3D-PRINTED HAPTIC “REVERSE” MODELS FOR PREOPERATIVE PLANNING IN SOFT TISSUE RECONSTRUCTION: A CASE REPORT MICHAEL P. CHAE, M.B.B.S., B.Med.Sc.,1,2,3 FRANK LIN, M.B.B.S., F.R.A.C.S.,1,2,3 ROBERT T. SPYCHAL, M.B.Ch.B., M.D., F.R.A.C.S.,1,2,3 DAVID J. HUNTER-SMITH, M.B.B.S., M.P.H., F.R.A.C.S., F.A.C.S.,1,2,3 and WARREN MATTHEW ROZEN, M.B.B.S., B.Med.Sc., M.D., Ph.D.1,2,3,4*
In reconstructive surgery, preoperative planning is essential for optimal functional and aesthetic outcome. Creating a three-dimensional (3D) model from two-dimensional (2D) imaging data by rapid prototyping has been used in industrial design for decades but has only recently been introduced for medical application. 3D printing is one such technique that is fast, convenient, and relatively affordable. In this report, we present a case in which a reproducible method for producing a 3D-printed “reverse model” representing a skin wound defect was used for flap design and harvesting. This comprised a 82-year-old man with an exposed ankle prosthesis after serial soft tissue debridements for wound infection. Soft tissue coverage and dead-space filling were planned with a composite radial forearm free flap (RFFF). Computed tomographic angiography (CTA) of the donor site (left forearm), recipient site (right ankle), and the left ankle was performed. 2D data from the CTA was 3D-reconstructed using computer software, with a 3D image of the left ankle used as a “control.” A 3D model was created by superimposing the left and right ankle images, to create a “reverse image” of the defect, and printed using a 3D printer. The RFFF was thus planned and executed effectively, without complication. To our knowledge, this is the first report of a mechanism of calculating a soft tissue wound defect and producing a 3D model that may be useful for surgical planning. 3D printing and particC 2014 Wiley ularly “reverse” modeling may be versatile options in reconstructive planning, and have the potential for broad application. V Periodicals, Inc. Microsurgery 35:148–153, 2015.
For optimal restoration of function and appearance in reconstructive surgery, an accurate anatomical understanding of the defect is required. To this effect, preoperative planning with appropriate imaging techniques benefits both the excisional and reconstructive surgeon.1–5 Computed tomographic angiography (CTA) is one technique that has previously shown to improve operative outcomes while minimizing donor site morbidity.6,7 It can aid in selecting the donor site, flap and vessel of choice for reconstruction.5 Furthermore, CTA is a relatively straightforward procedure.8 A number of investigators have proven its efficacy in reducing operative time and reconstructive outcomes.4,6,7,9–11 In contrast to CTA, which produces threedimensional (3D) visualization on a two-dimensional (2D) surface, rapid prototyping (RP) is a process of producing a 3D model layer-by-layer based on computeraided design (CAD) data or imaging that precisely represents the anatomical details of a defect. Having been
1 Department of Plastic and Reconstructive Surgery, Frankston Hospital, Peninsula Health, Frankston, VIC, Australia 2 Department of Surgery, Monash University, Monash Medical Centre, Clayton, VIC, Australia 3 Monash University Plastic and Reconstructive Surgery Unit (Peninsula Clinical School), Peninsula Health, Frankston, VIC, Australia 4 Department of Surgery, School of Medicine and Dentistry, James Cook University Clinical School, Townsville Hospital, Douglas, Townsville, QLD, Australia *Correspondence to: Warren M. Rozen, M.B.B.S., B.Med.Sc., M.D., Ph.D., Department of Plastic and Reconstructive Surgery, Frankston Hospital, Peninsula Health, 2 Hastings Road, Frankston, Victoria 3199, Australia. E-mail: [email protected] Received 7 April 2014; Revision accepted 3 July 2014; Accepted 7 July 2014 Published online 21 July 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/micr.22293
Ó 2014 Wiley Periodicals, Inc.
used for decades in industrial design, it has recently shown potential in medical applications, especially for implant design and preoperative planning.12 3D models provide surgeons with a physical object that they can interact with hands-on for easier understanding of the morphology. This “haptic-modeling” has been shown in some settings to reduce operative time and facilitate superior operative outcomes.4,6,10,13 Amongst numerous RP techniques, stereolithography is considered the gold standard in medical RP, but is labor-intensive, relatively expensive, slow, and recent publications bring into question issues regarding its environmental safety.12,14,15 3D printing (3DP) is the latest RP technique where photopolymer materials are “jetted” in ultrathin layers and then “cured” by UV light for immediate handling and use. In comparison to stereolithography, it is faster, more convenient, less expensive, and more appropriate for producing small complex structures. In reconstructive surgery, 3DP has been used to model vascular perforator anatomy16 and guide correction of pectus excavatum,17 mandibular deformities,12,18,19 facial deformities,20–23 nasal defects,24 and skull deformities.25 Although 3D printing itself has been widely described and increasingly used, a reproducible method for producing a 3D-printed “reverse model” has not yet been described. In this report, we present a case in which a reproducible method for producing a 3D-printed “reverse model” representing a skin wound defect was used for flap design and harvesting. CASE REPORT
An 82-year-old man has undergone elective ankle replacement surgery, which was complicated by wound
3D Printing in Reconstructive Surgery
Figure 1. Soft tissue defect overlay the right ankle, with ankle prosthesis exposed.
Figure 2. 3D reconstructed volume-rendered computed tomography (CT) image of the recipient site demonstrated the soft tissue defect, performed with Osirix software (Pixmeo, Geneva, Switzerland).
infection, dehiscence, and an exposed ankle prosthesis (see Fig. 1). Serial soft tissue debridements were performed by an orthopedic surgeon, and the patient was ultimately referred for soft tissue coverage and deadspace filling, with attempted salvage of the prosthesis.
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Reconstruction was planned with a composite radial forearm free flap, comprising a musculo-fascio-cutaneous flap. Preoperative imaging was performed as routine, with multi-slice CTA of both the flap donor site and the recipient site. All imaging was performed with institutional ethics committee approval. Scan acquisition comprised arterial phase scanning, which eliminated venous contamination, avoided confusion between different structures, and maximized arterial filling. We used a protocol that triggered the scan from the origin of the pedicle, and scanned in the direction of blood flow through the perforating vessels of the flap. Initial 2D software reconstruction used raw scan data recorded thin axial slices (0.7-mm-thick slices). Visual appreciation of the vascular anatomy was best achieved with the use of software-generated 3D reconstructions. The freeware program “Osirix,” a third-party software program (Osirix, Version 4.1, Pixmeo, Geneva, Switzerland) was used. First, the recipient site was 3D-reconstructed via volume rendering using the Osirix 3D preset of soft tissue CT (i.e., soft tissue 1 skin) available within the provided software, and this was used to apply the skin layer on top of the 3D image. Crop function and scissor mouse functions were used judiciously to narrow down to defect (see Fig. 2). The 2D images were 3D reconstructed using the surface rendering function. The 3D reconstructed image was exported in standard tessellation language (STL) format. To evaluate the volume and shape of the defect, we created a 3D surface-rendered image of the normal left ankle in STL format for use as “control.” The above steps for producing the right ankle 3D image were repeated using the Osirix software for surface rendering, or can be achieved using 3D printer software (Cubify, 3D systems, Rock Hill, SC). Volumetric and defect analysis were undertaken using Magics software (Materialise, Leuven, Belgium). STL files of both the right and left ankle were loaded on to the software and placed adjacent to each other in anatomical position (see Fig. 3a). Care was taken to align both objects on all X-, Y-, and Z-axis, using “interactive translate” function. In this illustrative case, a mirror image of the left ankle was produced by reflecting it on the Y–Z plane, so that it aligned with the right ankle pointing in the same direction (see Fig. 3b). Using the “interactive translate” function, the mirrored left ankle was superimposed on to the right ankle so that the defect was “covered” (see Fig. 3c). This was achieved by superimposing the significant anatomical landmarks (such as the heel and the malleoli) common to both ankles first. Correct superimposition was confirmed by rotating the image 360 and viewing it in all angles. Then, the image of the right ankle and the intersected area was “subtracted” from the mirrored left ankle using “Boolean” function (see Figs. 3d–3f). The “reverse image” representing the skin defect Microsurgery DOI 10.1002/micr
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Figure 3. (a) Cropped 3D images of the right and left ankle were loaded into Magics software (Materialise) and placed side-by-side in anatomical position. (b) Left ankle was reflected on Y–Z plane so that it was aligned and pointed in the same direction as the right ankle. (c) Mirror image of the left ankle was superimposed on the right ankle. (d–f) Right ankle and the intersected parts were “ subtracted” from the mirrored image of left ankle using Boolean function available in the Magics software.
was saved in STL format, essential since the 3D printer software can only recognize STL files. These images were directly loaded in to the Cubify software in lieu of the CT raw data to enable production of both anatomic models (see Fig. 4) and pre-designed models based on the above defect analysis (see Fig. 5). Volumetric flap planning was achieved using a 3D image of the donor site (i.e., left forearm). The same steps as described above for the production of the surface-rendered 3D image of the right ankle using Osirix were used (see Fig. 6). Using the Magics software, both forearm and the “reverse image” were placed adjacent to each other and aligned in the same direction (see Fig. 6a), and then superimposed over each other (see Figs. 6b and 6c). Using the “Boolean” function, the volume of the reverse image was “subtracted” away from the forearm (see Figs. 6d and 6e). This was used to preoperatively predict and intraoperatively guide flap harvest, to match the reconstructive needs of the recipient site. 3D printing of defect and flap models, after analysis by Cubify software (3D Systems), was achieved by a single jet Cube 2 printer (3D Systems). The 3D software modeling was exported from the Cubify software and transferred to the Cube 2 printer. Printing of the right Microsurgery DOI 10.1002/micr
Figure 4. 3D printed model of the right ankle was created using the Cubify software and printed by the Cube 2 printer.
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Figure 5. 3D printed model of the “ reverse image” was created using the Cubify software and printed by the Cube 2 printer.
Figure 6. (a) Cropped 3D images of the forearm donor site were loaded into Magics software (Materialise), with the previously developed “ defect analysis” image loaded side-by-side in anatomical positions. (b, c) The donor site and the “ reverse image” were superimposed. (d, e) The “ reverse image” was “ subtracted” from the forearm to evaluate the reconstructive needs during harvest.
ankle required approximately 12.5 hours and the reverse image 8.5 hours. Preoperatively, the 3D model of the right ankle was used to appreciate the size and the depth of the defect. The “reverse model” was placed immediately adjacent to the donor site to estimate the size of the flap for harvest-
ing. The flap was thus designed to appropriately fill the soft tissue defect (see Fig. 7), with a small skin graft needed for extension of the pedicle (given that this was not part of the initial defect for volumetric planning). The flap and graft both healed well, with no donor or recipient-site complications. Microsurgery DOI 10.1002/micr
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Figure 7. Defect was reconstructed with free radial forearm flap, and demonstrated appropriate filling of the soft tissue defect.
DISCUSSION
An accurate understanding of the anatomy that has been distorted by trauma, cancer, or disease is useful in reconstructive surgery, such as a free flap repair. The current standard of practice involves imaging complex defects with CTA of both donor site and the recipient site for 3D visualization of the anatomical structures.4 Multiple software programs can effectively model the 3D data in 2D images, which our previous research has demonstrated are easy to interpret by surgeons and better demonstrate anatomical relationships of each vessel in a single image.4,26 The raw data from CTA can be further processed to produce a 3D model by RP. The benefit of being able to physically interact with 3D models is that the models enhance the surgeon’s understanding of the morphology, which may be significantly altered by the underlying pathology, and enable hands-on preoperative planning. Subsequent benefits may include decreased length of operation, wound exposure time, exposure to general anesthesia, and intraoperative blood loss.12 Until recently, stereolithography has been considered the gold standard for medical RP. It is accurate to 0.1 mm and Microsurgery DOI 10.1002/micr
can produce large anatomical parts.27 However, it is relatively more labor-intensive and expensive because of the high cost of machine maintenance and the hardening materials used. Furthermore, a large model takes more than a day to manufacture, which is associated with increased production cost.14 Additionally, it may not be environmentally safe.15 In contrast, 3D printing provides an attractive alternative RP technique that can be accurate to 0.016 mm. It is faster, more convenient to use, and is associated with approximately one-third of the cost,12 and thus may be preferred for building smaller, more complex anatomical structures.16 Constructing a 3D model of an external surface is relatively straightforward, however a “reverse image” that represents the wound defect may be helpful for the surgeons in the selection of an appropriate flap shape and size. To the best of our knowledge, we are the first in the literature to report a method of producing such “reverse image” using 3D printing. We achieved this using the non-pathological left ankle as a control to the pathological right side. After the models are superimposed on the Magics software (Materialise), they are “subtracted” from each other leaving behind a “reverse image” that depicts the skin defect. This was used to assess the flap shape and size on the donor site. The advantage of our method lies in that it is flexible and can be applied to preoperative planning for a wide variety of free flap repair surgeries. Moreover, using appropriate printing materials, the 3D-printed models can be sterilized for intraoperative use. One limitation may be the relative cost despite being more affordable than stereolithography and the length of time required for production. We believe that as this technique becomes more widely accepted and used, the cost-benefit ratio will subsequently decrease. Operative outcomes in reconstructive surgery can be improved by preoperative planning. In contrast to the current 2D imaging modalities such as CTA, 3D-printed models can provide tactile feedback that may enable the surgeon to use a hands-on approach to operative planning. We describe here a technique where the “reverse image” of a skin wound defect was created and used for flap design. Although a small skin graft was needed to cover the pedicle that was outside of the volumetrically modeled plan, the defect was otherwise appropriately reconstructed with the technique described. 3D printing, and in particular “reverse” planning also has the potential for use in other surgical disciplines. Outcome studies with such models would be a useful means to assessing their efficacy in the future.
REFERENCES 1. Teunis T, van Voss MR, Kon M, van Maurik JF. CT-angiography prior to DIEP flap breast reconstruction: A systematic review and meta-analysis. Microsurgery 2013;33:496–502.
3D Printing in Reconstructive Surgery 2. Rosson GD, Shridharani SM, Magarakis M, Manahan MA, Stapleton SM, Gilson MM, Flores JI, Basdag B, Fishman EK. Three-dimensional computed tomographic angiography to predict weight and volume of deep inferior epigastric artery perforator flap for breast reconstruction. Microsurgery 2011;31:510–516. 3. Onoda S, Azumi S, Hasegawa K, Kimata Y. Preoperative identification of perforator vessels by combining MDCT, doppler flowmetry, and ICG fluorescent angiography. Microsurgery 2013;33:265–269. 4. Rozen WM, Ashton MW, Stella DL, Phillips TJ, Grinsell D, Taylor GI. The accuracy of computed tomographic angiography for mapping the perforators of the deep inferior epigastric artery: A blinded, prospective cohort study. Plast Reconstr Surg 2008;122:1003–1009. 5. Rozen WM, Chubb D, Grinsell D, Ashton MW. Computed tomographic angiography: Clinical applications. Clin Plast Surg 2011;38: 229–239. 6. Rozen WM, Ashton MW, Grinsell D, Stella DL, Phillips TJ, Taylor GI. Establishing the case for CT angiography in the preoperative imaging of abdominal wall perforators. Microsurgery 2008;28:306– 313. 7. Rozen WM, Anavekar NS, Ashton MW, Stella DL, Grinsell D, Bloom RJ, Taylor GI. Does the preoperative imaging of perforators with CT angiography improve operative outcomes in breast reconstruction? Microsurgery 2008;28:516–523. 8. Rozen WM, Phillips TJ, Stella DL, Ashton MW. Preoperative CT angiography for DIEP flaps: ‘must-have’ lessons for the radiologist. J Plast Reconstr Aesthet Surg 2009;62:e650–651. 9. Gravvanis A, Tsoutsos D, Papanikolaou G, Diab A, Lambropoulou P, Karakitsos D. Refining perforator selection for deep inferior epigastric perforator flap: The impact of the dominant venous perforator. Microsurgery 2014;34:169–176. 10. Dionyssiou D, Demiri E, Tsimponis A, Boorman J. Predesigned breast shaping assisted by multidetector-row computed tomographic angiography in autologous breast reconstruction. Plast Reconstr Surg 2014;133:100e–108e. 11. Rozen WM, Ashton MW, Whitaker IS, Wagstaff MJ, Acosta R. The financial implications of computed tomographic angiography in DIEP flap surgery: A cost analysis. Microsurgery 2009;29:168–169. 12. Cohen A, Laviv A, Berman P, Nashef R, Abu-Tair J. Mandibular reconstruction using stereolithographic 3-dimensional printing modeling technology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:661–666. 13. Rozen WM, Ting JW, Baillieu C, Leong J. Stereolithographic modeling of the deep circumflex iliac artery and its vascular branching: A further advance in computed tomography-guided flap planning. Plast Reconstr Surg 2012;130:380e–382e.
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14. Ono I, Gunji H, Suda K, Kaneko F. Method for preparing an exactsize model using helical volume scan computed tomography. Plast Reconstr Surg 1994;93:1363–1371. 15. Mankovich NJ, Samson D, Pratt W, Lew D, Beumer J III. Surgical planning using three-dimensional imaging and computer modeling. Otolaryngol Clin North Am 1994;27:875–889. 16. Gillis JA, Morris SF. Three-dimensional printing of perforator vascular anatomy. Plast Reconstr Surg 2014;133:80e–82e. 17. Wallmichrath J, Baumeister RG, Giunta RE, Holzbach T, Frick A. Correction of asymmetric pectus excavatum using a virtually designed silicone implant. Aesthetic Plast Surg 2014;38:146–150. 18. Chen Y, Niu F, Yu B, Liu J, Wang M, Gui L. Three-dimensional preoperative design of distraction osteogenesis for hemifacial microsomia. J Craniofac Surg 2014;25:184–188. 19. Xu H, Han D, Dong JS, Shen GX, Chai G, Yu ZY, Lang WJ, Ai ST. Rapid prototyped PGA/PLA scaffolds in the reconstruction of mandibular condyle bone defects. Int J Med Robot 2010;6:66–72. 20. Wang J, Liu JF, Liu W, Wang JC, Wang SY, Gui L. Application of computer techniques in repair of oblique facial clefts with outertable calvarial bone grafts. J Craniofac Surg 2013;24:957–960. 21. Lee SJ, Lee HP, Tse KM, Cheong EC, Lim SP. Computer-aided design and rapid prototyping-assisted contouring of costal cartilage graft for facial reconstructive surgery. Craniomaxillofac Trauma Reconstr 2012;5:75–82. 22. Herlin C, Koppe M, Beziat JL, Gleizal A. Rapid prototyping in craniofacial surgery: Using a positioning guide after zygomatic osteotomy—A case report. J Craniomaxillofac Surg 2011;39:376–379. 23. Cao D, Yu Z, Chai G, Liu J, Mu X. Application of EH compound artificial bone material combined with computerized threedimensional reconstruction in craniomaxillofacial surgery. J Craniofac Surg 2010;21:440–443. 24. Ciocca L, De Crescenzio F, Fantini M, Scotti R. Rehabilitation of the nose using CAD/CAM and rapid prototyping technology after ablative surgery of squamous cell carcinoma: A pilot clinical report. Int J Oral Maxillofac Implants 2010;25:808–812. 25. Ono I, Abe K, Shiotani S, Hirayama Y. Producing a full-scale model from computed tomographic data with the rapid prototyping technique using the binder jet method: A comparison with the laser lithography method using a dry skull. J Craniofac Surg 2000;11: 527–537. 26. Rozen WM, Phillips TJ, Ashton MW, Stella DL, Gibson RN, Taylor GI. Preoperative imaging for DIEA perforator flaps: A comparative study of computed tomographic angiography and Doppler ultrasound. Plast Reconstr Surg 2008;121:9–16. 27. Barker TM, Earwaker WJ, Lisle DA. Accuracy of stereolithographic models of human anatomy. Australas Radiol 1994;38:106–111.
Microsurgery DOI 10.1002/micr
In reconstructive surgery, preoperative planning is essential for optimal functional and aesthetic outcome. Creating a three-dimensional (3D) model from two-dimensional (2D) imaging data by rapid prototyping has been used in industrial design for decades but has only recently been introduced for medical application. 3D printing is one such technique that is fast, convenient, and relatively affordable. In this report, we present a case in which a reproducible method for producing a 3D-printed “reverse model” representing a skin wound defect was used for flap design and harvesting. This comprised a 82-year-old man with an exposed ankle prosthesis after serial soft tissue debridements for wound infection. Soft tissue coverage and dead-space filling were planned with a composite radial forearm free flap (RFFF). Computed tomographic angiography (CTA) of the donor site (left forearm), recipient site (right ankle), and the left ankle was performed. 2D data from the CTA was 3D-reconstructed using computer software, with a 3D image of the left ankle used as a “control.” A 3D model was created by superimposing the left and right ankle images, to create a “reverse image” of the defect, and printed using a 3D printer. The RFFF was thus planned and executed effectively, without complication. To our knowledge, this is the first report of a mechanism of calculating a soft tissue wound defect and producing a 3D model that may be useful for surgical planning. 3D printing and particC 2014 Wiley ularly “reverse” modeling may be versatile options in reconstructive planning, and have the potential for broad application. V Periodicals, Inc. Microsurgery 35:148–153, 2015.
For optimal restoration of function and appearance in reconstructive surgery, an accurate anatomical understanding of the defect is required. To this effect, preoperative planning with appropriate imaging techniques benefits both the excisional and reconstructive surgeon.1–5 Computed tomographic angiography (CTA) is one technique that has previously shown to improve operative outcomes while minimizing donor site morbidity.6,7 It can aid in selecting the donor site, flap and vessel of choice for reconstruction.5 Furthermore, CTA is a relatively straightforward procedure.8 A number of investigators have proven its efficacy in reducing operative time and reconstructive outcomes.4,6,7,9–11 In contrast to CTA, which produces threedimensional (3D) visualization on a two-dimensional (2D) surface, rapid prototyping (RP) is a process of producing a 3D model layer-by-layer based on computeraided design (CAD) data or imaging that precisely represents the anatomical details of a defect. Having been
1 Department of Plastic and Reconstructive Surgery, Frankston Hospital, Peninsula Health, Frankston, VIC, Australia 2 Department of Surgery, Monash University, Monash Medical Centre, Clayton, VIC, Australia 3 Monash University Plastic and Reconstructive Surgery Unit (Peninsula Clinical School), Peninsula Health, Frankston, VIC, Australia 4 Department of Surgery, School of Medicine and Dentistry, James Cook University Clinical School, Townsville Hospital, Douglas, Townsville, QLD, Australia *Correspondence to: Warren M. Rozen, M.B.B.S., B.Med.Sc., M.D., Ph.D., Department of Plastic and Reconstructive Surgery, Frankston Hospital, Peninsula Health, 2 Hastings Road, Frankston, Victoria 3199, Australia. E-mail: [email protected] Received 7 April 2014; Revision accepted 3 July 2014; Accepted 7 July 2014 Published online 21 July 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/micr.22293
Ó 2014 Wiley Periodicals, Inc.
used for decades in industrial design, it has recently shown potential in medical applications, especially for implant design and preoperative planning.12 3D models provide surgeons with a physical object that they can interact with hands-on for easier understanding of the morphology. This “haptic-modeling” has been shown in some settings to reduce operative time and facilitate superior operative outcomes.4,6,10,13 Amongst numerous RP techniques, stereolithography is considered the gold standard in medical RP, but is labor-intensive, relatively expensive, slow, and recent publications bring into question issues regarding its environmental safety.12,14,15 3D printing (3DP) is the latest RP technique where photopolymer materials are “jetted” in ultrathin layers and then “cured” by UV light for immediate handling and use. In comparison to stereolithography, it is faster, more convenient, less expensive, and more appropriate for producing small complex structures. In reconstructive surgery, 3DP has been used to model vascular perforator anatomy16 and guide correction of pectus excavatum,17 mandibular deformities,12,18,19 facial deformities,20–23 nasal defects,24 and skull deformities.25 Although 3D printing itself has been widely described and increasingly used, a reproducible method for producing a 3D-printed “reverse model” has not yet been described. In this report, we present a case in which a reproducible method for producing a 3D-printed “reverse model” representing a skin wound defect was used for flap design and harvesting. CASE REPORT
An 82-year-old man has undergone elective ankle replacement surgery, which was complicated by wound
3D Printing in Reconstructive Surgery
Figure 1. Soft tissue defect overlay the right ankle, with ankle prosthesis exposed.
Figure 2. 3D reconstructed volume-rendered computed tomography (CT) image of the recipient site demonstrated the soft tissue defect, performed with Osirix software (Pixmeo, Geneva, Switzerland).
infection, dehiscence, and an exposed ankle prosthesis (see Fig. 1). Serial soft tissue debridements were performed by an orthopedic surgeon, and the patient was ultimately referred for soft tissue coverage and deadspace filling, with attempted salvage of the prosthesis.
149
Reconstruction was planned with a composite radial forearm free flap, comprising a musculo-fascio-cutaneous flap. Preoperative imaging was performed as routine, with multi-slice CTA of both the flap donor site and the recipient site. All imaging was performed with institutional ethics committee approval. Scan acquisition comprised arterial phase scanning, which eliminated venous contamination, avoided confusion between different structures, and maximized arterial filling. We used a protocol that triggered the scan from the origin of the pedicle, and scanned in the direction of blood flow through the perforating vessels of the flap. Initial 2D software reconstruction used raw scan data recorded thin axial slices (0.7-mm-thick slices). Visual appreciation of the vascular anatomy was best achieved with the use of software-generated 3D reconstructions. The freeware program “Osirix,” a third-party software program (Osirix, Version 4.1, Pixmeo, Geneva, Switzerland) was used. First, the recipient site was 3D-reconstructed via volume rendering using the Osirix 3D preset of soft tissue CT (i.e., soft tissue 1 skin) available within the provided software, and this was used to apply the skin layer on top of the 3D image. Crop function and scissor mouse functions were used judiciously to narrow down to defect (see Fig. 2). The 2D images were 3D reconstructed using the surface rendering function. The 3D reconstructed image was exported in standard tessellation language (STL) format. To evaluate the volume and shape of the defect, we created a 3D surface-rendered image of the normal left ankle in STL format for use as “control.” The above steps for producing the right ankle 3D image were repeated using the Osirix software for surface rendering, or can be achieved using 3D printer software (Cubify, 3D systems, Rock Hill, SC). Volumetric and defect analysis were undertaken using Magics software (Materialise, Leuven, Belgium). STL files of both the right and left ankle were loaded on to the software and placed adjacent to each other in anatomical position (see Fig. 3a). Care was taken to align both objects on all X-, Y-, and Z-axis, using “interactive translate” function. In this illustrative case, a mirror image of the left ankle was produced by reflecting it on the Y–Z plane, so that it aligned with the right ankle pointing in the same direction (see Fig. 3b). Using the “interactive translate” function, the mirrored left ankle was superimposed on to the right ankle so that the defect was “covered” (see Fig. 3c). This was achieved by superimposing the significant anatomical landmarks (such as the heel and the malleoli) common to both ankles first. Correct superimposition was confirmed by rotating the image 360 and viewing it in all angles. Then, the image of the right ankle and the intersected area was “subtracted” from the mirrored left ankle using “Boolean” function (see Figs. 3d–3f). The “reverse image” representing the skin defect Microsurgery DOI 10.1002/micr
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Figure 3. (a) Cropped 3D images of the right and left ankle were loaded into Magics software (Materialise) and placed side-by-side in anatomical position. (b) Left ankle was reflected on Y–Z plane so that it was aligned and pointed in the same direction as the right ankle. (c) Mirror image of the left ankle was superimposed on the right ankle. (d–f) Right ankle and the intersected parts were “ subtracted” from the mirrored image of left ankle using Boolean function available in the Magics software.
was saved in STL format, essential since the 3D printer software can only recognize STL files. These images were directly loaded in to the Cubify software in lieu of the CT raw data to enable production of both anatomic models (see Fig. 4) and pre-designed models based on the above defect analysis (see Fig. 5). Volumetric flap planning was achieved using a 3D image of the donor site (i.e., left forearm). The same steps as described above for the production of the surface-rendered 3D image of the right ankle using Osirix were used (see Fig. 6). Using the Magics software, both forearm and the “reverse image” were placed adjacent to each other and aligned in the same direction (see Fig. 6a), and then superimposed over each other (see Figs. 6b and 6c). Using the “Boolean” function, the volume of the reverse image was “subtracted” away from the forearm (see Figs. 6d and 6e). This was used to preoperatively predict and intraoperatively guide flap harvest, to match the reconstructive needs of the recipient site. 3D printing of defect and flap models, after analysis by Cubify software (3D Systems), was achieved by a single jet Cube 2 printer (3D Systems). The 3D software modeling was exported from the Cubify software and transferred to the Cube 2 printer. Printing of the right Microsurgery DOI 10.1002/micr
Figure 4. 3D printed model of the right ankle was created using the Cubify software and printed by the Cube 2 printer.
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Figure 5. 3D printed model of the “ reverse image” was created using the Cubify software and printed by the Cube 2 printer.
Figure 6. (a) Cropped 3D images of the forearm donor site were loaded into Magics software (Materialise), with the previously developed “ defect analysis” image loaded side-by-side in anatomical positions. (b, c) The donor site and the “ reverse image” were superimposed. (d, e) The “ reverse image” was “ subtracted” from the forearm to evaluate the reconstructive needs during harvest.
ankle required approximately 12.5 hours and the reverse image 8.5 hours. Preoperatively, the 3D model of the right ankle was used to appreciate the size and the depth of the defect. The “reverse model” was placed immediately adjacent to the donor site to estimate the size of the flap for harvest-
ing. The flap was thus designed to appropriately fill the soft tissue defect (see Fig. 7), with a small skin graft needed for extension of the pedicle (given that this was not part of the initial defect for volumetric planning). The flap and graft both healed well, with no donor or recipient-site complications. Microsurgery DOI 10.1002/micr
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Figure 7. Defect was reconstructed with free radial forearm flap, and demonstrated appropriate filling of the soft tissue defect.
DISCUSSION
An accurate understanding of the anatomy that has been distorted by trauma, cancer, or disease is useful in reconstructive surgery, such as a free flap repair. The current standard of practice involves imaging complex defects with CTA of both donor site and the recipient site for 3D visualization of the anatomical structures.4 Multiple software programs can effectively model the 3D data in 2D images, which our previous research has demonstrated are easy to interpret by surgeons and better demonstrate anatomical relationships of each vessel in a single image.4,26 The raw data from CTA can be further processed to produce a 3D model by RP. The benefit of being able to physically interact with 3D models is that the models enhance the surgeon’s understanding of the morphology, which may be significantly altered by the underlying pathology, and enable hands-on preoperative planning. Subsequent benefits may include decreased length of operation, wound exposure time, exposure to general anesthesia, and intraoperative blood loss.12 Until recently, stereolithography has been considered the gold standard for medical RP. It is accurate to 0.1 mm and Microsurgery DOI 10.1002/micr
can produce large anatomical parts.27 However, it is relatively more labor-intensive and expensive because of the high cost of machine maintenance and the hardening materials used. Furthermore, a large model takes more than a day to manufacture, which is associated with increased production cost.14 Additionally, it may not be environmentally safe.15 In contrast, 3D printing provides an attractive alternative RP technique that can be accurate to 0.016 mm. It is faster, more convenient to use, and is associated with approximately one-third of the cost,12 and thus may be preferred for building smaller, more complex anatomical structures.16 Constructing a 3D model of an external surface is relatively straightforward, however a “reverse image” that represents the wound defect may be helpful for the surgeons in the selection of an appropriate flap shape and size. To the best of our knowledge, we are the first in the literature to report a method of producing such “reverse image” using 3D printing. We achieved this using the non-pathological left ankle as a control to the pathological right side. After the models are superimposed on the Magics software (Materialise), they are “subtracted” from each other leaving behind a “reverse image” that depicts the skin defect. This was used to assess the flap shape and size on the donor site. The advantage of our method lies in that it is flexible and can be applied to preoperative planning for a wide variety of free flap repair surgeries. Moreover, using appropriate printing materials, the 3D-printed models can be sterilized for intraoperative use. One limitation may be the relative cost despite being more affordable than stereolithography and the length of time required for production. We believe that as this technique becomes more widely accepted and used, the cost-benefit ratio will subsequently decrease. Operative outcomes in reconstructive surgery can be improved by preoperative planning. In contrast to the current 2D imaging modalities such as CTA, 3D-printed models can provide tactile feedback that may enable the surgeon to use a hands-on approach to operative planning. We describe here a technique where the “reverse image” of a skin wound defect was created and used for flap design. Although a small skin graft was needed to cover the pedicle that was outside of the volumetrically modeled plan, the defect was otherwise appropriately reconstructed with the technique described. 3D printing, and in particular “reverse” planning also has the potential for use in other surgical disciplines. Outcome studies with such models would be a useful means to assessing their efficacy in the future.
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Microsurgery DOI 10.1002/micr
