Design of Composite Parallel External Fixator for Multisegment Foot and Ankle Deformity Correction: A Correction Requirement- Dominated Approach

Abstract

Foot and ankle deformity is a common complaint in orthopedic surgery, among which the multisegment concurrent types are even more severe. As a key medical device for multisegment deformity correction, the composite parallel external fixator (PEF) design has a profound impact on the correction outcomes. However, existing PEFs share a single configuration and have inadequate adaptation to various deformity types, leading to problems, such as complex structural composition, excessive adjustment parameters, and uncomfortable wearing experience. To overcome these problems, this article proposes a novel correction requirement-dominated design approach for composite PEF. Multisite frame mounting modes and multitype struts are introduced to form required PEF configurations. Lower mobility struts can constrain the unwanted degrees-of-freedom, thus enabling the device to precisely match the requirement-function relationship. Taking the double-segment deformity as research object, clinical cases, and composite PEF assembly simulations are provided. Experiments are carried out on the mechanical prototype. The mounting test proves the interconverting ability and deformity-targeting property of the derived composite PEFs. Moreover, the motion test verifies that the device can distract patients of different weights to complete the correction path, and the stability test demonstrates that the device can resist external bumps, thus indicating the feasibility of the approach.