15. Anatomy of the Knee Flashcards
Knee Joint
Bicondylar
Articulation between distal femur and proximal tibia
Locking Mechanism
- Shape of femur
flexion: femoral surfaces round
extenstion: femoral surfaces flat - Rotation: medial rotation of femur on tibia in extension- tightens ligaments of the knee
- Centre of gravity
- maintains gravity
Femoral angle
femurs are slighty adducted, bringing knee joint under pelvis
critical for weight bearing
anatomical axis- follows adductions of femur
Q angle
difference between anatomical axis and mechanical axis
~15degrees
Varus deformity
where tibia is medially displaced relative to femur
Decrease in Q angle
‘Bow legged’
This causes increased stress which can lead to joint degeneration
tear of LCL
Valgus deformity
where tibia is laterally displaced relative to femur
Increase in Q angle
This causes increased stress which can lead to joint degeneration
Tear of MCL
Ligaments of the knee
Extracapsular- medial and lateral collateral- prevent valgus and varus movement
intracapsular- anterior and posterior cruciate- prevent anteroposterior movement
Lateral collateral ligaments
aka fibular ligaments
Extend from lateral epicondyle to head of fibula
strong round cord
prevents medial displacement of tibia
-prevents varus deformity
Medial collateral ligaments aka tibial ligaments
Extends from medial epicondyle to tibia
broad flat band
longer than lateral ligament
Prevents lateral displacement of tibia
-prevents valgus deformity
tearing this ligament is more common
Where is the medial meniscus attached to?
attached to medial collateral ligament
Anterior cruciate ligament
anterior in relation to tibia
- Attached to intercondylar fossa
- prevents anterior displacement of tibia relative to femur
weaker
commonly injured in sports
Posterior cruciate ligament
Posterior in relation to tiba
- Attached to intercondylar fossa
- prevents posterior displacement of tibia relative to femur
- Principle stabilizer when knee is flexed
Injury of anterior cruciate ligament
- Common sports injury
- caused by sharp twisting of knee
- Immediate decreased range of movement
Lachman test
Patient in supine position with knee bent 20-300 of flexion
- Move tibia anteriorly and posteriorly while maintaining position of femur
- Laxity during this manoeuvre indicates anterior cruciate ligament injury
Lateral and Medial menisci
Lateal- smaller, more circular
Medial menisci- larger
- Deepen articulating surfaces, stability
- Shock absorbers
- Provides smooth viscous film for joint
Medial menisci
Less mobile than lateral menisci
attached to medial collateral ligament
Unhappy triad
blow to side of knee
sudden twisting
locking of the knee
Rupture of
- anterior cruciate ligament
- medial collateral
- medial meniscus
poor blood supply to intracapsular structures- doesnt repair easily
Quadriceps function
- Extends leg
- Stabilizes muscles of the knee
- forms quadriceps tendon
Vastus medialis oblique
prevents lateral trafficking of patella
Extensor mechanism of knee
consists of quadriceps, quariceps tendon, patella, patellar ligament
Lateral and medial patellar retinaculum
help stabilised the knee
Patella
largest sesamoid bone
protects quadriceps tendon from stresses f
Extensor mechanism injury
Rupture of quadriceps tendon or patellar ligament
-Fracture of patella
-Dislocation of patella (common due to sudden twisting)
results in loss of active extension
Extensors of leg
Quadriceps
Flexors of leg. What are their other functions
Hamstrings and gastrocnemius
medial/lateral rotation of leg when knee is flexed and extends thigh
Gastrocnemius
powerful flexor of the leg at the knee joint
Popliteus muscle
Unlocks knee joint
origin: tibia
inserts: lateral condyle
Laterally rotates femur on tibia when foot is on ground
Bursae
fluid filled synovial sacs
protection of quadriceps tendon from sheering forces, reduce friction
suprapatellar- continuous with synovial membrane
Prepatellar
Infrapatellar bursa
Bursitis
-Inflammation of bursae
- Prepatellar bursae (seen in carpet fitters)
- Infrapatellar bursitis (‘clergyman’s knee’)
-due to repetitive movements or direct pressure
Baker’s (popliteal cyst) cyst
Accumulation of synovium in the poplital fossa
due to herniation or swelling of bursae
reduce movement at joint
Presents as swelling in the popliteal fossa
Treat by aspiration and cortisone injection
Blood Supply
-Anastomosis around knee
femoral artery and popliteal artery
-Limited blood supply to intracapsular structures
