knee anatomy and biomechanics Flashcards
what joints make up the knee joint?
Patella-femoral joint
Tibiofemoral joint
Superior tibio-fibular joint
why is the knee joint susceptible to trauma
stuck in the center of two lever arms
what provides inert stability to the knee?
ligament
meniscuc
articular surfaces
what provides dynamic stability to the knee joint?
muscles
what forms the normal Q angle of the knee
line from asis to center of the patella and from center of patella to tibial tibercle
what is associated w/ an increase in Q angle of the knee
increased lateral translation and thus increase stress on the side of PF joint
what attaches the patella to tibial tuberosity
patellar tendon
what is the function of the PF joint
pulley for the quad muscles and allows to decrease the friction b/w the quad tendon and the femoral condyles
what happens at the PF joint as the knee begins to flex
patella moves inferiorly and engage in the intercondylar groove
shifts medially by being pushed by the large lat femoral condule and tibial MR
what happens at the PF joint as the knee past 30 degree flexion
patella will either remain stable or shift laterally
at 0 degree of knee flexion (knee extension) where does contact of the patella occur?
no contract b/w patella and torchlear groove
at 10-30 degrees of knee flexion where does contact of the patella occur?
inferior pole of patella and trochlear groove
45-60 degrees of knee flexion where does contact of the patella occur?
contact area moves towards the central pole of the patella
at 90 degrees of knee flexion where does contact of the patella occur?
the top of the patella is in contact w/ the patellar groove
at 135 degrees of knee flexion where does contact of the patella occur?
medial and lateral sides of the trochlea now serve as contact points
how is the congruency of the knee joint?
incongruent due to the different shape of the articulating surfaces; patellar surface is smaller than femoral articulating surface
what act as dynamic stabilizers for the patella
quad tendon
patellar tendon
ITB
rectus femoris muscle
what acts as static stabilizers of the patella
medial and lateral patellar retinaculum
what may influence the position of the patella
imbalances in passive tension or change ion the line of pull of the dynamic stabilizers
what determines the vertical position of the patella in the femoral sulcus?
lenght of the patellar tendon
what is patella alta
condition that arises when the patellar tendon is abnormally long; leading for a higher raised patella on the femoral sulcus
what are consequences associated to patella alta?
subluxation and PFPS
what is the normal and abnormal raio for modified insall-salvatti ratio and what does it measure?
Ratio patella tendon length: patella length
Normal ratio = 1.25 : 1
Abnormal ratio = >2: 1
what does the joint reaction force on the knee depend on?
quad force and knee angle
what happens to the patella and joint rxn force when the knee is in increased flexion?
patella gets pulled up by the quad tendon and inferiorly by the patellar tendon leading to posterior compression
when is the compression force on the patella minimal?
w/ knee extension
when is compression force on the patella worse?
in 90 degree flexion and w/ quad contractions
what is the approximate compression force on the patella w/walking?
~25-50% BW
what is the approximate compression force on the patella w/ running
5-6x BW
when does the knee joint reaction force increase w/ CKC
w/ knee flexion
when does the knee joint reaction force increase w/ OKC
w/ knee extension
describe the osteokinematics of the TF joint?
Flexion= caudal glide
Extension: cranial glide
Tibia IR: lateral glide
Tibial ER: medial glide
what type of joint is the PF joint?
modified ovoid joint
what are the articulating surfaces of the TF joint
Femoral condyles: convex
Tibial plateau: concave
what are the abd and add mvmts of the knee considered as?
not physiological mvmt but can be assessed w/ glides
expain the arthrokinematics of the TF joint
flexion: posterior glide
extension: anterior glide
abd: lateral glide
add: medial glide
what is the resting position of the knee
30 degree flexion
what is the CPP of the knee
full extension and ER
what is the capsular pattern of the knee
greater limitation of flexion > extension
where is the prepatellar bursae of the knee?
b/w skin and anterior patella
what is the most commonly affected bursae of the knee?
prepatellar bursae
what is the suprapatellar bursae?
located b/w rectus femoris ms and femur
where is the deep infrapatellar bursae
b/w patellar tendon and tibia
where is the superficial/subcutaneous infrapatella bursa?
b/w skin and tibial tuberosity
where is the semimembranosis bursae located?
located b/w medial head of gastroc and capsule of the knee
where is the semitendinosis bursa
between tibia and pes anserine
when is the ST bursae generally an issue?
w/ knee over use injuries
how is the MCL of the knee
broad and flat shapes
ranges from medial femoral epicondyle to medial proximal shaft of the tibia and attachments to medial menisus
what happens on brush test w/ MCL tear of the knee
negative brush test (no effusion) since its a extra articular ligament
what is the function of MCL of the knee
prevents valgus stress and tibia IR
how is the LCL of the knee
round in shape
extends from lateral epicondyle of the femur to the upper end of the lateral fibula
does the LCL of the knee attach to meniscus
no
what happens on brush test w/ LCL of knee rupture?
- brush test since extraarticular
what is the function of LCL of the knee
prevents varus stress
where does the ACL of knee extend from?
From anterior medial aspect of the tibia and extends superiorly/ posteriorly to femoral condyle
what type of ligament is the ACL of the knee?
intra articular thus lot of swelling when injured
what is the fct of ACL of the knee?
Restrains anterior translation of tibia on femur
Backwards sliding of the femur and hyperextension of the knee
Controls tibia IR on the femur in femoral extension of 0-30 degrees
is there a difference b/w strain on ACL in CKC or OKC?
no difference
what can help control force on ACL in CKC
the hamstrings co-contraction
where does the PCL of the knee extend from
From posterior tibia and extends superiorly and anteriorly to medial femoral condyle
what type of ligament is the PCL?
Intra-articular and extra synovial ligament: issue will lead to knee effusion
what is the function of the PCL?
restrains posterior translation of the tibia on the femur
describe the medial meniscus?
c shaped
longer than lateral meniscus
adherent to MCL thus less mobile than LCL
covers ~50% of medial articular surface of tibia (less than lateral) and thus more prone to OA
describe the lateral meniscus?
u shaped
covers ~75% of tibial articular surface
no attachment to LCL thus more mobile
explain the vascularization of the meniscus?
peripheral 1/3 is well vascularized, inner 1/3 not well
what are the main function of the meniscus?
- Vital for knee stability
- Lubrification
- Nutrition
- Improve weight distribution
- Reduce friction
- Prevents excessive HE
- Prevents capsule from getting into the jt
- Shock absorption: protects/minimizes the amount of stress on articular cartilage
what happens in the event of a hyperpronated foot?
clacaneal valgus and thus increased stress on tendon
halux valgus of 1st MTP
increased tibia and femur IR
leg appears shorter
increase in Q angle leadingh to increased lateral translation of the patella
increased stress on lateral side of PF joint
what happens in a hyper supinated foot?
decreased shock absorption
increase stress in joint above
decreased tibia and femur IR