Chevron vs Oblique Medial Displacement Calcaneal Osteotomy - Which Is More Stable? Results From a Finite Element Analysis Study

Abstract

Category: Hindfoot; Ankle Introduction/Purpose: The medial displacement calcaneal osteotomy is used to correct hindfoot valgus in adult-acquired flatfoot disease(AAFD). This is done by means of an oblique cut, which is then translated medially. The chevron variant of the MDCO has gained popularity in recent times. This osteotomy involves a V-cut, with the apex of the V placed anteriorly. This is thought to be inherently more stable than the conventional MDCO owing to its geometrical design and higher contact area, especially with higher magnitudes of translation of the osteotomized fragment. However, it is technically more demanding, and many surgeons may not be familiar with the technique. Moreover, there is no literature comparing the stability of the chevron and oblique MDCO. Hence, we conducted this study to address this knowledge gap. Methods: Computed Tomography (CT) scan of the foot of a patient diagnosed with Johnson stage 2 AAFD was segmented and converted into a 3D computational model. Subsequently, oblique and chevron (160o V-angle) calcaneal osteotomies were performed virtually. For each variant, the osteotomized fragment was translated medially by 8-, 10- and 12-mm and then fixed virtually with two 6.5 mm screws. The six models were imported into a Finite Element Software (ANSYS v19) and subjected to 500 N axial loading through the tibia to simulate a single-leg stance. The von Mises stresses at the osteotomy interfaces and the screws, and the total displacement of the posterior fragment was recorded for each model. Results: The compiled simulation results are presented in Table 1. For both osteotomies, the overall stresses at the osteotomy contact site and the screws increased incrementally with increasing medial translation. Similarly, sagittal plane displacement of the anterior fragment was noted to follow a similar trend. Across all translation levels, the stresses were recorded to be lower for chevron MDCO when compared to the oblique variants. Relative fragment displacement was also noted to be lower for the chevron MDCO. Conclusion: The chevron osteotomy results in lower contact stresses and osteotomy fragment displacement and may prove to be a more stable alternative to the oblique MDCO. However, these results need to be replicated in a larger cohort of patients, as well as in cadaveric studies to determine if surgeons can permit early weight-bearing with the chevron MDCO.