Stance-phase aggregate contact stress and contact stress gradient changes resulting from articular surface stepoffs in human cadaveric ankles  Dr. T.O.

Presentation on theme: "Stance-phase aggregate contact stress and contact stress gradient changes resulting from articular surface stepoffs in human cadaveric ankles  Dr. T.O."— Presentation transcript:

1 Stance-phase aggregate contact stress and contact stress gradient changes resulting from articular surface stepoffs in human cadaveric ankles  Dr. T.O. McKinley, M.D., Dr. T. McKinley, M.D., M.J. Rudert, Ph.D., D.C. Koos, B.S., D.R. Pedersen, Ph.D., T.E. Baer, B.S., Y. Tochigi, M.D., T.D. Brown, Ph.D.  Osteoarthritis and Cartilage  Volume 14, Issue 2, Pages (February 2006) DOI: /j.joca Copyright © 2005 OsteoArthritis Research Society International Terms and Conditions

2 Fig. 1 The ankle loading fixture is shown; the forefoot and hindfoot are fixed to a plate with PMMA, allowing unconstrained midfoot, hindfoot, and ankle motion. The TekScan stress transducer (white arrow) is secured to the tibia after being inserted through small anterior and posterior arthrotomies. Axial load, applied by an MTS actuator, is coordinated with AP loads applied with a pneumatic actuator. Osteoarthritis and Cartilage  , DOI: ( /j.joca ) Copyright © 2005 OsteoArthritis Research Society International Terms and Conditions

3 Fig. 2 Ankle motion and AP forces were synchronized to simulate the stance-phase of gait. Posterior shear forces indicate the talus forced posteriorly relative to the tibia. A 600N compressive load is applied throughout the entire motion cycle. Osteoarthritis and Cartilage  , DOI: ( /j.joca ) Copyright © 2005 OsteoArthritis Research Society International Terms and Conditions

4 Fig. 3 A custom cutting fixture and sequence were used to produce consistent fragments with precise reductions. (a) An anterolateral fragment, created by the osteotomy, is shown. (b) Illustration shows final cuts completed with an osteotome, with the anatomic metallic spacer (white arrow) cemented in place with PMMA. (c) Illustration shows how the stepoffs were controlled by the insertion of incrementally thinner spacers (gray arrow) above the fragment. Osteoarthritis and Cartilage  , DOI: ( /j.joca ) Copyright © 2005 OsteoArthritis Research Society International Terms and Conditions

5 Fig. 4 Spatial mean and peak local aggregate contact stresses in intact and experimental configurations. Anatomic configurations had minimal increases in aggregate contact stresses, in contrast to stepoff configurations that had significant increases (* denotes significantly greater than intact configuration, P<0.05) in both mean and peak values. The greatest percentage increase occurred with the initial 1mm of stepoff. Osteoarthritis and Cartilage  , DOI: ( /j.joca ) Copyright © 2005 OsteoArthritis Research Society International Terms and Conditions

6 Fig. 5 Contour plots clearly demonstrate feature differences between intact and anatomic configurations, compared to stepoff configurations. The broad-based contact region is lost in stepoff configurations, with two focal peaks of aggregate contact stress accumulation emerging medial and posterior to the osteotomized fragment. Osteoarthritis and Cartilage  , DOI: ( /j.joca ) Copyright © 2005 OsteoArthritis Research Society International Terms and Conditions

7 Fig. 6 Spatial mean and peak local aggregate contact stresses' gradients in intact and experimental configurations. Stepoffs resulted in significant increases in both mean and peak values (* denotes significantly greater than intact configuration, P<0.05). Osteoarthritis and Cartilage  , DOI: ( /j.joca ) Copyright © 2005 OsteoArthritis Research Society International Terms and Conditions

8 Fig. 7 Composite aggregate vector plots contrast a broad contact region of low-magnitude, randomly oriented gradients in intact and anatomic configurations, vs two focal regions of high-magnitude, preferentially oriented gradients in stepoff configurations. Osteoarthritis and Cartilage  , DOI: ( /j.joca ) Copyright © 2005 OsteoArthritis Research Society International Terms and Conditions