Incongruity-dependent changes of contact stress rates in human cadaveric ankles.

Cartilage biosynthetic transduction and injury characteristics have been shown to be particularly sensitive to changes in contact stress rates. This study investigated incongruity-associated changes in contact stress rates that resulted from an articular surface stepoff of the distal tibia in human cadaveric ankles. Ten human cadaveric ankles were subjected to quasi-physiologic stance-phase motion and loading and instantaneous contact stresses were captured at 132 Hz over the entire articular surface using a custom-fabricated stress transducer. An osteoarticular fragment consisting of the anterolateral 25% of the distal tibia was osteotomized. Testing was repeated after displacing the fragment proximally between 0.0 mm to 4.0 mm in 1.0 mm increments. Transient contact stress measurements were used to calculate contact stress rates. Compared to intact ankles, the anatomic configuration had modest increases in global and peak postitive and negative contact stress rates throughout the motion cycle. In contrast, stepoff specimens had significant increases in global and complete motion cycle peak positive and negative contact stress rates, as high as 3.1X intact values in specimens with a 4.0 mm stepoff. Contour plots of contact stress rates also demonstrated an instability event during motion. An anterolateral stepoff of the distal tibia caused significant changes in positive and negative contact stress rates in cadaveric ankles. Incongruity-associated changes in contact stress rates and incongruity-associated instability events may be important pathomechanical determinants of post-traumatic arthritis.