The effect of incongruity and instability on contact stress directional gradients in human cadaveric ankles.
OBJECTIVE
Measure incongruity and instability-associated changes in transient contact stress directional gradients in a human cadaveric ankle model.


METHODS
Seven cadaveric ankles were subjected to quasi-physiologic forces and motion under intact conditions and with a stepoff incongruity of the anterior one-third of the distal tibia. Anterior/posterior forces were modulated to create incongruous specimens that either maintained a stable articulation between the talus and distal tibia or developed gross instability during motion. Real-time contact stresses were measured using a custom-designed ankle stress transducer at 132 Hz. Contact stress data were differentiated using a central-differencing formula to calculate transient contact stress directional gradients over the entire ankle articulation.


RESULTS
Transient 95th percentile contact stress directional gradient values increased by 30 and 100%, respectively, in stable-incongruous and unstable-incongruous conditions compared to intact conditions. Compared to stable-incongruous conditions, transient contact stress directional gradients increased by 60% in unstable-incongruous conditions.


CONCLUSIONS
Instability resulted in greater percentage increases in transient contact stress directional gradients compared to incongruity. Pathologic increases in contact stress directional gradients potentially play an important role in the etiology of post-traumatic arthritis.
Orthopaedics Biomechanics Laboratory, Department of Orthopaedic Surgery, University of Iowa, Iowa City, IA 52242, USA. todd-mckinley@uiowa.edu
T O
TO
McKinley
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Y
Tochigi
M J
MJ
Rudert
T D
TD
Brown
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016512:Ankle Injuries / Q000503:physiopathology*; D000843:Ankle Joint / Q000503:physiopathology*; D001168:Arthritis / Q000503:physiopathology*; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D008875:Middle Aged; D008954:Models, Biological; D016059:Range of Motion, Articular / Q000502:physiology; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology