Knee Flashcards
Tibiofemoral Joint Alignment: Longitudinal axis
Femur
- Directed inferiorly and medically from proximal to distal
Tibia
- Directed almost vertically
forms medical angle b/w femur and tibia of 180-185 degrees
Genu Valgum and Varum vs. normal
Greater than 185 degrees is genu valgum (knock knees, knees going inward, Disney knees)
Less than 175 degrees is genu varum (bow legged, knees going outward)
Normal: 180-185 degrees
Tibiofemoral Alignment: Normal, valgum, varum
Normal
- WBing line passes through the CENTER of the knee joint
-> loading is equally distributed btwn medial and lateral parts
Genu Valgum
- Increased COMPRESSIVE load on LATERAL aspect of knee
- Increased TENSILE stress on MEDIAL aspect of knee (gapping, stretch)
* Stress on Medial Collateral Ligament *
Genu Varum
- Increased COMPRESSIVE loads on MEDIAL aspect of knee
- Increased TENSILE loads on LATERAL aspect of knee
* Stress on Lateral Collateral Ligament *
Single Leg (SL) Activities
During SL activities such as gait…
Line of force shifts MEDIALLY
-> Increases compressive stresses medially
Menisci Functions
- Enhance jt congruence, wedged shaped
- Reduce friction b/w tibia and femur
- Distribute WBing forces
- Shock absorption
-> Menisci assume 50%-70% of load through the knee
Lateral meniscus covers greater % of lateral tibial surface than surface covered by medial meniscus
Articular cartilage of MEDIAL tibia plateau is MORE susceptible to injury
-> more exposed jt surface
-> greater compressive loads in medial compartment with daily activities
Meniscal Attachments
Medial Meniscus
- Attached to jt capsule via deep portion of MCL
- Anterior and posterior horns attach to ACL and PCL
- Semimembranosus attached
Has more ligamentous and capsular restraints than lateral
-> Less translational mobility
-> May contribute to increased injury
Lateral Meniscus
- Anterior horn shares tibial attachment site with ACL
- Attaches to PCL and medial femoral condyle posteriorly via meniscofemoral ligament
- Popliteus attached
Menisci Blood Vessels
1st year of life: blood vessels constrained t/o meniscal body
-> Once WBing, vascularity begins to diminish
In adults
- Only outer 25%-33% is vascularized by capillaries from joint capsule
Zones of vascularity
Red zone: most lateral
-> gets nutrition via blood vessels
Red white zone
-> Relies on diffusion of synovial fluid for nutrition
-> Intermittent loading from WBing and muscle contraction optimize diffusion
White zone: Innermost zone
-> Innervated with nociceptors and mechanoreceptors (play a role in proprioception and reflex mediated muscle responses)
What makes up the Extensor Retinaculum and what does it do?
Reinforced medially by…
- Medialpatellotibial ligament
- Medial patellofemoral ligament (MPFL)
-> blends with Vastus medialis and is important patellar stabilizer
resist excessive LATERAL translation (no pull/restrain medially, patella will move laterally)
Reinforced laterally by…
- Lateral patellofemoral ligament
- Lateral patellotibial ligament
resist excessive MEDIAL glide of patella (no pull/restrain laterally, patella will move medially)
Ligamentous Reinforcement of the Joint Capsule
- Posterior Oblique Ligament (POL)
-> reinforces capsule posteromedially - Arcuate Ligament (on fibula)
-> reinforces capsule posterolaterally - Oblique Popliteal Ligament
-> runs obliquely across posterior capsule
Joint Capsule: Synovial Layer
Inner lining of Joint Capsule
- Secretes & absorbs synovial fluid
Outside of synovium
- ACL & PCL but still w/in fibrous capsule
- Fat pads
Collateral Ligaments
Provide stability in medial-lateral direction
- Offer greatest % contribution to resistance of VARUS or VALGUS stresses when knee is at 25 degrees flexion
TAUT in knee extension and LAX in flexion
- Gives stability against rotation during extension, but allows rotation when knee is flexed
- MCL has good blood supply and does not usually require surgical repair
What does the MCL resist and what is the common MOI?
Medial Collateral Ligament (MCL)
Resists
- Valgus forces
- Excessive knee extension (esp ER of tibia)
Common MOI
- Valgus producing force with foot planted
- Severe Hyperextension
What does the LCL resist and what is the Common MOI?
Lateral Collateral Ligament (LCL)
Resists
- Varus forces
- Excessive knee extension
- Extremes of axial rotation
Common MOI
- Varus-producing force with foot planted
- Severe Hyperextension
What does the LCL and MCL both resist and what Common MOI do they prevent?
Both resist EXCESSIVE KNEE EXTENSION
Both Common MOI: SEVERE HYPEREXTENSION
What makes up the Anterior Cruciate Ligament ?
2 Functional Bundles (BOTH under tension in FULL EXTENSION)
- Anteromedial (AM) Bundle
-> Primarily resists anterior translation of tibia
-> Most taut b/w 45-60 degrees flexion
-> Undergoes less change in length than PL bundle t/o ROM - Posterolateral (PL) bundle
-> lax in flexion from 60-90 degrees to allow rotation of tibia
-> most taut in full extension
-> limits anterior translation of tibia at low angles of knee flexion (getting closer to full extension)
What is the function of the ACL and what is the Common MOI?
Function
- Most fibers resist excessive extension
-> Resists excessive anterior translation of tibia and/or excessive posterior translation of femur
- Resists extremes of varus and Valgus and tibial rotation
Common MOI
- Large Valgus producing force w/ foot planted
- Large axial rotation torque @ knee (in either direction), w/ foot planted
- Any combo of above, esp involving strong quadriceps contraction w/ knee in full or near-full extension
- Severe Hyperextension (tibia going anteriorly)
What is the Posterior Cruciate Ligament made of?
- Thicker and stronger than ACL, injured less often*
2 bundles
1. Anterolateral (AL) bundle
2. Posterolateral (PM) bundle
PCL more taut with greater angles of knee FLEXION
In flexion
- AL is more taut
- PM is more lax
In extension
- AL is more lax
- PM is more taut
What is the function of the PCL and what is the Common MOI?
Resists
- Posterior translation of tibia
- Limits extremes of knee flexion
- Resists extremes of varus and Valgus forces
- Resists tibial rotation
Common MOI
- Contact injuries/trauma
- “Dashboard injuries” during a car accident
- hyperflexion (tibia moving posteriorly on femur)
What does the oblique popliteal ligament limit?
Protects posterior knee from Hyperextension
What does the popliteofibular ligament limit?
Resists Posterolateral tibial rotation and posterior tibial translation
What does the Ligament of Humphrey (anterior meniscofemoral ligament) limit?
Anchors lateral meniscus
What does the ligament of Wrisberg (posterior meniscofemoral ligament) limit?
Stabilizes lateral meniscus
What does the Arcuate ligament limit?
Protects the Posterolateral capsule against Hyperextension and rotational forces
Locking Mechanism of knee (screw home)
Open Chain knee extension
- In the last 30 degrees, extension of tibia is coupled with ER of tibia
Closed chain extension
- IR of the femur occurs on the tibia during the last 30 degrees
Factors contributing to screw home mechanism
- shape of medial femoral condyle
- tension in ACL
- Lateral pull of quads
Arthrokinematics: open chain knee extension
Open chain knee extension: tibia rolls and slides anteriorly on femoral condyle
CVS
Arthrokinematics: open chain knee flexion
Open chain knee flexion: tibia rolls and slides posteriorly on femoral condyles
CVS
Arthrokinematics: closed chain knee extension
Femoral condyles roll anteriorly and slide posteriorly on the tibia
VCO
Arthrokinematics: closed chain knee flexion
Femoral condyles roll posteriorly and slide anteriorly on the tibia
Knee joint ROM & Open and Close Packed
Flexion: 130-140 degrees
Extension: 0 degrees (5-10 degrees Hyperextension)
Internal tibial rotation: 15 degrees
External tibial rotation: 20 degrees
tibial rotation is maximized at 90 degrees knee flexion
Open packed position: 25 degrees flexion (laying down knees bent)
Closed packed position: full extension
Stabilizing Factors of the Patellofemoral joint
- Tibiofemoral alignment
- passive support from the retinaculum
- distal portion of ITB
- shape of femoral groove
- ligamentous support
- quadriceps muscles
- neuromuscular control (timing of contraction)
- Kinematic chain (hip,foot,ankle)
Q angle
Represents the line of pull of quads
Formed by intersection of
- line from ASIS to center of patella
- line from center of patella to tibial tuberosity
Normal values:
8-14 degrees for males
15-17 degrees for females
Patellar motion
Glides in a curvilinear path
Flexion: moves inferiorly
- initially shifts medially
-> then remains centrally or shifts slightly laterally as flexion increases
Extension: moves superiorly
- shifts laterally
-> shifts laterally as full extension is approached
Simultaneously translates, tilts, and rotates during knee motion
Patella rotates with tibia
- Early knee flexion -> tibia and patella rotate medially
- Terminal knee extension -> tibia and patella rotate laterally (quads pull laterally)
Abnormal Tracking: Inverted “J” Sign
During initiation of flexion…
- patella suddenly moves medially to enter the trochlea (reverse during extension)
Sudden and pronounced movement of patella
Patellar shift/glide
Lateral and medial patellar shifts/glides are translations
Patellar Tilt
Medial tilt: medial surface approximates the medial femoral condyle
Lateral tilt: lateral surface approximates the lateral femoral condyle
Patellar rotation
Medial rotation: patella spins so apex moves medially
Lateral rotation: patella spins so that apex moves laterally
What are the Vertical Patellar Positions
Insall-Salvati index
- Ratio of length of patellar tendon to length of patella
- Typically ~ 1:1
Patella Baja
- Abnormally low position of patella
- Associated with a SHORTENED patellar tendon
Patella Alta (camel sign)
- Abnormally high position of patella
- Increases risk for patellar instability
- Reduces efficiency of extensor mechanism
- increase PFJ contact force during flexion, possibly leading to anterior knee pain
- Camel sign
1. High patella creates 1st “hump”
2. Infrapatellar fat pad (or inflamed infrapatellar bursa) becomes more prominent creating 2nd “hump”
Patellofemoral Joint Stresses
When quads contract… (knee flexion)
- patella moves superiorly by quadriceps tendon and patellar ligament resists the pull (pull in opposite directions)
-> Combined forces create a posterior COMPRESSION force of patella on femur
Flexion= Taut tendons
Extension= more Lax tendons
Patellofemoral joint stresses: joint angle
Full extension
- posterior compressive force from quads is minimized
-> allows for low PF joint stresses w/ knee @ full extension
Knee flexion
- angle of pull decreases
- Increases JRF, producing greater PF jt compressive forces
W/ passive flexion…
- passive tension in the tendons produces compressive forces
When quads are active…
- both active and passive elastic tension contribute to increasing compressive jt force
What increases as knee flexion increases during WBing?
As the knee is flexed further during WBing, the PF compressive load is INCREASED
What plane is knee flexion
TRANSVERSE PLANE
What knee flexors also produce medial (internal) rotation of tibia on fixed femur?
Semimembranosus, semitendinosus, Sartorius, gracilis, and popliteus
What knee flexor produces lateral (external) rotation of the tibia?
Biceps femoris
What does Sartorius, Gracilis, and Semitendinosus (pes anserinus muscles) do?
Group to resist Valgus forces and provide dynamic stability to knee joint
When can hamstrings produce the greatest amount of force and least force?
- Greater hamstring force as a knee flexor is produced with flexed hip
- Produce less force with hip extended and knee flexed to 90 degrees or greater due to ACTIVE INSUFFICIENCY
NWBing activities
* Hamstrings produce posterior shearing force of tibia *
-> Shearing increases w/ increasing knee flexion
-> Reduces strain on ACL, but increases strain on PCL
Semimembranosus assists in posterior movement of medial meniscus during active knee flexion (pulls it out of the way)
When does gastrocnemius produce the greatest torque?
- Produced greatest knee flexion torque when knee is fully extended
- often function more as a stabilizing muscle at knee rather than a mobilizing muscle
How does soleus and glute max influence knee joint function?
Soleus: when foot is fixed on ground
- assists with knee extension by pull tibia posteriorly
- can assist hamstrings in restraining excessive anterior displacement of tibia
Gluteus Maximus : when foot is flat on ground and knee is bent
- can generate knee extension by pulling the femur posteriorly
How does the patella increase MA of quad tendons?
- deflects line of pull of quads away from axis of rotation
- increases angle of pull to enhance quads ability to generate extension torque
Pulley function decreases in full flexion due to patella being fixed in intercondylar groove
Patella is farthest distance from AOR @ ~50 degrees knee flexion
-> peak torque btwn 45-60 degrees of knee flexion
-> MA decreases as knee moves into further extension
LOG of Quads during WBing
Standing posture
- Quad activity is minimal because LOG is anterior to knee axis
-> creates extension torque that maintains joint in extension (keeps us upright)
-> posterior capsule, ligaments, and posterior muscles prevent EXCESS extension
When knees flex in WBing, LOG shifts posterior to knee axis
- Creates knee flexion torque
-> Quad activity is needed to maintain position against gravity (so we dont collapse)
Quads are typically 50% stronger than hamstrings
NWBing exericse
Quads generate more torque (and force) as the knee approaches full extension
-> Needed to overcome increasing MA (and torque) of the resistance
What should Pts avoid with PFJ pain
- Deep flexion while doing WBing exercises
- Final 30 degrees of extension during non-WBing resisted knee extension
What is Dynamic Valgus
- A sign of functional weakness and/or poor motor control at the hip
- Usually a deficit of hip abductors and external rotators
Signs
- Contralateral hip drop
- knee moves medial to 1st toe
- hyperpronation
