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Related Concept Videos

Kinematic Equations: Problem Solving01:15

Kinematic Equations: Problem Solving

When analyzing one-dimensional motion with constant acceleration, the problem-solving strategy involves identifying the known quantities and choosing the appropriate kinematic equations to solve for the unknowns. Either one or two kinematic equations are needed to solve for the unknowns, depending on the known and unknown quantities. Generally, the number of equations required is the same as the number of unknown quantities in the given example. Two-body pursuit problems always require two...
Kinematic Equations - III01:18

Kinematic Equations - III

The first two kinematic equations have time as a variable, but the third kinematic equation is independent of time. This equation expresses final velocity as a function of the acceleration and distance over which it acts. The fourth kinematic equation does not have an acceleration term and provides the final position of the object at time t in terms of the initial and final velocities. This equation is useful when the value of the constant acceleration is unknown.
Using the kinematic equations,...
Kinematic Equations - II01:17

Kinematic Equations - II

The second kinematic equation expresses the final position of an object in terms of its initial position, the distance traveled with the initial constant velocity, and the distance traveled due to a change in velocity. Similar to the first kinematic equation, this equation is also only valid when the acceleration is constant throughout the motion of an object.
Suppose a car merges into freeway traffic on a 200 m long ramp. If its initial velocity is 10 m/s and it accelerates at 2 m/s2, then the...
Kinematic Equations for Rotation01:30

Kinematic Equations for Rotation

In mechanics, when one observes a rigid body in rotational motion with constant angular acceleration, it is possible to establish equations for its rotational kinematics. This process resembles how linear kinematics are dealt with in simpler motion studies.
For instance, imagine a point A on a rigid body engaged in circular motion. The translational velocity of this particular point can be calculated by taking the time derivatives of the displacement equation, which essentially measures the...
Kinematic Equations - I01:26

Kinematic Equations - I

When an object moves with constant acceleration, the velocity of the object changes at a constant rate throughout the motion. The kinematic equations of motions are derived for such cases where the acceleration of the object is constant. The first kinematic equation gives an insight into the relationship between velocity, acceleration, and time. We can see, for example:
Constraints and Statical Determinacy01:26

Constraints and Statical Determinacy

In structural engineering, the equilibrium of a system is not only determined by its equations of equilibrium but also with the help of constraints. Constraints refer to restrictions on the motion of a system. The proper combinations of constraints can minimize the total number of constraints needed to maintain a system in mechanical equilibrium. When this happens, the system is said to be statically determinate. For such systems, the unknown reaction supports can be estimated using equilibrium...

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Related Experiment Video

Updated: Jul 15, 2026

A Mini-Invasive Internal Fixation Technique for Studying Immobilization-Induced Knee Flexion Contracture in Rats
05:34

A Mini-Invasive Internal Fixation Technique for Studying Immobilization-Induced Knee Flexion Contracture in Rats

Published on: May 20, 2019

How effective are added constraints in improving TKR kinematics?

B H van Duren1, H Pandit, D J Beard

  • 1Nuffield Department of Orthopaedic Surgery, Botnar Research Centre, Nuffield Orthopaedic Ctr, University of Oxford, Oxford, OX3 7LD, UK; Department of Engineering Science, University of Oxford, UK.

Journal of Biomechanics
|April 17, 2007
PubMed
Summary

Posterior stabilized (PS) and medial pivot (MP) total knee arthroplasty designs aim for guided motion. MP designs show near-normal kinematics up to 50 degrees flexion, while PS designs exhibit paradoxical anterior movement.

Related Experiment Videos

Last Updated: Jul 15, 2026

A Mini-Invasive Internal Fixation Technique for Studying Immobilization-Induced Knee Flexion Contracture in Rats
05:34

A Mini-Invasive Internal Fixation Technique for Studying Immobilization-Induced Knee Flexion Contracture in Rats

Published on: May 20, 2019

Area of Science:

  • Orthopedic surgery
  • Biomechanics
  • Biomedical engineering

Background:

  • Total knee arthroplasty (TKA) designs increasingly incorporate enhanced constraint to guide knee motion.
  • Posterior stabilized (PS) and medial pivot (MP) are two distinct design philosophies aiming to restore natural knee kinematics.

Purpose of the Study:

  • To compare the knee kinematics of PS TKA, MP TKA, and normal knees.
  • To evaluate the in vivo motion and patellar tendon angle (PTA) in different TKA designs during functional activities.

Main Methods:

  • Fluoroscopic assessment of knee motion during step-up and deep knee bend exercises in 12 PS TKA patients, 13 MP TKA patients, and 10 normal subjects.
  • 3D model fitting of corrected fluoroscopic images to determine relative 3D motion.
  • 2D analysis of the patellar tendon angle (PTA) as a function of knee flexion.

Main Results:

  • PS TKA showed paradoxical anterior movement and limited posterior rollback despite cam-post engagement. Femoral external rotation occurred between 50-80 degrees, with abnormal PTA in extension and flexion.
  • MP TKA demonstrated minimal anterior movement and medial condyle motion, with posterior lateral contact point movement and continuous external femoral rotation. PTA was similar to normal until high flexion.
  • MP designs achieved near-normal kinematics from extension to 50 degrees flexion, but deviated at higher flexion angles.

Conclusions:

  • The PS TKA design does not fully prevent paradoxical anterior motion and offers minimal posterior rollback.
  • The MP TKA design provides near-normal kinematics in early to mid-flexion but does not replicate normal kinematics in deep flexion.
  • Neither PS nor MP designs fully restore normal knee kinematics across the entire range of motion, highlighting areas for future design improvements.