Knee Flashcards
Distal Femur Osteology
Lateral/medial condyles; intercondylar notch/groove
Tibial Articulation
Lateral/medial plateaus/condyles; intercondylar region
Medial is larger!
Fibula= no direct function at knee! Functions more as lateral stabilizer and attachment site for ACL
Patella Osteology
Sesamoid bone, base superiorly, apex inferiorly, anterior surface convex in all directions, posterior articular surface covered with cartilage
Anterior surface is convex in all directions
Posterior surface has concavities and convexities
Functions of Patella
Primary: increase angle of application (MA of quads)
Secondary: protect quads tendon from excessive friction
Normal Alignment of the Knee
Shaft of the femur is slightly medial (slight genu valgum)
Angle of less than 170 degrees is excessive “knock kneed”
Angle of greater than 180 degrees is excessive “bow leg”
Joint Capsule
Large, complexly attached and lax with serval recesses
Reinforced posteriorly by muscles and popliteal ligaments, M/L by collateral ligaments
VM and VL, MPFL, retinacula anteriorly
Synovial Lining of the knee
Most extensive and involved in the body
Bursa and fat pads
The fat pads are associated with the bursae and they reduce friction
Capsule most relaxed in slight flexion 20-25 degrees
Menisci
Crescent shaped, fibrocartilaginous
Medial= semicircular
Lateral= circular
Thick peripherally and thin centrally
Blood supply is greatest in the periphery (red-red, red-white, and white-white zones)
Anterior and posterior horns anchor at the end
Secondary attachments are quads, semimembranosus, popliteus (lateral)
Menisci Functions
Primary= reduce compressive stress, stabilize the joint during motion (restrict anterior and posterior translation of femoral condyles on tibia or tibia condyles on femur)
Secondary= lubricate articular cartilage, Proprioception, guide arthrokinematics
Meniscal Movement
In extension, the menisci will move (more deformation in flexion)
The femoral condyles put force on the meniscus and cause it to deform outwardly
Tears in the meniscus can block of restrict movement (knees will lock if fold/tear is in the way)
Osteokinematics of the Knee
2 DOF
Flex/ext in sagittal plane, and IR/ER in horizontal plane (if knee slightly flexed)
Knee will not IR/ER if the knee is extended (bony congruency in extension)
Flexion/Extension at the Knee
M-L AOR; migrating AOR
Proximal on distal or distal on proximal
Coupled Motion
Flex/extension do not occur as pure sagittal plane motions–axis oblique
TIbia moves from position of slightly lateral to femur to slightly medial to femur in full flexion
ER/IR
“Axial rotation,” longitudinal/vertical AOR
–increases with knee flexion
90 degrees of flexion yields 40-45 degrees of rot;
ER when tibial tuberosity is lateral to anterior distal femur
Arthrokinematics- Extension
Tibia on femur–>tibia rolls and glides anteriorly
Femur on Tiba–>femoral condyles roll anteriorly ad glide posteriorly
Arthrokinematics- Flexion
Tibia must 1st IR to “unlock” (popliteus)
Tibia on femur–>popliteus initiates tibial IR
Femur on tibia–>popliteus initiates femoral ER
Scream Home (locking) Mechanism
Obligatory ER of tibia during terminal knee extension (TKE)
–not voluntary or produced by muscular forces
Joint arthrology dictates arthrokinematics during the final 30 degrees of KE
Flexion force “unlocks” by medially rotating the tibia
—in femur-on-tibia movement, the femur will externally rotate
Collateral Ligaments
Provide frontal plane stability against varus/valgus force
-MCL and LCL
Cruciate Ligaments
Provide multi planar stability at knee
-ACL and PCL
MCL
Resists valgus stresses (reinforces capsule)
At full extension, 57% of restraining force
At 25 degrees of flexion, 78% of restraining force
(So, provides more force when the knee if flexed)
–2 degree role in preventing anterior translation—may place stress on ACL if injured
Vascularized, so has capacity to heal
LCL
Resists Varus stresses
At 5 degrees of flexion accounts for 55% of restraining force
At 25 degrees flexion accounts for 69% of restraining force
Cruciate ligaments function
Names for their attachment to the tibia
Together provide multiplane stability of the knee, mostly in sagittal plane
Guide arthrokinematics
Contribute to Proprioception
ACL
Runs from anterior tibial plateau to lateral femoral condyle
Primary restraint to anterior displacement of tibia on femoral condyles
Two bands wrap around each other–AMB and PLB
Most fibers taut with knee close to full extension
ACL Injury
Most commonly injured when knee is slightly flexed and tibia is rotated in either direction (non-contact or contact)
Forceful contraction of the quads pulls tibia anteriorly, so can strain ACL especially near full extension
PCL Function
Runs from posterior intercondylar area of tibia to medial femoral condyle
1 degree restraint to posterior displacement of the tibia on femoral condyles (or anterior displacement of femur on tibia in closed chain)
Has two bands PMB and ALB
PCL Injury
Majority of fibers remain taut throughout flexion/extension but most taut with greater flexion
Contraction of hamstring can slide tib/fib posterior, PCL can check the posterior translation
Most injuries are TRAUMATIC
Patellafemoral Joint
Interface between patella and intercondylar groove
As knee flexes and extends, slides over the intercondylar groove
Max contact only 30% of total surface area
What happens are patella-femoral moves from flexion to extension?
Contact of patella moves from superior (base) to inferior (apex)
Q-Angele
ASIS to mid-patella–tibial tuberosity to mid-patella
Approx 15 degrees in women and 11 degrees in men
Greater than 15 degrees is considered abnormal
Medial Directed Forces at Patella
Vastus Medialis Oblique, raised lateral facet of intercondylar groove, medial patellar retinacular fibers
Lateral Directed Forces of Patella
ITB, lateral patellar reitnacular fibers, bow stringing force
Extensors
Quadriceps
Efficiency created by patella, creates 2/3 greater force than hamstrings, maximal torque at mid range (40-70 degrees of flexion)
Dampens impact of loading
Accelerate the tibia or femur for tasks requiring knee extension
Quads responsible for shock absorption
Tibia on Femoral motion–moment arm
External moment arm increases as it gets into extended position (so more difficult to extend knee as you reach full extension)
Femoral on Tibia motion–moment arm
External moment arm decreases from flexion to extension (so easier to stand up from mini-squat)
Moment arm at 45 degrees of flexion?
Tibia-on-femur and femur-on-tibia motion–>moment arm is equal at 45 degrees (same amount of difficulty in tasks at 45 degrees)
Think about squats vs. quad sets
Flexors/Rotators–Hamstrings
Most active during walking/running
Accelerate or decelerate the tibia during tibia on femoral movements; Stabilize in femur on tibia movements
Maximal torque development near full knee extension
Flexors/Rotators–Sartorius/Gracilis
Pes anserine provides medial stability and functions to IR tibia
Flexors/Rotators–Popliteus
IR and flexor; “unlocks” the knee
