instability

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Related to patellofemoral instability: Jumper's knee

instability

1. tendency to variable or unpredictable behaviour
2. Physics a fast growing disturbance or wave in a plasma
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

instability

[‚in·stə′bil·əd·ē]
(control systems)
A condition of a control system in which excessive positive feedback causes persistent, unwanted oscillations in the output of the system.
(physics)
A property of the steady state of a system such that certain disturbances or perturbations introduced into the steady state will increase in magnitude, the maximum perturbation amplitude always remaining larger than the initial amplitude.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

instability

In a structure, the sudden loss of stiffness that limits its load-carrying capability, and in some cases results in the structure’s failure.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

instability

instabilityclick for a larger image
i. A state of the atmosphere in which a parcel of air will continue to rise, if for any reason, it is pushed up. Any instability in the atmosphere means turbulent conditions exist. The environmental lapse rate (ELR) in this case will be higher than both dry and saturated adiabatic lapse rates. Dry adiabatic lapse rate (DALR) is the rate of decrease of temperature with height of a parcel of dry air lifted adiabatically. Its value is 3°/1000 ft. Saturated adiabatic lapse rate (SALR) is the lapse rate of a parcel of saturated air and its value is 1.5°/1000 ft.
ii. A tendency of a body to continue moving away from its original state when disturbed by an external force and to continue after that force has been withdrawn.
iii. The failure of structures, such as the buckling of plates and panels under compression, and the failure of struts under end loads.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
References in periodicals archive ?
(1) Patients predisposed to patellofemoral instability may have an increased Q angle, dysplasia of the patella or trochlear groove, patella alta, or a dysplastic VMO.
(1) Simmons and Cameron achieved a 0% recurrence rate in patellofemoral instability when the tibial tubercle was transferred distally without medialization in patients with instability and significant patella alta.
Many proponents feel that this is the essential lesion in patellofemoral instability. (22,50,51) Nomura has devised a three-part classification for the chronically injured MPFL.
A recent biomechanical study by Bicos and coworkers created lateral patellofemoral instability in cadaveric knees by transferring the tibial tubercle laterally.
Patellofemoral instability can be difficult to treat.
Patellofemoral instability: Evaluation and management.