A novel intramedullary nail to control interfragmentary motion in diaphyseal tibial fractures

Abstract

Numerous animal and human studies have demonstrated the benefit of controlled interfragmentary motion on fracture healing. In this study, we quantified interfragmentary motion and load transfer in tibial fractures fixed using a novel intramedullary nail (IMN) that allows controlled axial motion. Fifty composite tibias with various fracture patterns were utilized. For all test conditions, two interlocking screws were used to fix the nail in the proximal metaphysis, and two interlocking screws through the distal metaphysis. The nail allowed either no motion (static mode) or 1 mm (dynamic mode) of cyclic axial motion between the two fracture fragments for every fracture pattern tested. As expected, strain shielding was more prominent under static nail conditions. In contrast, specimens tested under dynamic nail conditions transferred axial load between the fracture fragments such that strains near the fracture site were generally similar to those measured on an intact tibia. Maximum shear strains proximal to the fracture were significantly lower in specimens with oblique or butterfly fracture patterns (p < 0.01) compared to intact specimens. This decrease in shear strain indicates that strain shielding effects were likely present due to the implant. However, strain shielding appeared to be reduced in tensile and compressive principal strains. In summary, the novel IMN allowed controlled axial motion between the fragments in a variety of common diaphyseal tibial fracture patterns. Clinical Significance: The present in vitro biomechanical study investigated a novel intramedullary nail capable of controlled axial interfragmentary motion which may potentially enhance fracture healing.

Comparison of a 2.7-mm and 3.5-mm locking compression plate for ulnar fractures: a biomechanical evaluation

“…53 In this study, in addition to the measurement of interfragmentary motion, principal compressive and tensile strains on the cortical bone adjacent to the fracture site were measured. 54 Both the 2.7-mm and 3.5-mm constructs produced substantially lower magnitudes of principal strain than the intact ulna under the same loading conditions. Based on the results of this study, the 2.7-mm constructs produced generally equivalent or higher strains than the 3.5-mm constructs under both axial rotation and sagittal cantilever bending.…”

Comparison of dynamic versus static fixation of intramedullary nailing in tibial diaphyseal fractures: A systematic review and meta-analysis

“…Dynamic fixation permits interfragmentary motion and increases the contact area between bone fragments at the fracture site (22). Since callus formation requires small amounts of relative deformation (7), finite element biomechanical analyses have demonstrated significantly increased osteogenic response with appropriate axial loading, leading to earlier and stronger callus formation and eventual fracture bridging (23)(24)(25)(26)(27). Episodic stresses that affect fracture sites were also found to positively influence revascularization and tissue differentiation in fracture healing (28).…”