Novel Intramedullary nail controls axial interfragmentary motion, heals tibial fracture: Study

The authors from the Department of Surgery, Creighton University School of Medicine, Phoenix, Arizona, USA quantified interfragmentary motion and load transfer in tibial fractures fixed using a novel intramedullary nail (IMN) that allows controlled axial motion.

A total of fifty composite tibias with various fracture patterns were utilized for the research. 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, explained Navid Ziran, the lead authors of the study.

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.

Moreover, 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.

It was observed that the 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 indicated that the strain shielding effects were likely present due to the implant.

However, strain shielding appeared to be reduced in tensile and compressive principal strains. Hence, to summarize the authors noted that the novel IMN allowed controlled axial motion between the fragments in a variety of common diaphyseal tibial fracture patterns.

The clinical significance was that this in vitro biomechanical study investigated a novel intramedullary nail capable of controlled axial interfragmentary motion which may potentially enhance fracture healing.