week 5 Flashcards
Convex-concave golden rules
Rule #1: Where the “male” joint surface is moving then roll and glide occur in opposite directions
Rule #2: Where the “female” joint surface is moving then roll and glide occur in the same directions
What is the screw home mechanism?
- SPIN
*The rotation between the tibia and the femur that occurs during terminal knee extension
➢Medial femoral condyle is larger than the lateral femoral condyle
*“Knee locking”
When does it occur
*During extension, the lateral side of the joint completes the motion, resulting in the tibia laterally rotating in the last 20o of knee extension.
*Lateral rotation causes a passive tension in the ACL which creates a fulcrum for lateral rotation and causes it to cross over the PCL and “lock” the knee joint into extension.
How does the patella move?
- Extension: the patella is NOT in contact with the trochlear groove
- 10-20° of knee flexion: the inferior margin of patella articulates with trochlear groove of femur
- As knee flexion increases the contact area of the patella moves proximally
- As knee flexion increases the contact area of the condyles moves posteriorly
Factors contributing to stability at the knee joint
- STATIC(passive):combination of non contractile and bony elements
e.g. menisci, ligaments, capsule, articular cartilage, ITB - DYNAMIC (active): muscles acting on or across the
knee joint
Static: Menisci functions at knee joint
- withstand load bearing forces
2. increase contact area at the tibiofemoral joint → reduces stress at the joint surfaces
3. assist in movement of femoral condyles
4. assist in stabilising translatory movements
what attaches to Medial meniscus
- medial collateral lig
- anterior and posterior cruciate ligs
- semimembranosus
what attaches to Lateral meniscus
- posterior cruciate lig
- medial femoral condyle via meniscofemoral ligs
- popliteus
Movements of the menisci
Considerable distortion throughout range
* Both move posteriorly during flexion (lateral > medial)
* Keeps the menisci under the femoral condyles
*Both active and passive elements contribute to movt.
Static: Ligaments
- Combinations of structures provide stability at the knee – no single structure in isolation
* Concept of primary and secondary restraints
* ✓work together to provide stability
✓primary restraints – ‘workers’
✓secondary restraints – ‘helpers’
* If primary restraint is damaged, the secondary restraint takes the load -> deterioration and increased joint instability
static- anterior tibial displacement 1st & 2nd restraint
primary- ACL
secondary- MCL,ITB
static- posterior tibial displacement 1st & 2nd restraint
primary- PCL
secondary- MCL,LCL, obligue popliteal ligament
static- abductor (valgus) 1st & 2nd restraint
primary- MCL
secondary- ACL, PCL, posterior oblique ligament
static- adduction (varus) 1st & 2nd restraint
primary- not ligamentous
secondary- LCL, posterolateral corner
static-internal tibial rotation 1st & 2nd restraint
primary- MCL, posteromedial corner
secondary- ACL, PCL
static- external tibial rotators 1st & 2nd restraint
primary- posteolateral corner complex
secondary- ACL, PCL
Dynamic: Iliotibial band (ITB)
- Part of the more extensive fascia lata
- Attachments:
- From the fascia surrounding tensor fascia lata and gluteus maximus and medius
- Extends to the anterolateral tibia
- Attachments:
- Crosses both hip and knee
- Has fibrous connections to biceps femoris, vastus lateralis and the lateral patellar retinaculum – may influence patella tracking through these connections
iliotibial band functions
- Affords some lateral joint stability particularly in flexion
Assists ACL in preventing anterior slide of tibia on femur
Quadriceps femoris – function
- Major extensor of knee
- All parts of quadriceps femoris work
throughout the range of knee extension - Stabilises the patella within trochlear groove
- Greatest force needs to be developed at the end of extension range – final 15degs greatest mechanical disadvantage
Vastus medialis – actions and functions
- Vastus medialis – longitudinal fibres (strongly bound to vastus intermedius proximally)
- Knee extensor
- Vastus medialis – oblique fibres
- Weak knee extensor
- Prominent activation in last 40o of knee extension
- Medial patella stabiliser – prevents vastus lateralis from laterally dislocating the patella
- Increases the efficiency of vastus lateralis in knee extension by realigning pull
Tibiofibular joints
- Three joints:
- Superior tibiofibular joint
- synovial, mulitaxial, plane
- Intermediate tibiofibular joint
- fibrous(syndesmosis)
- interosseusmembrane
- long fibres
- Inferior tibiofibular joint
- fibrous(syndesmosis)
- short fibres
Ankle (talocrural) joint Classification and movement
- Classification
- Synovial, uniaxial, hinge
- Movements
- Dorsiflexion 30°
Plantarflexion 50°
Articular surfaces
- Tibia – “female” surface
Inferior (trochlear) surface of the tibia
Medial (tibial) and lateral (fibular) articular facets - Talus - male surface
Tibiotalar surface is weightbearing
Medial and lateral articular facets are non- weightbearing