Quantitative fit assessment of tibial nail designs using 3D computer modelling.

Intramedullary nailing is the standard fixation method for displaced diaphyseal fractures of the tibia in adults. The bends in modern tibial nails allow for an easier insertion, enhance the 'bone-nail construct' stability, and reduce axial malalignments of the main fragments. Anecdotal clinical evidence indicates that current nail designs do not fit optimally for patients of Asian origin. 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. We used 3D models of two different tibial nail designs (ETN (Expert Tibia Nail) and ETN-Proximal-Bend, Synthes), and 20 CT-based 3D cortex models of Japanese cadaver tibiae. With the aid of computer graphical methods, the 3D nail models were positioned inside the medullary cavity of the intact 3D tibia models. The anatomical fitting between nail and bone was assessed by the extent of the nail protrusion from the medullary cavity into the cortical bone, in a real bone this might lead to axial malalignments of the main fragments. The fitting was quantified in terms of the total surface area, and the maximum distance by which the nail was protruding into the cortex of the virtual bone model. 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 mm(2)) compared to the ETN (average 1044 mm(2)). Also, the maximum distance of the nail protruding from the medullary cavity was smaller for the ETN-Proximal-Bend (average 1.2mm) 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 it was possible 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. 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 a particular patient.

[1]  E. Wallenböck,et al.  [A break or bend in the unreamed tibial intramedullary nail. Experimental study]. , 1997, Langenbecks Archiv fur Chirurgie.

[2]  P. Guy,et al.  Long-Term Follow-up of Tibial Shaft Fractures Treated With Intramedullary Nailing , 2008, Journal of orthopaedic trauma.

[3]  B. Sangeorzan,et al.  Intramedullary Nailing of Proximal Quarter Tibial Fractures , 2006, Journal of orthopaedic trauma.

[4]  P. Rommens,et al.  Extending the indications of intramedullary nailing with the Expert Tibial Nail. , 2008, Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca.

[5]  P. Rommens,et al.  Extending the Indication of Intramedullary Nailing of Tibial Fractures , 2007, European Journal of Trauma and Emergency Surgery.

[6]  A. Tencer,et al.  Influences of Some Design Parameters on the Biomechanics of the Unreamed Tibial Intramedullary Nail , 1993, Journal of orthopaedic trauma.

[7]  B. Schmutz,et al.  Fit Assessment of Anatomic Plates for the Distal Medial Tibia , 2008, Journal of orthopaedic trauma.

[8]  Beat Schmutz,et al.  Using MRI for the imaging of long bones: first experiences , 2008 .

[9]  E. Wallenböck,et al.  Knick oder Krümmung beim unaufgebohrten Tibiamarknagel , 1997, Langenbecks Archiv für Chirurgie.

[10]  Klaus Püschel,et al.  Influence of intramedullary nail diameter and locking mode on the stability of tibial shaft fracture fixation , 2009, Archives of Orthopaedic and Trauma Surgery.

[11]  Peter Messmer,et al.  A CT Database for Research, Development and Education: Concept and Potential , 2007, Journal of Digital Imaging.

[12]  M. Doblaré,et al.  Computational comparison of reamed versus unreamed intramedullary tibial nails , 2007, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[13]  M. Ramakrishnan,et al.  The AO/ASIF proximal femoral nail antirotation (PFNA): a new design for the treatment of unstable proximal femoral fractures. , 2009, Injury.

[14]  K. Goyal,et al.  AN ABJS BEST PAPER: Analysis of Anatomic Periarticular Tibial Plate Fit on Normal Adults , 2007, Clinical orthopaedics and related research.