An Easy-To-Use External Fixator for All Hostile Environments, from Space to War Medicine: Is It Meant for Everyone's Hands?

Abstract

Long bone fractures in hostile environments pose unique challenges due to limited resources, restricted access to healthcare facilities, and absence of surgical expertise. While external fixation has shown promise, the availability of trained surgeons is limited, and the procedure may frighten unexperienced personnel. Therefore, an easy-to-use external fixator (EZExFix) that can be performed by nonsurgeon individuals could provide timely and life-saving treatment in hostile environments; however, its efficacy and accuracy remain to be demonstrated. This study tested the learning curve and surgical performance of nonsurgeon analog astronauts (n = 6) in managing tibial shaft fractures by the EZExFix during a simulated Mars inhabited mission, at the Mars Desert Research Station (Hanksville, UT, USA). The reduction was achievable in the different 3D axis, although rotational reductions were more challenging. Astronauts reached similar bone-to-bone contact compared to the surgical control, indicating potential for successful fracture healing. The learning curve was not significant within the limited timeframe of the study (N = 4 surgeries lasting <1 h), but the performance was similar to surgical control. The results of this study could have important implications for fracture treatment in challenging or hostile conditions on Earth, such as war or natural disaster zones, developing countries, or settings with limited resources.

Keywords: developing countries; external fixator; hostile environments; learning curve; space; tibial shaft fracture; war medicine.

Figure 1

Creation of the fractured leg model. Landmark of the fracture line with a laser ((a) above—red line) and vertical benchmarks to further evaluate fracture reduction ((a) below—white arrows). Bone cutting by the diamond bandsaw following the fracture landmark (b). Soft tissues assembly and fixation around the fractured bone, mounted on a foot prosthesis (c). Final fractured leg model (d). Adapted from Manon et al. [4].

Figure 2

Material needed to build the EZExFix (a). Final construct mounted on a broken artificial leg on a sagittal, frontal, and upper view, respectively (b). Broken artificial leg after removing soft tissues ready to measure analysis parameters on a sagittal, frontal, and upper view, respectively (c). Adapted from Manon et al. [4].

Figure 3

Measurement following six vectors (three translations and three rotations) into Cartesian coordinates (a). Ant: anterior, Post: posterior, Inf: inferior, Sup: superior, Med: medial, Lat: lateral, ER: external rotation, VR: varus, RC: recurvatum. For the procedure to harvest points position with the coordinate measuring machine, the pin has to point to the desired localization and a computer registers it (b). Points of interest to take measurements of anatomical world and pathologic world (c). The green and red dots are used to approximate the correct tibial axis and the blue ones are used to describe the fracture position.

Figure 4

Examples of points of interest (in green, red, blue, and magenta) encoded with the coordinate measuring machine and used to construct the global reference frame R_world fixed to the tibial plateau (green dots), the local reference frame R_p fixed to the proximal part of the fracture (blue dots), and the local reference frame R_d fixed to the distal part of the fracture (magenta dots).

Figure 5

Example of proximal (blue dots) and distal (magenta dots) parts of the fracture registered in the global reference frame R_world (a). The local reference frame R_p is fixed to the centroid of the blue dots. As an illustration, L_max is the maximum distance between proximal and distal parts of the fracture, measured in mm along the axis z_p. Example of results for the calculation of the location parameter between proximal and distal parts of the fracture (b). The blue curve represents the evolution of the location of the distal part along the circumference of the proximal part of the fracture. The horizontal red line is the 2 mm threshold. The horizontal green line the 1.5 mm threshold. The 2 mm and 1.5 mm bone-to-bone contacts are computed as the part of the blue curve lying under the red and green horizontal lines, respectively.

Figure 6

Average translational displacements of analog astronauts’ surgeries comparing to surgeon ones. A: anterior, P: posterior, M: medial, L: lateral, L+: lengthening, L−: shortening, ˟: mean, °: outliers, ns: nonsignificant.

Figure 7

Average angular displacements of analog astronauts’ surgeries compared to surgeon ones. VR: varus, VL: valgus, FL: flessum, RC: recurvatum, ER: external rotation, IR: internal rotation, ˟: mean, ns: nonsignificant, **: p < 0.01.

Figure 8

Bone-to-bone contact less than 2 and 1.5 mm for astronauts and the surgeon, represented on axial cross sections of the mid-shaft tibial fractures. The opaque surface corresponds to the bone contact percentage under the respective threshold. This contact zone is purely theoretical, not anatomical. Outcomes are expressed as the mean percentage over the total tibial circumference (+/−standard deviation).

Figure 9

Panel chart of the six different displacements and the bone-to-bone contacts expressed as mean scores (black bold straight lines) across the four successive sessions (Sessions S₁, S₂, S₃, S₄). As a reference, S_EVA and S_stress are represented by yellow and red lines, respectively, as a horizontal bar calibrated on the corresponding mean scores. Error bars show the standard deviation. Green area shows physiologic range and red warns about the pathologic one. A: anterior, P: posterior, M: medial, L: lateral, L+: lengthening, L−: shortening, VR: varus, VL: valgus, FL: flessum, RC: recurvatum, ER: external rotation, IR: internal rotation.