Knee Kinematics Flashcards
Name the articulations that compose the knee.
Tibiofemoral joint–has medial and lateral compartments.
Patellofemoral joint–femur moves under the patella.
Define the terms genu varum, genu valgum, and genu recurvatum and demonstrate each.
Genu varum–angulation is lateral, or distal segment (tibia) moves toward midline.
Genu valgum–angulation is medial, or distal segment (tibia) moves away from midline.
Genu recurvatum–hyperextension of the knee. (What I have/do).
State the functions of the menisci in the knee joint.
- Stability–stabilize (make the two bones fit together more micely–more congruent) the knee during movement. Drives the arthrokinematics.
- Reduce compressive stress (cushion)–fibrocartilage.
- Slide around in the joint and moves the synovial fluid around to lubricate the joint.
(The peripheral 1/3 edge gets blood supply. Where blood goes, so goes a nerve. There is a nerve in the meniscus.) - Provides **proprioception—mechanoreceptors sense body position, or position of a joint.
During osteokinematic motion of the knee, describe movement of the meniscii.
Medial and Lateral Condyles are bullies in the joint. If they roll forward or backward, they push the meniscus out of the way. It does not matter whether the femur or the tibia is moving. When abnormal mechanics occur, the menisci fight back, and lose–get torn.
In closed knee extension, as the condyles roll forward, the anterior horn of the medial and lateral meniscus get pushed forward to get out of the way. When the knee flexes, the condyles roll posterior. The posterior horns of the medial and lateral menisci are pushed posteriorly out of the way. It they do not move, the condyles will roll on top of the menisci, squish them, and potentially tear them.
List and demonstrate the osteokinematic motions and number of degrees of freedom for this joint. Associate the appropriate plane of motion with each osteokinematic motion.
Flexion/Extension in sagittal plane.
Internal/External rotation of knee in Transverse plane.
2 degrees of freedom.
(When the tibial tuberosity turns laterally, the knee externally rotates. When the tibial tuberosity turns medially, the knee internally rotates. )
What are the directions and locations of the axes for the osteokinematic motions of the knee?
Sagittal plane–medial/lateral. Axis runs from medial epicondyle of the femur to the lateral epicondyle of the femur.
Transverse plane–superior/inferior. Axis is somewhere over the center of proximal tibia between the 2 intercondylar eminences.
What is unique about the axis of motion occurring in the sagittal plane? Explain why this unique feature of the axis exists.
The axis of rotation changes throughout the range of motion of the knee. The migration of an axis is most pronounced in the knee joint.
This feature exists because the epicondyle is not spherical. Sharply curved posteriorly, flat inferiorly, and curved anteriorly.
Describe motion in the transverse plane during open kinematic chain conditions and closed kinematic chain conditions. How are these different?
Open chain is tibia moving on the femur. Closed chain is the femur moving on the tibia. The name of the rotation is determined by the position of the tibial tuberosity.
How does knee position in the sagittal plane effect motion in the transverse plane?
If knee is extended (close packed) or flexed (tense) in the sagittal plane, internal/external rotation is very limited.
Flexion at 90 degrees will give the knee the most rotation. Open packed position.
Describe knee joint arthrokinematics for internal/external rotation under closed chain conditions.
In closed-chain, the tibia (knee) is externally rotated when the femur internally rotates. The tibia (knee) is internally rotated when the femur externally rotates at the knee. Cannot conclude from these motions that the femur is internally or externally rotated at the hip
Describe knee joint arthrokinematics for flexion/extension under open and closed chain conditions.
Open chain flexion/extension; concave/convex. Roll/slide together.
Closed chain flexion/extension; roll/slide opposite.
What do the terms automatic rotation, terminal rotation, locking mechanism or ‘screw home’ mechanism refer to?
All mean the same thing. Screw home mechanism is the most common term used. The terms refer to how you lock the knee together at extension.
Screw home mechanism…twisting motion. Refers to the automatic twisting of the femur and tibia at the terminal end-range of knee extension period locking the femur and tibia together.
Explain for the screw home mechanism works under open and closed chain conditions.
Open chain, the tibia moves on femur. At end range the tibia has external rotation. As the knee moves into extension, the tibia, at the end range of extension, moves into external rotation on the femur.
Closed chain–the lateral femoral condyle reaches full knee extension before the medial compartment. The extra distance the medial compartment need to travel causes the little bit of rotation causing internal rotation of femur on tibia.
Identify the 4 “local stabilizers” for the patellofemoral joint (PF) that help to maintain tracking of the patella in the intercondylar groove.
The mechanics of the joint and how the knee is built causes problems for patients and PTs alike. At intercondylar groove, patellas fit into the notch. What holds it in that groove?
- Force of the quads.
- Tension in the passive restraints…Medial retinaculum/Lateral retinaculum.
- Patellar/Quadraceps tendon
- Fit of the joint surfaces. (1. depth of groove itself. 2. Height of lateral condylar ridge)
What portions of the posterior patella are in contact with the femur in 0, 20, 60 degrees of motion?
0 degrees = 0 contact, the knee is straight, and the patella is not in contact with the articular cartilage.
20 degrees; as the knee begins to flex, the inferior portion of patella touches the knee first.
60 degrees; the middle portion of patella contacts an area that is larger than 20 degrees.
