Page 250 - Advances in Biomechanics and Tissue Regeneration
P. 250

246               12. BIOMECHANICAL STUDY IN THE CALCANEUS BONE AFTER AN AUTOLOGOUS BONE HARVEST

           12.3.2 Displacements Varying Achilles Tendon Load Based on the Amount of Bone Extraction
              There was no change in either AP or ML translation in calcaneus with increasing Achilles tendon load based on the
           amount of bone extraction (Table 12.3). There was, however, an increase in translation across conditions as the load on
           the Achilles tendon increased.
              Maximum principle stresses (tension) were concentrated at the posterior aspect of the calcaneus (Table 12.3;
           Fig. 12.4). However, as the volume of bone removal increased and the load on the calcaneus increased in both the intact
           model and models with bone removal, we observed that maximum principal stresses were concentrated around the
           region of the extracted bone (Fig. 12.3).
              Minimum principal stress (compression) was concentrated at the support zone (Table 12.2; Fig. 12.4). When the load
           on the talus and the volume of bone extraction increased, compression stress in the healthy model and the simulated
           model with removal of bone material extended from the edge of the bone extracted site to the bottom and sides of the
           calcaneus, near the support zone planting (Fig. 12.4).
              Principal stresses varying by the Achilles tendon load (Table 12.4; Figs. 12.5 and 12.6).



                                                    12.4 DISCUSSION

              We used a 3-D FE model to create sequential simulations of calcaneus bone removal to mimic a graft harvest. The
                                                 3
           size of the maximum donor site was 1.30cm . Based on our results, we suggest that a calcaneal bone harvest should not
           exceed a volume of 2.4  0.7  0.75cm.
              Because we were interested in evaluating the mechanical properties of the calcaneus during functional tasks, we
           focused on the stance phase of gait, when the heel is on the ground. We also evaluated experimental conditions that
           mimicked daily tasks and had the potential to increase calcaneal stress, including conditions with an increase in force


           TABLE 12.3  Displacements as a Function of Achilles Tendon Load and Depth of Bone Removal. Load on the Talus Remains Constant
                                                                       Depth of bone excision
           Talus load    Displacement (mm)   Intact    24×7×1.5     24×7×3      24×7×4.5      24×7×6      24×7×7.5
           300N          AP                  1.445     1.446        1.452       1.461         1.467       1.469
                         ML                  0.543     0.543        0.541       0.537         0.536       0.535
           600N          AP                  1.984     1.985        1.992       2             2.013       2.016
                         ML                  0.738     0.738        0.735       0.73          0.728       0.727
           750N          AP                  2.254     2.254        2.261       2.276         2.286       2.289
                         ML                  0.836     0.836        0.832       0.827         0.874       0.824
           These data were previously published in Bayod et al. [24].

           TABLE 12.4  Principal Stress as a Function of Achilles Tendon Load and Depth of Bone Removal. Load on the Talus Remains Constant

                                                                        Depth of bone excision
                                Principal stress
           Achilles tendon load  (MPa)          Intact    24×7×1.5    24×7×3      24×7×4.5    24×7×6      24×7×7.5
           150N                 Tension          23.22     23.22        31.02      33.95        34.23      34.27
                                Compression      35.26     35.27       35.57       36.18       36.4        36.48
           300N                 Tension          33.33     37.23        62.73      68.37        68.86      68.95
                                Compression      19.23     18.98       31.95       20.54       20.54       20.65
           375N                 Tension          42.16     46.98        78.58      85.58        86.18      86.28
                                Compression      23.74     19.77       36.93       42.63       19.96
                                                                                               19.34
           These data were previously published in Bayod et al. [24].



                                                       I. BIOMECHANICS
   245   246   247   248   249   250   251   252   253   254   255