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Development of rapid prototype models for temporal bone dissection simulation.

1. INTRODUCTION

Practice is an essential part of otologic (ear) surgical training. It enables the acquisition of adequate sensorimotor skills and allows for the fine-tuning of cognitive processes under the guidance of experienced surgeons, to perform successful otologic surgical procedures without causing injury to the patient (Sewell et al., 2005). Mastoidectomy is a fairly common otologic surgical procedure performed to control middle ear and mastoid pathologic conditions. In mastoidectomy the surgeon drills through the mastoid part of the temporal bone (Figure 1) and removes spongiform bone to gain access and to remove inflammatory tissue from the mastoid and middle ear. The role of practice is especially significant in mastoidectomy as the surgeon is working in the immediate vicinity of minute, multifaceted and delicate structures such as auditory ossicles, lamellar bone, blood vessels and nerves.

[FIGURE 1 OMITTED]

Currently surgeons-in-training mostly practice in temporal bone laboratories (Zirkle et al., 2007) using cadaver temporal bones which are obtained through local donations or tissue banks. Apart from the obvious ethical challenges to be overcome for removing parts from dead bodies there is always at least a perceived risk of acquiring a disease from the cadaver. Further, there are no two cadaver dissections alike and repetition of unsuccessful procedures or having many trainees perform the procedure on a temporal bone dissection with the same anatomic structures is not possible. Also, with the limited supply and availability of practice material the opportunities to perfect one's skills do not arise.

Computer Based Education (CBE) methods, including interactive CD-ROMs and internet-based applications have recently been increasingly accompanied by virtual simulators which, utilizing technologies from the computer game industry, provide a relatively life-like 3-dimensional impression from several angles and haptic response for the surgeon (Kuppersmith et al., 1997; Wiet et al., 2002; Wiet et al., 2005). In the simulator the trainee uses both hands, one for drilling and the other to remove the resulting bone dust through rinsing and suction (Sewell et al., 2007). The advantages of the virtual simulators are the ability to adjust operational parameters as well as to simulate various disease states. They also provide ample opportunity for repetition, give immediate constructive and documentable feedback, and provide a non-threatening environment to learn from one's mistakes (Sewell et al., 2007; Mason et al., 1998; Basdogan et al., 2007; Fried et al., 2007). On the down-side, simulators are expensive and to-date technically imperfect. There are also problems with providing an exact match to reality in drilling bone.

Although CBE methods inarguably have their place in surgical training, real hands-on removal of mastoid tissue maintains its role, and real human tissue used in a cadaver laboratory has yet to be replaced by other materials. The possibility of solving some of the above mentioned problems by utilizing bone-like materials and rapid manufacturing technologies has not been adequately investigated (Lopponen et al., 1997). In this study we aimed at developing a RP temporal bone model for otologic surgical training.

2. RESEARCH DESIGN

The skull of a healthy male volunteer was radiographed by Cone Beam Computed Tomography (CBCT, Planmeca Oy, Finland). CBCT results in a tense pile of parallel grey-scale images of the "sliced" radiographed object thus depicting e.g. skull bone structure. Grey-scale values were used to distinguish bone structure from soft tissue. This segmentation was done to approximate exact bone boundaries. Topologically organized segments were interpolated to form a 3D-representation of the object. The 3D-representation was further converted into stl-format. OsiriX open source software was used for these operations. The stl-model was modified to cover temporal bone ("ear") areas. Corresponding RP-models were commissioned from four Finnish RP-service providers. The materials used were polyamide (PA), aluminium-filled polyamide (Al-PA), a liquid photopolymer (Photopolymer) and a gypsum-based composite powder (Composite). The manufacturing techniques used were Stereolithography (SLA), Selective Laser Sintering (SLS) and 3D-printing (3D-P) (Table 1).

An experienced ear surgeon performed cortical mastoidectomy on each of the different models and evaluated their suitability for temporal bone dissection training. In addition, four residents from the Otolaryngology--Head and Neck Surgery training program at the Helsinki University Hospital also performed a mastoidectomy using the RP models and provided a summative evaluation of the models.

3. RESULTS

The size and macroscopic structure of the models were comparable to a real temporal bone. The "feel" of drilling was fairly close to real bone in most of the studied models. The best result regarding this was achieved using the one made of composite powder.

The microstructures of the temporal bone models were not precise and some of the surgically and anatomically significant structures (lamellae, tympanic membrane, ossicles) were missing from the models. These problems and limitations have to be solved before the studied models can replace cadaver temporal bones in surgical training. However, the RP models were found suitable for the teaching of anatomic landmarks, basic principles and preoperative planning of otologic surgery. Resolution of microsurgical details still needs to be further developed. Various materials with different mechanical properties were also found to provide different handling environments.

4. CONCLUSIONS

The RP temporal bone model may be further developed as a training tool. We are currently improving the parameters concerning resolution and material properties of our model. We are also investigating the possibility to combine different manufacturing techniques with RP, to overcome the absence in the present models of some of the delicate but anatomically and surgically significant structures.

5. ACKNOWLEDGMENTS

This study was supported by grants from the University of Helsinki and the Finnish Funding Agency for Technology and Innovation (Tekes). The authors want to thank M.Sc.(tech) Pekka Paavola for the photograph.

6. REFERENCES

Basdogan, C.; Sedef, M.; Harders, M. & Wesarg, S. (2007). VR-based simulators for training in minimally invasive surgery. IEEE Comput Graph Appl, Vol. 27, (2007) 54-66

Fried, M. P.; Uribe, J. I. & Sadoughi, B. (2007). The role of virtual reality in surgical training in otorhinolaryngology. Curr Opin Otolaryngol Head Neck Surg, Vol. 15, (2007) 163-169

Kuppersmith, R. B.; Johnston, R.; Moreau, D.; Loftin, R.B. & Jenkins, H. (1997). Building a virtual reality temporal bone dissection simulator. Stud Health Technol Inform, Vol. 39, (1997) 180-186

Lopponen, H.; Holma, T.; Sorri, M., Jyrkinen, L.; Karhula, V.; Koivula, A.; Ilkko, E.; Laitinen, J.; Koivukangas, J.; Oikarinen, J. & Alamaki, O. (1997). Computed tomography data based rapid prototyping model of the temporal bone before cochlear implant surgery. Acta Otolaryngol Suppl, Vol. 529, (1997) 47-49

Mason, T. P.; Applebaum, E. L.; Rasmussen, M,; Millman, A.; Evenhouse, R. & Panko, W. (1998). The virtual temporal bone. Stud Health Technol Inform, Vol. 50, (1998) 346-352

Sewell, C.; Morris, D.; Blevins, N. H.; Barbagli, F. & Salisbury, K. (2005). Quantifying risky behaviour in surgical simulation. Stud Health Technol Inform, Vol. 111, (2005) 451-457

Sewell, C.; Morris, D.; Blevins, N. H.; Barbagli, F. & Salisbury, K. (2007). Evaluating drilling and suctioning technique in a mastoidectomy simulator. Stud Health Technol Inform, Vol. 125, (2007) 427-432

Wiet, G. J.; Stredney, D.; Sessanna, D.; Bryan, J. A.; Welling, B. & Schmalbrock, P. (2002). Virtual temporal bone dissection: an interactive surgical simulator. Otolaryngol Head Neck Surg , Vol. 127, (2002) 79-83

Wiet, G. J.; Schmalbrock, P.; Powell, K. & Stredney, D. (2005). Use of ultra-high-resolution data for temporal bone dissection simulation. Otolaryngol Head Neck Surg, Vol. 133, (2005) 911-915

Zirkle, M.; Roberson, D. W.; Leuwer, R. & Dubrowski, A. (2007). Using a virtual reality temporal bone simulator to assess otolaryngology trainees. Laryngoscope, Vol. 117, (2007) 258-263
Tab. 1. Materials and techniques used in the study.

Material Color Techn Trade Layer
 name thickness

PA White SLS PA2200 0,1 mm

Al-PA Grey SLS Alumide[R] 0.1 mm

Photo- Trans- SLA Somos[R] 0.1 mm
polymer parent 11120

Composite Blue- 3D-P ZP[R] 131 0.089 mm
 White
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Author:Maekitie, Antti; Paloheimo, Kaija Stiina; Paloheimo, Markku; Kanerva, Jukka; Bjoerkstrand, Roy; Rams
Publication:Annals of DAAAM & Proceedings
Article Type:Report
Date:Jan 1, 2008
Words:1274
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