Knee Flashcards
Tibiofemoral joint
- tibia and femur
- medial condyle has larger contact w/ tibia than patella
- trochlear groove is higher lateral than medial
Site of impingement for ACL
-intercondylar fossa
Sulcus angle
- measured via radiograph
- lines from the highest peaks of medial and lateral femoral condyle to the deepest part of the trochlear groove
- angles of 138* +/- 6* are normal
- more shallow groove = susceptible to dislocation
Congruency angle
- measured via radiograph
- reflects patella’s position in trochlear groove and midpoint of sulcus angle compared to lowest portion of patellar ridge
- if patellar ridge line falls medial to midpoint of sulcus angle, then value is negative and if lateral then value is positive
- medial tilt of patella 6* is normal and lateral tile of 16* may be associated with subluxation
Tibia: medial vs. lateral
- medial condyle is longer (A to P) than lateral
- osseus structure is less stable due to lack of bony congruency - role of menisci is really important to tibiofemoral jt
Genu valgum vs. varum
- medial angle >185* = valgum –> lateral joint line is compressed and medial is distracted
- angle <175* = varum –> medial compression and lateral distraction
Mechanical axis in single leg vs. double leg stance
-during single leg = axis is shifted medial due to shift in hip position
Menisci
- wedge-shaped fibrocartilaginous disks
- on tibial plateau (cover approx. 2/3 of it)
- disperse WB forces
- thick centers and thin edges
Lateral meniscus
-more O shaped
Medial meniscus
-more C-shaped
Vascular supply to mensici
- comes from periphery
- perihperal 1/3 receives blood supply from capsular arteries (red zone)
- other 2/3 have poor blood supply (red-white, white zone)
What holds the menisci in place?
- coronary ligaments
- other ligaments
- lateral meniscus is connected anteriorly to medial meniscus by transverse ligament and to patella by patellomeniscal ligament (thickening of anterior capsule), posteriorly to popliteus and PCL and to medial femoral condyle via meniscovemoral ligament
- medial meniscus attached to transverse and patellomeniscal ligaments, posteriorly to semimembranosus
Which meniscus is more mobile?
-lateral
Roles of meniscus
1) increased contact area
2) assist with joint gliding
3) limit hyperextension
4) provide cushion
5) support WB surfaces for tibiofemoral joint
Menisci innervation
- pain receptors
- joint mechanoreceptors
Lateral knee compartment
- 3 regions:
1) anterior - lateral retinaculum, ITB, arcuate complex
2) middle
3) posterior
Lateral retinaculum components
- superficial oblique layer extends from ITB to lateral patella
- transverse retinaculum extends from ITB to lateral patellar border
Arcuate complex
- lateral collateral ligament
- arcuate ligament
- popliteus tendon
LCL
- extracapsular
- lateral epicondyle to biceps femoris on femoral head
- restrains excessive lateral rotation of tibia
Medial compartment
- posterior 1/3 reinforced by posterior oblique ligament and semimembranosus
- oblique popliteal ligament reinforces posteromedial aspect
- anterior third consists of deep capsule and medial retinaculum
- middle third is MCL
Posterior oblique ligament
- thickening of medial capsular ligament from adductor tubercle of femur to tibia and posterior capsule
- provides resistance to valgus forces near full extension
MCL
- superficial portion is middle layer of medial compartment - originates in posterior medial femoral condyle and attaches below pes anserine on tibia
- superficial MCL restrains valgus stress
- MCL is on slack in a flexed position
- deep portions of MCL are separated from superficial by bursa
- meniscofemoral and meniscotibial ligaments
- role of deep layer is meniscal support and ctonrol
Knee joint capsule
- formed by tendons
- large lax capsule allows for freedom of motion
- anteromedial and anterior lateral capsules are thick
- posterior capsule is thin
Cruciate ligaments
- intracapsular
- blood supply from genicular artery
- innervated by branches of tibial nerve
- 3 different mechanoreceptors (ruffini, pacinian, golgi tendon)
ACL
- originates at lateral femoral condyle and attaches to intercondylar eminence
- 2 distinct bundles: anterior medial (smaller) and posterolateral
Posterolateral bundle of ACL
-taut in extension and provides greatest restraint to anterior translation in that position until 20* flexion
Anterior medial bundle - ACL
- tight throughout flexion and is tested when anterior translation tests are performed in flexed position
- anterior drawer will be positive even if posterolateral bundle is intact
- increases in tension from 20-90* flexion
Other motions that cause ACL to be taut
- internal rotation of tibia (specifically anterior medial bundle)
- provides stabilizing force against knee hyperextension and secondary support against varus or valgus motions
Non-contact injury to ACL
- often a deceleration injury that occurs in a position of slight flexionc oupled w/ medial or lateral tibial rotation
- in medial rotation ACL winds around PCL
- in lateral rotation ACL stretches over lateral condyle
Oblique popliteal ligament function
-reinforces posteromedial capsule obliquely on a lateral to medial diagonal from proximal to distal
Posterior oblique ligament function
-reinforces posteromedial capsule on a medial to lateral diagnoal from proximal to distal
Arcuate ligament lateral branch function
-reinforces posterolateral capsule on amedial to lateral diagonal from proximal to distal
PCL
- from femoral condyle to posterior tibial tubercle
- anterolateral bundle (larger - 95% of sustance) and posteromedial bundle (5% of substance)
Anterolateral bundle - PCL
- tight in flexion
- restoration of this bundle is surgical priority
- bears 50-75% of posterior force between 40-120*
Posteromedial bundle - PCL
- taut in extension
- bears 57% of posterior force beyond 120*
PCL restrains…
-posterior displacement of tibia on teh femur - 95% of stability between 30* and 90* flexion
When does the greatest posterior tibial translation occur?
-between 70-90* knee flexion since secondary restraints (posterolateral capsule, popliteus, MCL) are too lax to contribute at these angles
PCL - MOI
- most common for isolated injury is hyperflexion of knee
- direct tibial posterior translation such as dashboard injury results in injuries to secondary restraints
- ER of tibia in an isolated posterior lateral corner tear is increased at 30* of knee flexion
VMO fiber orientation
- oriented 55* medially
- has been called the primary restraint to lateral migration of the patella
VMO evidence
-evidence suggests that the VMO cannot be selectively recruited to preferentially strengthen
Knee flexion/extension and varus/valgus
- slight amount of valgus associated w/ ext
- slight amount of varus associated w/ flexion
Screw home mechanism
- lateral rotation of tibia at terminal knee extension
- medial rotation of tibia must occur to allow knee to unlock and initiate flexion
Patella
- largest sesamoid
- medial, lateral facet
- odd facet -medial edge of patella which contacts the femur in deep angles of knee flexion
- only the inferior pole is in contact with femur during full knee extension
Patellar plicae
- folds
- often asymptomatic, but can cause irritation and inflammation resulting in plica syndrome
ligamentum muscosum
- inferior plicae
- attaches from intercondylar fossa to inferior patellar pole