Biomechanical analysis between Orthofix® external fixator and different K-wire configurations for pediatric supracondylar humerus fractures

Abstract

BackgroundClosed reduction and percutaneous fixation are considered as the optional treatments for displaced supracondylar humerus fractures. However, there was no published report about the biomechanical analysis in Orthofix® external fixator. In this study, we developed a model of supracondylar humerus fractures and compared the biomechanical analysis of external fixator and different K-wires configurations in order to evaluate the stability of external fixator in supracondylar humerus fractures.MethodsWe developed an anatomic humerus model by third-generation synthetic composite, and 60 synthetic humeris were osteotomized to simulate the humeral transverse supracondylar fracture. Those fractures were reduced and fixed by external fixator or K-wires, and then biomechanical analysis was performed in extension, varus, valgus, and internal and external rotation loading. A paired-sample t test was used to evaluate the distance at the fracture site between the external fixator and K-wire configurations.ResultsDuring all direction loading, there was a significant statistical difference between external fixator and K-wires (P < 0.001 for all pairwise comparisons). In extension and internal rotation loading, the external fixator and three crossed K-wires had no comparable stiffness values (P = 0.572; P = 0.795), and both were significantly greater than two crossed and lateral K-wires (P < 0.05). In external rotation loading, there was no significance between the external fixator and K-wire configurations except two lateral K-wires (P > 0.05). In valgus loading, the stability of the external fixator was less than that of three crossed K-wires (P = 0.001) but was not significantly different with those of two crossed or three lateral K-wires (P = 0.126; P = 0.564). In varus loading, the stability of the external fixator was larger than those of two and three lateral K-wires (P = 0.000; P = 007).ConclusionsExternal fixator could provide enough stability for pediatric supracondylar humerus fractures without the injury of the ulnar nerve. Besides, it could enhance the rotational stiffness of the construct in rotation loading to avoid the complication of cubitus varus.

Bone cemented K-wire fixation versus elastic stable intramedullary nailing fixation of paediatric proximal humerus fractures: A prospective cohort study

“…[33] In biomechanical study of external fixator, Huang [31] found that the external fixator seemed to be superior to plate fixation in load bearing and resistance to torsional stress, the ultimate bearing capacity and load bearing were higher in the external fixator group (145.16 ± 17.42 N and 140 N, respectively) than plate group (120.21 ± 13.15 N and 69.63 ± 25.16-90.78 ± 17.18 N, respectively), and in the resistance to torsional stress, the external fixator's torque fluctuated (within 1 Nm) more evenly distributed than plate's torque (1-5 Nm), and external fixation provided the better rigidity. Li et al [30] also found that linking together the ends of fixation wires with external fixator could provide enough stability and could enhance the rotational stiffness of the construct. Lollino et al [29] reported that external fixator can achieve a rigid fixation in the treatment of PPHFs.…”

Pediatric distal humeral supracondylar fracture – achievement of optimal pinning configuration

“…Regarding biomechanical stability of different pin configurations, multiple literatures had reported that three crossed pins have the optimal stiffness against all directional forces, followed by two crossed pins and two lateral divergent pins, lastly parallel and convergent pins, respectively (9)(10)(11)(12)30). Zionts et al demonstrated that crossed pin configuration provides the most resistant torsional force (10).…”

“…Zionts et al demonstrated that crossed pin configuration provides the most resistant torsional force (10). Liu et al and Li et al also reported that three crossed pins technique provided the most optimal stiffness combination against translational and torsional forces regardless of fracture characteristics (9,30). In our cohort, 5% of lateral-entry only technique (1 of 20) subjected to re-displacement at follow-up, while only 1% of crossed pin technique (1 of 71) loss reduction.…”

Biomechanical investigation of external fixators for the treatment of supracondylar humerus fractures

“…In the past, EF has been the subject of biomechanical stability testing. In this regard, Li et al published an analysis comparing different k-wire configurations and external fixation in your Journal in 2018 [ 2 ]. They concluded: “External fixator could provide enough stability for pediatric supracondylar humerus fractures without the injury of the ulnar nerve.…”

“…They concluded: “External fixator could provide enough stability for pediatric supracondylar humerus fractures without the injury of the ulnar nerve. Besides, it could enhance the rotational stiffness of the construct in rotation loading to avoid the complication of cubitus varus” [ 2 ]. In the discussion section, they state that “there have been no published reports of biomechanical analysis in the external fixator in supracondylar humerus fractures” [ 2 ].…”