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Scapula pre-augmentation in sheep with polycaprolactone tricalcium phosphate scaffolds
J Stomatol Oral Maxillofac Surg 120 (2019) 116–121
Available online at
ScienceDirect www.sciencedirect.com
Original Article
Scapula pre-augmentation in sheep with polycaprolactone tricalcium phosphate scaffolds S. Spalthoff *, R. Zimmerer, J. Dittmann, P. Korn, N.-C. Gellrich, P. Jehn Department of Oral and Maxillofacial Surgery, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
A R T I C L E I N F O
A B S T R A C T
Article history: Received 25 May 2018 Accepted 14 October 2018 Available online 25 October 2018
A scapula free flap is a commonly used method to reconstruct intraoral defects of the mandible and maxilla. Despite its clear advantages, it shows some deficiencies concerning the amount and shape of the available bone, especially with respect to later implant placement. To overcome these limitations, we pre-augmented the scapula prior to a potential flap-raising procedure with polycaprolactone (PCL) tricalcium phosphate (TCP) scaffolds in a sheep model. In our study, the scapula angle was augmented with a block of PCL-TCP in three adult sheep. After 6 months, the amount of newly formed bone and scaffold degradation were evaluated using cone-beam computed tomography scans and histomorphometric analysis. All animals survived the study and showed no problems in the augmented regions. The scaffolds were attached firmly to the scapula and showed a bonelike consistency. A fair amount of the scaffold material was degraded and replaced by vital bone. Our method seems to be a valid approach to pre-augment the scapula in sheep. In further experiments, it will be interesting to determine whether it is possible to transplant a modified scapula flap to an intraoral defect site.
C 2018 Elsevier Masson SAS. All rights reserved.
Keywords: Pre-augmentation PCL-TCP Scapula flap Tissue engineering
1. Introduction The osteocutaneous scapula flap, described by Swartz et al. in 1986, is used regularly for mandibular and maxillary reconstruction in modern oro- and maxillofacial surgery to reconstruct composite tissue defects in the head and neck regions [1–3]. Miles and Gilbert reported on 39 patients with complex maxillary defects reconstructed with scapular angle osteomyogenous free flaps. In their retrospective analysis, 80% underwent maxillectomy for malignant neoplastic disease and 20% for benign disease. Of their patients, 51% underwent radiotherapy as part of their treatment. They found relatively low donor-site morbidity but a fairly high local complication rate of 46% associated with a high revision surgery rate of 41% [4]. There was no statistically significant difference between irradiated and non-irradiated patients. Choi et al. reported a flap failure rate of about 6% and an oroantral fistula in about 13% of their cases. All cases that they presented underwent maxillectomy for malignant neoplastic disease. Nevertheless, they stated that the flap has some clear advantages compared with other microvascular bone transplants: A long pedicle, low flap failure, the three-dimensional nature of the bone and soft tissues (chimeric flap), and low rate of donor-site * Corresponding author. E-mail address: [email protected] (S. Spalthoff). https://doi.org/10.1016/j.jormas.2018.10.001 C 2018 Elsevier Masson SAS. All rights reserved. 2468-7855/
morbidity with free ambulation [5]. Alternative donor sites for microvascular bone transfer in oro- and maxillofacial surgery are the fibula and iliac crest. The fibula is recommended for younger patients with extended defects and limited soft tissue requirements. It can be harvested by using a two-team approach with acceptable donor site morbidity. The length of the vascularized bone is unrivaled by other types of bone flaps although the softtissue component may have some limitations [6]. The iliac crest is widely used as a non-vascularized transplant or as a vascularized transplant with a deep circumflex iliac artery flap (DCIA). A DCIA flap is often used to reconstruct the mandible with good results regarding the survival rate and later implant placement [7]. The decision to use vascularized bone grafts (VGBs) versus nonvascularized bone grafts is mostly influenced by the size of the defect, the medical status of the patient, prior irradiation, and the surrounding soft tissue. If sufficient soft tissue coverage is possible, the patient has not undergone irradiation, and the defect size is less than 6 cm, reconstruction with a non-vascularized bone graft seems to be a suitable solution, especially if the patient is in a compromised medical status. Otherwise, a vascularized bone transfer is recommended [8,9]. Implant placement for dental rehabilitation has a reasonable success rate of over 90% in VBGs; however, a scapula bone flap seems to be slightly superior to a DCIA flap and fibula bone graft [10,11]. Nevertheless, the bone stock at the lateral border of the
[(Fig._1)TD$IG]
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[17]. In conclusion, the free scapula bone graft shows some clear advantages compared with other VGBs, but there can be problems with the shape and stock of the available bone, which can make prosthetic-driven dental implant placement difficult. In this pilot study, we attempted to address this problem by pre-augmenting the scapula with a polycaprolactone (PCL) tricalcium phosphate (TCP) scaffold prior to a flap-raising procedure in a sheep model. This should lead to increased bone stock in the position of choice, thus facilitating later implant placement. 2. Material and methods
Fig. 1. The polycaprolactone (PCL)-tricalcium phosphate (TCP) scaffold prior to implantation.
scapula is inferior to those of the iliac crest and fibula, which limits free implant placement [12]. Moreover, there is some variability throughout the course of the lateral border of the scapula, sometimes resulting in thin bone for implant placement [13]. In cadaver studies, there was at least one inadequate dimension for dental implants in 35% of the sections [14]. In addition, there is variance in the size of the lateral border depending on the patient’s sex; female patients more frequently demonstrate inadequate dimensions for implant placement. Therefore, Hirota et al. used vertical distraction osteogenesis to adapt the size of scapula transplants [15]. Other authors tried to compensate for the lack of bone stock by using shorter and smaller implants [16]. Mertens et al. reported in 2016 that about 14% of their patients (two out of 14) who underwent maxillary reconstruction with a free scapular tip graft needed additional bone grafting before implant placement
Ethical approval for this experimental study in sheep was provided by the Department for Veterinary Affairs, Oldenburg, Germany (AZ: 08/1621). Scaffolds (height, 10 mm; diameter, 20 mm; Fig. 1) consisting of a mixture of PCL and TCP (30% PCL and 70% TCP) (Synthes, West Chester, PA, USA) were used to augment the scapula of three healthy adult female German black-headed sheep in a split animal model. The scapula angle was exposed using the same approach described in our previous experiments [18– 20]. The cylinders were placed in a subperiosteal pocket, which was closed afterward with resorbable sutures (Fig. 2a–d). Six months later, all animals were euthanized by deep sedation (intramuscular midazolam 1 mg/kg, intravenous propofol 5 mg/ kg, and intravenous pentobarbital 80 mg/kg). After explantation of the scapulae bilaterally, a cone-beam computed tomography scan was acquired. Then, areas surrounding the implant were removed with a saw and the specimens were fixed in 3.5% neutral-buffered formalin, embedded in methyl methacrylate, and sectioned perpendicular to the axis of the scaffolds using a modified inner-hole diamond saw. Non-decalcified slices with a thickness of 30 mm were surface-stained with alizarin red S-methylene blue for standard light microscopy and histomorphometric analysis. Digital images of each slide were obtained using a Leica DM6 B
[(Fig._2)TD$IG]
Fig. 2. A. An intraoperative photograph showing the exposed scapula bone. B. An intraoperative photograph showing the subperiosteal pocket. C. An intraoperative photograph showing the scaffold inside the subperiosteal pocket. D. An intraoperative photograph showing wound closure by simple interrupted sutures.
[(Fig._3)TD$IG]
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S. Spalthoff et al. / J Stomatol Oral Maxillofac Surg 120 (2019) 116–121
Fig. 3. A cross-section of the augmented scapula surface stained with alizarin red S-methylene blue [red arrow, polycaprolactone (PCL); black arrow, bone; green arrow, tricalcium phosphate (TCP); and red stars, the original scapula bone].
[(Fig._4)TD$IG]
microscope equipped with a motorized stage and a Leica DFC7000T digital camera (Leica, Wetzlar, Germany). Images of entire crosssections of the scaffolds were obtained using Leica Las X software and the Mark and Find, Stitching, and Stage Overview modules (Leica). The total bone area and residual PCL-TCP area were quantified using CellSens Dimension V1 image analysis software (Olympus, Hamburg, Germany). Eight sections distributed evenly throughout the scapula were used for histomorphometric evaluations. To measure the degradation of the scaffold material, unused scaffolds were directly embedded in methyl methacrylate, sliced, and stained as described above. After histomorphometric analysis of these slices, the results were compared with those of the experimental group. Statistical analysis was performed using SigmaPlot 13.0 (Mann–Whitney Rank Sum Test, Systat Software, Inc., San Jose, CA, USA). A P-value < 0.05 was considered statistically significant.
3. Results All animals survived the experiment. They showed no sign of infection or prolonged swelling. Shoulder movement was not impaired, and the animals recovered from the operation quickly. The animals could be kept in groups without limiting their movement. When the scapula bone was explanted, the scaffold was firmly attached to the original bone. The former shape of the scaffold could still be identified easily. There was bleeding from the surrounding area and the scaffold showed a bone-like consistency. Microscopically, there was bone formation throughout all constructs (Fig. 3). New bone was mostly found in close relation to the original scapula surface but there was still some bone formation throughout the entire scaffold (Fig. 4). Evaluation of the cone-beam computed tomography scans showed good osseointegration and even some additional bone formation in the surrounding area outside the scaffolds. Radiologically, nearly all scaffolds maintained their original dimensions (Figs. 5 and 6). A significant amount of the PCL (median 32.29%, 25% 28.81, 75% 37.83 of the scaffold area before implantation versus median 13.53%, 25% 10.05, 75% 15.84 of the scaffold area after implantation, P < 0.001) and TCP (median 30.77%, 25% 26.54, 75% 35.27 of the scaffold area before implantation versus median 7.41%, 25% 5.51, 75% 10.95 of the scaffold area after implantation, P < 0.001) was degraded and new bone was observed throughout the whole scaffold (no bone before
Fig. 4. A magnification of Fig. 3 [red arrow, polycaprolactone (PCL); black arrow, bone; green arrow, tricalcium phosphate (TCP); and red stars, the original scapula bone].
implantation versus median 7.79%, 25% 6.25, 75% 9.52 of the scaffold area after implantation, P < 0.001) (Tables 1 and 2).
4. Discussion PCL-TCP was used previously to augment the mandible in minipigs in a guided bone regeneration approach. The material showed good osteoconductive properties but was still inferior compared with autogenous bone grafts with respect to new bone formation. The authors had some problems with intraoral exposure of the graft material and attributed the inferior
[(Fig._5)TD$IG]
[(Fig._6)TD$IG]
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Fig. 6. The contralateral scapula without a scaffold. Fig. 5. A cone-beam computed tomography scan of the augmented scapula.
there should be no problem transplanting the augmented scapula into an intraoral defect, for example, after tumor resection. Connecting the scapula free flap to the local blood supply through microvascular anastomosis will guarantee reperfusion of the whole transplant immediately, allowing the delivery of nutrition and immune defenses, even throughout the grafted area. This should minimize the risk of graft exposure and consequent infection. The fact that the PCL-TCP scaffolds almost maintained their original dimensions should permit precise planning of the desired bone transplant. This should facilitate a prosthetic-driven design for optimal implant placement. Dimensional and mechanical stability are known benefits of PCL-TCP scaffolds. In 2014, Li et al. showed that after 12 months in a spinal fusion experiment in sheep, the autograft-free spinal fusion cage consisting of PCL-TCP
performance of the PCL-TCP graft to concomitant inflammatory reactions [21]. In another clinical study in monkeys, Goh et al. reconstructed facial wall defects after tooth extraction in a singlestep implantation procedure with PCL-TCP scaffolds. Similar to the first experiment mentioned, they also reported problems with graft exposure and found only a very small amount of newly formed bone in the PCL-TCP grafts [22]. Other studies that used a PCL-TCP graft outside the oral cavity showed promising results. In rabbit calvarial defects [23] and rabbit femoral head defects [24], PCL-TCP grafts were incorporated successfully without any sign of exposure. In our study, we attempted to circumvent these obvious limitations of PCL-TCP grafts regarding their direct use in the oral cavity. Pre-augmenting the scapula allows protected incorporation of the scaffolds inside a thick muscle cuff. Following complete integration of the PCL-TCP scaffold into the local blood circulation,
Table 1 Areas of TCP, bone, and PCL reported as percentages of the scaffold area after 6 months of cultivation and a comparison of scaffolds after 6 months of cultivation versus scaffolds pre-implantation (Mann–Whitney rank sum test, P-values < 0.05 show a significant difference). TCP
PCL
Bone
%
Median
25%
75%
P
%
Median
25%
75%
P
%
Median
25%
75%
P
7.10 17.54 9.66 5.98 15.08 10.87 7.72 3.68 2.20 4.84 6.64 6.16 2.63 6.39 5.44 4.03 8.84 8.02 5.53 15.08 6.19 27.37 11.18 9.58
7.41
5.51
10.95
< 0.001
11.94 10.06 16.14 15.09 9.79 15.97 10.29 15.29 10.14 10.19 15.84 15.69 14.27 15.85 15.85 10.03 10.01 17.24 12.78 16.40 10.88 9.89 9.00 15.73
13.53
10.05
15.84
< 0.001
15.27 11.71 7.82 16.11 6.14 9.35 6.51 8.71 6.29 5.36 11.06 9.38 13.63 9.11 7.95 6.14 4.31 8.15 9.93 2.80 7.75 4.60 7.67 6.70
7.79
6.25
9.52
< 0.001
TCP: tricalcium phosphate; PCL: polycaprolactone.
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Table 2 Areas of TCP, bone, and PCL as percentages of the scaffold area pre-implantation. TCP
PCL
Bone
%
Median
25%
75%
%
Median
25%
75%
%
Median
25%
75%
30.77 23.59 22.36 35.19 31.02 29.97 29.49 35.35
30.77
26.54
35.27
27.79 34.76 32.29 29.97 34.41 34.89 38.88 29.83
32.29
28.81
34.83
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00
0.00
0.00
TCP: tricalcium phosphate; PCL: polycaprolactone.
showed the same mechanical strength as a titanium cage filled with autologous bone. Surprisingly, the PCL-TCP cage also showed better bone ingrowth, so they concluded that the PCL-TCP cage is a promising autograft-free fusion cage for clinical application [25]. In a pilot study in dogs, mandibular defects were reconstructed with PCL-TCP scaffolds. The degradation time was evaluated, and after 9 months, 46.9% of the scaffold material remained. The author concluded from further investigation that the entire scaffold would disintegrate soon [26]; therefore, an estimated degradation time of 1 year seems feasible in our opinion. This is crucial for certain procedures, for example, augmentation or reconstruction of midfacial structures, because too rapid degradation of the scaffold material would exceed the bone ingrowth or new bone formation and lead to undesired volume loss in the area of augmentation. There are different technical methods to produce patientspecific scaffolds consisting of PCL-TCP or other combinations of PCL and osteoconductive materials [27–29] allowing any desired modification of the scapula. This should allow implant-driven, backward-planned bone augmentation [30] even in complex cases after tumor resection. This pilot study showed that it possible to modify the shape of the bony scapula by pre-augmentation with PCL-TCP scaffolds. The scaffold material maintained a stable osteoinductive environment allowing bony ingrowth and there seemed to be a transformation of the matrix material to vital bone while maintaining approximately the original dimensions. Whether PCL-TCP is the material of choice in our model remains to be proven in further experiments. It may be possible that different materials or different compositions of PCL and TCP could lead to more bone transformation while maintaining stable scaffold dimensions. However, bony ingrowth and new bone formation distant from the scapula surface in all animals are promising results and could lead to the hypothesis that the experimental model worked quite well. Further experiments are required to prove this assumption and determine if it is possible to reconstruct and augment a large bony defect in the orofacial region using this new method by increasing the shape and stock of the scapula bone without the abovementioned problems of graft exposure, infection, and consequent graft failure. Sources of funding AO Foundation (research Grant F-07-58K). Ethical approval Ethical approval for this experimental study in sheep was provided by the Department for Veterinary Affairs, Oldenburg, Germany (AZ: 08/1621). Disclosure of interest The authors declare that they have no competing interest.
Acknowledgments We gratefully thank DePuy Synthes for providing the PCL-TCP scaffolds for this study.
References [1] Swartz WM, Banis JC, Newton ED, Ramasastry SS, Jones NF, Acland R. The osteocutaneous scapular flap for mandibular and maxillary reconstruction. Plast Reconstr Surg 1986;77:530–45. [2] Ferrari S, Ferri A, Bianchi B. Scapular tip free flap in head and neck reconstruction. Curr Opin Otolaryngol Head Neck Surg 2015;23:115–20. [3] Yoo J, Dowthwaite SA, Fung K, Franklin J, Nichols A. A new angle to mandibular reconstruction: the scapular tip free flap. Head Neck 2013;35:980–6. [4] Miles BA, Gilbert RW. Maxillary reconstruction with the scapular angle osteomyogenous free flap. Arch Otolaryngol Head Neck Surg 2011;137:1130–5. [5] Choi N, Cho JK, Jang JY, Cho JK, Cho YS, Baek CH. Scapular tip free flap for head and neck reconstruction. Clin Exp Otorhinolaryngol 2015;8:422–9. [6] Dowthwaite SA, Theurer J, Belzile M, Fung K, Franklin J, Nichols A, et al. Comparison of fibular and scapular osseous free flaps for oromandibular reconstruction: a patient-centered approach to flap selection. JAMA Otolaryngol Head Neck Surg 2013;139:285–92. [7] Qu X, Zhang C, Yang W, Wang M. Deep circumflex iliac artery flap with osseointegrated implants for reconstruction of mandibular benign lesions: clinical experience of 33 cases. Ir J Med Sci 2013;182:493–8. [8] Foster RD, Anthony JP, Sharma A, Pogrel MA. Vascularized bone flaps versus nonvascularized bone grafts for mandibular reconstruction: an outcome analysis of primary bony union and endosseous implant success. Head Neck 1999;21:66–71. [9] Moura LB, Carvalho PH, Xavier CB, Post LK, Torriani MA, Santagata M, et al. Autogenous non-vascularized bone graft in segmental mandibular reconstruction: a systematic review. Int J Oral Maxillofac Surg 2016;45:1388–94. [10] Burgess M, Leung M, Chellapah A, Clark JR, Batstone MD. Osseointegrated implants into a variety of composite free flaps: a comparative analysis. Head Neck 2017;39:443–7. [11] Ch’ng S, Skoracki RJ, Selber JC, Yu P, Martin JW, Hofstede TM, et al. Osseointegrated implant-based dental rehabilitation in head and neck reconstruction patients. Head Neck 2016;38(Suppl. 1):E321–7. [12] Clark JR, Vesely M, Gilbert R. Scapular angle osteomyogenous flap in postmaxillectomy reconstruction: defect, reconstruction, shoulder function, and harvest technique. Head Neck 2008;30:10–20. [13] Mu¨cke T, Ho¨lzle F, Loeffelbein DJ, Ljubic A, Kesting M, Wolff KD, et al. Maxillary reconstruction using microvascular free flaps. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2011;111:51–7. [14] Frodel Jr , Funk GF, Capper DT, Fridrich KL, Blumer JR, Haller JR, et al. Osseointegrated implants: a comparative study of bone thickness in four vascularized bone flaps. Plast Reconstr Surg 1992;92:449–58. [15] Hirota M, Mizuki N, Iwai T, Watanuki K, Ozawa T, Maegawa J, et al. Vertical distraction of a free vascularized osteocutaneous scapular flap in the reconstructed mandible for implant therapy. Int J Oral Maxillofac Surg 2008;37:481–3. [16] Lanzer M, Gander T, Gra¨tz K, Rostetter C, Zweifel D, Bredell M. Scapular free vascularised bone flaps for mandibular reconstruction: are dental implants possible? J Oral Maxillofac Res 2015;6:e4. [17] Mertens C, Freudlsperger C, Bodem J, Engel M, Hoffmann J, Freier K. Reconstruction of the maxilla following hemimaxillectomy defects with scapular tip grafts and dental implants. J Craniomaxillofac Surg 2016;44:1806–11. [18] Spalthoff S, Jehn P, Zimmerer R, Mo¨llmann U, Gellrich NC, Kokemueller H. Heterotopic bone formation in the musculus latissimus dorsi of sheep using beta-tricalcium phosphate scaffolds: evaluation of an extended prefabrication time on bone formation and matrix degeneration. Int J Oral Maxillofac Surg 2015;44:791–7.
S. Spalthoff et al. / J Stomatol Oral Maxillofac Surg 120 (2019) 116–121 [19] Kokemueller H, Spalthoff S, Nolff M, Tavassol F, Essig H, Stuehmer C, et al. Prefabrication of vascularized bioartificial bone grafts in vivo for segmental mandibular reconstruction: experimental pilot study in sheep and first clinical application. Int J Oral Maxillofac Surg 2010;39:379–87. [20] Kokemu¨ller H, Jehn P, Spalthoff S, Essig H, Tavassol F, Schumann P, et al. En bloc prefabrication of vascularized bioartificial bone grafts in sheep and complete workflow for custom-made transplants. Int J Oral Maxillofac Surg 2014;43:163–72. [21] Yeo A, Cheok C, Teoh SH, Zhang ZY, Buser D, Bosshardt DD. Lateral ridge augmentation using a PCL-TCP scaffold in a clinically relevant but challenging micropig model. Clin Oral Implants Res 2012;23:1322–32. [22] Goh BT, Chanchareonsook N, Tideman H, Teoh SH, Chow JK, Jansen JA. The use of a polycaprolactone-tricalcium phosphate scaffold for bone regeneration of tooth socket facial wall defects and simultaneous immediate dental implant placement in Macaca fascicularis. J Biomed Mater Res A 2014;102:1379–88. [23] Yeo A, Wong WJ, Teoh SH. Surface modification of PCL-TCP scaffolds in rabbit calvaria defects: evaluation of scaffold degradation profile, biomechanical properties and bone healing patterns. J Biomed Mater Res A 2010;93:1358–67. [24] Kawai T, Shanjani Y, Fazeli S, Behn AW, Okuzu Y, Goodman SB, et al. Customized, degradable, functionally graded scaffold for potential treatment of early stage osteonecrosis of the femoral head. J Orthop Res 2018;36:1002–11.
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[25] Li Y, Wu ZG, Li XK, Guo Z, Wu SH, Zhang YQ, et al. A polycaprolactonetricalcium phosphate composite scaffold as an autograft-free spinal fusion cage in a sheep model. Biomaterials 2014;35:5647–59. [26] Rai B, Ho KH, Lei Y, Si-Hoe KM, Jeremy Teo CM, Yacob KB, et al. Polycaprolactone-20% tricalcium phosphate scaffolds in combination with platelet-rich plasma for the treatment of critical-sized defects of the mandible: a pilot study. J Oral Maxillofac Surg 2007;65:2195–205. [27] Lohfeld S, Cahill S, Barron V, McHugh P, Du¨rselen L, Kreja L, et al. Fabrication, mechanical and in vivo performance of polycaprolactone/tricalcium phosphate composite scaffolds. Acta Biomater 2012;8:3446–56. [28] Neufurth M, Wang X, Wang S, Steffen R, Ackermann M, Haep ND, et al. 3D printing of hybrid biomaterials for bone tissue engineering: calcium-polyphosphate microparticles encapsulated by polycaprolactone. Acta Biomater 2017;64:377–88. [29] Go´mez-Liza´rraga KK, Flores-Morales C, Del Prado-Audelo ML, A´lvarez-Pe´rez ˜ a-Barba MC, Escobedo C. Polycaprolactone- and polycaprolactone/ MA, Pin ceramic-based 3D-bioplotted porous scaffolds for bone regeneration: a comparative study. Mater Sci Eng C Mater Biol Appl 2017;79:326–35. [30] Essig H, Rana M, Kokemueller H, von See C, Ruecker M, Tavassol F, et al. Preoperative planning for mandibular reconstruction – a full digital planning workflow resulting in a patient specific reconstruction. Head Neck Oncol 2011;3:45.
Available online at
ScienceDirect www.sciencedirect.com
Original Article
Scapula pre-augmentation in sheep with polycaprolactone tricalcium phosphate scaffolds S. Spalthoff *, R. Zimmerer, J. Dittmann, P. Korn, N.-C. Gellrich, P. Jehn Department of Oral and Maxillofacial Surgery, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
A R T I C L E I N F O
A B S T R A C T
Article history: Received 25 May 2018 Accepted 14 October 2018 Available online 25 October 2018
A scapula free flap is a commonly used method to reconstruct intraoral defects of the mandible and maxilla. Despite its clear advantages, it shows some deficiencies concerning the amount and shape of the available bone, especially with respect to later implant placement. To overcome these limitations, we pre-augmented the scapula prior to a potential flap-raising procedure with polycaprolactone (PCL) tricalcium phosphate (TCP) scaffolds in a sheep model. In our study, the scapula angle was augmented with a block of PCL-TCP in three adult sheep. After 6 months, the amount of newly formed bone and scaffold degradation were evaluated using cone-beam computed tomography scans and histomorphometric analysis. All animals survived the study and showed no problems in the augmented regions. The scaffolds were attached firmly to the scapula and showed a bonelike consistency. A fair amount of the scaffold material was degraded and replaced by vital bone. Our method seems to be a valid approach to pre-augment the scapula in sheep. In further experiments, it will be interesting to determine whether it is possible to transplant a modified scapula flap to an intraoral defect site.
C 2018 Elsevier Masson SAS. All rights reserved.
Keywords: Pre-augmentation PCL-TCP Scapula flap Tissue engineering
1. Introduction The osteocutaneous scapula flap, described by Swartz et al. in 1986, is used regularly for mandibular and maxillary reconstruction in modern oro- and maxillofacial surgery to reconstruct composite tissue defects in the head and neck regions [1–3]. Miles and Gilbert reported on 39 patients with complex maxillary defects reconstructed with scapular angle osteomyogenous free flaps. In their retrospective analysis, 80% underwent maxillectomy for malignant neoplastic disease and 20% for benign disease. Of their patients, 51% underwent radiotherapy as part of their treatment. They found relatively low donor-site morbidity but a fairly high local complication rate of 46% associated with a high revision surgery rate of 41% [4]. There was no statistically significant difference between irradiated and non-irradiated patients. Choi et al. reported a flap failure rate of about 6% and an oroantral fistula in about 13% of their cases. All cases that they presented underwent maxillectomy for malignant neoplastic disease. Nevertheless, they stated that the flap has some clear advantages compared with other microvascular bone transplants: A long pedicle, low flap failure, the three-dimensional nature of the bone and soft tissues (chimeric flap), and low rate of donor-site * Corresponding author. E-mail address: [email protected] (S. Spalthoff). https://doi.org/10.1016/j.jormas.2018.10.001 C 2018 Elsevier Masson SAS. All rights reserved. 2468-7855/
morbidity with free ambulation [5]. Alternative donor sites for microvascular bone transfer in oro- and maxillofacial surgery are the fibula and iliac crest. The fibula is recommended for younger patients with extended defects and limited soft tissue requirements. It can be harvested by using a two-team approach with acceptable donor site morbidity. The length of the vascularized bone is unrivaled by other types of bone flaps although the softtissue component may have some limitations [6]. The iliac crest is widely used as a non-vascularized transplant or as a vascularized transplant with a deep circumflex iliac artery flap (DCIA). A DCIA flap is often used to reconstruct the mandible with good results regarding the survival rate and later implant placement [7]. The decision to use vascularized bone grafts (VGBs) versus nonvascularized bone grafts is mostly influenced by the size of the defect, the medical status of the patient, prior irradiation, and the surrounding soft tissue. If sufficient soft tissue coverage is possible, the patient has not undergone irradiation, and the defect size is less than 6 cm, reconstruction with a non-vascularized bone graft seems to be a suitable solution, especially if the patient is in a compromised medical status. Otherwise, a vascularized bone transfer is recommended [8,9]. Implant placement for dental rehabilitation has a reasonable success rate of over 90% in VBGs; however, a scapula bone flap seems to be slightly superior to a DCIA flap and fibula bone graft [10,11]. Nevertheless, the bone stock at the lateral border of the
[(Fig._1)TD$IG]
S. Spalthoff et al. / J Stomatol Oral Maxillofac Surg 120 (2019) 116–121
117
[17]. In conclusion, the free scapula bone graft shows some clear advantages compared with other VGBs, but there can be problems with the shape and stock of the available bone, which can make prosthetic-driven dental implant placement difficult. In this pilot study, we attempted to address this problem by pre-augmenting the scapula with a polycaprolactone (PCL) tricalcium phosphate (TCP) scaffold prior to a flap-raising procedure in a sheep model. This should lead to increased bone stock in the position of choice, thus facilitating later implant placement. 2. Material and methods
Fig. 1. The polycaprolactone (PCL)-tricalcium phosphate (TCP) scaffold prior to implantation.
scapula is inferior to those of the iliac crest and fibula, which limits free implant placement [12]. Moreover, there is some variability throughout the course of the lateral border of the scapula, sometimes resulting in thin bone for implant placement [13]. In cadaver studies, there was at least one inadequate dimension for dental implants in 35% of the sections [14]. In addition, there is variance in the size of the lateral border depending on the patient’s sex; female patients more frequently demonstrate inadequate dimensions for implant placement. Therefore, Hirota et al. used vertical distraction osteogenesis to adapt the size of scapula transplants [15]. Other authors tried to compensate for the lack of bone stock by using shorter and smaller implants [16]. Mertens et al. reported in 2016 that about 14% of their patients (two out of 14) who underwent maxillary reconstruction with a free scapular tip graft needed additional bone grafting before implant placement
Ethical approval for this experimental study in sheep was provided by the Department for Veterinary Affairs, Oldenburg, Germany (AZ: 08/1621). Scaffolds (height, 10 mm; diameter, 20 mm; Fig. 1) consisting of a mixture of PCL and TCP (30% PCL and 70% TCP) (Synthes, West Chester, PA, USA) were used to augment the scapula of three healthy adult female German black-headed sheep in a split animal model. The scapula angle was exposed using the same approach described in our previous experiments [18– 20]. The cylinders were placed in a subperiosteal pocket, which was closed afterward with resorbable sutures (Fig. 2a–d). Six months later, all animals were euthanized by deep sedation (intramuscular midazolam 1 mg/kg, intravenous propofol 5 mg/ kg, and intravenous pentobarbital 80 mg/kg). After explantation of the scapulae bilaterally, a cone-beam computed tomography scan was acquired. Then, areas surrounding the implant were removed with a saw and the specimens were fixed in 3.5% neutral-buffered formalin, embedded in methyl methacrylate, and sectioned perpendicular to the axis of the scaffolds using a modified inner-hole diamond saw. Non-decalcified slices with a thickness of 30 mm were surface-stained with alizarin red S-methylene blue for standard light microscopy and histomorphometric analysis. Digital images of each slide were obtained using a Leica DM6 B
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Fig. 2. A. An intraoperative photograph showing the exposed scapula bone. B. An intraoperative photograph showing the subperiosteal pocket. C. An intraoperative photograph showing the scaffold inside the subperiosteal pocket. D. An intraoperative photograph showing wound closure by simple interrupted sutures.
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Fig. 3. A cross-section of the augmented scapula surface stained with alizarin red S-methylene blue [red arrow, polycaprolactone (PCL); black arrow, bone; green arrow, tricalcium phosphate (TCP); and red stars, the original scapula bone].
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microscope equipped with a motorized stage and a Leica DFC7000T digital camera (Leica, Wetzlar, Germany). Images of entire crosssections of the scaffolds were obtained using Leica Las X software and the Mark and Find, Stitching, and Stage Overview modules (Leica). The total bone area and residual PCL-TCP area were quantified using CellSens Dimension V1 image analysis software (Olympus, Hamburg, Germany). Eight sections distributed evenly throughout the scapula were used for histomorphometric evaluations. To measure the degradation of the scaffold material, unused scaffolds were directly embedded in methyl methacrylate, sliced, and stained as described above. After histomorphometric analysis of these slices, the results were compared with those of the experimental group. Statistical analysis was performed using SigmaPlot 13.0 (Mann–Whitney Rank Sum Test, Systat Software, Inc., San Jose, CA, USA). A P-value < 0.05 was considered statistically significant.
3. Results All animals survived the experiment. They showed no sign of infection or prolonged swelling. Shoulder movement was not impaired, and the animals recovered from the operation quickly. The animals could be kept in groups without limiting their movement. When the scapula bone was explanted, the scaffold was firmly attached to the original bone. The former shape of the scaffold could still be identified easily. There was bleeding from the surrounding area and the scaffold showed a bone-like consistency. Microscopically, there was bone formation throughout all constructs (Fig. 3). New bone was mostly found in close relation to the original scapula surface but there was still some bone formation throughout the entire scaffold (Fig. 4). Evaluation of the cone-beam computed tomography scans showed good osseointegration and even some additional bone formation in the surrounding area outside the scaffolds. Radiologically, nearly all scaffolds maintained their original dimensions (Figs. 5 and 6). A significant amount of the PCL (median 32.29%, 25% 28.81, 75% 37.83 of the scaffold area before implantation versus median 13.53%, 25% 10.05, 75% 15.84 of the scaffold area after implantation, P < 0.001) and TCP (median 30.77%, 25% 26.54, 75% 35.27 of the scaffold area before implantation versus median 7.41%, 25% 5.51, 75% 10.95 of the scaffold area after implantation, P < 0.001) was degraded and new bone was observed throughout the whole scaffold (no bone before
Fig. 4. A magnification of Fig. 3 [red arrow, polycaprolactone (PCL); black arrow, bone; green arrow, tricalcium phosphate (TCP); and red stars, the original scapula bone].
implantation versus median 7.79%, 25% 6.25, 75% 9.52 of the scaffold area after implantation, P < 0.001) (Tables 1 and 2).
4. Discussion PCL-TCP was used previously to augment the mandible in minipigs in a guided bone regeneration approach. The material showed good osteoconductive properties but was still inferior compared with autogenous bone grafts with respect to new bone formation. The authors had some problems with intraoral exposure of the graft material and attributed the inferior
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Fig. 6. The contralateral scapula without a scaffold. Fig. 5. A cone-beam computed tomography scan of the augmented scapula.
there should be no problem transplanting the augmented scapula into an intraoral defect, for example, after tumor resection. Connecting the scapula free flap to the local blood supply through microvascular anastomosis will guarantee reperfusion of the whole transplant immediately, allowing the delivery of nutrition and immune defenses, even throughout the grafted area. This should minimize the risk of graft exposure and consequent infection. The fact that the PCL-TCP scaffolds almost maintained their original dimensions should permit precise planning of the desired bone transplant. This should facilitate a prosthetic-driven design for optimal implant placement. Dimensional and mechanical stability are known benefits of PCL-TCP scaffolds. In 2014, Li et al. showed that after 12 months in a spinal fusion experiment in sheep, the autograft-free spinal fusion cage consisting of PCL-TCP
performance of the PCL-TCP graft to concomitant inflammatory reactions [21]. In another clinical study in monkeys, Goh et al. reconstructed facial wall defects after tooth extraction in a singlestep implantation procedure with PCL-TCP scaffolds. Similar to the first experiment mentioned, they also reported problems with graft exposure and found only a very small amount of newly formed bone in the PCL-TCP grafts [22]. Other studies that used a PCL-TCP graft outside the oral cavity showed promising results. In rabbit calvarial defects [23] and rabbit femoral head defects [24], PCL-TCP grafts were incorporated successfully without any sign of exposure. In our study, we attempted to circumvent these obvious limitations of PCL-TCP grafts regarding their direct use in the oral cavity. Pre-augmenting the scapula allows protected incorporation of the scaffolds inside a thick muscle cuff. Following complete integration of the PCL-TCP scaffold into the local blood circulation,
Table 1 Areas of TCP, bone, and PCL reported as percentages of the scaffold area after 6 months of cultivation and a comparison of scaffolds after 6 months of cultivation versus scaffolds pre-implantation (Mann–Whitney rank sum test, P-values < 0.05 show a significant difference). TCP
PCL
Bone
%
Median
25%
75%
P
%
Median
25%
75%
P
%
Median
25%
75%
P
7.10 17.54 9.66 5.98 15.08 10.87 7.72 3.68 2.20 4.84 6.64 6.16 2.63 6.39 5.44 4.03 8.84 8.02 5.53 15.08 6.19 27.37 11.18 9.58
7.41
5.51
10.95
< 0.001
11.94 10.06 16.14 15.09 9.79 15.97 10.29 15.29 10.14 10.19 15.84 15.69 14.27 15.85 15.85 10.03 10.01 17.24 12.78 16.40 10.88 9.89 9.00 15.73
13.53
10.05
15.84
< 0.001
15.27 11.71 7.82 16.11 6.14 9.35 6.51 8.71 6.29 5.36 11.06 9.38 13.63 9.11 7.95 6.14 4.31 8.15 9.93 2.80 7.75 4.60 7.67 6.70
7.79
6.25
9.52
< 0.001
TCP: tricalcium phosphate; PCL: polycaprolactone.
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Table 2 Areas of TCP, bone, and PCL as percentages of the scaffold area pre-implantation. TCP
PCL
Bone
%
Median
25%
75%
%
Median
25%
75%
%
Median
25%
75%
30.77 23.59 22.36 35.19 31.02 29.97 29.49 35.35
30.77
26.54
35.27
27.79 34.76 32.29 29.97 34.41 34.89 38.88 29.83
32.29
28.81
34.83
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00
0.00
0.00
TCP: tricalcium phosphate; PCL: polycaprolactone.
showed the same mechanical strength as a titanium cage filled with autologous bone. Surprisingly, the PCL-TCP cage also showed better bone ingrowth, so they concluded that the PCL-TCP cage is a promising autograft-free fusion cage for clinical application [25]. In a pilot study in dogs, mandibular defects were reconstructed with PCL-TCP scaffolds. The degradation time was evaluated, and after 9 months, 46.9% of the scaffold material remained. The author concluded from further investigation that the entire scaffold would disintegrate soon [26]; therefore, an estimated degradation time of 1 year seems feasible in our opinion. This is crucial for certain procedures, for example, augmentation or reconstruction of midfacial structures, because too rapid degradation of the scaffold material would exceed the bone ingrowth or new bone formation and lead to undesired volume loss in the area of augmentation. There are different technical methods to produce patientspecific scaffolds consisting of PCL-TCP or other combinations of PCL and osteoconductive materials [27–29] allowing any desired modification of the scapula. This should allow implant-driven, backward-planned bone augmentation [30] even in complex cases after tumor resection. This pilot study showed that it possible to modify the shape of the bony scapula by pre-augmentation with PCL-TCP scaffolds. The scaffold material maintained a stable osteoinductive environment allowing bony ingrowth and there seemed to be a transformation of the matrix material to vital bone while maintaining approximately the original dimensions. Whether PCL-TCP is the material of choice in our model remains to be proven in further experiments. It may be possible that different materials or different compositions of PCL and TCP could lead to more bone transformation while maintaining stable scaffold dimensions. However, bony ingrowth and new bone formation distant from the scapula surface in all animals are promising results and could lead to the hypothesis that the experimental model worked quite well. Further experiments are required to prove this assumption and determine if it is possible to reconstruct and augment a large bony defect in the orofacial region using this new method by increasing the shape and stock of the scapula bone without the abovementioned problems of graft exposure, infection, and consequent graft failure. Sources of funding AO Foundation (research Grant F-07-58K). Ethical approval Ethical approval for this experimental study in sheep was provided by the Department for Veterinary Affairs, Oldenburg, Germany (AZ: 08/1621). Disclosure of interest The authors declare that they have no competing interest.
Acknowledgments We gratefully thank DePuy Synthes for providing the PCL-TCP scaffolds for this study.
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