Knee Flashcards
What are the key features of the knee? (4 bones and 2 joints)
- Femur
- Tibia
- Patella (lies in intercondylar fossa of femur)
- Fibula
- Tibiofemoral joint
- Patellofemoral joint
What are the femur, patella and tibia covered in and why?
- They are covered in articular cartilage
- Articular cartilage is hard and smooth, designed to decrease friction forces
How is the fibula involved in the knee joint?
- Fibula is smaller than tibia
- It is attached to the tibia via the superior tibiofibular joint
- It is not directly part of the knee joint but it provides a surface for important muscles and ligaments to attach
- It does NOT articulate with patella or femur
What is the anatomy of the proximal femur?
- Head = articulates with acetabulum (covered in articular cartilage)
- Neck = projects in a superior and medial direction. It is at 135 degrees to the shaft which allows increased range of movement at the hip joint
- Greater trochanter = lateral projection. Site of attachment of gluteus medius, gluteus minimus, piriformis and vastus lateralis
- Lesser trochanter = posteromedial projection. Site of attachment for illpsoas
- Intertrochanteric line = anteriorly spans the 2 trochanters. It becomes the pectineal line posteriorly
- Intertrochanteric crest = on posterior side of femur, connects the trochanters
- Gluteal tuberosity = above linea aspera. Insertion of gluteus maximus
- Linea aspera = roughened ridges of bone which splits to form medial and lateral supracondylar lines. Formed from pectineal line and gluteal tuberosity.
- Medial and lateral supracondylar lines = the flat popliteal surface lies between them
- Medial supracondylar line has a tubercle called the adductor tubercle where adductor magnus lies
- The shaft descends in a medial direction bringing the knees closer to the body’s centre of gravity, increasing the stability
What is the anatomy of the distal femur?
- Medial and lateral condyles = articulate with menisci and tibia posteriorly, and the patella anteriorly. Lateral condyle is more prominent, preventing lateral movement of patella but makes lateral dislocation more likely.
- Medial and lateral condyles in anterior surface are connected by the patella surface. This engages the patella in early flexion.
- Medial and lateral epicondyles = give rise to medial and lateral collateral ligaments
- Adductor tubercle on medial supracondylar line = adductor Magnus attaches here
- Intercondylar fossa = deep notch on the posterior surface of femur between the 2 condyles. Anterior cruciate ligament attaches to the lateral lip; posterior cruciate ligament attaches to the medial lip.
What is the anatomy of the tibia?
- 2nd largest bone in the body
- Medial and lateral condyles = involved in weight bearing. They form a flat surfaces called tibial plateaus
- Tibial plateaus = flat surfaces formed from medial and lateral condyles. They articulate with femoral condyles to form tibiofemoral joint
- Intercondylar eminence = between the tibial condyles
- Medial and lateral intercondylar tubercles = projection upwards of intercondylar eminence. Involved in knee extension. They become logdged in the intercondylar fossa of femur in extension, adding stability to joint.
- Anterior surface is marked by tibial tuberosity
- Posterior surface is marked by soleal line. There’s a nutrient artery nearby
- Lateral surface is marked by interroseous border. Attaches to interroseous membrane that binds tibia and fibula
- Medial malleolous = bony projection on medial aspect of tibia. Articulates with tarsal bones to form a part of ankle joint
- Fibular notch = where fibula is bound to tibia
- Diameter of proximal tibia is much greater than the shaft posteriorly which is sloped at 7-10 degrees to facilitate flexion of femoral condyles on tibia
- Tibiofemoral joint is relatively unstable as the plateaus are slightly convex anteriorly and posteriorly- this emphasises the importance of other structures such as menisci.
Why the Tibiofemoral joint relatively unstable?
Because the tibial plateaus are slightly convex anteriorly and posteriorly so there’s reduced congruence. This emphasises the importance of other structures such as menisci
What the anatomy of the patella?
- Triangular sesamoid bone
- Base (at the top) = provides attachment for quadriceps tendon
- Apex (at the bottom) = connected to tibial tuberosity by patellar ligament
- Medial facet = articulates with medial condyle of femur
- Lateral facet = articulates with lateral condyle of femur
Patella resides within quadriceps tendon. It increases the power of knee extension by increasing efficiency of quadricep contractions. It’s not on the tibia
-Contraction of quadriceps pulls the patella upwards and extends the knee
What 2 articulations form the knee joint?
- Tibiofemoral joint
- Patellofemoral joint
What kind of joint is the knee joint? And what plane does the knee joint move in?
- Tibiofemoral joint (between medial condyles of femur and tibial plateaus) = synovial hinge joint
- Patellofemoral joint (between patellar surface of femur and posterior surface of patella) = plane synovial joint
Plane of movement = Sagittal plane (forwards and backwards - flexion and extension).
What happens if there are tears in meniscus?
- Unable to withstand hoopstress
- Can’t absorb force
- Lose control of translation and rotation
- Lose control of range of motion control
- It can cause pain, instability and reduced range of motion which can cause locking
- It can lead to contact between femoral condyles and tibial plateaus so more force is transferred from femur to tibia
Treatment:
- You can remove meniscus if it’s stuck which will help to unlock but the other problems will still be there
- If your meniscus doesn’t function, you can get osteoarthritis
How do the menisci act as shock absorbers?
- When weight is applied to femur, it is applied onto the meniscus which then applies it to tibia
- This force pushes out the meniscus which is counteracted by hoop stresses —> this allows shock absorbing
-Tear in meniscus affects ability to withstand ability to withstand hoop stress
What are the menisci? (How many, their shape, structure, location, blood supply, arrangement of fibres)
- There are 2 menisci (medial and lateral). They are intracapsular
- They are dynamic fibrocartilage structures
- They are present between the femoral and tibial condyles
- They are crescent shaped and have triangular cross section
- The surface of each meniscus is concave superiorly and flat inferiorly to provide congruous surfaces for the femoral condyles and tibial plateaus.
- They essentially correct the lack of congruence between the articular surfaces of tibia and femur
- They increase the joint surface area and deepen articular structure of tibia, increasing stability
- They help create concave shape in tibia as femur is convex. Provides joint congruency
- They act as shock absorbers
- Important stabilisers of knee
- Poor blood supply (medial, lateral and inferior genicular arteries). They are fully vascularised at the 1st year of life but it diminishes to the outer third, and this area being the only part that has an ability to heal. The non vascularised part gets nutrition through diffusion of synovial fluid.
- The arrangement of fibres of menisci allow axial loads to be dispersed radially, decreasing the wear on the hyaline articular cartilage.
What is the anatomy of the medial meniscus?
- Medial meniscus is larger and has C shaped (as horns are further apart)
- Medial meniscus is less mobile due to its attachment of tibial collateral ligament and knee joint capsule. Hence damage to tibial collateral ligament can damage medial menisci
What is the anatomy of the lateral meniscus?
- Smaller
- More O shaped
- No attachment to collateral ligament, and only weakly attached to joint capsule, hence more mobile
What are the 3 ligaments that stabilise the menisci?
- Transverse intermeniscal ligament
Connect the medial and lateral menisci - Coronary ligaments
Connect meniscus to the tibial plateaus - Meniscofemoral ligaments
Consist of Humphrey ligament and Wrisberg ligament
What are the 4 important knee ligaments? Why are they important?
- Anterior cruciate ligament
- Posterior cruciate ligament
- Medial collateral ligament
- Lateral collateral ligament
They maintain knee stability.
Cruciate ligaments prevent femur and tibia slippage
What is the anterior cruciate Iigament?
- Intracapsular joint
- 2 bundles: anteromedial (tibial aspect) and posterolateral (femoral aspect)
- Attaches at intercondylar region of tibia and intercondylar fossa of femur
- Twists medially as it travels proximally
- It resists anterior translation of tibia onto femur and anterior sheering forces on knee
- Prevents excess rotation (medial and lateral) and valgus/various stress
- Depending on position of knee, it will determine which bundle is stretched
- When knee is fully extended, posterolateral bundle will be stretched and resisting the force
- When knee moves into flexed position, the anterioromedial bundle will be stretched.
- At 30 degrees of flexion, neither of the bundles are stretched, allowing greater anterior translation here
What do the 2 bundles of the anterior cruciate ligaments do? Which is more effective at providing rotary stability of knee? What happens at 30 degrees of flexion?
- Anteromedial bundle: stretches/tighter in knee flexion
- Posterolateral bundle: stretches/tighter in knee extension
Posterolateral bundle is theorised to be the most effective at providing rotatory stability of the knee.
At 30 degrees of flexion, neither bundle stretches so there is greater anterior translation available of the tibia onto the femur.
Where is anterior cruciate ligament injury common?
- In sports such as football and netball.
- It can also rupture due to stress e.g quadriceps use
What is the posterior cruciate ligament?
- Intracapsular ligament
- 2 bundles: posteromedial and anterolateral
- Attaches at posterior surface of tibia and attach to femoral medial condyle
- Thicker and higher tensile strength than ACL hence less injured
- Under tension when knee is in flexion
- It restricts posterior translation of tibia on femur
- Resists valgus and varus stress
- When the knee is near full extension, the posteromedial bundle are tightened and the anterolateral bundle are relaxed
- When the knee is 80-90 degrees flexed, the anterolateral bundle are tightened and the posteromedial bundle are relaxed.
- The posterior cruciate ligament is best at resisting medial tibial rotation at 90 degrees flexion but is not good at resisting lateral tibial rotation.
- If the posterior cruciate ligament becomes damaged, the popliteaus muscle plays an important role in stabilising the knee from posterior sheering forces
-In a person with PCL deficiency, hamstring contraction and gastrocnemius contractions can destabilise knee joint.
What are the collateral ligaments?
- Static stabilisers
- Prevents XS medial and lateral movement
- Stabilises the hinge joint
-Medial and collateral ligaments are very different to each other
What is the medial collateral ligaments?
- Extracapsular but blends in with capsule
- Has superficial and deep fibres
- Runs from medial epicondyle of femur to medial condyle of tibia
- The deep fibres are continuous with the capsule. Deep fibres resist internal rotation.
- Deep fibres are attached to the medial meniscus
- Larger than LCL
- Well vascularised and nerve supply so can heal well. But painful in injury due to nerves
- Medial collateral ligament resists valgus force (most effectively in extension)
- Resists lateral rotation of tibia onto the femur
- Restrains anterior translation of tibia on femur
What is the lateral collateral ligament?
- Extracapsular
- From lateral condyle of femur to depression on lateral surface of fibular head
- Joins with tendon of biceps femoris
- Smaller than MCL
- Poor vasculature and nerve supply. Harder to heal
- Resists varus forces (prevents sideway movement of knees outward)
- If injured, it is accompanied by ACL or PCL injury
