Knee Flashcards
Distal Femur
Lateral/medial condyles
Intercondylar notch/groove - separates condyles posteriorly - cruciate ligaments travel through
Knee joint - tibiofemoral and patella-femoral joint
Condyles are continuous anteriorly
Medial condyle travels little further distally than does lateral condyle
Tibia sits more horizontal - puts femur in angle
Tibial Articulation
Lateral/medial tibial plateaus and condyles
Medial has a larger surface area (allows the femur to go more anteriorly)
Patella
Sesamoid bone
Base superiorly, apex inferiorly
Anterior surface - convex in all directions
Posterior surface - covered by articular cartilage
Embedded in the quad tendon
Articular surface inserts w/ intercondylar groover
Patella Functions - Primary Function
Increase angle of application (moment arm of quads)
Look at CoR - patella increases the moment arm
Remove patella - lose MA
Lengthens quads - on slack
Position of active insufficiency when patella is removed (muscle contracts so much - can’t extend knee)
Stand in ext - least force from quads
Patella Functions - Secondary Function
Protect quads tendon from excessive friction
Normal Alignment
Shaft of femur slightly medial
Medial condyle is longer, which is why shaft toward midline is longer
Normally sit in valgus - tibia going away in midline
Genu valgum and varus - frontal plane angles
Genu Valgum
Slight - normal
Angle is <170 degrees is excessive
Knock kneed
Knee femur closer together, tibia further apart
M/L jt line - symmetrical
Medical surface is further away (unweighting medial jt line) and lateral is closer together (closing down on lateral jt line - more force)
Static valgum - standing up straight
Dynamic algum - go into this position w/ mvt
Genu Varum
Angle is greater than 180 degrees is excessive
Bow leg
Anything beyond straight
Abnormal
Joint Capsule
Large, complexly attached and lax w/ several recesses
Reinforced posteriorly by muscles and popliteal ligaments, M/L by collateral ligaments
Vastus medals and vastus lateralis, MPFL (medial patella femoral ligament), retinacula anteriorly
Ligamens, fascia, muscle that reinforce knee capsule
Provides stability to joint
Menisci
Crescent shaped, fibrocartilaginous discs
Medial is semicircular, lateral is circular
Thick peripherally, thin centrally
Blood supply greatest in periphery
Receives blood flow from papillary vessels and synovial membrane (red red zone, red white zone, white white zone)
Anterior and posterior horns anchor at the end
Secondary attachments - quads (bilaterally), semimembranosus (bilaterally), popliteus to lateral only
Menisci - Functions
Primary function - reduce compressive stress, stabilize jt during motion
Secondary function - lubricate articular cartilage, proprioception, guide arthrokinematics
Osteokinematics
2 DOF
Flex/ext in sagittal plane - M/L AoR (migrating)
IR/ER in horizontal plane (if knee is slightly flexed)
Flex - 0 to 135 degrees
Ext - 0 to 15 degrees
IR - 20 to 30 degrees
ER - 30 to 40 degrees
Coupled Motion
Flex/ext don’t occur as pure sagittal plane motions
Axis is oblique
Tibia moves from position of slightly lateral to femur to slightly medial to femur in full flex
One motion occurs, obligatory second motion occurs
At knee jt, coupled motion b/c transverse/sagittal plane motion
As tibia flexes/extends, coupled IR/Er of tibia occurring (extend - tib tub moved laterally - ER) (bend knee - rotate back in - IR)
Tibia IR/ER
Axial rotation - longitudinal/vertical AoR
Increases w/ knee flex
90 degrees of knee flex, 40-45 degrees total of axial rotation
ER: when tibial tuberosity lateral to anterior distal femur
Available ROM increase w/ knee flex
Arthrokinematics - Extension
Tibia (concave) on femur (convex) - tibia rolls and glides anteriorly
Femur on tibia - femoral condyles roll anteriorly and glide posteriorly
Arthrokinematics - Flexion
Opposite of extension
Tibia on femur - rolls and glides posteriorly
Femur on tibia - femoral condyles roll posteriorly and glide anteriorly
Tibia must 1st IR to unlock when going from ext to flex
Tibia on femur - popliteus initiates tibial IR
Femur on tibia - popliteus initiates femoral ER
Femoral IR results in sane mvt as tibial ER
Screw Home (Locking) Mechanism
Obligatory ER of tibia during TKE (not voluntary or produced muscular forces)
Jt arthrology dictates arthrokinematics during final 30 degree KE
Flex force “unlocks” by medially rotating
Medial epicondyle of tibia extends further than lateral epicondyle (femur/tibia gliding, medial femur is going to extend more anteriorly - medial concavity is deeper)
Dictated by size of medial epicondyle
Ligaments
Collateral - primarily provide frontal plane stability against varus/valgus force (MCL/LCL)
Cruciate - provide multiplanar stability @ knee (ACL/PCL)
MCL
Resists valgus stresses (reinforces capsule)
- At full ext, 57% of restraining force
- At 25 degrees of flex, 78% of restraining force
Secondary role in preventing anterior translation (may place increased stress on ACL if injured)
Vascularized - capacity to heal
Does more w/ slightly knee flexed than extended
More commonly injured structures
LCL
Resists varus stresses
At 5 degrees of flexion accounts for 55% of restraining force
At 25 degree knee flex accounts for 69% of restraining force
Resist more various forces when knee is slightly flexed
Cruciate (ACL/PCL)
Named for their attachments to the tibia
Together, multiplayer stability of knee, mostly in sagittal plane (b/c they cross)
Guide arthrokinematics
Contributes to proprioception
Both together prevent rotation
ACL
Runs from anterior tibial plateau to lateral femoral condyles - crosses joint diagonally
Primary restraint - anterior displacement of tibia on femoral condyles
Two bands wrap around each other: anteriomedial (AMB) and posterolateral (PLB)
Most fibers taut w/ knee close to full ext
Forceful contraction of quads - ACL pulls tib tub and translate tibia anteriorly (guide arthrokinematics)
Most commonly injured when knee is slightly flexed and tibia rotated in either direction
- Contact: external force
- Non-contact: change of direction, quick pivoting, more ACL tears
Forceful contraction of quads pulls tibia anteriorly, so can strain ACL esp near full ext
When we flex knee and in valgus - ER of tibia occurring
-Quads turn on to extend the knee - why patients tear ACL in this position
PCL
Runs from posterior intercondylar area of tibia to medial femoral condyle
Primary restraint - posterior displacement of tibia on femoral condyles (or anterior displacement of femur on tibia in closed chain)
Also has 2 bands: posteromedial bundle (PMB) and anterolateral bundle (ALB)
Majority of fibers remain taut thru/out flex/ext but most taut w/ greater flex
Contraction of hamstring can slide tib/fib posterior
PCL can check posterior translation arthrokinematics
Most injuries - contact (trauma, football, MVA)
Flex/Ext with ACL/PCL
Flexion - PCL taut, ACL slack
Extension - ACL taut, PCL slack
Patellofemoral Joint
Interface b/w patella and intercondylar groove
As knee flexes and extends, slides over intercondylar groover
Max contact: only 30% of total surface
Extend knee - many angles of forces are coming to guid and track patella into groove
As knee flexes, patella moves down
As knee extends, patella moves up
Motions of Patella
M/L tilt and M/L rotation
Reference rotation off inferior aspect of patella
Q-Angle
ASIS to mid-patella
Tib tub to mid-patella
Approx. 15 degrees in women
Approx. 11 degrees in men
> 15 degrees - abnormal
Wider ASIS - larger Q-angle
Huge Q-angle - bowstring of patella (quads pulling patella laterally)
PF Joint Kinetics
Resultant force based on concurrent forces (quads and patellar tendn) - summative force toward knee joint
Knees far in front of toes - resultant force is greater
Squatting w/ bad mechanics can cause knee pain - increased forces on patello-femoral joint
Extensors
Quads
Efficiency affected by patella
Creates force 2/3 greater than hamstrings, max torque at mid range (40-70 degrees flex)
Dampens impact loading (esp during high impact losing, such as landing from jump, running, descending from high step)
Accelerates tibia or femur for tasks requiring knee ext
Eccentrically - quads control rate of descent of body’s CoM, such as sitting/stooping; shock absorber for knee; controls flexion
Tibial on Femoral External MA
External MA increases from 90 to 0 degrees of knee flexion
External MA during knee ext - greater
Gravity has gained an advantage when going thru this mvt - why parents feel like it’s harder to move to knee ext
Quadriceps Lag
To complete last 15 degrees of knee ext, 60% increase in force of quads muscles is required
Lag - quads are not strong enough to fully extend knee (TKE)
Femoral on Tibial External MA
External MA decreases from 90 to 0 degrees of flexion
Line of force anterior to jt - quads don’t need to do work to extend knee (ext moment)
Bending - external MA gets larger - gravity takes over
Flexors/Rotators - Hamstrings
Most active during walking/running
Accelerate/decelerate tibia during tibia on femur mets
Stabilizer in femur on tibial mvts
Max torque development near full knee ext
Flexors/Rotators - Sartorius/Gracilis
Pes anserine provides medial stability and functions to IR tibia
Flexors/Rotators - Popliteus
IR and flexor
“Unlocks” knee
Abnormal Patella
Patella squinting - knees in
Patella frog eye - knees out
Patella Alta and Baja
Alta - higher
Baja - lower than normal
Genu Recurvatum
Hyperext of knees
Baker’s/Popliteal Cyst
Fluid pools in posterior aspect of knee
Valgus Stress Test
Purpose: to screen for one-plane medial instability at knee (MCL)
Procedures: pt supine, examiner applied valgus force at knee w/ ankle in slight lateral rotation, test performed in full knee ext and w/ knee flexed 20-30 degrees
Positive - gapping of tibia away from femur, pain in MCL
Positive w/ knee flexed - more likely an indication of one-plane instability (MCL, post oblique ligament, PCL, capsule)
Positive w/ knee extended - major disruption and will likely find pos rotatory instability tests (MCL, PCL, ACL, capsule, M quad expansion, semimem)
Negative - no gapping or pain
Varus Stress Test
Purpose: to screen for one-plane lateral instability at knee (LCL)
Procedure: pt supine, examiner applied varus force at knee w/ ankle in stabilized, test performed in full knee ext and w/ knee flexed 20-30 degrees
Positive - gapping of tibia away from femur, pain at LCL
Positive w/ knee flexed - more likely an indication of one-plane instability (LCL, capsule, ITB, biceps fem tendon, arcuate-popliteus complex)
Positive w/ knee extended - major instability and will likely find pos rotatory instability tests (LCL, capsule, ITB, biceps fem tendon, arcuate-popliteus complex, PCL, ACL, lateral gastroc)
Negative - no gapping or pain
Lachman Test
Purpose: screen for one-plane anterior instability at knee (ACL)
Procedure: pt supine w/ knee flex b/w 0 and 30 degrees, examiner stabilize distal femur w/ outside hand and anteriorly translates proximal tibia w/ inside hand
Positive - mushy/soft end feel, excessive displacement/gapping
Negative - normal end feel, no excessive motion
McMurray Test
Purpose - screen for medial and lateral meniscal injury
Procedure - pt supine with knee fully flexed, examiner passively IR tibia and maintains position while extending knee (lateral meniscus), then ER tibia and extend knee (medial meniscus)
Positive - clunk, snap, click, accompanied by pain that occurs b/w full flex and 90 degrees of flexion
Negative - painfree and smooth motion
Apley’s Test
Purpose - screen for medial and lateral meniscal injury
Procedure - pt prone w/ knee flexed at 90 degrees, examiner stabilize pt’s thigh using own knee, examiner M/L rotates tibia, combined w/ distraction (distal tib-fib) and repeated w/ compression
Positive - restriction, excessive mvt or discomfort w/ compression, pain/hypermobility w/ distraction is more likely associated w/ ligamentous injury
Negative - no pain, restriction or excessive motion w/ compression or distraction
Clarke’s Sign (Patellar Grind Test)
Purpose - screen for retropatellar dysfunction
Procedure - pt supin w/ knee ext, examiner gently uses web of hand to press down just prox to pole of patella, w/ pressure sustained, pt performs quad set
Postive - pain/grinding during quad contraction
