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