- Email: [email protected]
Bone welding – A histological evaluation in the jaw
ARTICLE IN PRESS Ann Anat 189 (2007) 350—355
www.elsevier.de/aanat
Bone welding – A histological evaluation in the jaw Ronald Maia,, Gu ¨nter Lauera, Eckart Pillinga, Roland Jungc, Henry Leonhardta, Peter Proffb, Bernd Stadlingera, Winnie Pradela, ¨neld, Tomas Gedrangeb Uwe Eckelta, Jochen Fangha a
Department of Oral and Maxillofacial Surgery, Medical Faculty ‘‘Carl Gustav Carus’’, Technische Universitaet Dresden, Fetscherstrasse 74, D-01307 Dresden, Germany b Clinic for Orthodontics and Preventive and Paediatric Dentistry, University of Greifswald Dental School, Rotgerberstrasse 8, D-17487 Greifswald, Germany c Animal Experimental Centre, Medical Faculty ‘‘Carl Gustav Carus’’, Technische Universitaet Dresden, Fetscherstrasse 74, D-01307 Dresden, Germany d Department of Oral Anatomy, University of Greifswald Dental School, Rotgerberstrasse 8, D-17487 Greifswald, Germany Received 21 December 2006; accepted 20 February 2007
KEYWORDS Bone welding; Bone histology; Condylar neck fractures; Mandible; Osteosynthesis
Summary The expansion of biodegradable osteosynthesis systems in clinical application correlates well to the progress in development of new materials as to the improvement of application methods. One of those new application methods is the ultrasound-aided insertion of Resorb-Xs pins. The aim of this study was the histological evaluation of possible thermal damage to bone due to the ultrasound insertion. For this purpose, condylar neck fractures in 12 sheep were produced, repositioned and fixed by Resorb-Xs plates and pins. The animals were sacrificed in two groups, one after 2 weeks and one after 9 weeks. The bone–pin interlinkage and the structure of the bone were histologically evaluated. After 2 weeks a tight bone–polymer interlinkage was seen. Neither a pronounced foreign body reaction nor an interposition of fibrous tissue at the interface or a thermally induced necrosis was observed. The late phase of wound healing after 9 weeks showed pathomorphological characteristics within the normal range of bone healing. The bone seemed to be free of any alteration caused by process engineering. We conclude that thermal stress caused by ultrasound-aided pin insertion does not lead to cellular reaction in the bone. The fast and easy application of this improved biodegradable osteosynthesis system will bring a clear advantage in clinical use. & 2007 Elsevier GmbH. All rights reserved.
Corresponding author. Tel.: +49 (0) 351 458 5205; fax: +49 (0) 351 458 5382.
E-mail address: [email protected] (R. Mai). 0940-9602/$ - see front matter & 2007 Elsevier GmbH. All rights reserved. doi:10.1016/j.aanat.2007.02.023
ARTICLE IN PRESS Bone welding – A histological evaluation in the jaw
351
Introduction Biodegradable osteosynthesis materials are not estimated being toxic for the surrounding tissue. In recent times, these biodegradable osteosynthesis systems have been used increasingly frequent in traumatology as well as in plastic and reconstructive surgery. The expansion of these materials in clinical application correlates well to the progress in development of new materials as well as to the improvement of application methods. The application of biodegradable screws is limited by various factors. As there is low mechanical stability of the material, difficult handling and the time-consuming fixation of screws. The need of cutting threads is a time-consuming factor and limits easy handling especially for smaller screw diameters. Furthermore, the insertion of conventional biodegradable osteosynthsis systems is limited by shear forces between screws and plate due to non-axial, angular drill holes (Ricalde et al., 2005; Neff et al., 2004). Another limitation for the use of biodegradable screws is the difficult relation between screw axis, osteosynthesis plate and the drill hole in the bone. The general suitability of poly-L-lactide/polyglycolide (PLLA-PGA) copolymers as a biodegradable osteosynthesis material with regards to resorption and biocompatibility has been shown (Becker et al., 1999). Aim of the development of an ultrasoundaided pin fixation was the creation of a new method of interlinkage between osteosynthesis plate and bone. So the mentioned limitations in application could be avoided. A specially designed pin is inserted in the drill hole with the aid of ultrasound. The pin surface is fixed by a melting (welding) process into the trabecular bone structure. At the same time, the pin and the osteosynthesis plate are welded together (Fig. 1). Due to this welding, the pins can be applied even in cases of difference in axis between the pin, the osteosynthesis plate and the drill hole. Critical torque forces on screw heads can be avoided. Furthermore, there is no more need for threads. These advantages lead to improved handling and shorten osteosynthesis operations (Eckelt et al., 2005). The aim of this study was the histological evaluation of the newly developed ultrasoundaided pin osteosynthesis system for the therapy of condylar neck fractures. Because of the rise in temperature while inserting the pins, a potential thermal impairment of the bone should be evaluated. Focus of interest was the cellular reaction caused by a possible thermally induced initial inflammation.
Figure 1. Welded pin in bone (Resorb X).
Material and methods By authority of the Regional Commission Dresden in Saxonia-Germany (animal experiment application AZ 24-9168.11-1-2003-10) the in vivo tests were performed under strict compliance with the high standards of ethics in animal experiments. Operations were performed on 12 sheep. For initial sedation, each sheep was given Dormicum& (midazolam) at a dose rate of 1 mg/kg body weight via an i.v. canula. Anaesthesia was induced by the application of the anaesthetic agent propofol. Immediately afterwards a tracheal tube was placed and anaesthesia was maintained using a volumecontrolled inhalation of isofluran and nitrous oxide. The depth of anaesthesia was often reduced by a supplementary i.v. application of the analgesic agent fentanyl. To assure a post-operative pain prophylaxis, the animals were given buprenorphine during the operation. The left mandibular ramus was dissected via a cutaneous and sub-cutaneous approach (periangular approach) from the posterior edge of the ramus. The facial nerve was prevented from damage. Deep collum fractures were produced by subperiosteal preparation and osteotomy with an oscillating saw (Fig. 2). After dislocation of the fractures they were re-positioned and fixed by a combination of resorbable miniplates and ultrasound inserted pins (Resorb-X-System: 2.3 mm pin and four hole plates). Osteosynthesis was performed with two plates. The anterior and posterior plates were fixed on the lateral face of the condylar neck with four pins per plate (Fig. 3). One titanium miniscrew was placed at each end of a plate for histological analysis and radiological detection of the resorbable plates. After performing osteosynthesis in the above-mentioned pattern a multilayer wound closure was done with resorbable sutures.
ARTICLE IN PRESS 352
R. Mai et al. dependent overdose of T61& (embutramide, mebezonium iodide, tetracaine) was used. The sequentional sacrifice allowed the dynamic evaluation of inflammation and resorption. Intervals 2 weeks (six animals) 9 weeks (six animals)
Figure 2. Deep column fractures were produced by subperiosteal preparation and osteotomy with an oscillating saw.
Focus of interest Inflammation, early healing, bulging of pins Bone degradation, resorption, late healing
After radiological detection of the titanium screws the test area was resected en bloc with a 1 cm safety margin. A second macroscopic reduction was performed using a micro band saw sectioning system (Exakt&, Walter–Messner, Oststeinbek, Germany). This allowed for preparation of the samples for histological embedding. The samples were fixed in 70% ethanol for 3 days. A tissue-embedding unit TP120 (Leica, Bensheim, Germany) prepared the samples under constant motion and vacuum conditions in the following order: 70% ethanol 80% ethanol 3 96% ethanol 3 100% ethanol
48 h, 48 h, 3 48 h, 3 48 h.
Finishing this process, the Exakt& Infiltration Unit HS501 (Walter-Messner, Oststeinbek, Germany) enabled a sequential infiltration with Technovit& 7200 VLC (Heraeus Kulzer, Wehrheim, Germany). The infiltration was accomplished without xylene treatment to assure the chemical integrity of the polymer. After the two stage polymerisation: 1. low light intensity+polymerisation temperature o40 1C for 4 h, 2. ultraviolet light for 8 h,
Figure 3. Test area, osteosynthesis. Anterior and a posterior plate (Resorb X) were fixed at the lateral face the condylar neck with four pins per each plate.
The animals were sacrificed in groups of six animals at defined times of interest. For this purpose, an i.v. application of a body weight
a guided dissection longitudinal to the pin axis was performed using a diamond precession saw (Exakt&). Consecutively, the prepared sections were reduced to 30 mm in thickness and polished using a roll grinder containing sandpaper (Exakt&). The sections were deacrylated on the surface using an acetone and ethanol (100%) mixture. A Masson–Goldner staining was performed afterwards. The sections were imaged and analysed using light microscopy (Olympus BX 61, Hamburg, Germany). With the support of a Merzha ¨user&scanning table, the full texture of the section could be evaluated using the multiple alignment technique.
ARTICLE IN PRESS Bone welding – A histological evaluation in the jaw
Figure 4. Polymer–bone tissue interlinkage of a inserted pin. Masson–Goldner trichrome staining (Original magnification 20 ).
353
Figure 5. Early phase of wound healing (2 weeks). Normal range of adequate bone healing without signs of inflammation. Masson–Goldner trichrome staining (Original magnification 40 ).
Results Early phase of wound healing (2 weeks) After ultrasound-aided insertion of the pins, melted polymer penetrated into neighbouring spongious bone structures. The core of the pin kept its integrity and filled the drill hole with the exception of the deepest part of the hole. This forms a tight polymer–bone tissue interlinkage. An apparent osteoid formation can be detected at the bone–polymer interface, representing a normally structured extracellular matrix. Therefore the primary osteoneogenesis was initiated from the adjoining bone bed. Infiltration of polymorph–core neutrophilic granulocytes, lymphocytes and plasma cells representing the two stages of inflammation could not be observed around the drill holes. These cells were only occasionally found around the pin head. Then they are integrated into a thin layer of fibroblasts and fibrocytes. This is a typical sign of a soft tissue reaction. Multinuclear giant cells from the monocyte macrophage cell line were occasionally situated at the polymer–bone interface. Neither a pronounced foreign body reaction nor an interposition of fibrous tissue at the interface was observed (Fig. 4). Fibrous tissue would be a demarcation between the polymer and bone induced by an adverse tissue reaction. Apart from the drill hole, the texture of the bone bed remained unchanged. Alterations in structure caused by ultrasound-dependent triggers were not observed. There were no signs of bone necrosis visible. In contrast to necrosis the pins were bordered by vital, active layers of osteoblasts at
the interface. No sign of thermally induced damage to the tissue was found. The investigated pathomorphological characteristics were within the normal range of adequate bone healing (Fig. 5). Formation of extracellular matrix was observable at the interface. No initial signs of polymer resorption were detectable.
Late phase of wound healing (9 weeks) In the histological analysis, mainly cells with resorptive functions were found at the interface. Multinuclear phagocytic cells with resorption lacunas at the polymer surface are signs of initial resorption. At the same time, the synthesis rate of osteoid declines, as the pin surface is covered by vital woven bone. No micro abscess formations or foreign body granulomas were found. An encapsulation of the polymer with demarcating granulation tissue was not visible. The pin structure showed no signs of fragmentation. Polarisation microscopy did not show any micro ruptures. Pronounced cement lines could be observed in the bone bed. They represented the active synthesis capability of vital osteoblasts. Woven bone was transformed to mature lamellar bone in a process of transformation free of any pathological infiltration or vascular malformation. Focal osteolysis representing a late osseous foreign body reaction with signs of bone resorption and degradation were not observable in any area of the bone bed. As in the early phase of this study the late phase of healing also seemed to be free of any alteration caused by process engineering (Fig. 6).
ARTICLE IN PRESS 354
R. Mai et al. found no clinically relevant inflammation in the soft tissues around different biodegradable polylactide implants (Prokop et al., 2004). Further advantages of the method are the easy intraoperative handling and the reduction in operating time due to the fact that thread cutting is no longer required. This was emphasised in a paper by Eckelt et al. (2005). Stability is made possible by a sufficient interlinkage of the polymer with the trabecular structures. These characteristics should be analysed in a further study.
Conclusion Figure 6. Late phase of wound healing (9 weeks). New formation of bon around the polymer. Signs of polymer resorption. Masson–Goldner trichrome staining (Original magnification 20 ).
Discussion The biomechanics of the human skull with its numerous connections and dependencies is complex (Fanghanel et al., 2006; Gundlach, 1999; Sellers and Crompton, 2004). Therefore special requirements for osteosynthesis are necessary. Resorbable miniplate systems are a well-established technique in osteosynthesis in craniomaxillofacial surgery (Becker et al., 1999; Landes et al., 2003; Eppley et al., 2004). The new Bone Welding technology offers an increased primary stability and a stronger fixation of the fracture fragments. The mechanical stability is equivalent to those obtained by a comparably sized metallic fixation screw (Ferguson et al., 2005). The application of this new technique raised the question of tissue reaction to thermal exposure. Based on this analysis, we found that thermal stress caused by ultrasoundaided pin insertion does not lead to a cellular reaction in the peri-pin area. There is neither clinical nor histological evidence of an initial inflammation induced by the ultrasound insertion. Important preconditions for the introduction of this improved method of biodegradable osteosynthesis into clinical practice are the tight attachment of fibrous tissue to the pin head, the absence of any inflammation in the bone and the very stable character of the interlinkage between pin, plate and bone. The stability of this interlinkage was already investigated and the startling results were published in different papers (Eckelt et al., 2005; Ferguson et al., 2005). The observed absence of inflammation in the pin surrounding bone area clearly confirms the results of Prokop, who had
Based on this analysis, we conclude that thermal stress caused by ultrasound-aided pin insertion does not lead to a cellular reaction in the peri-pin area. There is neither clinical nor histological evidence of an initial inflammation induced by the ultrasound insertion.
References Becker, H.J., Wiltfang, J., Merten, H.A., Luhr, H.G., 1999. Biodegradable miniplates (lactosorb) in cranioosteoplasty – experimental results with the rapidly maturing, juvenile minipig. Mund Kiefer Gesichtschir. 3, 275–278. Eckelt, U., Pilling, E., Stelnicki, E., 2005. A new resorbable fixation technique in craniofacial surgery. Int. J. Oral Maxillofac. Surg. 34, 84. Eppley, B.L., Morales, L., Wood, R., Pensler, J., Goldstein, J., Havlik, R.J., Habal, M., Losken, A., Williams, J.K., Burstein, F., Rozzelle, A.A., Sadove, A.M., 2004. Resorbable PLLA-PGA plate and screw fixation in pediatric craniofacial surgery: clinical experience in 1883 patients. Plast. Reconstr. Surg. 114, 850–856. Fanghanel, J., Gedrange, T., Proff, P., 2006. The facephysiognomic expressiveness and human identity. Ann. Anat. 188, 261–266. Ferguson, S.J., Weber, U., von Rechenberg, B., Mayer, J., 2005. Enhancing the mechanical integrity of the implant–bone interface with BoneWelding(R) technology: determination of quasi-static interfacial strength and fatigue resistance. J. Biomed. Mater. Res. B Appl. Biomater. October. 6, 124–129. Gundlach, K.K., 1999. Malformations of the temporo– mandibular joint in laboratory animals and in man. Ann. Anat. 181, 73–75. Landes, C.A., Kriener, S., Menzer, M., Kovacs, A.F., 2003. Resorbable plate osteosynthesis of dislocated or patological mandibular fractures: a prospective clinical trial of two amorphous L-DL-lactide copolymer 2-mm miniplate systems. Plast. Reconstr. Surg. 111, 601–610. Neff, A., Muhlberger, G., Karoglan, M., Kolk, A., Mittelmeier, W., Scheruhn, D., Horch, H.H., Kock, S.,
ARTICLE IN PRESS Bone welding – A histological evaluation in the jaw
355
Schieferstein, H., 2004. Stability of osteosyntheses for condylar head fractures in the clinic and biomechanical simulation. Mund Kiefer Gesichtschir. 8, 63–74. Ricalde, P., Engroff, S.L., von Fraunhofer, J.A., Posnick, J.C., 2005. Strength analysis of titanium and resorbable internal fixation in a mandibulotomy model. J. Oral Maxillofac. Surg. 63, 1180–1183.
Prokop, A., Jubel, A., Helling, H.J., Eibach, T., Peters, C., Baldus, S.E., Rehm, K.E., 2004. Soft tissue reactions of different biodegradable polylactide implants. Biomaterials 25, 259–267. Sellers, W.I., Crompton, R.H., 2004. Using sensitivity analysis to validate the predictions of a biomechanical model of bite forces. Ann. Anat. 186, 89–95.
www.elsevier.de/aanat
Bone welding – A histological evaluation in the jaw Ronald Maia,, Gu ¨nter Lauera, Eckart Pillinga, Roland Jungc, Henry Leonhardta, Peter Proffb, Bernd Stadlingera, Winnie Pradela, ¨neld, Tomas Gedrangeb Uwe Eckelta, Jochen Fangha a
Department of Oral and Maxillofacial Surgery, Medical Faculty ‘‘Carl Gustav Carus’’, Technische Universitaet Dresden, Fetscherstrasse 74, D-01307 Dresden, Germany b Clinic for Orthodontics and Preventive and Paediatric Dentistry, University of Greifswald Dental School, Rotgerberstrasse 8, D-17487 Greifswald, Germany c Animal Experimental Centre, Medical Faculty ‘‘Carl Gustav Carus’’, Technische Universitaet Dresden, Fetscherstrasse 74, D-01307 Dresden, Germany d Department of Oral Anatomy, University of Greifswald Dental School, Rotgerberstrasse 8, D-17487 Greifswald, Germany Received 21 December 2006; accepted 20 February 2007
KEYWORDS Bone welding; Bone histology; Condylar neck fractures; Mandible; Osteosynthesis
Summary The expansion of biodegradable osteosynthesis systems in clinical application correlates well to the progress in development of new materials as to the improvement of application methods. One of those new application methods is the ultrasound-aided insertion of Resorb-Xs pins. The aim of this study was the histological evaluation of possible thermal damage to bone due to the ultrasound insertion. For this purpose, condylar neck fractures in 12 sheep were produced, repositioned and fixed by Resorb-Xs plates and pins. The animals were sacrificed in two groups, one after 2 weeks and one after 9 weeks. The bone–pin interlinkage and the structure of the bone were histologically evaluated. After 2 weeks a tight bone–polymer interlinkage was seen. Neither a pronounced foreign body reaction nor an interposition of fibrous tissue at the interface or a thermally induced necrosis was observed. The late phase of wound healing after 9 weeks showed pathomorphological characteristics within the normal range of bone healing. The bone seemed to be free of any alteration caused by process engineering. We conclude that thermal stress caused by ultrasound-aided pin insertion does not lead to cellular reaction in the bone. The fast and easy application of this improved biodegradable osteosynthesis system will bring a clear advantage in clinical use. & 2007 Elsevier GmbH. All rights reserved.
Corresponding author. Tel.: +49 (0) 351 458 5205; fax: +49 (0) 351 458 5382.
E-mail address: [email protected] (R. Mai). 0940-9602/$ - see front matter & 2007 Elsevier GmbH. All rights reserved. doi:10.1016/j.aanat.2007.02.023
ARTICLE IN PRESS Bone welding – A histological evaluation in the jaw
351
Introduction Biodegradable osteosynthesis materials are not estimated being toxic for the surrounding tissue. In recent times, these biodegradable osteosynthesis systems have been used increasingly frequent in traumatology as well as in plastic and reconstructive surgery. The expansion of these materials in clinical application correlates well to the progress in development of new materials as well as to the improvement of application methods. The application of biodegradable screws is limited by various factors. As there is low mechanical stability of the material, difficult handling and the time-consuming fixation of screws. The need of cutting threads is a time-consuming factor and limits easy handling especially for smaller screw diameters. Furthermore, the insertion of conventional biodegradable osteosynthsis systems is limited by shear forces between screws and plate due to non-axial, angular drill holes (Ricalde et al., 2005; Neff et al., 2004). Another limitation for the use of biodegradable screws is the difficult relation between screw axis, osteosynthesis plate and the drill hole in the bone. The general suitability of poly-L-lactide/polyglycolide (PLLA-PGA) copolymers as a biodegradable osteosynthesis material with regards to resorption and biocompatibility has been shown (Becker et al., 1999). Aim of the development of an ultrasoundaided pin fixation was the creation of a new method of interlinkage between osteosynthesis plate and bone. So the mentioned limitations in application could be avoided. A specially designed pin is inserted in the drill hole with the aid of ultrasound. The pin surface is fixed by a melting (welding) process into the trabecular bone structure. At the same time, the pin and the osteosynthesis plate are welded together (Fig. 1). Due to this welding, the pins can be applied even in cases of difference in axis between the pin, the osteosynthesis plate and the drill hole. Critical torque forces on screw heads can be avoided. Furthermore, there is no more need for threads. These advantages lead to improved handling and shorten osteosynthesis operations (Eckelt et al., 2005). The aim of this study was the histological evaluation of the newly developed ultrasoundaided pin osteosynthesis system for the therapy of condylar neck fractures. Because of the rise in temperature while inserting the pins, a potential thermal impairment of the bone should be evaluated. Focus of interest was the cellular reaction caused by a possible thermally induced initial inflammation.
Figure 1. Welded pin in bone (Resorb X).
Material and methods By authority of the Regional Commission Dresden in Saxonia-Germany (animal experiment application AZ 24-9168.11-1-2003-10) the in vivo tests were performed under strict compliance with the high standards of ethics in animal experiments. Operations were performed on 12 sheep. For initial sedation, each sheep was given Dormicum& (midazolam) at a dose rate of 1 mg/kg body weight via an i.v. canula. Anaesthesia was induced by the application of the anaesthetic agent propofol. Immediately afterwards a tracheal tube was placed and anaesthesia was maintained using a volumecontrolled inhalation of isofluran and nitrous oxide. The depth of anaesthesia was often reduced by a supplementary i.v. application of the analgesic agent fentanyl. To assure a post-operative pain prophylaxis, the animals were given buprenorphine during the operation. The left mandibular ramus was dissected via a cutaneous and sub-cutaneous approach (periangular approach) from the posterior edge of the ramus. The facial nerve was prevented from damage. Deep collum fractures were produced by subperiosteal preparation and osteotomy with an oscillating saw (Fig. 2). After dislocation of the fractures they were re-positioned and fixed by a combination of resorbable miniplates and ultrasound inserted pins (Resorb-X-System: 2.3 mm pin and four hole plates). Osteosynthesis was performed with two plates. The anterior and posterior plates were fixed on the lateral face of the condylar neck with four pins per plate (Fig. 3). One titanium miniscrew was placed at each end of a plate for histological analysis and radiological detection of the resorbable plates. After performing osteosynthesis in the above-mentioned pattern a multilayer wound closure was done with resorbable sutures.
ARTICLE IN PRESS 352
R. Mai et al. dependent overdose of T61& (embutramide, mebezonium iodide, tetracaine) was used. The sequentional sacrifice allowed the dynamic evaluation of inflammation and resorption. Intervals 2 weeks (six animals) 9 weeks (six animals)
Figure 2. Deep column fractures were produced by subperiosteal preparation and osteotomy with an oscillating saw.
Focus of interest Inflammation, early healing, bulging of pins Bone degradation, resorption, late healing
After radiological detection of the titanium screws the test area was resected en bloc with a 1 cm safety margin. A second macroscopic reduction was performed using a micro band saw sectioning system (Exakt&, Walter–Messner, Oststeinbek, Germany). This allowed for preparation of the samples for histological embedding. The samples were fixed in 70% ethanol for 3 days. A tissue-embedding unit TP120 (Leica, Bensheim, Germany) prepared the samples under constant motion and vacuum conditions in the following order: 70% ethanol 80% ethanol 3 96% ethanol 3 100% ethanol
48 h, 48 h, 3 48 h, 3 48 h.
Finishing this process, the Exakt& Infiltration Unit HS501 (Walter-Messner, Oststeinbek, Germany) enabled a sequential infiltration with Technovit& 7200 VLC (Heraeus Kulzer, Wehrheim, Germany). The infiltration was accomplished without xylene treatment to assure the chemical integrity of the polymer. After the two stage polymerisation: 1. low light intensity+polymerisation temperature o40 1C for 4 h, 2. ultraviolet light for 8 h,
Figure 3. Test area, osteosynthesis. Anterior and a posterior plate (Resorb X) were fixed at the lateral face the condylar neck with four pins per each plate.
The animals were sacrificed in groups of six animals at defined times of interest. For this purpose, an i.v. application of a body weight
a guided dissection longitudinal to the pin axis was performed using a diamond precession saw (Exakt&). Consecutively, the prepared sections were reduced to 30 mm in thickness and polished using a roll grinder containing sandpaper (Exakt&). The sections were deacrylated on the surface using an acetone and ethanol (100%) mixture. A Masson–Goldner staining was performed afterwards. The sections were imaged and analysed using light microscopy (Olympus BX 61, Hamburg, Germany). With the support of a Merzha ¨user&scanning table, the full texture of the section could be evaluated using the multiple alignment technique.
ARTICLE IN PRESS Bone welding – A histological evaluation in the jaw
Figure 4. Polymer–bone tissue interlinkage of a inserted pin. Masson–Goldner trichrome staining (Original magnification 20 ).
353
Figure 5. Early phase of wound healing (2 weeks). Normal range of adequate bone healing without signs of inflammation. Masson–Goldner trichrome staining (Original magnification 40 ).
Results Early phase of wound healing (2 weeks) After ultrasound-aided insertion of the pins, melted polymer penetrated into neighbouring spongious bone structures. The core of the pin kept its integrity and filled the drill hole with the exception of the deepest part of the hole. This forms a tight polymer–bone tissue interlinkage. An apparent osteoid formation can be detected at the bone–polymer interface, representing a normally structured extracellular matrix. Therefore the primary osteoneogenesis was initiated from the adjoining bone bed. Infiltration of polymorph–core neutrophilic granulocytes, lymphocytes and plasma cells representing the two stages of inflammation could not be observed around the drill holes. These cells were only occasionally found around the pin head. Then they are integrated into a thin layer of fibroblasts and fibrocytes. This is a typical sign of a soft tissue reaction. Multinuclear giant cells from the monocyte macrophage cell line were occasionally situated at the polymer–bone interface. Neither a pronounced foreign body reaction nor an interposition of fibrous tissue at the interface was observed (Fig. 4). Fibrous tissue would be a demarcation between the polymer and bone induced by an adverse tissue reaction. Apart from the drill hole, the texture of the bone bed remained unchanged. Alterations in structure caused by ultrasound-dependent triggers were not observed. There were no signs of bone necrosis visible. In contrast to necrosis the pins were bordered by vital, active layers of osteoblasts at
the interface. No sign of thermally induced damage to the tissue was found. The investigated pathomorphological characteristics were within the normal range of adequate bone healing (Fig. 5). Formation of extracellular matrix was observable at the interface. No initial signs of polymer resorption were detectable.
Late phase of wound healing (9 weeks) In the histological analysis, mainly cells with resorptive functions were found at the interface. Multinuclear phagocytic cells with resorption lacunas at the polymer surface are signs of initial resorption. At the same time, the synthesis rate of osteoid declines, as the pin surface is covered by vital woven bone. No micro abscess formations or foreign body granulomas were found. An encapsulation of the polymer with demarcating granulation tissue was not visible. The pin structure showed no signs of fragmentation. Polarisation microscopy did not show any micro ruptures. Pronounced cement lines could be observed in the bone bed. They represented the active synthesis capability of vital osteoblasts. Woven bone was transformed to mature lamellar bone in a process of transformation free of any pathological infiltration or vascular malformation. Focal osteolysis representing a late osseous foreign body reaction with signs of bone resorption and degradation were not observable in any area of the bone bed. As in the early phase of this study the late phase of healing also seemed to be free of any alteration caused by process engineering (Fig. 6).
ARTICLE IN PRESS 354
R. Mai et al. found no clinically relevant inflammation in the soft tissues around different biodegradable polylactide implants (Prokop et al., 2004). Further advantages of the method are the easy intraoperative handling and the reduction in operating time due to the fact that thread cutting is no longer required. This was emphasised in a paper by Eckelt et al. (2005). Stability is made possible by a sufficient interlinkage of the polymer with the trabecular structures. These characteristics should be analysed in a further study.
Conclusion Figure 6. Late phase of wound healing (9 weeks). New formation of bon around the polymer. Signs of polymer resorption. Masson–Goldner trichrome staining (Original magnification 20 ).
Discussion The biomechanics of the human skull with its numerous connections and dependencies is complex (Fanghanel et al., 2006; Gundlach, 1999; Sellers and Crompton, 2004). Therefore special requirements for osteosynthesis are necessary. Resorbable miniplate systems are a well-established technique in osteosynthesis in craniomaxillofacial surgery (Becker et al., 1999; Landes et al., 2003; Eppley et al., 2004). The new Bone Welding technology offers an increased primary stability and a stronger fixation of the fracture fragments. The mechanical stability is equivalent to those obtained by a comparably sized metallic fixation screw (Ferguson et al., 2005). The application of this new technique raised the question of tissue reaction to thermal exposure. Based on this analysis, we found that thermal stress caused by ultrasoundaided pin insertion does not lead to a cellular reaction in the peri-pin area. There is neither clinical nor histological evidence of an initial inflammation induced by the ultrasound insertion. Important preconditions for the introduction of this improved method of biodegradable osteosynthesis into clinical practice are the tight attachment of fibrous tissue to the pin head, the absence of any inflammation in the bone and the very stable character of the interlinkage between pin, plate and bone. The stability of this interlinkage was already investigated and the startling results were published in different papers (Eckelt et al., 2005; Ferguson et al., 2005). The observed absence of inflammation in the pin surrounding bone area clearly confirms the results of Prokop, who had
Based on this analysis, we conclude that thermal stress caused by ultrasound-aided pin insertion does not lead to a cellular reaction in the peri-pin area. There is neither clinical nor histological evidence of an initial inflammation induced by the ultrasound insertion.
References Becker, H.J., Wiltfang, J., Merten, H.A., Luhr, H.G., 1999. Biodegradable miniplates (lactosorb) in cranioosteoplasty – experimental results with the rapidly maturing, juvenile minipig. Mund Kiefer Gesichtschir. 3, 275–278. Eckelt, U., Pilling, E., Stelnicki, E., 2005. A new resorbable fixation technique in craniofacial surgery. Int. J. Oral Maxillofac. Surg. 34, 84. Eppley, B.L., Morales, L., Wood, R., Pensler, J., Goldstein, J., Havlik, R.J., Habal, M., Losken, A., Williams, J.K., Burstein, F., Rozzelle, A.A., Sadove, A.M., 2004. Resorbable PLLA-PGA plate and screw fixation in pediatric craniofacial surgery: clinical experience in 1883 patients. Plast. Reconstr. Surg. 114, 850–856. Fanghanel, J., Gedrange, T., Proff, P., 2006. The facephysiognomic expressiveness and human identity. Ann. Anat. 188, 261–266. Ferguson, S.J., Weber, U., von Rechenberg, B., Mayer, J., 2005. Enhancing the mechanical integrity of the implant–bone interface with BoneWelding(R) technology: determination of quasi-static interfacial strength and fatigue resistance. J. Biomed. Mater. Res. B Appl. Biomater. October. 6, 124–129. Gundlach, K.K., 1999. Malformations of the temporo– mandibular joint in laboratory animals and in man. Ann. Anat. 181, 73–75. Landes, C.A., Kriener, S., Menzer, M., Kovacs, A.F., 2003. Resorbable plate osteosynthesis of dislocated or patological mandibular fractures: a prospective clinical trial of two amorphous L-DL-lactide copolymer 2-mm miniplate systems. Plast. Reconstr. Surg. 111, 601–610. Neff, A., Muhlberger, G., Karoglan, M., Kolk, A., Mittelmeier, W., Scheruhn, D., Horch, H.H., Kock, S.,
ARTICLE IN PRESS Bone welding – A histological evaluation in the jaw
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Schieferstein, H., 2004. Stability of osteosyntheses for condylar head fractures in the clinic and biomechanical simulation. Mund Kiefer Gesichtschir. 8, 63–74. Ricalde, P., Engroff, S.L., von Fraunhofer, J.A., Posnick, J.C., 2005. Strength analysis of titanium and resorbable internal fixation in a mandibulotomy model. J. Oral Maxillofac. Surg. 63, 1180–1183.
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