to ASIS
What is the extensor retinaculum at the knee and what does it do?
it is a fibrous sheath that provides stability
what is dynamic verse static support
dynamic: muscular
static: bones and ligaments and tendons
What is the role of the menisci
dissipate force from Body weight and ground reaction force
What is the blood supply like for the menisci
the blood supply is on the outside and therefore central tears do not heal well
Describe the medial menisci shape and attachments
~ C- shaped
~ thicker
~ attached to MCL, semimembranousus and tibia
Describe the lateral menisci shape and attachments
~ O shaped due to the rotation of the femur on the tibia
~ more mobile
~ attached to PCL, popliteus, Joint capsule, and coronary ligament, sometimes ACL
Describe the normal forces that the menisci receive in weight bearing
-walking
-ascending stairs
-running
-max isokinetic knee extension
-walking: 2.5-3 x body weight
-ascending stairs: 4 times BW
-running: 5-6 body weight
-max isokinetic knee extension: 9x body weight
- 40%-60% of the force is absorbed by the menisci and ligaments and muscles absorb the rest of the force
Clinical considerations when removing the meniscus versus a meniscus repair
Remove the meniscus:
- changes in Weight bearing
- increase contact pressures by 230%
Repair:
- considerations for healing
What are the osteokinematics of the knee
flexion: 0-140
extension: 0-5-10
what happens with knee movement such as ER/IR in a flexed versus extended position
- in a flexed position you can get one medial and lateral rotation where as in extension you cannot because this is closed pack position
-this rotation occurs as well during movement due to th medial condyle being longer anterior to posterior
ROM for knee
-sitting
-walking
-other activities like squatting, sitting cross legged on the floor ETC
- sitting: 90º of flexion
-Walking:- level surface: 0-70º
- up and down the stairs 0-80º
-other: 115º
Describe the screw home mechanism
-medial is longer anterior to posterior and therefore causes a rotation around the lateral side
-ER of tibia on femur as you come into terminal extension in last 35º
-IR of the femur on the tibia as you come into terminal extension in closed chain
Contributions to screw home mechanism
- shape of medial condyle
- tension in ACL
- Lateral pull of quads
What adds to tibiofemoral joint stability
- capsule
- extension retinaculum
- synovial lining
- ligaments:
- muscles
What does the ACL resist
anterior translation of tibia on femur and controls rotation (always under tension)
What does PCL resist
posterior translation of tibia on femur and controls rotation
(always under tension)
Arthrokinematics of flexion and extension in open chain
flexion: posterior roll and glide and a medial pivot to unlock the knee
Extension: anterior roll and glide
Arthrokinematics of flexion and extension in closed
flexion: posterior roll and anterior glide/lateral rotation
extension: anterior roll and posterior glide/medial rotation
Describe the pressure points on the patella during flexion
20º flexion: towards apex
60º flexion: superior to 20º
90º flexion: towards the base of the patella
135º flexion: towards the odd facets (get tilted due to rotation)
Anterior/posterior stability
ACL/PCL
-synovial membrane wraps around them
-more elastin in ligaments
-interwoven to increase strength against tensile forces
-good vascular supply
Medial/lateral stability
MCL/LCL
rotational stability
Medial: MCL is twisted
Lateral: LCL is twisted
ACL
-resists
-mechanism of injury
Resists:
1. anterior shear/translation
2. extension
3. varus/valgus/axial rotation
Mechanism of injury:
1. hyperextension
2. large valgus force
3. axial rotation with valgus or extension
PCL
-resists
-mechanism of injury
-resists
1. posterior shear/translation
2. flexion
3. hyperextension
4. varus/valgus/axial rotation
-mechanism of injury
1. hyper flexion
2 posterior translation of tibia on fetus
3. hyperextension
4. valgus or varus
MCL
-resists
-mechanism of injury
-resists
1. valgus
2. extension
3. axial rotation
-mechanism of injury
1. valgus force
2. hyperextension
LCL
-resists
-mechanism of injury
-resists
1. varus
2. extension
3. axial rotation
-mechanism of injury
1. varus force
2. hyperextension
Anterior drawer test
pulling the tibia out to see if it is restricted
-anterior shear created by the quads
Posterior drawer test
pushing the tibia to see if it is restricted
-tibia gets posterior shear from the hamstrings
Ratio of length of patellar tendon to patella
1:1
Patella baja
when the tendon is shorter than patella and therefore the patella sits more distal in the leg
Patella alta
the tendon is longer and the knee is more likely to dislocate or sublux
-the patella sits more proximal
Patella tracking patterns (how can it move)
-the patella can tilt, rotate and more side to side
Patella stability in flexion and extension
Full extension: passive and active tension
- muscles, tendons and retinaculum
as flexion increases more stability from boney contact
Patellectomy
the patella increases the moment arm of the quads, need this for terminal extension
-extensor lag can occur without the patella and therefore they will not get into terminal extension (an active lag with full PROM)
- a lot of swelling can also call extensor lag
Where is the resultant force vector for the quads pointed
up and laterally in the same direction the patella moves
Where is the major force on the patella from the quads?
Superior and laterally
Where is the more torque generated during knee extension by the quads?
about 45 degrees of flexion
(due to the two joint muscles if causes the force to shift away from mid range)
Where is the most torque generated during knee flexion by the hamstrings
Maximum torque is generate at 5 degrees of knee flexion
Which muscles produces the most torque at the knee
-the vastus
-hamstrings
-rectus femoris (designs motion not torque production)
-gastrocnemius
-other (popliteus and planteris)
Shearing in the tibiofemoral joint
also increases when the quads are working
Shear/compressive forces as you go into extension during Open chain
- as you go into extension compressive forces decrease
-shearing forces increase as you go into OC terminal extension due to patella pulling anteriorly
Shearing and compressive forces as you go into extension in Closed chain
-flexion closed chain
-as you go into extension there is higher compressive forces and decreased shearing by activating hamstrings - as you go into flexion: patella compressive forces increases and the shear forces increase
How can you reduce shearing and compression to protect the ACL
-OC: in more flexion; Go from 90-30 to reduce the rotation that occurs in terminal rotation
-CC: in more terminal extension; control the tibia by cocontracting with the hamstrings
How can you reduce shearing and compression to protect the Patella
OC/CO: outside of the painful arc (above and below)
How can you reduce shearing and compression to protect the meniscus
OC in mid range limit WB/terminal extension to limit the rotation and watch the activation of the hamstings
Where in the gait cycle are you closetes to full extension and then closest to most flexion?
-extension: mid stance
-flexion: from toe off to mid swing due to bringing it closest to the axis of rotation and use less energy
What are the knee kinematics in the front plane during gait?
-condyles can rock a little bit
-switching sides are the peaks of of the rocking
-motion is minimal
-abduction and adduction
Internal and external rotation of the knee during gait
-internal rotation is associated with the knee flexion
-external rotation is associated with knee extension
What is the unhappy triad?
-mutlidirection instability of rotation instability (ligament injuries)
-usually ACL, MCL, and medial or lateral meniscus
-medial = valgus force and more anterior; tears are normally in the perpherial
-lateral = varus, posterior, compressive or central tears
Osteochondritis Dissecans
-Stage 1 a bulge on medial femoral condyle
-stage 2: separation of the medial condyle
-stage 3: fragment of cartilage and bone separates
(loose body)
-ROM is sometimes limited when it is stuck
Osteoarthritis cause
-reduces hip abductor torque potential
-abnormal forces due to weak hip ER and ABD
Genu valgum vs varus
-genu valgum corresponds to coxa vara, and excessive pronation
- genu varum corresponds to coxa valgum and excessive supination
Genu Recurvatum
-young females are more prone to this
-hyper extended knees cause stretch in the posterior structures
-change in compressive foreces in the anterior
-quads are weak and therefore the screwhome mechanism makes it more stable
