The impact of configuration of the Ilizarov fixator on its stiffness and the degree of loading of distraction rods

3D printing feasibility of a controlled dynamization device for external circular fixation

AIM

to assess the small-scale 3D printing feasibility and cost estimation of a device for controlled dynamization.

MATERIALS AND METHOD

The two-part device previously developed by our research group was printed with a carbon fiber-reinforced nylon filament (Gen3 CarbonX™ PA6+CF, 3DXTECH Additive Manufacturing) by a professional 3D printer (FUNMAT HT, Intamsys). Electricity, material, and labor costs for production in a Brazilian city in the Santa Catarina state were calculated.

RESULTS

The devices for controlled dynamization were successfully printed in accordance with the planned design and dimensions. Six out of 38 printed devices presented defects in the bolt hole and were discarded. The average printing time per device was 1.9 h. The average electricity, material, and labor costs per printed device were respectively US$0.71, US$13.55, and US$3.04. The total production cost per device reaches approximately US$20 by adding the average cost of defective devices (15 %).

CONCLUSION

3D printing of the controlled dynamization device is feasible and its cost seems affordable to most healthcare services, which could optimize the consolidation of diaphyseal fractures and reduce treatment time for patients.

Locking the Taylor Spatial Frame - The effect of three additional longitudinal rods on osteotomy site movements

BACKGROUND

In clinical practice, even when the fixator is locked, a noticeable laxity of the construct can be observed. This study was designed to measure the stiffness of the fixator and to analyze the movements of the osteotomy site. Furthermore, the effect of three additional longitudinal rods on the locking of the construct was analyzed.

METHODS

Five synthetic tibia/fixator models (Model A) were tested under rotational torque (40 Nm) and axial compression (700 N). Three additional rigid rods were subsequently mounted, and the tests were repeated (Model B). The movements of the fixator as well as the osteotomy site were registered by a digital optical measurement system. Load- deformation curves, and so stiffness of the models, were calculated and compared.

FINDINGS

Under rotational and axial loadings, Model A was found to be less rigid than Model B (p = 0.034; p = 0.194). Notably, Model A showed a region of laxity around neutral rotational (ΔF = 5 Nm) and axial (ΔF = 16.64 N) loading before a linear deformation trend was measured. Concomitantly, greater osteotomy site movement was measured for Model A than for Model B under full loading (p = 0.05) and within the region of increased laxity (p = 0.042).

INTERPRETATION

The fixator showed an element of laxity around neutral axial and rotational loading, which transferred to the bone and led to a notable amount of osteotomy gap movement. Mounting three additional rods increased the stiffness of the construct and therefore reduced the movement of the osteotomy site.