Mitchell's osteotomy augmented with bio-absorbable pins for the treatment of hallux valgus: A comparative finite element study

Abstract

Background: There is an inadequacy of conventional means to assess the surgical outcomes of a bunion surgery. We used the Finite Element Analysis for evaluating the typical Mitchell's procedure outcomes with or without bio-absorbable pins.

Methods: We developed a 3D FE model based on the CT images of a female volunteer with hallux valgus. A typical procedure was simulated on the foot model and two pins were virtually inserted for enhancing the fixation. We validated our model by comparing the predicted pressure results with the plantar pressure measured by a specific platform.

Results: The comparison of the plantar pressure distribution revealed similar patterns. A greater displacement was observed on the medial side of the osteotomy, but it was decreased after using pins. The maximum average pressure under the 1^st metatarsal head was decreased after the osteotomy. The respective pressure under the 3^rd and 5^th metatarsal head was decreased more after using pins, while, under the 2^nd and 4^th metatarsal head, an increase was developed.

Conclusion: The use of pins had no significant influence on the healing process but gave additional stability inside the osteotomy and could be used in cases where enhancement is needed. The surgeon should be familiar with the expected stress rising to the other metatarsal, considering the concomitant pathology or the additional interventions that should be performed.

Figure 1

Finite element model consisted of the foot including bones, cartilages, ligaments, and soft tissue. (a) En-face view (b) Profile view.

Figure 2

Finite element model of 1^st metatarsal bone (a) before and (b) after the simulation of a typical Mitchell’s osteotomy.

Figure 3

Two holes, one in the distal and the other in the proximal fragment, were drilled and suture properties were given at the respective elements to simulate the fixation method of the step-cut osteotomy.

Figure 4

3D free-body diagram depicting the boundary and loading conditions of the FE model.

Figure 5

(a) Finite element predicted plantar pressure distribution (MPa), and (b) plantar pressure distribution (MPa) measured with EPS Platform, both for standing in the weight-bearing upright position.

Figure 6

Average peak principal strain within the osteotomy site (excluding the region of holes due to the pins) during the healing process for 3 different models (only with suture, with suture and 1 pin, and with suture and 2 pins). The highlighted area depicts the bone remodelling threshold[39].

Figure 7

The stability of the osteotomy was examined by the distal displacement in relation to the proximal part. Two neighboured nodes of the dorsal (A) of the plantar (B) and of the lateral (C) side were selected and the displacement between them was predicted for each one of the 3 post-operative models.