Knee Flashcards
What kind of joint is the knee?
Condyloid joint - 2 degrees of freedom (flexion/extension; IR/ER when flexed)
Stability of the knee comes primarily from
Soft tissues, ligaments, and muscles, not bones
Normal genu valgum
170-175 degree angle on the lateral side of the knee; formed by the femur which is angled medially (due to the 125 degree inclination) and the tibia which runs straight up and down.
Should be developed by 3 years of age
Excessive genu valgum
Less than 165 degrees
Genu varum
Greater than 180 degrees.
As one ages and developed arthritis, it’s more common for people to develop genu varum because the medial compartment shuts down and you begin to have compression medially and tension laterally
Why would someone have a poor squat position? (knock kneed position)
(Knock kneed position is femoral adduction and IR)
Weak gluteus medius, and poor eccentric control of the posterior lateral hip muscles, they can’t eccentrically control the femur from collapsing. Requires major proximal strengthening neuromuscular control program for the hips
Capsule encloses … and is reinforced by …
Medial and lateral tibiofemoral joints and PFJ.
Capsule is reinforced by fascia, ligaments, and muscles
Patella
Top called the base or superior pole. Bottom called the apex or inferior pole.
Posterior side has 3 facets: lateral, medial, and odd facet (most medial).
Sesamoid bone - increases mechanical advantage (increases IMA). If you don’t have a patella you can’t produce as much quad torque
Tibiofemoral joint
Between the convex femoral condyles and the flat (concave) tibial plateaus.
Shape of this joint permits extensive motion in the sagittal plane (0-140 degrees of flexion).
Stability from muscles, ligaments, and fascia
Menisci are what type of discs
Fibrocartilaginous discs - handles compressive forces much better than hyaline cartilage does
The menisci are anchored to the
intercondylar region of the tibia plateau by their anterior and posterior horns
External edges of the menisci are attached to the tibia and capsule by
Coronary (meniscotibial) ligaments
Coronary ligaments are
Relatively loose, allowing the menisci to pivot, especially lateral
What connects the two menisci anteriorly?
Transverse ligament
What attaches to the medial meniscus? The lateral meniscus?
Semimembranosis attaches to the medial, and the popliteus attaches to the lateral.
They stabilize the menisci during movement
Blood supply to the meniscus is
Greatest near the periphery, otherwise it’s 75% avascular, can’t really heal themselves
Where does the pain come from when the menisci are torn?
It comes from the inflammatory process, not the tear itself. Menisci are predominately aneural, except near the anterior and posterior horns, so there are no pain fibers to the meniscus. People with arthritis can have tears and not know because they have such small degenerative tears that they never elicited an inflammatory process and aren’t capable of producing pain by themselves
Medial meniscus
C-shaped, external border attaches to MCL
Lateral meniscus
Circular shaped, external border attaches only to lateral capsule. Also attaches to the femur via posterior meniscofemoral ligaments
Popliteus tendon passes between
LCL and lateral meniscus
What happens when surgeon does a meniscectomy?
Removes piece of meniscus, changes the weight bearing forces to the articular cartilage. Individual is likely to develop early arthritis, so whenever possible the surgeon wants to save as much of the meniscus as they can
Primary function of the menisci
To reduce compressive stress at the TFJ
Secondary functions of the menisci
Stabilize the joint during movement Lubricating articular cartilage Reducing friction Guiding the knee's arthrokinematics Increase bony fit of TFJ
Osteokinematics of the TFJ
Flexion and extension happen in the sagittal plane, medial-lateral axis.
Migrating axis alters length of the IMA of the flexors and extensors.
IR/ER happen in transverse plan, vertical axis of rotation, only when the knee is flexed 40-50 degrees total
Tibia on femoral extension
Concave tibia rolls and slides anteriorly on the convex femoral condyles
Femoral on tibia extension
Convex femoral condyles roll anteriorly and slide posteriorly on the concave tibia
What directs the roll for knee extension?
The quads
When going into knee extension which way does the menisci go?
Anteriorly
Tibia on femoral flexion
Tibia rolls and slides posteriorly
Femoral on tibia flexion
Femur rolls posteriorly and slides anteriorly
What directs the roll for knee flexion?
The hamstrings
When going into knee flexion which way does the menisci go?
Posteriorly
Screw home rotation
During tibia on femoral knee extension, the last 10 degrees of extension requires ER of the tibia.
During femoral on tibia knee extension, the femur will IR during the last 10 degrees of knee extension
Reasons for the screw home mechanism
- Shape of medial femoral condyle - slightly longer than the lateral condyle. To accommodate for this during extension there needs to be involuntary rotation so the medial condyle doesn’t get stuck on medial tibial plateau so that you can lock your knee in 0 degrees and land on your heel in heel strike.
- Passive tension of ACL - ACL runs from lateral femoral condyle to medial tibial plateau so there is greatest tension developed in the ACL during extension and it ER’s the tibia
- Lateral pull of quads - because of this you get ER of the tibia during terminal knee extension
What unscrews the screw home mechanism>
The popliteus muscle
Patellofemoral joint
Between the articular surface of the inferior aspect of the patella and the trochlea groove.
Tibia on femoral, patella slides against femur.
Femoral on tibia, femur slides against patella.
Patellofemoral pain syndrome
Femur is not moving right. Strengthening the posterior lateral hip muscles is a great advantage to most patients who have anterior knee pain because that femur during closed chain motion is not on the track, and if it’s not on the track and it starts to collapse into femoral adduction and IR you’re going to rub against the cartilage of the patella and that is going to become painful.
Doing straight leg raises are good for
Patellofemoral pain because you haven’t engaged the patella on the femur yet so it doesn’t cause irritation.
Have good isometric quad contraction.
Extensor lag - secondary to weak quad muscles
At 135 degrees of knee flexion the patella contacts the femur near its
Superior pole only.
Lateral edge of lateral facet and the odd facet share articular contact with the femur
90-60 degrees of flexion PFJ
Occupies greatest contact area with the femur
As the knee extends through the last 20 degrees of knee flexion the primary contact point
Migrates to the inferior pole
In full knee extension the patella
Rests above the intercondylar notch (or above trochlear groove) against the suprapatella fat pad, not contacting the femur at all.
Patella is most mobile in the fully extended knee
MCL attachments
Runs from medial femoral condyle to medial tibial condyle.
Anterior fibers attach just posterior to the pes anserine. Posterior fibers attach to the post-med capsule, medial meniscus, and semimembranosis
LCL attachements
Runs from lateral femoral condyle and attaches to fibula head with the biceps femoris. Does not attach to lateral meniscus.
Functions of the MCL and LCL
Primary function is to limit motion in the frontal plane: MCL resists valgus forces, LCL resists varus forces.
Second function collaterals limit knee extension shared with posterior capsule OPL, knee flexor muscles, ACL.
Limited resistance ER/IR in flexion
Cruciate ligaments
Both intra-articular and extrasynovial.
Supplied from the medial/lateral geniculate arteries.
Provide great stability to the knee especially in anterior/posterior direction.
Can limit extremes of all motion
ACL attachments and function
Attaches from the medial side of lateral femoral condyle to the anterior intercondylar area of the tibial plateau.
Posterior-lateral bundle is the main component, (also anterior-medial bundle).
Prevents anterior tibial translation or posterior femoral translation
Where is the ACL taut?
Most fibers especially the PL bundle is taut as knee approaches knee extension, but some fibers remain taut throughout knee ROM
Mechanism of injury to the ACL
Hyperextension of the knee
Valgus face with foot planted
Either of the above combined with large violent internal axis rotation torque
Most common ligament damaged in the knee
Rehab non-op vs reconstruction
Only 7-8% chance of getting back to competitive play without reconstruction
PCL attachments and function
Lateral side of medial femoral condyle to posterior intercondylar area of the tibia.
Anterior-lateral bulk and posterior-medial.
Prevents posterior translation of the tibia or anterior translation of the femur
When is the PCL taut?
Majority of fibers are taut with extreme flexion, but some fibers are taut throughout knee ROM
Mechanism of injury to PCL
Hyperflexion or hyperextension Pre-tibial trauma (dashboard injury) Large valgus or varus force Above with severe axial rotation Most surgeons will not reconstruct isolated PCL injuries - heals well on its own with conservative management
Knee extensors: quads
Rectus femoris origin: AIIS
Vastus lateralis origin: greater trochanter
Vastus medialis origin: medial lip of linear aspera
Vastus intermedius origin: anterior/lateral fermoral shaft
All insert on tibial tuberosity via patella tendon
All innervated by femoral nerve
Rectus can do hip flexion because it crosses the hip
Vastus médiales obliques (VMO)
Runs in medial direction to try to stabilize the patella. The overall force of the patella is lateral.
Knee flexors: hamstrings
All originate on ischial tuberosity (except short head of biceps which is posterior aspect of proximal femur).
Semitendinosis insertion: pes anserine
Semimembranosis insertion: posterior medial tibia
Biceps femoris insertion: fibular head
All innervated by sciatic nerve
Can also all do hip extension (except short head of biceps)
The hamstrings can also help with
Rotation (semitendinosis and semimembranosis can do IR, biceps femoris can do ER)
In flexion the MCL is
On slack. If you splint this person in flexion you’ve destroyed the gait cycle, can’t heel strike, and will have hard time getting extension back. If you splint then in extension the MCL is going to be so tight that it will be very difficult getting flexion back. So don’t splint them at all, let them get normal ROM throughout the day and it should be fine
Which sagittal plane motion is easier to get back in the knee?
Flexion! You should always try to get extension back first
