Knee Kinetics Flashcards
What functional role does an isometric, eccentric, and /or concentric activation/contraction of the quadriceps serve at the knee? open chain v closed chain.
Isometric–Closed chain. Stabilize, compress femur into tibia.
Eccentric–Closed chain. Lengthening contraction, decelerate** to control rate in which knee flexes (squatting, sitting, running). Has a cushioning or dampening effect on joint reaction forces (jump absorption, compression).
Concentric–Open and closed chain–accelerates knee into extension.
How does one improve patellar tracking?
There is 0 evidence that the Vastus Medialis and Vastus Medialis Oblique will selectively strengthen or weaken for patellar tracing. The entire quad has to be strengthened overall to improve patellar tracking. Another thought is to strengthen muscles that control the femur. Hip Abductors and External Rotators.
What is the difference in demand on the quadriceps (from external sources ie. a weight or gravity on body weight) in open vs closed kinematic chain knee extension?
The point in the range of motion where the quad demand is the greatest is different. Open chain, when seated, at full extension, gravity has greatest effect on the quad. When standing, closed chain, knee flexion is the highest demand. (Great implications for patella femoral pain patients.)
What function does the patella perform in the knee extensor mechanism and how does it accomplish this function?
The patella’s function deflects the angle of pull on the tibia. This changes the angle that the quadricep has on the tibia. Patella increases moment arm for knee extensor mechanism. Because torque is the product of force and its moment arm, the presence of the patella augments the extension torque at the knee. pg 558. two images, one w and w/o a patella. W/o the patella, the moment arm is much smaller. Not much force is pulling on the tibia. W patella, the moment arm is much bigger. W/o, it’s virtually impossible to extend knee in closed or open chain.
Describe the normal joint reaction force of the PFJ in the sagittal plane with normal quadriceps function in a closed kinematic chain. Name two factors that increase PFJ compression.
It’s a bowstring effect. Everytime the muscle contracts, it creates a bowstring. It pushes the patella into the knee.
1. a deeper squat or
2. a stronger quad contraction at a given flexion point in the range.
(w/ patella femoral pain, this is why you don’t give them full ROM exercises, because they cannot take the pressure from the patella.
What is the Q-angle and what is its normal effect on PFJ reaction forces in the frontal plane?
Q-angle is Quadricep Angle. Angle formed betweena line of force from the mid-point of the patella to the ASIS, and a line of fore from the middle of the patella to the middle tibial tuberosity. Always wants to push the patella laterally.
Define ‘optimal tracking’ of the PFJ as well as list and explain the local and global factors that relate to optimal tracking.
Movement of the patella over the femur with optimal contact–greatest amount of surface area. Which optimizes the compression forces that goes through the patella to the knee.
Local factors can be structural and are unchangeable. To optimize tracking. Height of lateral condylar ridge. Line of pull of vastus medialis. Retinaculum fibers (thin layer of ligamentous tissue to keep patella tethered) pull laterally and medially. Global factors can be strengthened. Amount of Valgus angulation and amount of tibial external rotation.
Relate how concentric and eccentric contractions of the hamstring muscles function in an open chain.
Open chain–concentric–knee flexion with acceleration.
Open chain–eccentric–deceleration to slow tibia down during leg extension.
Identify the muscle and explain its function in the initial unlocking of the knee in a closed chain. (Special focus 13-7)
The popliteus makes the knee joint externally rotate the femur just a little bit to unlock the joint. Cosses from medial tibia to lateral epicondyle of the femur. After the popliteus unlocks the knee, the quads control knee flexion in the closed chain environment to flex the knee (sit down).
Relate knee joint position to hamstring moment arm and to flexion torque. What effect does hip flexion have on hamstring flexion torque and why?
Page 552, Fig 13-33. Maximum torque capability is at about 5 degrees from full extension when prone. (hip is neutral). Moment arm is longest at 90 even though torque is lowest at 90. This is because the length-tension relationship of the actin/myosin cross-bridge is no longer optimal due to active insufficiency. Adding a little bit of hip flexion would increase torque at 90 degrees because it changes the optimization of length-tension relationships throughout the range.
What is the very basic difference in how the knee flexors functioning open v closed kinematic chains (what bone is being ‘controlled’ in a closed chain situation)?
Closed-chain–tension in hamstrings is controlling the pelvis and controlling eccentric hip flexion. Control amount of anterior/posterior (sagittal plane)
Open-chain–tension in hamstring controls knee flexion.
What are typical and atypical movement combinations found at the hip and knee joints (see clinical connection 13-4 p564)? Clinical significance?
Atypical–Hip flexes and then extends knee. Shortened hip flexion and extend knee, double joint motions.
Also extend hip and then flex knee.
This is bad because it Pre-shortens a two-joint muscle, kills efficiency and causes cramps.
Clinical significance–atypical movements limit effectiveness of therapeutic exercises.
