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Tactile Surgical Navigation System for Complex Acetabular Fracture SurgeryTakahiro Niikura, MD; Maki Sugimoto, MD; Sang Yang Lee, MD; Yoshitada Sakai, MD; Kotaro Nishida, MD; Ryosuke Kuroda, MD; Masahiro Kurosaka, MD

An acetabular fracture is an intra-articular frac-

ture of the hip joint, which is generally treated by open re-duction and internal fixation if displaced.1-5 Anatomical reduction and stable fixation

are important for good func-tional recovery.1-3,6 However, the anatomical complexity of acetabular fractures makes them particularly challenging and technically demanding to treat surgically.7 Precise

understanding of fracture pat-terns is difficult because of the complex 3-dimensional (3D) anatomy of the pelvis and ac-etabulum, and assessment and classification of acetabular fractures can be difficult even for experienced surgeons.

Improved understanding of the anatomy and fracture pat-terns should improve surgical outcomes. Tools that could assist in the assessment of complicated fracture patterns would be useful. Traditional radiological assessment of acetabular fractures involves plain radiography (Figure 1) and computed tomography (CT). However, these modali-ties provide only 2-dimension-al (2D) images of the complex 3D anatomy. The 3D digital images reconstructed from CT data (Figure 2) can be rotated and viewed from any angle, but are still viewed as 2D im-ages on a flat screen.

The design and manufac-turing industries now use com-puter-aided design and rapid prototyping to manufacture 3D prototypes. Using this technol-ogy and specialized software,

CT scans can be converted into 3D data, which can then be used to manufacture life-size 3D models of the bony pelvis using a 3D printer. Application of such computer-aided design and rapid prototyping to the field of orthopedics has been reported in trauma, compli-cated fractures, hand surgery, and osteotomies to correct de-formities.8-16

Some previous reports have described using rapid prototyping to manufacture 3D models of the bony pelvis prior to surgery for acetabular fractures.8,17-20 However, these models were for preoperative use only. It is difficult for less experienced surgeons, and even experienced surgeons, to achieve precise intraoperative understanding of acetabular fracture patterns. Surgical teams do not always consist of experienced surgeons, and sharing information and com-municating effectively are important to achieving good surgical results and educating surgeons.

The authors report the pre-operative and intraoperative

The authors are from the Department of Orthopaedic Surgery (TN, SYL, YS, KN, RK, MK) and the Department of Gastroenterology (MS), Kobe Uni-versity Graduate School of Medicine, Kobe, Japan.

The authors have no relevant financial relationships to disclose.Correspondence should be addressed to: Takahiro Niikura, MD, Depart-

ment of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan (tniikura@med.kobe-u.ac.jp).

Received: January 17, 2013; Accepted: September 5, 2013; Posted: April 15, 2014.

doi: 10.3928/01477447-20140401-05

Abstract: The authors describe a tactile surgical navigation system using custom 3-dimensional (3D) models of the bony pelvis for complex acetabular fracture surgery. The bone area of interest was extracted from the Digital Imaging and Communications in Medicine (DICOM) data of computed tomography scans. A standard triangulated language file was used to create 3D models of the bony pelvis by layered manu-facturing using a 3D printer and non-cytotoxic, sterilizable, acrylic-based photopolymers. No infections and no toxic or other adverse events were observed. The models were useful for preoperative assessment, planning, and simulation; intra-operative assessment; obtaining informed consent; and edu-cation. [Orthopedics. 2014; 37(4):237-242.]

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use of tactile 3D models of the bony pelvis manufactured us-ing a 3D printer. They describe the usefulness of these models based on their experience and previous reports.

Materials and MethodsA preoperative 0.5-mm-

slice CT scan of the pelvis was obtained using a 64-row multidetector-row CT scanner (Aquilion; Toshiba Medical Systems Corp, Otawara, Ja-pan). After 3D reconstruction of the images (OsiriX; open-source Digital Imaging and Communications in Medicine [DICOM] application, http://

osirix-viewer.com), the bone area of interest was extracted from the DICOM data using the surface rendering function and converted to standard tri-angulated language or stereo-lithography (STL) data. The STL data were imported into computer-aided design soft-ware and processed using a modeling operation to prevent separation at the fracture site. The processed STL data were used to manufacture 3D mod-els of the bony pelvis using the layered manufacturing process on a 3D printer (Connex500; Objet Japan, Chiba, Japan).

This inkjet printer uses acryl-ic-based photopolymers (Full-Cure720 and VeroWhitePlus FullCure835; Objet Japan) and stiffens them via ultraviolet ir-radiation. These materials are

not cytotoxic and can tolerate gas sterilization. Polymers were layered in 16-µm-thick slices using sliced data created from the imported STL data. A mirror image of the contralat-

Figure 1: A plain radiograph provides only a 2-dimensional image of the complex 3-dimensional anatomy.

Figure 2: A 3-dimensional digital im-age reconstructed from computed tomography data is viewed on a flat screen.

Table

Uses for the 3-Dimensional Models of the Bony Pelvis

PreoperativelyAssessment and understanding of the complex fracture patternSurgical planning and simulationPre-bending of platesDetermining the appropriate screw trajectories and lengthsCan be performed by the operating surgeon and assistant sur- geons Obtaining informed consentEasily understood by patients and their families

IntraoperativelyAssessment of the fracture Can be performed by the operating surgeon and assistant sur- geons

PostoperativelyEducational tool for surgeons, other physicians, and medical studentsCan be used as a library of various fracture types

Figure 3: Photographs of the model showing that the fracture can be viewed from multiple directions, and that the intra-articular surface can be visualized (same patient as in Figures 1 and 2).

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eral uninjured hemipelvis was also prepared.

This process was under-taken for 5 patients with ac-

etabular fractures. Four of these patients had both anteri-or and posterior column frac-tures, and 1 had an anterior column fracture only. All pa-tients gave written informed

consent for inclusion in the study.

surgical techniquesThe custom-made models

were used in the operative field

Figure 4: The 3-dimensional model of the bony pelvis provides both visual and tactile information.

Figure 7: Touching and viewing the model helps to assess the fracture intra-operatively.

Figure 5: The life-size model of the mirror image of the contralateral un-injured pelvis is useful for determin-ing the appropriate lengths (A) and bending (B) of the plates.

Figure 6: Discussion among surgeons using the 3-dimensional model, help-ing to ensure that each surgeon has a similar understanding of the anatomy of the fracture.

B

A

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to assess the fractures. An-terior column fractures were exposed via an ilioinguinal ap-proach, and posterior column fractures were exposed via the Kocher-Langenbeck approach. The fractures were surgically reduced and fixed using stan-dard screws and reconstruc-tion plates.

resultsSolid, durable models were

successfully manufactured in all cases. The models were gas sterilized, and no infections were observed after using them in the operative field. No toxic or other adverse events were observed.

The 3D model has 3 axes: x, y, and z. The accuracy of the authors’ manufacturing process along the z axis was 16 µm, which was the thick-ness of each layer. The accura-cy along the x axis and along the y axis depended on the accuracy of the printer head; they were approximately 100 µm each. The minimum thick-ness of each CT slice was 500 µm; therefore, the authors’ manufacturing process was capable of precisely duplicat-ing the configuration from the DICOM data. Manufactur-ing of the models was fast; a

1-cm width could be built in 1 hour and a full-size pelvic model in 1 day.

Postoperative CT assess-ments showed no screw pen-etration into the hip joints. Bone union was achieved in all cases with no loss of reduc-tion. All patients regained the ability to walk.

discussionThe 3D models of the bony

pelvis were useful for gaining a better understanding of many aspects of the complex acetab-ular fractures (Table) preop-eratively, intraoperatively, and postoperatively.

The authors’ models were useful for preoperative as-sessment and understanding of complex fracture patterns, surgical planning, and simu-lation. The models assisted surgeons in understanding the anatomy of complex fractures, which could be viewed from multiple directions. Although the intraoperative view of the intra-articular fracture surface was obscured by the femoral head, the intra-articular sur-face was easily assessed us-ing the model (Figure 3). The models provided both visual and tactile information for the surgeons (Figure 4). The life-size model of the mirror image of the contralateral un-injured pelvis was useful for determining the appropriate lengths and bending of the plates (Figure 5), which may be challenging in complex fractures. Use of 3D pre-bent titanium implants has been reported in craniomaxillofa-cial surgery.21-23 The models were also useful for deter-

Figure 8: Both the bones and the implants can be modeled. The bones and metal are manufactured in different colors.

Figure 9: Life-size hemi-pelvis and reduced in size full-pelvis models. Using smaller models reduces costs.

Figure 10: The models are useful educational tools for surgeons, other physi-cians, and medical students.

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mining the appropriate screw trajectories and lengths. The rapid manufacturing process allowed all surgeons on the team to assess and discuss the fracture preoperatively, ensuring that they each had a similar understanding of the fracture, and to plan the pro-cedure (Figure 6).

Hurson et al20 reported us-ing a similar process for the assessment and classification of acetabular fractures, and preoperative planning. They reported that this process sig-nificantly reduced the degree of interobserver variability in fracture classification, particu-larly among less experienced surgeons. Brown et al17,18 de-scribed rapid prototyping of an interpositioning template to facilitate screw placement during surgery for acetabular fractures. Deshmukh et al19 and Bagaria et al8 recently described the use of rapid prototyping for the treatment of acetabular fractures. They reported that modeling of the fracture helped in surgical planning and simulation and reduced operative time.

The authors’ models were also useful for obtaining in-formed consent. It is difficult for patients and their fami-lies to understand complex fracture patterns by viewing radiographs and CT images. The models dramatically fa-cilitated understanding among patients and their families.

The authors’ system dif-fers from other systems in that the model can be used in the operative field. The models are manufactured from non-cytotoxic, acrylic-based pho-

topolymers that can endure gas sterilization, unlike mod-els manufactured from nylon20 or wax/plaster.17,18 Touching and viewing the model during surgery helps the surgeons as-sess and understand the frac-ture pattern (Figure 7). The models can also improve com-munication among members of the surgical team. Previous reports have suggested that the use of such models can decrease intraoperative fluo-roscopy time and operative time.8,9

The authors’ technique can be used to model both the bones and the implants. Fig-ure 8 shows a postoperative model of the pelvic bones and implants. With this technique, the authors can assess fracture reduction and the placement of implants, and can deter-mine the direction of screws, by using a colored material for metal and a white mate-rial for bone. The authors can also use the models to create custom implants for individual patients. The actual size, con-figuration, and curvature vary among individuals. The au-thors’ technique precisely du-plicates an individual’s anato-my. The model can be used to create custom hardware that fits the individual’s bone per-fectly. As demonstrated in Fig-ure 8, the authors can create a prototype of the implant. This prototyping leads to manufac-turing custom-made implants.

The cost of manufactur-ing the models depends on the costs of materials and operat-ing the 3D printers, as extrac-tion of the bone area of interest and conversion of the DICOM

data to STL data using open source 3D reconstruction software were performed by the authors. However, if the authors manufacture a life-size whole pelvis, the cost is approximately $1000 (US). The cost could be reduced by decreasing the amount of ma-terials used. For example, if the model is reduced to 80% of the life-size model, the amount of materials needed decreases to 50%. If the model is reduced to 50% of the life-size model, the amount of materials needed decreases to 12.5%. The authors could manufacture a life-size hemi-pelvis model and a reduced in size full-pelvis model (Figure 9). The life-size model is nec-essary for determining the ap-propriate lengths and bending of the plates, but the cost could be reduced by making a hemi-pelvis rather than a full pelvis. A reduced in size model is suf-ficient for understanding the complex fracture pattern.

After surgery, the models can be used as a library of vari-ous fracture types. Such a col-lection is a useful educational tool for surgeons, other phy-sicians, and medical students (Figure 10).

conclusionManufacturing 3D models

of the bony pelvis using non-cytotoxic and sterilizable ma-terial is useful for improving understanding of the anatomy of complex acetabular frac-tures for assisting in preopera-tive assessment, planning, and simulation; intraoperative as-sessment; obtaining informed consent; and education.

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