Knee muscles and arthrology (wk3) Flashcards
Knee function
-Knee joint
-Links 2 of the longest bones in the body (femur and tibia)
-It is the largest and one of the most complex joints
-Tibiofemoral joint is between the femur and tibia
-Patellofemoral joint is between the femur an knee cap
Knee function
-Functions of the knee joint
-Supports body weight
-Transmit forces between the femur and tibia (stability) e.g walking, running
-Provide movement for locomotion (walking, running about) and activities of daily living (mobility)
Knee function
-Stability and mobility
Stability examples:
-When walking, there is force through the knee joint which is about 2-4 x body weight -> the knee needs to be stable to allow walking to happen
-When landing from a jump, the there is a force of around 24 x body weight which goes through the knee joint
Mobility examples:
-The knee needs to be ale to bend in football to run, jump and kick
-In tennis, the knee needs to be able to rotate so that the foot can go at different angles at the ground
-To allow for activities of daily living, such as sitting in a chair (need around 90 degrees of knee flexion to do this) or kneeling to tie your shoe laces
Knee function
-A joint of compromise
-The knee wants to be mobile and stable at the same time -> this can be achieved through a compromise
-When a knee is straight, its at extension and is where it has it’s greatest stability + when the knee is bent, it’s at flexion, where it has a lot of mobility
Identify the 2 bones that make up the tibiofemoral joint
-A synovial bicondylar (2 femoral condyles) joint between;
1. Femoral condyles
2. Tibial articular surfaces
Tibiofemoral joint:
Identify the femoral and tibial condyles + describe the shape of their articular surfaces:
-The femoral condyles are at the distal end of the femur
-The lateral condyle’s articular profile is longer
-Right femur, posterior view of femoral condyle
-Inferior view of femoral condyle (it is convex and cartilage-covered)
-Tibial condyles have their prominence at the proximal end
-Tibial condyle articular surfaces. Medial condyle -> large and more oval. Lateral condyle -> smaller and circular
Tibiofemoral joint
-Identify the medial and lateral menisci and describe their attachments and function:
-On top of the articular surfaces are fibrous cartilage discs called semi-lunar fibrocartilage discs which are the menisci
-The medial meniscus is more of a semi-circle
-The lateral meniscus covers a larger area. It covers 4/5 of the circle.
-Functions of the menisci;
1. Increases the congruence between articular surfaces
2. Assist weight bearing across joint
3. Acts as shock absorbers
4. Facilitate accessory movements (small automatic movements)
Tibiofemoral joint
-Identify the four main ligaments of the tibiofemoral joint, and describe their attachments and function:
- Medial Collateral ligament (MCL) (outside) -> Broad, flat band, 10cm long, extracapsular. The MCL is designed to prevent Valgus Displacement (which is when your knee gets into a knocked knee position)
- Lateral Collateral ligament (outside) (LCL) -> Extra-capsular, a strong cord. It helps to prevent varus displacement (a bow-legged position)
- Anterior Cruciate ligament (inside) (ACL) -> Intracapsular, from anterior intercondylar area of tibia to lateral femoral condyle. Prevents anterior tibial displacement.
- Posterior Cruciate ligament (inside) (PCL) -> Intracapsular, from posterior intercondylar area of tibia to medial femoral condyle. Prevents posterior tibial displacement.
Patellofemoral joint
-Identify the bones that make up patellofemoral joint
-Is a synovial saddle joint, between;
1. Articular surface of the patella
2. Patella surface of the femur
The patellofemoral joint
-Identify and describe the shape of the articular surfaces on the patella and femur:
femur:
-Oval-shaped and cartilage covered
-It is shiny because it is covered in hyaline cartilage
-Vertical ridge separates medial and lateral areas
-Patella surface of femur -> cartilage-covered surface which articulates with the patella
-Patellofemoral joint (inferior view) -> patella ridge articulates with groove of patella surface
The patellofemoral joint
-Describe the function and movement of the patella
-The patella is the largest sesamoid bone in the body. It is embedded in the tendon of the quadriceps.
-Patella function;
1. Acts as an anatomic pulley
2. Reduces friction between quadriceps tendon and femoral condyles
-Moves proximally in extension
-Moves distally in flexion
Tibiofemoral and patellofemoral joints
-Shared features between the joints +describe the function of the joint capsule and bursae at the knee joint:
-Joint capsule -> No complete, independent fibrous capsule. Joint surrounded by sheath composed of ligaments and tendons. It is ‘incomplete’. It is reinforced by a number of ligaments and tendons.
-Bursae -> Fluid-filled sacks that are used to reduce friction. There are around 13-15 found at the knee. One is called the ‘pes anserinus bursa’ which stops the MCL rubbing on the three tendons
Describe the movements possible at the knee joints:
-Tibiofemoral joint is bi-axial. This means movement can occur in 2 planes/ around 2 axis.
-Movements possible;
1. Flexion and extension -> About horizontal axis in sagittal plane.
- On average, the knee can flex up to 140 degrees and extend straight (0 degrees)
-Hyperextension allows greater extension at the knee
2. Medial and lateral rotation -. About vertical axis in transverse plane
-If you bend your knee to 90 degrees flexion, you can achieve 25 degrees of medial rotation and 40 degrees of lateral rotation
Explain the locking mechanism at the knee:
-Close-packed position (knee locking mechanism) of knee is full extension. No rotation is possible in this position.
-When moving to full extension of the knee joint, the femur rotates medially during last 30 degrees of movement; this pulls all major ligaments of the knee joint taut, ‘locking’ the knee and making it very stable.
-To flex the knee from full extension, joint must first be unlocked by contracting the popliteus muscles which rotates the femur laterally
-The femur rotates medially during last 30 degrees of extension, due to shape of condyles
-The tibia externally rotates in an open chain exercise like the leg extension machine
-The femur internally rotates in a close chain exercise like the squat
-The automatic rotation occurs due to the inequality of the articular surface of femur condyles
Knee muscles
-Knee flexors
-Biceps femoris (short and long head)
-Biceps femoris (long head) -> O: Ischial tuberosity, I: Head of the fibula, F: Flexion
-Biceps femoris (short head) -> O: Femur, I: Head of the fibula F: Flexion
