Numerical evaluation of the mechanical properties of a novel expandable intramedullary nailing: A new alternative to standard interlocking nailing

Evaluation of the mechanical behaviour of the expandable wedge locked nail fixation in retrograde use: A finite element study

INTRODUCTION

In literature, there have been many studies conducted to research the alternatives of standard interlocking intramedullary nailing. The expandable wedge locked nail fixation, which is thought as a new alternative to the standard interlocking nailing, has been presented in previous numerical studies. The antegrade usage of the wedge locked nail fixation has provided promising results. From this point, the aim of the study is to evaluate mechanical behavior of its retrograde usage on femur models. Additionally, another aim of the study is to investigate the effect of fracture level on mechanical properties of the fixation.

MATERIALS AND METHODS

The mechanical behaviors of the wedge locked nail and standard interlocking nail fixations were compared by finite element methods. Sawbones femurs having osteotomies at five different levels to simulate different fractures were fixed with wedge locked nail or interlocking nail by using retrograde approach. With respect to the fracture level, two different nail lengths were used. Axial compression load was applied to fixations. The mechanical behaviors of the fixations were evaluated with respect to stiffness of the fixations and stresses occurred on both implants and bones.

RESULTS

Any of the wedge locked nail fixation did not slip at canal. The stress and stiffness results were mostly close with each other for both nail types. The maximum stresses at locking elements or bones contacting these elements increased with decreased distance between the fracture and relevant locking elements.

DISCUSSION

The wedge locked nail fixation showed comparable results to the standard interlocking nail fixation with respect to the stiffness and stress. Under axial loading, wedge locked nail provided a secured fixation without any slippage and preserved its position inside the medullary canal. It may be thought as a safe alternative to the standard interlocking nail fixation for retrograde usage. Additionally, according to stress results, it is advised to the surgeons to avoid a close locking to the fracture line.

Which of the three different intramedullary nail designs is superior in the treatment of femoral shaft fractures?

Aim: The aim of this study a retrospective comparison was the clinical and radiological results results of patients with femoral shaft fracture made oftreated with three different types of intramedullary nail (IMN). Material and Method: The study included 54 patients operated on in our clinic because of femoral shaft fracture. The records were retrospectively examined of 18 patients applied with locked IMN (LIMN), 17 with blade expandable IMN (BEIMN), and 19 with talon distalfix IMN (TDIMN). The groups were compared statistically in respect of age, gender, BMI, affected side, operating time (mins), radiation exposure (number of shots), time to union (weeks), visual analog scale (VAS) score, soft tissue problems associated with implant irritation, amount of shortening (mm), coronal, sagittal and torsional angulation (degrees). Results: The mean VAS score of the TDIMN group was determined to be statistically significantly higher than that of the LIMN and BEIMN groups (p=0.008, p=0.045). The operating times were similar in the BEIN and TDIMN groups (p=0.768) and significantly shorter than in the LIMN group (p

Mechanical comparison of standard interlocking, clawed, and expandable wedge locked nail fixations: An experimental and numerical study

INTRODUCTION

Intramedullary nailing has been used as a standard in the treatment of the long bone fractures with its clinical and mechanical advantages. However, using distal locking screws has been associated with longer operative times, higher radiation exposure rates, and complications like breakages of distal screw or nail at the screw hole level. Therefore, attempts to eliminate distal locking screws has been always present for intramedullary nail fixation. With a similar purpose, the present study has been carried out to compare mechanical behaviors of intramedullary nail fixations with different distal locking elements.

MATERIALS AND METHODS

In this study, mechanical behaviors of standard interlocking and clawed nail fixations were compared experimentally in the first part. Six fourth generation Sawbones femurs, which have a simulated subtrochanteric fracture, were divided equally and were fixed with standard interlocking and clawed nails. During axial compression tests, experimental strain measurements were taken from all fixations. After validation of numerical models with using experimental strains and stiffnesses, mechanical behaviors of standard interlocking, clawed, and wedge locked nail fixations were compared numerically under axial compression loads. In numerical comparison, the stress-strain distributions were evaluated.

RESULTS

Experimental results showed that although that there was no significant difference in stiffnesses, standard nail fixation bore two times higher loads than clawed nail fixations. Under loading, decrease in the distance between fracture surfaces was approximately seven times higher in the clawed nail fixation when compared to standard nail fixations. Numerical results showed that wedge locked nail fixation provided equivalent mechanical behavior to standard interlocking nail.

DISCUSSION

In experiments of clawed nail fixation, the high decrease in the distance between fracture surfaces was evidence of the slippage of nail in the medullary canal. For a safe fixation, claws should be deployed when they are completely in contact with the cortical bone, they should be stuck into the bone in a fair amount, and the deployment in the distal third of the femur should be avoided. According to experimentally validated numerical analyses, wedge locked nail fixation may be an alternative for standard interlocking nail fixation if experimental studies support the present results.