Knee Pathologies - Anatomy and Kinesiology

what is the strongest bone of the human body?

femur

what can be located on the distal femur?

• linea aspera

• femoral trochlea

• lateral epicondyle

• medial epicondyle

• adductor tubercle

• medial and lateral condyles

• intercondylar notch

what is important to note about the femoral trochlea?

there is an anterior depression through whic patella glides

what is important to note about the medial and lateral condyles?

• have distinct anterior/posterior curvature in frontal plane

• medial articular surface is longer than lateral side

• share common anterior surface that diverges posteriorly

what is important to note about the intercondylar notch?

posterior separation between condyles

what are the structures that can be found on the proximal tibia?

• medial and lateral tibial plateaus

• tibial tuberosity

• pes anserine

• Gerdy’s tubercle

what is important to note about the medial and lateral tibial plateaus?

• correspond to the femoral condyles

• concave

• medial tibial plateau is 50% larger than lateral plateau

what is important to note about the tibial tuberosity?

patella tendon attachment site

what bones are outside the patellofemoral articulation that directly affect stability and function of the knee?

• patella

• fibula

how is the patella important for knee stability and function?

• sesamoid bone within patella tendon

• improves mechanical function of quads during knee extension

• dissipates forces

• protects anterior knee

how is the fibula important for knee stability and function?

• attachment site for soft tissue on the lateral side

• fracture of fibular head or proximal tibiofibular syndesmosis can affect stability of knee

what are the articulations for the tibiofemoral joint?

type of joint: hinge

movements: flexion/extension

axis of rotation: frontal

what are the articulations for the proximal tibiofibular joint?

type of joint: syndesmosis

movements: N/A

axis of rotation: N/A

what happens to the knee when it is flexed at the tibiofemoral joint?

flexion and extension around x axis

internal and external rotation around the y axis

how many DOF does the tibiofemoral joint have?

2 DOF

• sagittal plane

  • extension and flexion

• transverse plane

  • internal and external rotation

why does a locking mechanism occur during the final degrees of extension?

due to unequal sizes of the femoral condyles and tightening of the cruciate ligaments as they wind upon themselves

what is the screw home mechanism during NWB extension?

tibial externally rotates 5-7 degrees on the femur

(sitting down and extending the knee)

what is the screw home mechanism during WB extension?

tibia is relatively fixed and therefore the screw home mechanism occurs due to a combination of some tibial external rotation and femoral internal rotation

(femur rotates and the tibia is fixed here)

what must happen to the tibia and femur for flexion to occur?

the tibia and femur must unlock

for WB of flexion, how can the tibia and femur unlock?

contraction of popliteus, semi-membranous and semi tendinous

for NWB of flexion, how can the tibia and femur unlock?

contraction of popliteus

what are the factors that are guiding the screw home mechanism?

• shape of medial femoral condyle

  • it curves 30 degrees laterally as it approaches the trochlear groove

• passive tension in the ACL

• slight lateral pull of the quadriceps muscle

go through the arthrokinematics of tibial on femoral extension with the starting position of knee flexed when standing:

roll: anterior/inferior

slide: anterior/inferior

spin: tibial ER (screw home)

go through the arthrokinematics of tibial on femoral extension with the starting position of knee flexed when seated:

roll: anterior/superior

slide: anterior/superior

spin: tibial ER (screw home)

go through the arthrokinematics of tibial on femoral flexion with the starting position of knee extended when standing:

roll: posterior/superior

slide: posterior/superior

spin: IR of tibia (unscrew)

go through the arthrokinematics of tibial on femoral flexion with the starting position of knee straight when seated:

roll: posterior/inferior

slide: posterior/inferior

spin: IR of tibia (unscrew)

go through the arthrokinematics of femoral on tibial extension with the starting position of being seated:

roll: superior/anterior

slide: posterior

spin: IR of femur (screw home)

go through the arthrokinematics of femoral on tibial extension with the starting position of standing:

roll: posterior/inferior

slide: anterior

spin: ER of femur (unscrew)

what elements are always associated with the joint capsule?

• articular cartilage

• joint (articular) capsule

• synovial membrane

• synovial fluid

• ligaments

• blood vessels

• sensory nerves

what is the type of articular cartilage that can be found at the end of all bones?

hyaline cartilage

what are the layers to the articular capsule?

• external layer

• internal layer

what composes the external layer of the articular capsule?

fibrous layer that is made of dense connective tissues

what composes the internal layer of the articular capsule?

the synovial membrane

what is the synovial membrane?

its cells (specialized connective tissue) manufacture synovial fluid

what is the synovial fluid useful for?

• reduces the friction between the joint surfaces as well as provides nourishment to articular cartilage

• fluid id clear or pale yellow, slightly viscous (cracked egg)

what does the thickness of the ligaments depend on?

the functional demand that is placed on them

which ligaments are usually thicker?

capsular ligaments

what are capsular ligaments?

consist of broad sheets of fibers that when pulled taut, resist movements in two or often three planes

how far do blood vessels go into the joint capsule?

as deep as the junction of the fibrous layer of the joint capsule and adjacent synovial membrane

what do the sensory nerves serve for the joint capsule?

supply the external layer of the capsule and ligaments with receptors for pain and proprioception

what elements are sometimes associated with the joint capsule?

• intra-articular discs or menisci

• peripheral labrum

• fat pads

• bursa

• synovial plicae

what are intra-articular discs or menisci?

• pads of fibrocartilage imposed between articular surfaces

• increase articular congruency and improve force dispersion

• found in various joints

what is the peripheral labrum?

fibrocartilage that extends from the bony rims of the glenoid fossa in the shoulder and from the rim of the acetabulum in the hip

what are fat pads?

• reinforce internal aspects of the capsule as well as fill non-articulating joint spaced formed by incongruent bony contours

• distributed throughout the body, often interposed between the fibrous layer and the synovial membrane. if the fat pad becomes inflamed or enlarged, it can alter the mechanics of the joint

• absorb force, protect periarticular connective tissues

what are bursae?

• often adjacent to fat pads. it is an extension or outpouching of the synovial membrane of a diarthrodial joint

• filled with synovial fluid

• exists in area of high or potential stress

• absorb force, protect periarticular connective tissues

what are synovial plica?

• slack, overlapping pleats of tissue composed of the innermost layers of the joint capsule

• usually in joints with large capsular surface area (knee, elbow)

• plicas increase synovial surface area and allow full joint motion without undue tension on the synovial lining

• if the folds are too extensive or become thickened or adherent due to inflammation, they can produce pain and alter mechanics

what are the components of the fibrous joint capsule of the knee?

• medial reinforcement

• lateral reinforcement

• posterior reinforcement

• anterior reinforcement

what are the subcomponents of the medial reinforcement?

• MCL

• medial patellofemoral ligament

• medial patellar retinaculum

what are the subcomponents of the lateral reinforcement?

• LCL

• lateral patellar retinaculum

• lateral patellofemoral ligament

• IT band

what are the subcomponents of the posterior reinforcement?

• posterolateral corner

what are the subcomponents of the anterior reinforcement?

• patella tendon

where does the synovial joint capsule sit in the knee?

• lines the articular portion

• surrounds the articular condyles of the femur and the anterior, medial, and lateral tibia

• posteriorly, synovium runs runs anterior along the intercondylar notch of the femur and the intercondylar eminence of the tibia

what are the collateral ligaments of the knee?

• medial collateral ligament (MCL)

• lateral collateral ligament (LCL)

what are the layers of the medial collateral ligament?

• superficial layer (larger)

• deep layer

• bursae

where does the superficial layer of the medial collateral ligament run?

• parallel running fibers, 10 cm long

• arise from medial epicondyle (just below adductor tubercle), blends into the medial patella retinaculum (thinner), and attaches just posterior to the pes anserine

where does the deep layer of the medial collateral ligament run?

• short and more oblique

• thickening of the joint capsule

• attaches to medial meniscus, and semimembranosus

when is the MCL tight?

during knee extension

what is the primary restraint of the MCL?

valgus force (lateral)

what are the secondary restraints of the MCL?

external rotation and anterior translation of the tibia

what is the lateral collateral ligament?

• Short, cord like, primary lateral stabilizer

• runs from lateral epicondyle to head of fibula

• blends in with tendons from biceps femoris

• does not attach to meniscus or joint capsule

• considered part of posterolateral corner

where does the popliteus course through?

between LCL and lateral meniscus

what is the primary restraint of the LCL?

varus forces and external tibial rotation

what is the secondary restraint of the LCL?

internal tibial rotation

what are the cruciate ligaments of the knee?

• anterior cruciate ligament (ACL)

• posterior cruciate ligament (PCL)

what is the ACL the static stabilizer against?

• anterior translation of the tibia on femur

• internal rotation of the tibia on femur

• external rotation of the tibia on the femur

• hyperextension of the tibiofemoral joint

what are the distinct segments of the ACL?

1. anteromedial bundle

2. posteromedial bundle

how are the bundles of the ACL named?

named according to their attachment site on the tibia

what do the bundles of the ACL do during extension and flexion of the knee?

extension: bundles are parallel

flexion: bundles wind upon themselves

which bundle of the ACL is tight during extension?

posterior bundle

which bundle of the ACL is tight during flexion?

anterior bundle

the amount of strain on the ACL is influenced by what?

influenced by the type of movement and the subsequent translation of the tibia

what are some important things to note about PROM of the ACL?

• strain on ACL is minimal when tibia is in neutral position

• last 15 degrees of extension, internal rotation of the tibia increases strain on ACL; external rotation decreases strain relative to IR

• valgus and varus stress increased stress on ACL

what are some important things to note about AROM of the ACL?

• during open chain knee extension the quads pull tibia anteriorly, the strain on ACL is greatest between 0-30 degrees of flexion

• during closed chain knee exercises, strain on ACL is not as significant

which cruciate ligament is stronger and wider than the other?

the PCL is stronger and wider than the ACL

what cruciate ligament is the primary stabilizer of the knee?

the PCL

what are the 2 components to the PCL?

1. anterolateral bundle

2. posteromedial bundle

when is the anterolateral bundle of the PCL tight and lax?

tight when knee is flexed, laxer when extended

when is the posteromedial bundle of the PCL lax and tight?

lax when the knee is flexed, tighter when extended

what is the primary restraint of the PCL?

against posterior tibial displacement

what is the secondary restraint of the PCL?

against external tibial rotation

how is the function of the PCL supported?

supported by meniscofemoral ligament and structures of the posterolateral corner

what are the stabilizers of the posterolateral corner?

• dynamic stabilizers

• static stabilizers

what is the primary function of the posterolateral corner?

integral in providing stability against varus stress, external tibial rotation, and anterior/posterior forces

how can profound injury result in the posterolateral corner?

if multiple structures are damaged

• posterolateral rotational instability

list the key stabilizers of the knee:

• popliteofibular ligament

• popliteus complex (muscle and tendon)

• arcuate ligament

• fabella - sesamoid bone

where does the popliteofibular ligament originate and insert?

inserts on femur via popliteal tendon and originates from fibula and tibia

what does the popliteofibular ligament stabilize?

stabilizes against posterior tibial translation, varus force, and ER

where does the popliteus complex (muscle and tendon) attach?

attaches to posterior horn of lateral meniscus

wha does the popliteus complex resist?

resists ER between 20-130 degrees of flexion

what does the popliteus complex include?

• popliteofibular ligament

• popliteotibial fascicles

• popliteomeniscal fascicles

what does the arcuate ligament run from?

runs from fibular head over the popliteal muscle and diverges into intercondylar area of tibia and posterior aspect of femurs lateral epicondyle

is the fabella present in the knee?

not normally, no

if the fabella is present in the knee, where would it be?

lies in the lateral head of the gastrocnemius and increases thickening of the posterolateral corner

what are the layers of the posterolateral corner?

• superficial layer

• middle layer

• deep layer

what is in the superficial layer of the posterolateral corner?

1. lateral fascia

2. iliotibial band

3. biceps femoris tendon

what can be found in the middle layer of the posterolateral corner?

1. patellar retinaculum

2. patellofemoral ligament

besides the posterolateral corner, what are other corners that are involved in rotational instabilities?

• anterolateral corner

• anteromedial corner

• posterolateral corner

• posteromedial corner

true or false: the proximal tibiofibular syndesmosis is less stable than the distal tibiofibular syndesmosis

false. the proximal syndesmosis is more stable than the distal syndesmosis

where does the stability of the proximal tibiofibular syndesmosis joint come from?

• superior anterior tibiofibular ligament

• superior posterior tibiofibular ligament

• interosseous membrane

where will the most proximal fibular instabilities occur?

posteriorly which can potentially affect the common peroneal nerve