l15:anatomy of the knee Flashcards
what is the articulation between the distal femur and proximal tibia
The knee aka synovial bicondylar hinge joint
Articulation between femur and patella
what are the functions of the knee
-Weight-bearing
- Mobility
- -extension/flexion
- -some rotation when flexed
what are the different factors that help improve stability and strength
Bony factors:
- Bony expansions
- Locking mechanism
- Femoral angle
Soft tissue factors:
- Ligaments
- Menisci
- Muscles
go over bony expansions and what they provide for the leg
intercondylar fossa
tibial condyles
epicondyles
femoral condyles
Provides a strong base
locking mechanism 1: describe the shape of the femur
- in flexion:- femoral surfaces round
- in extension- femoral surfaces flat
locking mechanism 2 : describe rotation of the knee
Medial rotation of femur on tibia in extension
- Tightens ligaments of the knee
locking mechanism 3 :describe the centre of gravity
Centre of gravity in front of knee
- Maintains extension
what is the importance of the femoral angle
Adducted femur brings knee joint under pelvis
Critical for weight bearing
Occurs during development
what is the femoral angle made up of
- anatomical axis
- mechanical axis
- forming the Q angle
what is the normal alignment of the knee
Normal alignment of joint (mechanical axis) :
Vertical line through centre of femoral head,
centre of knee and centre of ankle
what is the anatomical axis and mechanical axis
Anatomical: follows Asis
mechanical: vertical line through centre of femoral head, centre of knee and centre of ankle
where weight and force are distributed
describe the varus deformity Genu Varum
Deformity in the angle between femur and tibia
Medial displacement of the tibia
- Common in children under 2, rickets
Pushes knees apart - ‘Bow-legged’= Decrease in Q angle
caused by increased stress which causes joint degeneration
describe Valgus deformity (Genu valgum)
Lateral displacement of the tibia
- Common in children aged 2-4, rickets, arthritis
Brings knees together - ‘Knock-kneed’
= Increase in Q angle
the stress also results in joint degeneration
what are the ligaments of the knee
2 groups:
Extracapsular – outside capsule
- Medial collateral - Lateral collateral
&
Intracapsular – inside capsule
- Anterior cruciate - Posterior cruciate
describe the lateral/fibular collateral ligament
Strong round cord
- Prevents medial displacement of tibia
what does a tear in the LCL cause
Tear of LCL = Varus deformity (medial)
describe the Medial/tibial collateral ligament
Broad flat band
- Reinforces joint capsule
- Prevents lateral displacement of tibia
what does a tear of the MCL cause
= Valgus deformity (lateral)
what is the intracapsular ligament
divided into the anterior cruciate ligament
- posterior cruciate ligament
- anterior and posterior in relation to tibia
what is the function of the posterior and anterior cruciate
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
describe the cruciate ligaments
look at slide 16
what is the 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
what happens with the weakness of Anterior cruciate ligament
Weaker - can become injured
- Common sports injury
- Caused by sharp twisting of knee
- Immediate decreased range of movement
does the posterior cruciate ligament
Stronger - Rarely injured
- Principle stabilizer when knee flexed
describe the menisci of the joint
Crescent-shaped plates of fibrocartilage
- Deepen the articulating surfaces/stability - Shock absorbers - Provides smooth viscous film for joint
what are the 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
what is the unhappy triad
Twisting on a flexed knee/blow to lateral side Contact sports (rugby tackle) Locking of the knee Rupture: - Anterior cruciate ligament - Medial collateral ligament - Medial meniscus (attached to MCL)
what is the iliotibial tract
Iliotibial tract
- Reinforces joint capsule
- Stabilizes extended knee
(gluteus maximus, tensor fascia lata)
what muscles are involved in extension of the leg
Quadriceps extends leg
Major stabilizing muscle of the knee
4 heads - Rectus femoris
Vastus lateralis
Vastus intermedialis
look at slide 24
Vastus medialis
what is the extensor mechanism
Patella
- Protects quadriceps tendon from stresses during locomotion
- Smooth oval facet of posterior surface for articulation with femur
- Lateral patellar retinaculum
- Medial patellar retinaculum
what is the 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
what are the flexors of the leg
Hamstrings and gastrocnemius flex leg
Hamstrings actually three muscles:
- Biceps femoris
- Semimembranosus
- Semitendinosus
- Also medially and laterally rotates leg when knee flexed
- And extends thigh
describe unlocking of extended leg
- Popliteus unlocks the knee joint
- Laterally rotates femur on tibia when foot is on ground
what is the synovial membrane
From margins of articular surfaces of femur to tibia
Attached to patella
Extends superiorly behind quadriceps tendon
Cuffs anterior surface of cruciate ligaments
describe the bursae
Synovial fluid filled sac lined by synovial membrane
- Protection
- Reduce friction
describe other bursae
32
describe 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
describe Infrapatellar bursitis (‘clergyman’s knee’)
- After prolonged periods of prayer clergymen sat back on their heels bringing infrapatellar bursa in contact with floor
describe the Bakers (popliteal) cyst
Abnormal fluid filled sacs in popliteal fossa
- Due to herniation of synovial membrane/bursa
Common in patients with chronic
inflammatory joint disease (e.g. arthritis)
- Presents as swelling in the popliteal fossa
- Can affect joint movement
describe the vascular supply
Anastomosis around knee
- Femoral artery
- Popliteal artery
Limited blood supply to intracapsular structures
- Poor repair following injury
