Article
Quantitative fit assessment of tibial nail designs using 3D computer modelling
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Authors
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B. Schmutz
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
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K. Rathnayaka
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
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M. E. Wullschleger
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
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J. Meek
- Synthes GmbH, Oberdorf, Switzerland
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M. A. Schuetz
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
| Published: | October 15, 2009 |
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Outline
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Problem: Intramedullary nailing is the standard treatment for displaced diaphyseal fractures of the tibia in adults. The bends in modern tibial nails allow for an easier insertion, enhance the æbone-nail constructÆ stability, and reduce axial malalignments of the main fragments. However, anecdotal clinical evidence indicates that current nail designs do not fit optimally for patients of Asian origin. Therefore, the aim of this study was to develop a method to quantitatively assess the anatomical fitting of two different nail designs for Asian tibiae by utilising 3D computer modelling.
Methods: We used 3D models of two different tibial nail designs (ETN (Expert Tibia Nail) and ETN-Proximal-Bend, Synthes), and 20 computer tomography (CT) based 3D cortex models of Japanese cadaver tibiae. With the aid of computer graphical methods (Rapidform2006, Inus Technology), the 3D nail models were positioned inside the medullary cavity of the intact 3D tibia models. While keeping the proximal end of the nail fixed at the entry point, the nailÆs position was then iteratively adjusted until the nail was in the correct surgical position. The anatomical fitting between nail and bone was assessed by the extent of the nail protrusion from the medullary cavity into the cortical bone, which in a real bone would lead to axial malalignments of the main fragments. The fitting was quantified in terms of the total surface area, and the maximum distance (in the axial plane) by which the nail was protruding into the cortex of the virtual bone model.
Results and conclusion: In all 20 bone models, the total area of the nail protruding from the medullary cavity was smaller for the ETN-Proximal-Bend (average 540 mm2) compared to the ETN (average 1044 mm2). Also, the maximum distance of the nail protruding from the medullary cavity was smaller for the ETN-Proximal-Bend (average 1.2 mm) compared to the ETN (average 2.7 mm). The differences were statistically significant (p < 0.05) for both the total surface area and the maximum distance measurements.
By utilising computer graphical methods we were able to conduct a quantitative fit assessment of different nail designs. The ETN-Proximal-Bend shows a statistical significantly better intramedullary fit with less cortical protrusion than the original ETN. The expected clinical implications of an improved anatomical fitting (less protrusion) are: a reduction in malalignments of the fractured bone, less pain, a lower likelihood of stress fractures, and easier nail insertion. In addition to the application in implant design, the developed method could potentially be suitable for pre-operative planning, enabling the surgeon to choose the most appropriate nail design for the anatomy of a particular patient.
