Lecture 8 - Knee Kinematics Flashcards
What is the capsule of the knee?
- Encloses med/lat TF and PF joints - multiple connective tissue reinforcements:
- Anterior, lateral, posterior and Posterior-lateral
What makes up the anterior capsule of the knee?
Anterior: patella and tendon
What is the connective tissue reinforcement and muscular reinforcement of the anterior knee?
- Connective tissue reinforcement: reinforced by med/lat retinacular fibers.
(These are extensions of ITB/vastus lat & med – connections to femur/tibia/patella /quads/pat tendon/collateral ligs/menisci) - Muscular reinforcement: quads
What are the connective tissue and muscular reinforement of the lateral knee?
- Connective tissue reinforcement: LCL, lat patellar retinacular fibers, ITB
- Muscular reinforcement: biceps femoris, tendon of popliteus, lat head of gastroc
What are the connective tissue reinforcement and muscular reinforcement of the posterior knee?
- Connective tissue reinforcement: oblique popliteal lig, arcuate popliteal lig
- Muscular reinforcement: popliteus, gastrocs, hamstrings (esp SM)
What are the connective tissue reinforcement and muscular reinforcement of the posterior-lateral knee?
- Connective tissue arcuate popliteal lig, LCL, popliteofibular lig
- Muscular reinforcement: tendon of the popliteus
What is a fabella? Where is it?Does everyone have one?
- a sesamoid bone in the posterolateral capsule of the human knee joint.
- The presence of the fabella in humans varies widely and is reported in the literature to range from 20% to 87% [1-7]. - The fabella is located in the posterior aspect of the knee where lines of tensile stress intersect.
What are the 3 parts of the connective tissue reinforcement of the medial knee?
- Anterior 1/3: thin layer of fascia – medial pat retinacular fibers
- Middle 1/3: medial pat retinacular fibers, superficial and deep MCL
- Posterior 1/3: thick – starting near adductor tubercle blending with SM tendinous expansion and posterior capsule and posterior oblique ligament. Pes anserine reinforces this.
What is the muscular reinforcement of the medial knee?
- Muscular reinforcement: SM, SGT – pes anserine
What is the capsule of the knee?
Internal capsule lined with synovial membrane
How many bursa in the knee? Where?
14 bursae at inter-tissue junctions that encounter friction with motion
Some are extensions of synovial membrane, some external to capsule
What are the fat pads of the knee called?
suprapatellar and deep infrapatellar
What is the TF joint made up of?
TF joint: large convex femoral condyles and flat, smaller tibial plateaus
What do the menisci act as for the femoral condyles?
act as gaskets to form seats for the femoral condyles
Where are the menisci anchored to the intercondylar region of the tibia?
@ anterior/posterior horns
What attached the external edge of each meniscus to the tibia and the capsule?
coronary ligaments
- allow pivoting
What connects the coronary ligaments anteriorly?
transverse ligament
What do the secondary attachments of muscles to mensici help stabilize?
- quads (both)
- SM (both)
- popliteus to lateral
What do the medial and lateral meniscus attach to?
- Medial oval shape attaches to MCL and adjacent capsule
- Lateral more circular, only attaches to lateral capsule, popliteus passes between LCL and lateral meniscus
What are the red zone and white zone of the menisci?
– peripheral 1/3 direct from
genicular arteries (off popliteal), this zone is called the “red zone”
- inner 2/3 avascular “white-zone” and
nutrition from synovial fluid.
What is the primary function of the TF joint?
↓ compressive forces (triples joint contact area ↓ pressure on articular cartilage
What is the secondary function of the TF joint?
stabilizing joint during motion,
lubricating articular cartilage,
providing proprioception (Mechanoreceptors
have been identified in the anterior and posterior
horns of the menisci)
Help guide arthrokinematics
What should we know about meniscal tears?
MOST COMMON
- Often associated with forceful, axial rotation of the femoral condyles over a flexed WB knee (can pinch and dislodge the meniscus)
- A dislodged or folded flap (bucket handle) can mechanically block knee motion
- Medial injured twice as frequently – valgus force (large stress on MCL/post-med capsule)
- Risk increases with ligamentous laxity (esp ACL) and malalignment
What mechanism do we lose with a meniscal tear?
Loss of hoop stress capacity with meniscal tear – especially avulsion tear at medial posterior horn
What are the osteokinematics of flx/ext of the knee TF joint?
- 2 degrees of freedom (F/E and rot)
- Knee slightly flexed to have rotation occur
- Frontal plane is passive only 6-7 deg
- Flexion/extension M-L axis in sagittal plane and it moves (IAR – ‘evolute’) within the femoral condyles
- 130-150 and 5-10 hypertext
- Tibial-on-femoral and femoral-on-tibia
What is axial rotation of the knee TF joint?
Axial rotation: Longitudinal axis through tibia (influenced by the sagittal plane motion) little in ext…
Whats the difference in IR / ER at the TF joint?
At 90 deg: 40-45 deg of axial rotation; ER 2:1 exceeds IR
What is rotation of the knee TF joint named for?
Rotation named by position of tibial tuberosity relative to the anterior distal femur
What are the arthrokinematics of tibia-on-femoral ext?
tibia rolls and slides anteriorly on femur; meniscus pulled anteriorly by quads
What are the arthrokinematics of femoral-on-tibial ext?
femoral condyles roll anteriorly and slide posteriorly on tibia
** quads direct the roll and stabilizes the meniscus vs posterior shear of femur.
What is “screw home” during ext of the TF joint?
Full ext requires 10 deg ER during last 30 deg of ext (…is linked not indep motion); increases joint congruence/stability. OC tibia ER; CC femur IR
What is “screw home” driven by?
Driven by:
1. Shape of the femoral condyle (tibial follows medial condyle and creates ER)
2. Passive tension in ACL
3. Slight lateral pull of quads
What is different about the flexion screw home mechanism?
Flexion is the opposite:
the unlocking IR happens
first – driven by the popliteus
(can rotate the femur or tibia)
What are the arthrokinematics of IR/ER of the TF joint?
- knee must be flexed
- Spin between the menisci and articular surfaces of tibia and femur
- Axial rotation of femur over tibia causes menisci to deform/compress – popliteus and SM help stabilize
What is the shape of the MCL? regions?
flat and broad
Superficial and deep parts
What should we know about the superficial MCL?
well-defined parallel fibers @ 10 cm med epicondyle to med pat retinaculum fibers to med proximal tibia (just posterior to pes anserine)
What should we know about the deep MCL?
slightly posterior and distal: shorter and oblique attaches to capsule/medial meniscus/SM tendon
What is the shape of the LCL? Where does it run?
Short cord-like
Runs vertical lateral epicondyle femur to head of fibula
Does the LCL attach to the meniscus?
- Does not attach to the adjacent meniscus (tendon of popliteus runs between them)
What muscle tendon does the LCL blend with?
- Distally it blends with tendon of biceps femoris
What are the primary functions of the MCL and LCL?
function to limit motion in frontal plane
Knee extended: MCL vs valgus force, LCL vs varus force
What are the secondary functions of the MCL/LCL?
Secondary function – provide general stabilizing tension (esp walking near ext and loading)
Protect against rotation extremes (MCL at extreme of ER)…ex planting R foot and body cut L.
What are the ACL and PCL’s relation to each other?
- Cross within the intercondylar notch Intracapsular, covered by extensive synovial membrane
- Poor blood supply
- Named for attachment on tibia, are thick and strong
What do the ACL and PCL do as a pair?
Together resist extremes of all motions – but primarily A-P shear forces between tibia and femur – in sagittal plane motions, cutting (frontal and horizontal planes)
Helps guide arthrokinematics and provides proprioceptive feedback (has mechanoreceptors!!!)
What/Where is the ACL?
Anterior tibia
Runs posterior, superior and lateral to medial side of lateral condyle
Collagen fibers twist on each other (2 sets – Ant Med and Post Lat)
When are the fibers of the ACL taut?
At any given point some of the fibers are taut in flexion – but increasingly taut as reach ext (esp post-lat bundle - along with post capsule, knee flexor muscles, parts of the collateral ligs)
When is the tibia pulled anterior during extension of the knee? What limits this?
Last 50-60 deg ext – force of quads pulls tibia ant (needed slide) and thus tension in ACL limits the slide. (>est at full ext)
What is the anterior drawer test?
leg in 90 deg – pull prox tibia ant. ACL is 85% of passive resistance to ant glide 8mm or 1/3 inch > contralat LE possible tear (HS spasm may prevent good test)
What are factors in injury of the ACL??
speed and direction of GRF; amount and direction of compressive and shear forces; control and timing of muscular forces; integrity and strength of tissues; alignment of trunk and lower limb
What should we know about injury of the ACL?
- Most frequently ruptured lig in the knee
- Half in ages 15-25 – high velocity sports
- Transient subluxation with secondary trauma (menisci, cartilage, MCL)
- Chronic instability and further degeneration
70% of sports related ACL injuries are …
70% of sports related ACL are non-contact: landing, decelerating, cutting, pivoting over single limb
Why is hyperext also a MOI for the ACL?
Hyperextension also a mechanism of injury- Reduced ER and abd strength might lead to this…..
What is the PCL?
- Slightly thicker than ACL
- Post tibia – lateral medial femur
- 2 primary bundles
- With flexion – twists and changes length and orientation
When is the PCL taut? slack?
- Some fibers taut in F and E – however majority of PCL becomes increasingly taut with greater flexion (90-120 >est)
- Slack in 30/40 into ext
What tibial glide is limited by the PCL?
Posterior glide – tibia (as in HS contraction) partially limited by PCL
What is the posterior drawer test?
- Prox end tibia posterior, knees in 90 deg (95% of resistance) 0-30 provides no resistance
- Limits ant translation femur
(rapid descent into deep squat) - ‘sag’ @ 90/90
What are common MOI for the PCL?
high-energy trauma
Rare – 2-10% of all knee injuries
Falling onto a fully flexed knee, ‘dashboard injury’
What is the PF joint?
Articular side of patella and trochlear groove
Stabilizer is quad
Chronic ant knee pain and degeneration
What glide is important with the PF joint?
Tibial-on-femoral patella slide relative to fixed
trochlear groove (patella pulled in direction of tibia)
Femoral-on-tibial (squat) the trochlear groove slides
relative to fixed patella.
(held by eccentric quads and patellar tendon)
What are the patellofemoral kinematics?
- 135 deg sup pole below groove @ lat and odd facets
- 90 deg
- 90-60 now in trochlear groove – contact area the greatest (still only 1/3 area)
- 20-30 contact at inf pole – has lost much of its mechanical engagement with groove (45% of that at 60 deg)
- Full ext - rests completely prox to groove, on suprapatellar fat pad (if quads relaxed pat moves freely)
