Page 247 - Advances in Biomechanics and Tissue Regeneration

12.3 RESULTS 243

To determine the effect of calcaneal bone excision in a sequential manner, calculations were performed using a
model of an intact foot as a reference point. Sequential elimination of calcaneus mesh elements from the model
3
mimicked surgical extraction until a region of 24 7 7.5mm (1260mm ) had been removed. The initial excision
beganatthe topofthe dorsal posterior tuberosityofthe calcaneus, creating the first layer in a block with dimen-
3
sions of 24 7 1.5mm (252mm ). Subsequent excisions removed layers approximately 1.5mm deep, creating
3
3
3
blocks of 24 7 3mm (504mm ), 24 7 4.5mm (756mm ), 24 7 6mm (1008mm ), and 24 7 7.5mm
3
(1260mm ).
Additionally, in the intact foot model and the model in which 7.5mm of bone had been extracted, loads of 600N and
750N (2 and 2.5 times walking) were applied to the talus to evaluate the impact of gait variations.
Finally, we evaluated the effect of Achilles tendon traction on the calcaneus during gait.
The typical traction while walking is 150N. Consistent with evaluating loads on the talus at 2 and 2.5 by walking, we
evaluated Achilles tendon loads of 300 and 375N with a constant value of 300N maintained against the talus.

12.3 RESULTS

12.3.1 Displacements Varying the Talus Load and Constant Achilles Tendon Load Based on the
Amount of Bone Extraction
There was no change in either anterior/posterior (AP) or medial/lateral (ML) translation of calcaneus with increas-
ing loads on the talus and a constant Achilles tendon load based on the amount of bone extraction (Table 12.1). There
was, however, an increase in translation across conditions as the load on the talus increased.
Maximum principal stresses (tension) were concentrated at the posterior aspect of the calcaneus (Table 12.2;
Fig. 12.3).

TABLE 12.1 Displacements as a Function of Load Variation on the Talus and Depth of Bone Removal. Load on the Achilles Tendon
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 2.348 2.349 2.362 2.376 2.386 2.389
ML 0.891 0.891 0.891 0.894 0.895 0.895
750N AP 2.797 2.798 2.814 2.831 2.842 2.895
ML 1.07 1.071 1.075 1.078 1.08 1.081
These data were previously published in Bayod et al. [24].

TABLE 12.2 Principal Stress as a Function of Load Variation on the Talus and Depth of Bone Removal. Load on the Achilles Tendon
Remains Constant

Depth of bone excision
Principal stress
Talus load (MPa) Intact 24×7×1.5 24×7×3 24×7×4.5 24×7×6 24×7×7.5
300N Tension 23.22 23.22 31.02 33.95 34.23 34.27
Compression 35.27 35.27 35.57 36.18 36.4 36.48
600N Tension 51.14 51.14 51.17 51.12 51.09 51.08
Compression 93.88 93.9 94.25 95.09 95.39 95.49
750N Tension 65.3 65.31 65.33 65.25 65.2 65.19
Compression 123.6 123.6 124 125 125.3 125.54
These data were previously published in Bayod et al. [24].

I. BIOMECHANICS