Anatomy of the knee Flashcards
Knee joint
Articulation between distal demur and proximal tibia
Synovial bicondylar hinge joint
Articulation between femur and patella
Functions of the knee
Weight bearing
Mobility
- extension/ flexion
- some rotation when flexed
Factors strengthening the joint
Bony factors
- bony expansion
- locking mechanism
- femoral angle
Soft tissue factors
- ligaments
- menisci
- muscles
Bony expansions
Provides strong base
Epicondyles
Femoral condyles
Tibial condyles
Intercondylar fossa
Locking mechanism
Shape of femur
Rotation
Centre of gravity
Shape of femur
In flexion
- femoral surfaces round
In extension
- femoral surfaces flat
Rotation
Medial rotation of femur on tibia in extension
Tightens ligaments of the knee
Centre of gravity
Centre of gravity in front of knee
Maintains extension
Femoral angle
Adducted femur brings knee joint under pelvis
Critical for weight bearing
Occurs during development
Varus deformity
Deformity in the angle between femur and tibia
Medial displacement of the tibia
- common in children under 2, rickets
Bow legged
Valgus deformity
Lateral displacement of the tibia
- common in children aged 2-4, rickets, arthritis
Knock kneed
Ligaments of the knee
Provide stability
Two groups of strong ligaments
Extracapsular
- medial collateral
- lateral collateral
Intracapsular
- anterior cruciate
- posterior cruciate
Lateral/ fibular collateral ligament
Strong round cord
Prevents medial displacement of tibia
Tear of LCL= varus deformity (medial)
Medial/ tibial collateral ligament
Broad flat band
Reinforces joint capsule
Prevents lateral displacement of tibia
Tear of MCL- valgus deformity
Intracapsular ligaments
Anterior cruciate ligament
Posterior cruciate ligament
Cruciate= cross shaped
Function of cruciate ligaments
Anterior cruciate
- prevents anterior displacement of tibia on femur
Posterior cruciate
- prevents posterior displacement of tibia on femur
Maintain femur against tibia
- always one ligament tense
Cruciate ligaments
Posterior cruciate ligament
- passes upward, forward and medially
Anterior cruciate ligament
- passes upwards, backwards and laterally
Anterior cruciate ligament
Weaker- can become injured
- common sports injury
- caused by sharp twisting of knee
- immediate decreased range of movement
Lachman test
- patient in supine position with knee ben 20-30’ of flexion
Move tibia anteriorly and posteriorly while maintaining position of femur
Laxity during this manoeuvre indicates anterior cruciate ligament injury
Posterior cruciate ligament
Stronger- rarely injured
Principle stabiliser when knee flexed
Menisci of joint
Crescent shaped plates of fibrocartilage
Deepen the articulating surfaces/ stability
Shock absorbers
Provides smooth viscous film for joint
Menisci attachments
Horns of menisci attached to intercondylar area of tibia
Mobile- accommodates rolling of femoral condyles
Medial meniscus less mobile
- attached to medial collateral ligament
Unhappy triad
Twisting on a flexed knee/ blow to lateral side
Contact sports
Locking of the knee
Rupture
- anterior cruciate ligament
- medial collateral ligament
- medial meniscus
Poor blood supply to intracapsular structures so doesn’t repair easily
Muscles acting on knee joint
Knee reinforced by tendons from surrounding muscles and iliotibial tract
Iliotibial tract
- reinforces joint capsule
- stabilises extended knee
Extensors of leg
Quadriceps extends leg
Major stabilising muscles of the knee
4 heads
- rectus femoris
- vastus lateralis
- vastus intermedialis
- vastus medialis
Patella
Protects quadriceps tendon from stresses during locomotion
Smooth oval facet of posterior surface for articulation with femur
Extensor mechanism injury
Rupture of quadriceps tendon or patellar ligament
Fracture of the patella
- due to fall or blow to knee
Results in loss of active extension
Dislocation of patella common
- due to sudden twisting/ jumping or ligamentous laxity
Flexors of leg
Hamstrings and gastrocnemius flex leg
Hamstrings are three muscles
- biceps femoris
- semimembranosus
- semitendinosus
Also medially and laterally rotates leg when knee flexed and extends thigh
Unlocking of extended leg
Popliteus unlocks knee joint
Laterally rotates femur on tibia when foot is on ground
Synovial membrane
From margins of articular surfaces of femur to tibia
Attached to patella
Extends superiorly behind quadriceps tendon
Cuffs anterior surface of cruciate ligament
Bursae
Synovial fluid filled sac lined by synovial membrane
Protection
Reduce friction
Bursitis
Inflammation of bursae
Due to repetitive movements or direct pressure
Prepatellar bursitis (housemaid's knee) - seen in carpet fitters
Leaning forward on the knees brings the prepatellar bursa in contact with floor
Baker’s (popliteal) cyst
Abnormal fluid filled sacs in popliteal fossa
- due to herniation of synovial membrane/ bursa
Common in patients with chronic inflammatory joint disease
Presents as welling in the popliteal fossa
Can affect joint movement
Vascular supply
Anastomosis around knee
Femoral artery
Popliteal artery
Genicular branches come from these
Limited blood supply to intracapsular structures
- poor repair following injury
