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Wang, et al.
stability of bone under different fixation conditions [4,5] . 2. Materials and methods
Structure properties of composite Sawbones such as
mineral density and elastic modulus approach to the 2.1. Study design
human bone ensure compliance with the requirements Fourteen fourth-generation composite femurs
of bone mechanical testing [6-8] . Therefore, composite (Model 3406; Pacific Research Laboratories, Vashon,
Sawbones and human cadavers have often been used Washington, USA) were used to simulate osteotomy.
in mechanical trials. Establishment of bone traumatic Bone materials properties and geometrical parameters
models according to standard fracture classifications were close to fresh-frozen cadaveric femurs (Table 1
requires precise and shape-matching osteotomy. and Figure 1) [6,17-20] . Computed tomography (CT)
However, the osteotomy methods vary among different scans of one composite Sawbone was performed on
research groups [5,8-11] , restricting the homogenization, a 64-slice CT scanner (Siemens Sensation Open,
and universality of different mechanical study to some Erlangen, Germany). Scan slice thickness was 5 mm.
extent. Digital Imaging and Communications in Medicine files
To date, few bone biomechanical studies used (DICOM) of the selected CT scans were retrieved and
the osteotomy-aided modules for precise creation of loaded in Mimics software (Version 20.0, Materialise,
fracture sample. Windolf et al. firstly introduced their Belgium). The femur and medullary cavity models
[9]
osteotomy-aided modules named custom-made saw- were then reconstructed in Mimics. Subsequently, the
guide for unstable 31-B2 fracture models and realized the above 3D reconstructions were imported into 3-Matic
smooth osteotomy. Rupprecht et al. subsequently utilized (Version 12.0, Materialise, Belgium) in STL formats
this device for biomechanical analysis . In addition, to design osteotomy models. The osteotomy models
[12]
another osteotomy module featuring cutting navigation were, then, obtained and imported into 3D printer
was proposed by Windell et al. in a biomechanical study (OBJET EDEN260V, Stratasys Ltd, Rehovot, Israel)
[8]
comparing different implants in periprosthetic femoral to manufacture anatomical osteotomy modules for
fracture. Unfortunately, the study did not evaluate the intertrochanteric fracture. Finally, after assembling
accuracy of osteotomy. Challenges such as time- and the composite Sawbones and osteotomy modules,
manpower-consuming aspects and high cost in industrial osteotomy was performed using horizontal band-saw.
designs and application also limit the experimental use of The study flowchart is shown in Figure 2.
these device.
Computer-aided design (CAD) technique can 2.2. Computer-aided design (CAD)
precisely establish the three-dimensional (3D) digital bone 2.2.1. Osteotomy models
models, extract local parameters at the site of interest, and
design precise osteotomy-aided modules with the help of We used AO/OTA 31 A2.3 intertrochanteric unstable
engineering software . 3D printing technique has been fracture model design as an example. The central axis
[13]
recently applied to the domains of regenerative medicine of femoral shaft was established in 3-Matic, and a plane
of tissues and organs, surgical decisions-making, perpendicular to the placing plane was obtained through
[13]
personal design of tissue engineering scaffolds materials, the central axis . The plane was rotated 20° clockwise
and prosthetic or implants in orthopedic . Compared with Y-plane as the rotation center, and a set of parallel
[14]
with traditional industrial design, 3D printing technique osteotomy reference planes could be established based on
reduces labor and material costs, simplifies workflows, the obtained plane. The horizontal plane (parallel to the
and improves consistency. The advantages of 3D printing XY plane) was established based on the tip of the greater
applied to medical devices design are numerous, such as
high production efficiency, high level of design precision,
fine anatomical fitting, and good repeatability [15,16] .
Based on above, we believe that the combination
of CAD and 3D printing techniques can help establish
precise osteotomy-aided modules matching bone
morphology and confirm homogenization. Further
studies are warranted. Therefore, considering the design
of AO/OTA 31 A2.3 intertrochanteric unstable fracture
models as an example, the present study aims to design
a new method of osteotomy-aided module production
for bone biomechanical study with the help of 3D
printing coupled with CAD and to test the accuracy of
osteotomy. Figure 1. Geometrical parameters of Sawbones.

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