Mechanical conditions in the internal stabilization of proximal tibial defects

doi:10.1016/S0268-0033(01)00102-4

Clinical Biomechanics

Volume 17, Issue 1, January 2002, Pages 64-72

https://doi.org/10.1016/S0268-0033(01)00102-4 Get rights and content

Abstract

Objectives. The goal was to design a method which would permit an assessment of the suitability of a newly developed implant under physiological-like loading conditions. Information obtained from such an analysis is expected to delineate more clearly the indications for a new device prior to clinical utilization.

Design. In vitro mechanical stiffness testing and finite element analysis.

Methods. From in vitro testing of proximal tibiae with defects, the stiffness of an internal stabilization system was determined. Using a finite element model, the loading of both the implant and bone was analyzed including all muscle forces. The variation in implant loading and interfragmentary strain for different defect locations was also investigated.

Results. Conventional stiffness testing demonstrated the comparability of the experimental findings with the finite element predictions. Under physiological-like loading the implant experienced high bending and von Mises stresses if defects in the region of the shaft were stabilized. A short working length increased implant loading up to the yield strength of the material.

Conclusions. The finite element analysis illustrated the appropriateness of this new device for proximal defects of the tibia, but the implant should be used hesitantly in fractures or defects extending into the diaphyseal region of the bone.
Relevance

This new analytical approach helped to identify clinical indications for the implant in which its mechanical attributes would prove advantageous.

Introduction

Nail, plate and external fixator have for decades been the most frequently used stabilizers for the surgical treatment of dia- and metaphyseal defects. They have been greatly improved in recent years and their indications have been broadened [1]. The choice of the osteosynthesis device has thereby become an issue of special interest since the local mechanical properties associated with the fixation may influence the process of bone healing [2]. The mechanical environment generated in defect situations provides an essential stimulus for bone formation [2], [3] and affects the healing rate [4].

In this respect, the stiffness of the fixation system has a substantial effect on the healing process [5]. This especially holds true in bone defect situations in which load is not transferred through the defect ends but solely through the implant itself. A change in bone loading after osteosynthetic stabilization is indeed expected on the local as well as on the global level. Extensive sections of the bone may be subjected to un- or overloading leading to bone resorption and remodeling [6]. Within the fixation system, high stresses and fatigue due to repetitive loading can lead to its technical failure. A better understanding of the loading of the implant as well as the strain distribution within the bone will certainly help improve understanding of the mechanical aspects of the biological healing process. Furthermore, a thorough comprehension of the loading of implant and bone is essential when selecting an appropriate fixation system in the clinic.

In vitro experiments have been frequently employed to determine the stiffness of the bone-implant construct. Methods have been provided for the complete description of the 3D-fixation stiffness of an external stabilizer [7]. Compression, bending, and torsional tests have been performed to compare the stiffness and fatigue behavior of various plate and interlocking nail systems [8], [9], [10]. These studies provide essential information on the overall stiffness of the implant-bone construct. However, the behavior of an osteosynthesis under physiological conditions including the muscle forces remains unknown. The significance of a comprehensive understanding of the loading of long bones has been previously demonstrated [11].

The goal was to introduce a method which in addition to conventional stiffness testing allows an assessment of the suitability of a newly developed implant with regard to the loading of the implant, the bone and the tissue at the defect site. Information obtained from such an analysis is expected to delineate more clearly the indications for a new device prior to its clinical use.

Section snippets

In vitro testing

Five fresh un-matched human cadaveric tibiae without any known histories of musculo-skeletal disorders were explanted and immediately after dissection stored in a freezer until mechanical testing. Defect stabilization was performed with a new, internal fixator with locking screws (angular stability) [12] using the standard instrumentation supplied by the producer (5-hole LISS, Less Invasive Stabilization System, Synthes Bochum, Germany). An internal fixator was selected to stabilize this defect

In vitro testing

In vitro compression testing lead to a complex movement between proximal and distal segment with moderate variations between individual specimens (Fig. 3). In relation to the distal segment, the proximal segment moved by mean 0.18 (SD, 0.01) mm dorsally and 0.33 (SD, 0.13) mm laterally. The defect side was compressed by mean 0.29 (SD, 0.07) mm. In the finite element analysis, relative movements of 0.15 mm dorsally, 0.27 mm laterally and a compression by 0.27 mm were calculated.

Finite element calculations

A survey of the

Discussion

Conventional stiffness testing allows a comparison of the stiffness characteristics of a newly developed implant with those of implants with known characteristics. Usually, the intention is to compare the stiffness data with clinical experience of the analyzed implants. From this, the suitability of a new design or method of defect stabilization can be assessed. The aim of this work was to analyze the potential of a new approach which, in addition to conventional stiffness testing, considers

Acknowledgements

The authors would like to acknowledge the contributions of Dr. Michael Schütz, Trauma and Reconstructive Surgery, Charité and Dr. Jörg Goldhahn and Markus Hehli, AO Development Institute, Davos. Further, the authors would like to thank Prof. Dr. Richard Brand, Orthopedic Biomechanics Laboratory, The University of Iowa for providing the anatomical and muscle force data. Thanks to Mr. Klaus Dannenberg for developing the in vitro test set-up and to Prof. Dr. Stephan Perren, AO Research Institute,

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Citation Excerpt :
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Mechanical conditions in the internal stabilization of proximal tibial defects

Abstract

Introduction

Section snippets

In vitro testing

In vitro testing

Finite element calculations

Discussion

Acknowledgements

The new unreamed AO nails for the tibia and the femur

Acta Orthop. Belg.

Effect of dynamization on gap healing of diaphyseal fractures under external fixation

Clin. Biomech.

The influence of induced micromovement upon the healing of experimental tibial fractures

J. Bone Joint Surg, Br

Axial movement and tibial fractures. A controlled randomized trial of treatment

J. Bone Joint Surg, Br

Controlled mechanical stimulation in the treatment of tibial fractures

Clin. Orthop.

A uniform strain criterion for trabecular bone adaptation: Do continuum-level strain gradients drive adaptation?

J. Biomech.

A method to determine the 3D stiffness of fracture fixation devices and its application to predict inter-fragmentary movement

J. Biomech.

Biomechanical study of nine different tibia locking nails

J. Orthop. Trauma

Geometrical properties and torsional fatigue life of a tibial interlocking intramedullary nail segment

J. Orthop. Trauma

A comparative biomechanical evaluation of three systems for the internal fixation of distal femur fractures

Trans. Orthop. Res. Soc.

Influence of muscle forces on femoral strain distribution

J. Biomech.

LISS – Ein neuer Fixateur intern für distale Femurfrakturen

OP J.

Mechanical behavior of Ilizarov ring fixators. Effect of frame parameters on stiffness and consequences for clinical use

Unfallchirurg

Current status of surgical technique for unreamed nailing of tibial shaft fractures with the UTN (unreamed tibia nail)

Unfallchirurg

Axisymmetric finite element analysis of the lateral tibial plateau

J. Biomech.