27.12.2012 Views

ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

A FINITE ELEMENT COMPARISON OF LOCKING PLATE AND<br />

DYNAMIC COMPRESSION PLATE FRACTURE FIXATION<br />

Alisdair R. MacLeod 1 , Pankaj Pankaj 2 and A. Hamish R.W. Simpson 3<br />

1. ABSTRACT<br />

Finite element modelling is being extensively used to evaluate the biomechanical<br />

behaviour of fractured bone treated with fixation devices. While locking plate fixation is<br />

becoming increasingly popular for complex and osteoporotic fractures, for the majority<br />

of indications compression plating remains the standard choice. This study uses finite<br />

element models to examine the more recent locking plate device (LCP), which produces<br />

a ‘fixed angle construct’, with traditional plating in which the screws are free to toggle<br />

in plate holes (dynamic compression plate or DCP). A novel technique utilising material<br />

expansion and contraction to simulate the effects of the various pre-loads is employed.<br />

Predictions of strain within the bone using a compression plate are contrasted against<br />

those produced using a locking plate. In addition, the effect that the two plating systems<br />

have on older or osteoporotic bone is investigated. The results showed that an<br />

incomplete fracture reduction results in increased strain concentration around screw<br />

holes and therefore an increased likelihood of screw loosening. This effect was most<br />

pronounced in compression plated osteoporotic bone which resulted in large regions of<br />

very high levels of strain. The pattern of stress produced by the DCP is different to<br />

locking plates, particularly around screw hole locations, and suggests that compression<br />

plating should be used carefully in osteoporotic bone.<br />

2. INTRODUCTION<br />

Finite element modelling is being extensively used to evaluate the biomechanical<br />

behaviour of fractured bone treated with fixation devices. While locking plate fixation is<br />

becoming increasingly popular for complex and osteoporotic fractures, for the majority<br />

of indications compression plating remains the standard choice.<br />

It has been suggested that locking plates perform better than conventional plates in older<br />

or weaker bone. The failure load of locking plates, for example, has even been said to<br />

be “independent of bone quality” [1].<br />

Compression plates are complex to model due to the screw insertion producing axial<br />

pre-load in the screw (pulling the plate towards the bone), radial pre-load within the<br />

bone (forcing a screw into a pilot hole), and interfragmentary compression caused by<br />

1<br />

PhD Student, School of Engineering, The <strong>University</strong> of Edinburgh, Edinburgh, EH9 3JL, Scotland, UK<br />

2<br />

Senior Lecturer, School of Engineering , The <strong>University</strong> of Edinburgh, Edinburgh, EH9 3JL, Scotland,<br />

UK<br />

3<br />

Professor, Edinburgh Orthopaedic Engineering Centre, The <strong>University</strong> of Edinburgh, Edinburgh, EH16<br />

4SU, Scotland, UK

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!