Exam 3 lectures

• purpose of knee

  allow bending to clear foot during gait, to lower body and COM and to transfer forces
• knee stability provided by

  active and passive soft tissues

  muscles, ligaments, and menisci
• facets of the patella

  medial facet

  odd facet (most medial)

  lateral facet

  medial and lateral facet separated by vertica
• tibial vs. femoral facets

  tibial medial condyle is larger and has a larger meniscus

  femoral condyle is steeper and higher on lateral side to protect from lateral dislocation
• medial femoral condyle


  goes more distal
• Q-angle

  mild genu-valgum is normal

  females: 20

  males: 12
• Synovium projects inward to exclude what from the synovial cavity

  ACL/PCL (intra-articular but extra-synovial ligaments)
• what bursa of the knee communicates with the joint cavity

  supra-patellar bursa
• plicae

  synovial pleats/ folds

  can cause friction

  Can remodel over time, but may not, and when it remains, it can become thickened and cause friction-related pain from rubbing on articular cartilage (surgical removal is common)
• infrapatellar fat pad movement with flexion/extension

  flexion: posterior movement

  extension: anterior movement

  Sometimes the scarring after a BPTB graft can impinge on the infrapatellar fat pad

  The pad can also simply become impinged in the joint and cause pain (Infrapatellar fat pad syndrome, or “Hoffa’s Syndrome”)
• active/ passive structures affecting motion

  arthrokinematics (passively): ligaments, capsule, and retinaculum

  osteokinematic motion: induces by tendons
• medial patellofemoral ligament

  main patella stabilizer
• anterior/posterior stability of the knee

  ACL: taut in extension

  PCL: taut in flexion

  do not heal on their own due to synovial fluid that can flood capsule with a tear
• menisci purpose

  reduce stress, stabilize, provide proprioception, lubricate, guide arthrokinematics

  medial meniscus injured more and DJD more common
• posterior stability of the knee

  Passive: oblique popliteal ligament reinforces posterior capsule

  active: popliteus
• why don't external devices match up with the axis of the femur?

  moving/migrating axis "evolute"
• screw home mechanism

  rotation of the knee during the last few degrees of extension

  OKC: tibial ER on fixed femur

  CKC: femoral IR on fixed tibia

  popliteus: unlocks knee through flexion and rotation; only rotator in extension with good leverage and stability for unlocking the extended knee

  passive only, does not occur in isolation
• factors causing the screw-home mechanism

  shape of medial femoral condyle, tension in ACL, lateral pull of quads
• menisci movement during femoral movement

  flexion: posterior

  extension: anterior

  lateral meniscus moves farther due to not being attached to LCL
• mechanism of injury: ACL

  foot planted, large valgus force, axial rotation in either direction, hyperextension

  never gains full function/strength if torn due to grafts needing time to revascularize and necrosis occurring until vascularization is complete

  greater risk in females
• ACL protection in landing

  hip/glute landing strategy

  greater sharing of demand between quads and hip extensors
• quads protect?

  PCL
• hamstrings protect?

  ACL
• greatest patellofemoral contact at?

  90-60 degrees

  least at full extension: apex has the most contact
• axes of patellar motion

  medial/lateral tilt (sagittal axis)

  nodding (flex/ext) (frontal axis)

  spinning along z-axis (transverse axis)
• function of patella

  increase MA
• why is the compressive force higher as the squat gets deeper

  decreased angle for torque
• Patellar tracking is most affected by what tendon

  patellar tendon/quad tendon
• extensor muscles of the knee function

  isometric: stabilization

  eccentric: control rate of descent of COM, shock absorption, the extent of flexion, dampens the impact of loading

  concentric: accelerate tibia or femur toward extension, raise COM
• knee torque

  OKC increase from 90-0 (most in full ext, least in flex)

  CKC decreases from 90  to 0 deg (most in deep squat, least in standing upright)
• extensor lag

  strains ACL graft

  can't do SLR due to dissociation between nerve and muscle
• flexor action in gait

  Accelerate and lift during swing phase of gait (concentric)

  Decelerate during terminal swing of gait (eccentric)
• glute max gait

  Increases load on patellofemoral joint, leading to OA and/or overuse
• varus deformity

  GRF is medial to knee and causes varus torque or moment.

  doesn’t have as much freedom as lateral compartment, and it is more exposed due to C-shaped medial meniscus.
• valgus deformity

  caused by coxa vara, obesity, stretched MCL, genetics, m weakness, foot pronation

  increased Q angle with slight IR
• genu recurvatum

  BW anterior to knee

  treated by hamstring strengthening, heel lift
• chondromalcia patella

  softening/breakdown of retropatellar cartilage (usually due to disuse)
• unhappy triad

  ACL, MCL, medial meniscus
• Pliability of the foot purpose


  proprioception

  during the loading response as the foot molds to the surface
• purpose of rigidity in the foot

  change in motion

  with supination during toe off so that we have a rigid lever to use for propulsion