In silico comparative biomechanical analysis of oblique and chevron medial displacement calcaneal osteotomies for pes planus deformity

Abstract

Background: Medializing displacement calcaneal osteotomy is commonly performed as part of reconstructive surgery for patients with valgus hindfoot and progressive pes planus deformity. Among several types of calcaneal osteotomies, the oblique and Chevron osteotomy patterns have been commonly described in the literature and gained popularity as they are easily reproducible through percutaneous techniques. Currently, there is scarce evidence in the literature on which cut pattern is superior in terms of stability. To investigate the impact of cut pattern and posterior fragment medialization level on foot biomechanics, computational methods are employed.

Methods: Ankle weightbearing computer tomography (CT) scans of seven patients diagnosed with stage II pes planus deformity are segmented and converted into 3D computational models. Oblique and Chevron osteotomy patterns are modeled independently for each patient. The posterior fragments are medially translated by 8-, 10- and 12-mm and subsequently fixated to the anterior calcaneus with two screws. A total of 42 models are exported to finite element software for biomechanical simulations. Among the investigated parameters, the higher stiffness and lower von Mises stress at the osteotomy interface and the screw site are assumed to be precursors of better stability.

Results: It is recorded that as the medialization level increases, the stiffness decreases, and overall stresses increase. Also, it is observed that the Chevron cut produces a stiffer construct while the overall stresses are lower, indicating better stability when compared to the oblique cut. The statistical comparisons of the relevant groups that support these trends are found to be significant (p < 0.05).

Conclusion: Chevron osteotomy showed superior stability compared to the oblique osteotomy while underscoring the negative impact of increased medialization of the posterior fragment.

Clinical relevance: Opting for a lower medialization level and implementing the Chevron technique may facilitate union and earlier weightbearing.

Keywords: Finite element analysis; Medializing displacement calcaneal osteotomy; Pes planus deformity; Weightbearing computed tomography.