The present study is the first large cohort study to compare the LC-DCP and DCR-ESIN techniques for fixing diaphyseal fractures of the adult humerus. Although several studies proved that locking plates were superior to LC-DCPs in cadaveric models [10,11,12], the clinical results showed no difference between locking plates and LC-DCPs . In our study, a major finding was that the DCR-ESIN technique had shorter union times and less complications than the LC-DCP technique. The results indicate that the DCR-ESIN may be an alternative internal fixation for diaphyseal fractures of the adult humerus.
Surgical fixation of diaphyseal fractures generally involves plating or nailing. Kurup et al.  conducted an intervention review of five small trials to compare dynamic compression plating vs. locked intramedullary nailing for humeral shaft fractures in adults. No significant difference in fracture union, operating time, blood loss during surgery, or iatrogenic radial nerve injury between the two fixation methods was found. However, there was a statistically significant increase in shoulder impingement following nailing when compared with the LC-DCP technique. Use of the DCR-ESIN technique can theoretically avoid shoulder impingement or cuff violations. In addition, explorations were minimally invasive. In our study, the DCR-ESIN group had superior functional outcomes and less complications than the LC-DCP group, as discussed in the following paragraphs.
Chen et al.  and Chiu et al.  reported that the Ender nail, a flexible intramedullary nail, had superior outcomes with regard to blood loss, operative times, and union times. However, those two studies mixed the two entry methods of the nail group. Moreover, the retrograde methods used in the two aforementioned studies were based on methods from DeLong et al.  and were different from our methods. We believe that the inevitable backout and loss of rotational stability may happen. Using our DCR-ESIN methods, a three-point fixation may reduce the inevitable backouts and strengthen the rotational stability .
Discussions involving the union and nonunion of humeral diaphyseal fractures have led to controversies in recent years . Maresca et al.  concluded that there were three main factors in humeral shaft nonunion: fracture type, grade of open fracture, and type of osteosynthesis. In our study, the LC-DCP group and the DCR-ESIN group showed similar results in union rates. However, the DCR-ESIN group had shorter union times than the LC-DCP group. These results indicate that the evacuation of hematoma plus periosteal stripping in the plating group may cause prolonged union times or increase the probability of nonunion or delayed union.
Infections, prolonged union times, and radial nerve palsy are general concerns about the LC-DCP technique . Conventional techniques involve an extensive surgical approach for the open reduction of fractures . In our study, three cases in the plating group required oral antibiotics or local debridement for surgical site infections, while there were no cases of infection in the DCR-ESIN group. In addition, radial nerve palsy, including temporary and permanent radial nerve injury, was also found in the LC-DCP group, with no radial nerve injury in the DCR-ESIN group. Due to the extensive surgical approach, the radial nerve would be retracted for a prolonged period of time, potentially resulting in ischemia due to manipulation or small vessel destruction or potential damage caused by implants or drilling [20,21,22].
With the DCR-ESIN technique, the two different entry points may reduce cortical cracking, and the nail, pre-bent into a ‘C’ curve, may provide three-point fixation. Two double-crossed nails can provide rotational stability. Additional wire was suggested when encountering long-spiral or large-wedge fragments, as it provides additional stability and more bone contact. This retrograde method can prevent the shoulder stiffness generated in the antegrade method.
There are some limitations of our study. This study had a retrospective design, which may have introduced selection bias and, therefore, been more susceptible to data loss and confounding than a prospective study. Additionally, subgroups were too small to be independently identified and analyzed. In our study, we did not intend to debate operative versus nonoperative treatment of diaphyseal fracture of the adult humerus. The choice between nonoperative and operative treatment of this fracture should be made on an individual basis. In addition, a postoperative CT scan, which was not included in the National Health Insurance, was not obtained as a means to evaluate rotation. Even though around one-quarter of the patients in the DCR-ESIN group needed additional wiring with a minimally invasive technique, the remaining three-quarters of the patients benefited from closed reduction with DCR-ESIN instrumentation. However, the most suitable technique for a particular fracture pattern cannot be determined based on this study. Further research is therefore warranted for different fracture patterns. In addition, we suggest that a prospective randomized controlled trial could be performed to compare these two methods.