The other name of three-dimensional printing (3DP) is rapid prototyping, which constracts 3D models layer by layer. It is an additive manufacturing process that promote the production of the complex geometrical. The development of imaging modalities and the 3D printing technology enables a big advancement in the use of 3D printing models of some operation practices. (10,11).
Nowadays, the use of 3D printing technology in clinical practice focuses on 3D printing models(12-15). Previous researchers made a lot of researches(16-18) in virtual and haptic patient specific anatomical models, often termed biomodels (19). It can help surgeons to plan the operations in advance and save their operation time. So we operated this special operation:3D printing models assisted complex THA.
According to the previous researches, surgeons all around the world hold the opinion that the 3D printing models are quite beneficial when they are operating difficult operations.  Previously, before and during the operations, most of the surgeons relied on two-dimensional (2D) images, for example, X-ray, CT and/ or MRI. And the 1:1 scale 3D printing models could provide the surgeons with the better understanding of the anatomy compared to the 2D visualization.
Also, before the operations, we can sterilize these models. In that way, surgeons could use these models to get a template to review intra-operatively[21,22]. However, the work people have done on the models is limited. Previous researches have found that, compared to traditional operations, the application of 3D printing models can offer more accurate evaluation of relevant surgical structures in complex cases, for example, acetabular fractures and spinal deformities.
Besides the subjective benefits, we can also find some other objective advantages of the 3D printed models. Researchers found that compared to traditional operations, the surgery time, intraoperative blood loss and fluoroscopy time are much less[23-30], which improves the quality of planned placement of implants and selection of instrumentation. And thus the need to contour and the implants number of adjustments intraoperatively are reduced.
Nowadays, surgeon often use subtrochanteric shortening osteotomy to deal with the type IV DDH. And in our study, with the usage of the 3D printing models, the surgery time, intraoperative blood loss and fluoroscopy time are much less, which is of great benefit.
Disadvantages are also obvious. First is the cost. For better evaluation, we have to compare the potential savings of the improved operations and production cost of the 3D printing models. Second is that the 3D printing model don’t include the soft tissue structures, as well as the nerves and blood vessels. To better serve the clinical practice, further studies and a streamlined protocol for the 3D printing models are needed in the future.