T2 L15 Anatomy of the knee Flashcards
What is the knee joint?
Articulation between distal femur and proximal tibia
Articulation between femur and patella
What type of joint is the knee joint?
Synovial bicondylar hinge joint
What are the functions of the knee?
Weight bearing
Mobility
What factors strengthen the knee joint?
Bony factors - bony expansions - locking mechanism - femoral angle Soft tissue factors - ligaments - menisci - muscles
How do bony expansions strengthen the knee joint?
Provide strong base
Why does the locking mechanism strengthen the knee joint?
Reduces amount of energy required when extended
What are the 3 ways the locking mechanism strengthens the knee joint?
Shape of femur
- in flexion femoral surfaces are founded
- in extension the femoral surfaces are flat
Rotation
- medial rotation of femur on tibia in extension tightens the ligaments
Centre of gravity
- brings centre of gravity in front of knee to maintain extension
How does the femoral angle strengthen the knee joint?
Adducted femur brings knee joint directly under hip joint
Critical for weight bearing
What is the anatomical axis?
Follows long axis of femur
What is the mechanical axis?
Vertical line through centre of femoral head, centre of knee and centre of angle
Normal alignment of joint
How is the Q angle measured clinically?
Angle between anatomical and mechanical axis
Anatomical axis from ASIS to patella
Mechanical from tibial tuberosity through patella
What should the Q angle be?
Around 15 degrees
What is varus deformity?
Genu varum
Medial displacement of tibia pushes knees apart (bow-legged)
Decrease in Q angle
Common in children under 2 and rickets
Increased stress eventually results in joint degeneration
What is valgus deformity?
Genu valgum
Lateral displacement of tibia brings knees together (knock kneed)
Common in children aged 2-4, rickets, arthritis
Increased in Q angle
Increased stress eventually results in joint degeneration
What are the 2 groups of ligaments around the knee?
Extracapsular
Intracapsular
What are the 2 extracapsular ligaments?
Medial collateral ligament
Lateral collateral ligament
What are the 2 intracapsular ligaments?
Anterior cruciate ligament
Posterior cruciate ligament
What is the lateral / fibular collateral ligament and what does it do?
Strong round cord from lateral epicondyle of femur to head of fibular
Prevents medial displacement of tibia
What does a tear in the lateral collateral ligament cause?
Varus deformity
What is the medial / tibial collateral ligament and what does it do?
Broad, flat band from medial epicondyle on femur to medial condyle of tibia
Reinforces joint capsule
Prevents lateral displacement of tibia
What does a tear in the medial collateral ligament cause?
Valgus deformity
Describe the anterior cruciate ligament
Anterior in relation to tibia
Attaches to anterior intercondylar region of tibia, blends with medial meniscus and attaches to femur in intercondylar fossa
Passes upwards, backwards and laterally
What is the role of the anterior cruciate ligament?
Prevent anterior dislocation of tibia onto femur
How can the anterior cruciate ligament be injured and how would it present?
Common sports injury
Caused by sharp twisting of knee
Immediate decrease in range of movements
What is the Lachman test for?
Indicates anterior cruciate ligament injury
How is the Lachman test performed?
Patient in supine position with knee bent with 20-30 degrees of flexion
Move tibia anteriorly and posteriorly while maintaining position of femur
Laxity during this manoeuvre indicates anterior cruciate ligament injury
Describe the posterior cruciate ligament
Posterior in relation to tibia Attaches to posterior intercondylar region of tibia and to anteromedial femoral condyle Passes upwards, forward and medially Stronger ligament Principle stabiliser when knee is flexed
What is the role of the posterior cruciate ligament?
Prevent posterior dislocation of tibia onto femur
What are menisci?
Crescent-shaped plates of fibrocartilage
What is the function of the menisci?
Deepen articulating surfaces / stability
Shock absorbers
Provides smooth viscous film for joint
Which meniscus is larger?
Medial
What do the horns of the menisci attach to?
Intercondylar areas of tibia
Why is the medial meniscus less mobile?
Attached to medial collateral ligament
What is the unhappy triad?
Injury to anterior cruciate ligament, medial collateral ligament and medial meniscus
What can cause the unhappy triad?
Twisting on flexed knee / blow to lateral side
Contact sports
Locking of knee
What is the function of the iliotibial tract?
Reinforces joint capsule
Stabilises extended knee
What are the extensors of the leg?
Quadriceps
What are the 4 heads of the quadriceps?
Rectus femoris
Vastus lateralis
Vastus intermedialis
Vastus medialis
What prevents the patella moving laterally?
Oblique fibres of vastus medialis
What is the function of the patella?
Protects quadriceps tendon from stresses during locomotion
Smooth oval facet of posterior surface for articulation with femur
What flexes the leg?
Hamstrings
Gastrocnemius
What 3 muscles make up the hamstrings?
Biceps femoris
Semimembranosus
Semitendinosus
What is the function of the hamstrings?
Flexion at knee
Extension at hip
Medial and lateral rotation when knee is flexed
What does popliteus do?
Laterally rotates femur on tibia when foot is on ground to loosen ligaments.
Describe 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
What are bursa?
Synovial fluid-filled sac lined by synovial membrane
What is the function of bursae?
Protection
Reduce friction
What is bursitis?
Inflammation of bursa
What can cause bursitis?
Repetitive movements
Direct pressure
What is pre patellar bursitis?
Housemaid’s knee
Seen in carpet fitters
Leaning forward on knees brings pre patellar bursa in contact with floor
What is infrapatellar bursitis?
Clergyman’s knee
After prolonged periods of prayer, clergymen sat back on the heels bringing infrapatellar bursa in contact with floor
What is a baker’s 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 swelling in popliteal fossa
Can affect joint movement
How is a baker’s cyst treated?
Aspiration
Cortisone injection
