Biomechanical study of a low-cost external fixator for diaphyseal fractures of long bones

Abstract

Background: External fixation improves open fracture management in emerging countries. However, sophisticated models are often expensive and unavailable. We assessed the biomechanical properties of a low-cost external fixation system in comparison with the Hoffmann® 3 system, as a reference. Methods: Transversal, oblique, and comminuted fractures were created in the diaphysis of tibia sawbones. Six external fixators were tested in three modes of loading-axial compression, medio-lateral (ML) bending, and torsion-in order to determine construction stiffness. The fixator construct implies two uniplanar (UUEF1, UUEF2) depending the pin-rods fixation system and two biplanar (UBEF1, UBEF2) designs based on different bar to bar connections. The designed low-cost fixators were compared to a Hoffmann® 3 fixator single rod (H3-SR) and double rod (H3-DR). Twenty-seven constructs were stabilized with UUEF1, UUEF2, and H3-SR (nine constructs each). Nine constructs were stabilized with UBEF1, UBEF2, and H3-DR (three constructs each). Results: UUEF2 was significantly stiffer than H3-SR (p < 0.001) in axial compression for oblique fractures and UUEF1 was significantly stiffer than H3-SR (p = 0.009) in ML bending for transversal fractures. Both UUEFs were significantly stiffer than H3-SR in axial compression and torsion (p < 0.05), and inferior to H3-SR in ML bending, for comminuted fractures. In the same fracture pattern, UBEFs were significantly stiffer than H3-DR (p = 0.001) in axial compression and torsion, while only UBEF1 was significantly stiffer than H3-DR in ML bending (p = 0.013). Conclusions: The results demonstrated that the stiffness of the UUEF and UBEF device compares to the reference fixator and may be helpful in maintaining fracture reduction. Fatigue testing and clinical assessment must be conducted to ensure that the objective of bone healing is achievable with such low-cost devices.

Locally developed external fixators as definitive treatment of open tibia diaphyseal fractures: a clinical prospective study conducted in Ivory Coast

“…1). The xator design consisted of a unilateral uniplanar external xator or biplanar external xator [12] (Fig. 2), with the frame made of a 304L stainless steel cylindrical tube.…”

“…Although numerous sophisticated models are available on the market, they prove to be ather expensive [11]. The development of a locally-developed external xator (LDEF) sought to build an inexpensive external xator, whose biomechanical properties are comparable to those of a validated reference xator [12]. The nal objective was that patients who could not afford conventional expensive xators would nevertheless be treated appropriately.…”

An engineering review of external fixators

“…From an orthopaedic point view, its relatively simple structure, coupled with the possibility of using half pins promotes its useability [ 45 , 46 , 47 ]. Similarly, depending on the planes along which pins are inserted for the purpose of treatment, bi-planar [ 48 , 49 , 50 ] and mono-planar [ 51 , 52 , 53 ] variants of the unilateral EFs have previously been used. Below is a discussion on other variations of the linear, circular and hybrid EFs.…”

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Fig. 6 Experimental setups used for (a) axial, (b) bending and (c) torsional tests [ 49 , 114 , 115 ].

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“…INSTRON uniaxial testing machines have been used to conduct the axial compression tests. Generally, the bone-EF setup has been loaded up to the range of 700 N, which is the corresponding weight of a human weighing 70 kg in a one-legged stance [ 49 , 114 , 116 ]. The loading rate for these tests are generally in the order of 10 −4 m/s, which falls under the static range [114] .…”