The external skeletal fixation technique is a minimally invasive operation in which nails are percutaneously implanted and connected with external frames. The stress transmitted between nails stimulates the regeneration and reconstruction of bone tissue[8]. Previous studies have justified the benefits of an external fixator in the treatment of fractures, as it can (1) maintain fracture stability by resisting rotation, shearing and varus-valgus forces[9, 10]; (2) alleviate articular surface stress for articular fractures, thus protecting the articular surface[11]; and (3) supply a suitable environment for soft tissue and muscle recovery[12]. At present, external fixators are rarely used in trauma scenes, especially in field medical treatment. Hybrid external fixators have relatively more functions, but a large number of components must be used to meet the needs of different types of fractures[6, 13]. In addition, when an external fixator is attached to a joint, it will affect joint movement to some extent. Joint stiffness is a well-documented complication during treatment external fixators, even resulting in heterotopic ossification[13–16].
In this study, we designed a novel external fixator that aims to overcome the shortcomings of existing external fixators that cannot be well adapted to control the fixation of an accident victim’s injury site. The new external fixator is not only convenient for performing damage-controlled fixation of various complex fractures but can also be flexibly adjusted. The UJ external fixator is an intensive device that has a number of advantages over traditional external fixators. Several of these are listed as follows.
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Convenient delivery. The new fixator is small and requires no extra components.
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Easy learning. The only tools required are an electric drill, a wrench and a nailer; junior physicians can manipulate the external fixator quickly.
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Broad versatility. When applied to many kinds of fractures, the UJ external fixator can continue noninvasive controlled fixation to the final fixation.
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No Sterilization. External fixators and tools can carry bacteria, but only the nails need to be sterilized, which makes the new fixator suitable for reuse in battle fields and disaster areas.
In our study, we observed a good fixation effect in which fracture patients healed well during follow-up according to radiographic observation. Because the UJ external fixator can be adjusted flexibly, joint deformity and stiffness can be avoided, and cross-joint fixation does not require pre-nail implantation after fixation. Therefore, the dynamic external fixator is a reliable and effective device for treating fractures, allowing early postoperative functional rehabilitation and restoring joint function. During the treatment, the UJ external fixator was fixed firmly without nail loosening and displacement. Moreover, there were no intraoperative or postoperative complications, including infection, delayed union or breakage of the UJ external fixators. Given that it supplies a suitable condition for fracture healing, the UJ external fixator achieved an acceptable treatment result.
Previous studies have confirmed that fixator stiffness is closely related to stability and fracture healing[17–19]. The overall stiffness of the fracture fixation device directly impacts the axial, torsional, and shear interfragmentary movement at the fracture site[20–22]. During axial and lateral biomechanical testing, we used a maximum load of 600 N, which is similar to the weight of an average adult, to estimate the mechanical performance of the UJ external fixator. Our data suggest that the UJ external fixator exhibited biomechanical stability similar to that of AO external fixators, which indicates that the UJ external fixator conformed to clinical application standards. We found no significant differences in the stiffness of the rotational planes with a load below 40 N m. This demonstrates that the UJ external fixator had a normal anti-torsion effect. Therefore, the UJ external fixator, with its good biomechanical stability, will lead to shear interfragmentary movement and promote fracture healing.
Some limitations should not be ignored. First, because the UJ external fixation technology was new to them, the patients and their guardians were fully informed of the purpose and the potential advantages and disadvantages of the device before surgery, as that was when we were able to communicate with them. Second, the relatively small sample size resulted in insufficient power for identifying significant differences, and a larger study will be performed to assess the mechanical stability.