Elsevier

Clinical Biomechanics

Volume 30, Issue 7, August 2015, Pages 713-719
Clinical Biomechanics

A new approach to prevent contralateral hip fracture: Evaluation of the effectiveness of a fracture preventing implant

https://doi.org/10.1016/j.clinbiomech.2015.05.001Get rights and content

Highlights

  • We assessed the biomechanical performance of a hip fracture preventive device.

  • The device increases both load and energy to fracture of the proximal femur.

  • The performance is maintained after 30 load cycles during multiple fall simulation.

  • None atypic fracture was observed during the mechanical tests.

Abstract

Background

Among the millions of people suffering from a hip fracture each year, 20% may sustain a contralateral hip fracture within 5 years with an associated mortality risk increase reaching 64% in the 5 following years. In this context, we performed a biomechanical study to assess the performance of a hip fracture preventing implant.

Methods

The implant consists of two interlocking peek rods unified with surgical cement. Numerical and biomechanical tests were performed to simulate single stance load or lateral fall. Seven pairs of femurs were selected from elderly subjects suffering from osteoporosis or osteopenia, and tested ex-vivo after implantation of the device on one side.

Findings

The best position for the implant was identified by numerical simulations. The loadings until failure showed that the insertion of the implant increased significantly (P < 0.05) both fracture load (+ 18%) and energy to fracture (+ 32%) of the implanted femurs in comparison with the intraindividual controls. The instrumented femur resisted the implementation of the non-instrumented femur fracture load for 30 cycles and kept its performance at the end of the cyclic loading.

Interpretation

Implantation of the fracture preventing device improved both fracture load and energy to fracture when compared with intraindividual controls. This is consistent with previous biomechanical side-impact testing on pairs of femur using the same methodology. Implant insertion seems to be relevant to support multiple falls and thus, to prevent a second hip fracture in elderly patients.

Introduction

The number of hip fractures, representing about 2 million in 2010, will increase by 215% to reach 6.3 million in 2050 (Cooper et al., 1992) if the fracture rate remains stable. This increase reflects the aging of the population, and the prevalence of osteoporosis. Indeed, hip fracture is often the result of a reduction in bone mineral density (BMD), and occurs after low-energy falls.

In this context of bone fragility, a first hip fracture is a warning signal. Among the 2 million people suffering from a hip fracture each year, 20% will sustain a contralateral hip fracture at 5 years. This event often leads to a radical worsening in the way of life (dependency), and these patients, highly weakened physically, see their mortality risk increase to reach 64% during the 5 following years (Ryg et al., 2009).

Therefore, prevention of a contralateral hip fracture is a global public health issue. Preventive treatments mainly consist of drug therapies to reduce the rate of bone loss for people suffering from osteoporosis. However, their efficiency is put in doubt, especially as considering the lack of adherence of the patients to these long-term treatments. Moreover, their side effects are more and more criticized. Efficacy of techniques such as external hip protectors has not been proven too, and they are rarely used.

Several scientific studies have evaluated the biomechanical performance of different preventive measures (mostly femoroplasty) for strengthening the proximal femur to avoid fracture due to a fall. Two previous studies proposed by Heini et al. (2004) and Sutter et al. (2010) with a filling of the femoral head with 40 ml of PMMA cement showed very good results with an increase of the fracture load of + 82% and + 37% respectively. These tests also demonstrated a significant increase in the energy to fracture (+ 188% and + 154% respectively). Despite the good performance measured, these solutions have significant disadvantages: the rise in temperature due to the use of a very large amount of PMMA cement (28 to 40 ml), the occurrence of sub-trochanteric fractures and especially the occurrence of atypical fractures involving the femoral shaft, making very complex necessary revision. Tests with silicone gum by Van der Steenhoven et al. (2009) led to a weakening of the femoral head strength, but this type of filling prevents the dislocation of the bone in case of fracture, making the fracture fixation easier. Another concept, developed by Beckmann et al. (2011), consists of making a central or centro-dorsal perforation (diameter 8 mm) and injecting 8–18 ml of PMMA cement. This amount of cement, significantly lower than used by Heini and Sutter (40 ml), showed rather good results: + 23% to 35% for the fracture load, and + 160% for the energy to fracture, for femurs from 66-year-old donors.

We studied a new medical device, dedicated to the prevention of hip fracture. We assessed its efficiency to improve the biomechanical performance of the proximal femur.

Section snippets

Hip fracture preventive device

The device (Y-STRUT®, Hyprevention®, Pessac, France) consists of two interlocking rods. The rods have multiple perforations enabling the extrusion of injected bone cement (Fig. 1). The implants are made of PEEK Optima® (Invibio). The cement used is a standard PMMA bone cement (Cortoss®, Stryker®, Kalamazoo, USA), with a threefold function:

  • It ensures the connection of the two components of the implant.

  • It increases the contact surface with the surrounding bone by seeping through the multiple

Finite element analysis

The fracture risks were assessed in the two load simulations: monopodal stance and lateral fall.

In the case of an axial compressive load, Y-STRUT® reduced the risk of femoral neck fracture from 25% to 28% (depending on the failure criterion i.e. stress based RF or strain based RF) when it was implanted in the upper third of the femoral head. No significant decrease was observed when the device was implanted in a central position.

In the case of a trochanteric load (sideways fall simulation),

Discussion

Results support the hypothesis that Y-STRUT® improves the biomechanical resistance to fracture of the femur. Finite element analysis allowed to identify the best location for the device, showing a high potential decrease in the risk of femoral neck fracture (− 28%) and trochanteric fracture (− 52%) when the device was placed in the upper third of femoral head. This result could be explained by the bone structure. The lower part of the femoral neck has a strong dense trabecular structure, and

Conclusions

This study demonstrates the potential of Y-STRUT® to improve the biomechanical performance of the proximal femur. Implant insertion seems to be relevant to support multiple falls and thus, to prevent a second hip fracture in elderly patients. A clinical trial is ongoing to assess the feasibility and the safety of the surgical procedure.

Conflict of interest

The study was sponsored by Hyprevention. MS, RG, MA, CV: Cofounder, shareholder of Hyprevention. CD: Hyprevention employee. NG, SE: No conflict of interest.

Acknowledgments

The authors gratefully acknowledge Professor Jean-Charles LE HUEC, Director of the DETERCA – Département de Techniques et de Recherches Chirurgicales Appliquées – for providing anatomical specimens and facilities, and Haut Lévêque Hospital - CHU Bordeaux for the DXA scans.

References (19)

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