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Treatment of fractures of the condylar head with resorbable pins or titanium screws: an experimental study
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British Journal of Oral and Maxillofacial Surgery 51 (2013) 421–427
Treatment of fractures of the condylar head with resorbable pins or titanium screws: an experimental study Matthias Schneider a,∗ , Richard Loukota b , Anne Kuchta a , Bernd Stadlinger c , Roland Jung d , Katrin Speckl d , Robert Schmiedekampf a , Uwe Eckelt a a
Department of Oral and Maxillofacial Surgery, University Hospital Carl Gustav Carus, Technical University Dresden, Germany Department of Oral and Maxillofacial Surgery, Leeds Teaching Hospitals NHS Trust, Leeds, UK c Clinic of Cranio-Maxillofacial and Oral Surgery, University of Zurich, Switzerland d Experimental Centre, Medical Faculty, Technical University Dresden, Germany b
Accepted 27 July 2012 Available online 17 August 2012
Abstract We aimed to compare in vivo the stability of fixation of condylar fractures in sheep using sonic bone welding and standard titanium screws. We assessed stability of the osteosynthesis and maintenance of the height of the mandibular ramus. Height decreased slightly in both groups compared with the opposite side. The volume of the condyle increased considerably in both groups mainly because callus had formed. The results showed no significant disadvantages for pin fixation compared with osteosynthesis using titanium screws. © 2012 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Keywords: Trauma; Condylar fracture; Resorbable material; Sheep; Titanium screw
Introduction Surgical treatment and osteosynthesis of fractures of the condylar head are technical challenges. As the typical fracture line runs from inside to outside the joint they are described as diacapitular rather than intracapsular fractures. Limiting factors for operation are difficulties exposing the fracture, repositioning, and osteosynthesis, but a randomised multicentre study showed that patients benefit from surgical treatment.1,2 Several studies3–5 have shown that anatomically accurate reconstruction of the surface of the joint is the best indicator of long term function. Osteosynthesis with miniscrews6,7 has been established in the treatment of
∗ Corresponding author at: Department of Oral and Maxillofacial Surgery, University Hospital Carl Gustav Carus, Technical University Dresden, Fetscherstr. 74, 01307 Dresden, Germany. Tel.: +49 351 4583382; fax: +49 351 4585382. E-mail addresses: [email protected], [email protected] (M. Schneider).
diacapitular fractures, but without intraoperative radiography,8 screws can be malpositioned with medial, ventral, or cranial perforation of the condyle being visible only on postoperative radiographs. Use of SonicWeld® resorbable pins (KLS Martin, Jacksonville, USA) can avoid the condyle being perforated by screws,9 and this method of osteosynthesis has already been established in the treatment of midfacial fractures and in craniofacial surgery.10–13 In our study it is of particular interest that the SonicWeld® pins can be anchored efficiently in the cortex of the bone and also in cancellous bone because they melt; this does not occur with titanium screws. Extensive studies to test the stability of pin osteosynthesis14 and to evaluate the optimal configuration for drill holes have already been done.9 Resorbable pins have been used in the treatment of diacapitular fractures of the condyle and also for fractures of other joints.15 However, 1.3 mm diameter and 40 mm long poly p-dioxanone (PDA) pins (Ethipins® , Ethicon) as applied by Rasse4 were resistant only to shear forces.
0266-4356/$ – see front matter © 2012 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bjoms.2012.07.015
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M. Schneider et al. / British Journal of Oral and Maxillofacial Surgery 51 (2013) 421–427
Macroscopic, histological, and radiological evaluation at the end of the trial period enabled us to evaluate the long-term stability of the fractures, the behaviour of the resorbable pins, and the dynamics of fracture healing. We acknowledge that sheep have a more ruminant diet than humans, but this may be an advantage as the increased number of chewing cycles subject the osteosynthesis to more extreme stress than may be seen in human patients.
miniscrews) in diameter was drilled from the lateral pole of the condyle perpendicular to the surface of the fracture. The optimal configuration of holes in terms of a step drill 1.6 or 2.1 mm in diameter had previously been decided in vitro using analogous synthetic bone.9 After the first pin or screw had been inserted another hole of the same size was drilled and an additional pin or screw inserted (Fig. 2). Stability was tested by moving the mandible before the wound was closed in layers using resorbable polyglactin 910 (Vicryl® ). Intravital polyfluorochrome sequence labelling
Materials and methods A study in large animals was necessary because of the size of the osteosynthesis pins, and the anatomical configuration of the mandibular condyle in sheep is similar to that in humans. We used 20 adult sheep aged between 2 and 4 years and between 63 and 88 kg in weight. The Commission for Animal Studies at the district government office Dresden, Germany gave approval for the study. The study was done in the experimental centre of the medical faculty of the Technical University, Dresden. Animals were randomly assigned to 2 groups: 10 sheep were treated using resorbable pins and 10 were treated using titanium screws. After operation they were kept outside on a farm and fed a species-appropriate diet. A unilateral fracture through the condyle was created in every animal. To allow mastication and to impair the animal as little as possible, the temporomandibular joint (TMJ) of the contralateral side was not affected. After fracture, osteosynthesis was done using 2–3 resorbable SonicWeld® pins (2.1 × 17 and 2.1 × 11 mm in diameter) in 10 animals. The other 10 served as a control group and had fractures treated using 2–3 conventional mini titanium screws (2.0 × 17 and 2.0 × 11 mm in diameter). The postoperative examination period was 3 months. To enable bony healing to be analysed we used intravital polyfluorochrome sequence labelling. It was not possible to protect the operated joint or feed a specialised diet. After the sheep were killed, the mandibles were resected including the TMJ, and 40 specimens were obtained for macroscopic analysis and radiological three-dimensional evaluation. Operation The articular capsule was exposed and opened using a preauricular approach (Fig. 1) under general anaesthesia. The fragments of the articular capsule were marked by resorbable sutures to enable them to be repositioned correctly, and the fracture line was marked by a narrow Lindemann burr in a position as close as possible to comparable human fractures (diagonally downwards from the lateral condyle to the medial condylar base). The osteotomy was completed by a narrow osteotome (Fig. 2). The fragment was stabilised with a special repositioning pin16 then a hole 1.6 mm or 2.1 mm (or 1.5 mm for
The following fluorochromes were injected intramuscularly: doxycycline 30 mg/kg at 2 weeks; alizarin 30 mg/kg at 4 weeks; calcein green 20 mg/kg at 6 weeks; and xylenol 90 mg/kg at 8 weeks. Macroscopic evaluation Initially, the preparations were examined macroscopically and fixed in Schaffer’s solution after all the tissue had been removed. The TMJ of the unoperated side was also resected for radiological and macroscopic comparison. The position and the possible deformation of the mandibular condyle, the width of the fracture gap, the height of the ascending ramus, remaining pin material, and formation of callus, were assessed. This qualitative observation was done in direct comparison with the condyle on the other side. Radiological three-dimensional measurement Three-dimensional stability was quantitatively evaluated using computer-assisted analysis of computed tomograms (CT). Axial layer CT was used to examine all the condyles in pairs (operated and unoperated side). Data were saved in DICOM format and transferred to a BrainLAB® (Brainlab AG, Munich, Germany) workstation using iPlan® cranial 2.6 software. For this purpose the mandibular fragments were initially automatically segmented. The condylar heads of both sides were then segmented and the volume measured (Fig. 3) to quantify the amount of callus that had formed and the increase in volume of the condylar head. An important aim of the surgical treatment of condylar fractures is to maintain or re-establish vertical height. A consistent height of the joint is important for undisturbed articulation of both TMJ; shortening of 1 mandibular condyle leads to dysfunction because of the interdependent movements of both joints. Another effect is the structural change, which can also occur in the healthy joint of the opposite side. In general, the height of the ascending mandibular ramus is measured to the condylar head. The CT data were manipulated using the iPlan® cranial 2.6 software as described by Lindqvist and Iizuka.17 A tangent was placed at the edge of the ascending ramus with another perpendicular tangent placed at the angle of the jaw. The vertical height was then measured from the intersection of the tangential lines to the
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Fig. 1. Preauricular approach to the temporomandibular joint in a sheep.
Fig. 2. Creation of an artificial fracture (upper row) and fixation of the condylar fragment with titanium screws in the control group (n = 10 animals). Fixation of the condylar fragment with ResorbX® pins (KLS Martin, Jacksonville, USA) in the pin group (n = 10 animals) (lower row).
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neck of the mandibular condyle (Fig. 4) and was compared with that on the healthy side. Histological reprocessing and qualitative evaluation of the fracture line
Fig. 3. Detecting volume after segmentation with the software iPlan® cranial 2.6 (Brainlab AG, Munich, Germany): operated joint (left), healthy contralateral joint for comparison (right).
The specimens were retained in 10% formalin, dehydrated in increasing concentrations of ethanol under vacuum in a tissue processor. After polymerisation in 2 stages, the preparations were ground to 50 m and stained (Masson-Goldner). Three vertical sections of each sample were produced. An automated image analysis system combined with a computerassisted research microscope was used for the qualitative evaluation. To measure the entire fracture, the fracture gap was divided into 3 visual fields (lateral, median, and medial) because if its size. Six measurements/field were made using transmission light microscopy. The data were assessed for any significant difference between the 2 procedures, and the variability of the measurements, rates of variance of the variables that resulted from this method, and 95% confidence intervals for the estimated effect on changes of the method were calculated.
Fig. 4. Measuring the height of the ascending mandibular ramus with the software iPlan® cranial 2.6 (Brainlab AG, Munich, Germany).
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Statistical analysis Results were analysed using the Statistical Package for the Social Sciences (SPSS version 20, IBM). A total of 540 readings were used for microscopic analysis of the fracture gap. We were looking for a significant difference in osteosynthesis between the 2 techniques. To avoid an error caused by pseudoreplication, a mixed-effects model was adjusted, which showed the dependency structure of the data within the method. It was necessary to convert the values logarithmically to obtain homogeneity of variance.
Results All animals survived the operation and follow-up period, and their ability to eat and their general condition were not impaired. During polyfluorochrome sequence labelling, clinical inspection showed that the operated area was healing well in all animals. Macroscopic analysis At the time of resection all fractures showed normal healing, and subjectively, stability was fully restored in all cases. Remnants of pins could still be seen, but unlike the screws, the areas of insertion were covered with callus. The shape of the condylar head had been preserved and there was no visibly detectable reduction in height. The former fracture line was barely detectable macroscopically in any operated joint. Three-dimensional, radiological evaluation Quantitative data on condylar volume and a possible reduction in height compared with the opposite side were collected using CT. Differences between the 2 groups were not significant (p = 0.66) (Fig. 3). In both groups there was a slight reduction in the height of the ascending ramus compared with the opposite side. The pin group showed a mean (SD) reduction of 1.33 (1.8) mm (range −4.2 to 2.1). Analysis of the screw group resulted in a mean (SD) reduction of 1.75 (2.5) mm (range −5.6 to 3.0). In some cases there was a slight increase in height in both groups, but differences were not significant (p = 0.68).
Fig. 5. Reflective light microscopic image of a pin-fixed diacapitular fracture of the condyle with the fracture gap in the centre.
significant individual differences. This applied particularly to the area of osteosynthesis. No differences between the groups could be detected. Analysis of the polyfluorochrome labels showed that alizarin (red) and xylenol (orange) were predominant whereas doxycycline and calcein were hardly detectable (Fig. 6). An essential degradation of the pins was not observed
Microscopic and histological evaluation There were no histopathologal abnormalities in the medullary cavities of the fractures and no subcortical resorption in the vertical section. Fluorochrome labelling showed regular layers. Callus developed mainly around the lateral pole and, to a much smaller extent, around the base of the medial fracture (Fig. 5). Articular surfaces appeared normal. There were no signs of resorption or necrosis of the small fragment in either group, and in all cases the proximal fragment consisted of vital bone. The extent of callus showed
Fig. 6. Fracture gap in polychrome light analysis (newly formed bone in orange), cross-section of pin in the middle (arrowed).
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during the 3-month period. New bone had formed and sporadic foreign body cells were present in areas around the pins. The ultrasound-melted polymer had infiltrated the trabecular structures of the surrounding host bone and created a consolidated fusion. Osteoids had formed at the interface. The use of ultrasound when the pins were inserted might have affected the host bone but we found no evidence of this; the polymer was surrounded by vital activated osteoblasts. Except for signs of drilling, the texture of the host bone remained intact and did not show any discontinuation of trabecular structures as signs of thermal alteration triggered by ultrasound. First signs of resorption could be detected by the dyes in the area around the pins. Early formation of lamellar bone could be seen in the fracture gap. The width of the histologically detectable fracture gap differed and ranged between 500 and 2800 m independent of group. The variance within individuals was larger than that between groups and for this reason, comparison of pin and miniscrew osteosynthesis was not significant.
Discussion This animal study showed no significant difference between pin and screw fixation for the treatment of condylar head fractures of the mandible. Both methods reduced the height by 1–2 mm. This is considered to be of minimal importance, and does not cause any clinical problems in humans. A reduction in height of up to 15 mm (in some cases more) may occur in condylar fractures that are not treated surgically, and those that heal in the wrong position may cause serious functional disturbances and irregularities in the condylar pathway.1,2 Both groups showed a considerable increase in the volume of the operated condyles (caused by the growth of callus), and there were no significant differences between the groups. In humans this has not been seen to such an extent when titanium screws were used and it may have been because it was impossible to immobilise the animals postoperatively. Humans can have intermaxillary immobilisation (actively) and a reduction in activity (passively). In our study the operated fracture was loaded a few minutes after operation so stability on exercise and full weight bearing need to be considered. Also, as a Lindemann burr and a surgical chisel had been used to create the fractures, their surfaces were smoother than those that occur naturally. This implies higher demands for the stability of the osteosynthesis material. Three-dimensional analysis showed mainly an increase in volume at the lateral pole where the pins and screws had been inserted. The fracture gap had little callus. It can be assumed that immediate postoperative movement leads to scars being formed with consequent transformation to callus. Generally, all fractures were stable after killing, but healing was not complete. It is possible that scar and callus may reduce during a longer healing period. Histological examination showed normal consolidation of the fracture gap, which
could barely be detected, and it indicated primary healing in both groups. The resorbable pin systems with expanding pins for osteosynthesis as described by Obwegeser18 could be considered precursors of SonicWeld® pins. The pins are particularly suitable for thin osseous structures and problems caused by resorbable and relatively brittle polylactides were not seen. Pistner et al.19 reported the use of pin systems in craniofacial surgery which were considered to stabilise bony fragments sufficiently. Despite the theoretical risks of SonicWeld® (the rise in temperature, pressure during insertion, and the need to resorb polylactides) vital osseous tissue formed in most cases. In our study this tissue had not been interwoven with connective tissue and there were no signs of necrosis around the pins. Pilling et al.11 have already shown that ultra short-term warming during insertion does not damage bone. In summary, we found no disadvantages of osteosynthesis with pins compared with titanium screws. Insertion and resorption of the pin material have already been examined in animal experiments and in clinical applications for different indications in humans.10–13 Advantages of the resorbable material (ability to degrade and no material to remove) predominate. Our results support the use of sonic welding for fractures of the condylar head in humans.
Conflict of interest The authors confirm they have no conflict of interest.
References 1. Eckelt U, Schneider M, Erasmus F, Gerlach KL, Kuhlish E, Loukota R, et al. Open versus closed treatment of fractures of the mandibular condylar process – a prospective randomized multi-centre study. J Craniomaxillofac Surg 2006;34:306–14. 2. Schneider M, Erasmus F, Gerlach KL, Kuhlisch E, Loukota R, Rasse M, et al. Open reduction and internal fixation versus closed treatment and mandibulomaxillary fixation of fractures of the mandibular condylar process: a randomized, prospective, multicenter study with special evaluation of fracture level. J Oral Maxillofac Surg 2008;66: 2537–44. 3. Hlawitschka M. Klinische, radiologische und funktionsdiagnostische Ergebnisse konservativ funktionell und operativ behandelter Frakturen des Caput mandibulae [Clinical, radiological and functional outcomes of conservative, functional and surgical management of condylar head fractures]. Dresden: Technische Universität Dresden; 2002. 4. Rasse M. Diakapituläre Frakturen der Mandibula. Die operative Versorgung – Tierexperiment und Klinik [Condylar head fractures. The operative outcome, animal experimental and clinical study]. Habilitationsschrift: Medizinische Fakultät der Universität Wien; 1992. 5. Neff A, Kolk A, Neff F, Horch HH. Operative vs. konservative Therapie diakapitulärer und hoher Kollumfrakturen. Vergleich mit MRT und Axiographie [Operative vs. conservative therapy for condylar head and high condylar neck fractures. Comparison of MRI and axiography]. Mund Kiefer Gesichtschir 2002;6:66–73. 6. Neff A, Kolk A, Deppe H, Horch HH. Neue Aspekte zur Indikation der operativen Versorgung intraartikulärer und hoher
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Kiefergelenkluxationsfrakturen [New indications for the operative management of intraarticular and high condylar neck fractures]. Mund Kiefer Gesichtschir 1999;3:24–9. Silve C, Lopez E, Vidal B, Smith DC, Camprasse S, Camprasse G, Couly G, et al. Nacre initiates biomineralization by human osteoblasts maintained in vitro. Calcif Tissue Int 1992;51:363–9. Klatt J, Heiland M, Blessmann M, Blake F, Schmelzle R, Pohlenz P. Clinical indication for intraoperative 3D imaging during open reduction of fractures of the neck and head of the mandibular condyle. J Craniomaxillofac Surg 2011;39:244–8. Schneider M, Meissner H, Richter G, Reitemeier B, Stadlinger B, Eckelt U. Bone bloc fixation via ultrasound-aided resorbable pins—an in vivo study for the improvement of stability. Int J Oral Maxillofac Surg 2009;38:464. Meissner H, Pilling E, Richter G, Koch R, Eckelt U, Reitemeier B. Experimental investigations for mechanical joint strength following ultrasonically welded pin osteosynthesis. J Mater Sci Mater Med 2008;19:2255–9. Pilling E, Mai R, Theissig F, Stadlinger B, Loukota R, Eckelt U. An experimental in vivo analysis of the resorption to ultrasound activated pins (Sonic weld) and standard biodegradable screws (ResorbX) in sheep. Br J Oral Maxillofac Surg 2007;45:447–50. Eckelt U, Nitsche M, Müller A, Pilling E, Pinzer T, Roesner D. Ultrasound aided pin fixation of biodegradable osteosynthetic materials in cranioplasty for infants with craniosynostosis. J Craniomaxillofac Surg 2007;35:218–21. Pilling E, Meissner H, Jung R, Koch R, Loukota R, Mai R, et al. An experimental study of the biomechanical stability of ultrasound-activated
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pinned (SonicWeld Rx + Resorb-X) and screwed fixed (Resorb-X) resorbable materials for osteosynthesis in the treatment of simulated craniosynostosis in sheep. Br J Oral Maxillofac Surg 2007;45:451–6. Schneider M, Eckelt U, Reitemeier B, Meissner A, Richter G, Loukota R, Stadlinger B, et al. Stability of fixation of diacapitular fractures of the mandibular condylar process by ultrasound-aided resorbable pins (SonicWeld Rx((R)) System) in pigs. Br J Oral Maxillofac Surg 2011;49:297–301. Meyer-Marcotty MV, Lahoda LU, Hahn MP, Muhr G. Die Differenzialtherapie der Radiusköpfchenfraktur: Eine kritische Analyse anhand der Ergebnisse von 53 Patienten [The different treatments of radial head fractures: a critical analysis of the outcomes of 53 patients]. Unfallchirurg 2002;105:532–9. Schneider M, Loukota R, Eckelt U. Reduction of diacapitular fractures of the mandibular condyle using a special repositioning pin. Br J Oral Maxillofac Surg 2009;47:558–9. Lindqvist C, Iizuka T. Condylar neck fracture miniplates: extraoral approach. In: Härle F, Champy M, Terry B, editors. Atlas of craniomaxillofacial osteosynthesis: miniplates, microplates, and screws. Stuttgart: Thieme; 1999. Obwegeser JA. Resorbier- und umbaubare Osteosynthesematerialien in der Mund-Kiefer- und Gesichtschirurgie [Resorbable and alternative osteosynthesis materials in maxillofacial surgery]. Mund Kiefer Gesichtschir 1998;2:288–308. Pistner H, Mühling J, Reuther J. Resorbierbare Materialien zur Osteosynthese in der kraniofazialen Chirurgie [Resorbable materials for the osteosynthesis in craniofacial surgery]. Fortschr Kiefer Gesichtschir 1991;36:77–9.
British Journal of Oral and Maxillofacial Surgery 51 (2013) 421–427
Treatment of fractures of the condylar head with resorbable pins or titanium screws: an experimental study Matthias Schneider a,∗ , Richard Loukota b , Anne Kuchta a , Bernd Stadlinger c , Roland Jung d , Katrin Speckl d , Robert Schmiedekampf a , Uwe Eckelt a a
Department of Oral and Maxillofacial Surgery, University Hospital Carl Gustav Carus, Technical University Dresden, Germany Department of Oral and Maxillofacial Surgery, Leeds Teaching Hospitals NHS Trust, Leeds, UK c Clinic of Cranio-Maxillofacial and Oral Surgery, University of Zurich, Switzerland d Experimental Centre, Medical Faculty, Technical University Dresden, Germany b
Accepted 27 July 2012 Available online 17 August 2012
Abstract We aimed to compare in vivo the stability of fixation of condylar fractures in sheep using sonic bone welding and standard titanium screws. We assessed stability of the osteosynthesis and maintenance of the height of the mandibular ramus. Height decreased slightly in both groups compared with the opposite side. The volume of the condyle increased considerably in both groups mainly because callus had formed. The results showed no significant disadvantages for pin fixation compared with osteosynthesis using titanium screws. © 2012 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Keywords: Trauma; Condylar fracture; Resorbable material; Sheep; Titanium screw
Introduction Surgical treatment and osteosynthesis of fractures of the condylar head are technical challenges. As the typical fracture line runs from inside to outside the joint they are described as diacapitular rather than intracapsular fractures. Limiting factors for operation are difficulties exposing the fracture, repositioning, and osteosynthesis, but a randomised multicentre study showed that patients benefit from surgical treatment.1,2 Several studies3–5 have shown that anatomically accurate reconstruction of the surface of the joint is the best indicator of long term function. Osteosynthesis with miniscrews6,7 has been established in the treatment of
∗ Corresponding author at: Department of Oral and Maxillofacial Surgery, University Hospital Carl Gustav Carus, Technical University Dresden, Fetscherstr. 74, 01307 Dresden, Germany. Tel.: +49 351 4583382; fax: +49 351 4585382. E-mail addresses: [email protected], [email protected] (M. Schneider).
diacapitular fractures, but without intraoperative radiography,8 screws can be malpositioned with medial, ventral, or cranial perforation of the condyle being visible only on postoperative radiographs. Use of SonicWeld® resorbable pins (KLS Martin, Jacksonville, USA) can avoid the condyle being perforated by screws,9 and this method of osteosynthesis has already been established in the treatment of midfacial fractures and in craniofacial surgery.10–13 In our study it is of particular interest that the SonicWeld® pins can be anchored efficiently in the cortex of the bone and also in cancellous bone because they melt; this does not occur with titanium screws. Extensive studies to test the stability of pin osteosynthesis14 and to evaluate the optimal configuration for drill holes have already been done.9 Resorbable pins have been used in the treatment of diacapitular fractures of the condyle and also for fractures of other joints.15 However, 1.3 mm diameter and 40 mm long poly p-dioxanone (PDA) pins (Ethipins® , Ethicon) as applied by Rasse4 were resistant only to shear forces.
0266-4356/$ – see front matter © 2012 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bjoms.2012.07.015
422
M. Schneider et al. / British Journal of Oral and Maxillofacial Surgery 51 (2013) 421–427
Macroscopic, histological, and radiological evaluation at the end of the trial period enabled us to evaluate the long-term stability of the fractures, the behaviour of the resorbable pins, and the dynamics of fracture healing. We acknowledge that sheep have a more ruminant diet than humans, but this may be an advantage as the increased number of chewing cycles subject the osteosynthesis to more extreme stress than may be seen in human patients.
miniscrews) in diameter was drilled from the lateral pole of the condyle perpendicular to the surface of the fracture. The optimal configuration of holes in terms of a step drill 1.6 or 2.1 mm in diameter had previously been decided in vitro using analogous synthetic bone.9 After the first pin or screw had been inserted another hole of the same size was drilled and an additional pin or screw inserted (Fig. 2). Stability was tested by moving the mandible before the wound was closed in layers using resorbable polyglactin 910 (Vicryl® ). Intravital polyfluorochrome sequence labelling
Materials and methods A study in large animals was necessary because of the size of the osteosynthesis pins, and the anatomical configuration of the mandibular condyle in sheep is similar to that in humans. We used 20 adult sheep aged between 2 and 4 years and between 63 and 88 kg in weight. The Commission for Animal Studies at the district government office Dresden, Germany gave approval for the study. The study was done in the experimental centre of the medical faculty of the Technical University, Dresden. Animals were randomly assigned to 2 groups: 10 sheep were treated using resorbable pins and 10 were treated using titanium screws. After operation they were kept outside on a farm and fed a species-appropriate diet. A unilateral fracture through the condyle was created in every animal. To allow mastication and to impair the animal as little as possible, the temporomandibular joint (TMJ) of the contralateral side was not affected. After fracture, osteosynthesis was done using 2–3 resorbable SonicWeld® pins (2.1 × 17 and 2.1 × 11 mm in diameter) in 10 animals. The other 10 served as a control group and had fractures treated using 2–3 conventional mini titanium screws (2.0 × 17 and 2.0 × 11 mm in diameter). The postoperative examination period was 3 months. To enable bony healing to be analysed we used intravital polyfluorochrome sequence labelling. It was not possible to protect the operated joint or feed a specialised diet. After the sheep were killed, the mandibles were resected including the TMJ, and 40 specimens were obtained for macroscopic analysis and radiological three-dimensional evaluation. Operation The articular capsule was exposed and opened using a preauricular approach (Fig. 1) under general anaesthesia. The fragments of the articular capsule were marked by resorbable sutures to enable them to be repositioned correctly, and the fracture line was marked by a narrow Lindemann burr in a position as close as possible to comparable human fractures (diagonally downwards from the lateral condyle to the medial condylar base). The osteotomy was completed by a narrow osteotome (Fig. 2). The fragment was stabilised with a special repositioning pin16 then a hole 1.6 mm or 2.1 mm (or 1.5 mm for
The following fluorochromes were injected intramuscularly: doxycycline 30 mg/kg at 2 weeks; alizarin 30 mg/kg at 4 weeks; calcein green 20 mg/kg at 6 weeks; and xylenol 90 mg/kg at 8 weeks. Macroscopic evaluation Initially, the preparations were examined macroscopically and fixed in Schaffer’s solution after all the tissue had been removed. The TMJ of the unoperated side was also resected for radiological and macroscopic comparison. The position and the possible deformation of the mandibular condyle, the width of the fracture gap, the height of the ascending ramus, remaining pin material, and formation of callus, were assessed. This qualitative observation was done in direct comparison with the condyle on the other side. Radiological three-dimensional measurement Three-dimensional stability was quantitatively evaluated using computer-assisted analysis of computed tomograms (CT). Axial layer CT was used to examine all the condyles in pairs (operated and unoperated side). Data were saved in DICOM format and transferred to a BrainLAB® (Brainlab AG, Munich, Germany) workstation using iPlan® cranial 2.6 software. For this purpose the mandibular fragments were initially automatically segmented. The condylar heads of both sides were then segmented and the volume measured (Fig. 3) to quantify the amount of callus that had formed and the increase in volume of the condylar head. An important aim of the surgical treatment of condylar fractures is to maintain or re-establish vertical height. A consistent height of the joint is important for undisturbed articulation of both TMJ; shortening of 1 mandibular condyle leads to dysfunction because of the interdependent movements of both joints. Another effect is the structural change, which can also occur in the healthy joint of the opposite side. In general, the height of the ascending mandibular ramus is measured to the condylar head. The CT data were manipulated using the iPlan® cranial 2.6 software as described by Lindqvist and Iizuka.17 A tangent was placed at the edge of the ascending ramus with another perpendicular tangent placed at the angle of the jaw. The vertical height was then measured from the intersection of the tangential lines to the
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Fig. 1. Preauricular approach to the temporomandibular joint in a sheep.
Fig. 2. Creation of an artificial fracture (upper row) and fixation of the condylar fragment with titanium screws in the control group (n = 10 animals). Fixation of the condylar fragment with ResorbX® pins (KLS Martin, Jacksonville, USA) in the pin group (n = 10 animals) (lower row).
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neck of the mandibular condyle (Fig. 4) and was compared with that on the healthy side. Histological reprocessing and qualitative evaluation of the fracture line
Fig. 3. Detecting volume after segmentation with the software iPlan® cranial 2.6 (Brainlab AG, Munich, Germany): operated joint (left), healthy contralateral joint for comparison (right).
The specimens were retained in 10% formalin, dehydrated in increasing concentrations of ethanol under vacuum in a tissue processor. After polymerisation in 2 stages, the preparations were ground to 50 m and stained (Masson-Goldner). Three vertical sections of each sample were produced. An automated image analysis system combined with a computerassisted research microscope was used for the qualitative evaluation. To measure the entire fracture, the fracture gap was divided into 3 visual fields (lateral, median, and medial) because if its size. Six measurements/field were made using transmission light microscopy. The data were assessed for any significant difference between the 2 procedures, and the variability of the measurements, rates of variance of the variables that resulted from this method, and 95% confidence intervals for the estimated effect on changes of the method were calculated.
Fig. 4. Measuring the height of the ascending mandibular ramus with the software iPlan® cranial 2.6 (Brainlab AG, Munich, Germany).
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Statistical analysis Results were analysed using the Statistical Package for the Social Sciences (SPSS version 20, IBM). A total of 540 readings were used for microscopic analysis of the fracture gap. We were looking for a significant difference in osteosynthesis between the 2 techniques. To avoid an error caused by pseudoreplication, a mixed-effects model was adjusted, which showed the dependency structure of the data within the method. It was necessary to convert the values logarithmically to obtain homogeneity of variance.
Results All animals survived the operation and follow-up period, and their ability to eat and their general condition were not impaired. During polyfluorochrome sequence labelling, clinical inspection showed that the operated area was healing well in all animals. Macroscopic analysis At the time of resection all fractures showed normal healing, and subjectively, stability was fully restored in all cases. Remnants of pins could still be seen, but unlike the screws, the areas of insertion were covered with callus. The shape of the condylar head had been preserved and there was no visibly detectable reduction in height. The former fracture line was barely detectable macroscopically in any operated joint. Three-dimensional, radiological evaluation Quantitative data on condylar volume and a possible reduction in height compared with the opposite side were collected using CT. Differences between the 2 groups were not significant (p = 0.66) (Fig. 3). In both groups there was a slight reduction in the height of the ascending ramus compared with the opposite side. The pin group showed a mean (SD) reduction of 1.33 (1.8) mm (range −4.2 to 2.1). Analysis of the screw group resulted in a mean (SD) reduction of 1.75 (2.5) mm (range −5.6 to 3.0). In some cases there was a slight increase in height in both groups, but differences were not significant (p = 0.68).
Fig. 5. Reflective light microscopic image of a pin-fixed diacapitular fracture of the condyle with the fracture gap in the centre.
significant individual differences. This applied particularly to the area of osteosynthesis. No differences between the groups could be detected. Analysis of the polyfluorochrome labels showed that alizarin (red) and xylenol (orange) were predominant whereas doxycycline and calcein were hardly detectable (Fig. 6). An essential degradation of the pins was not observed
Microscopic and histological evaluation There were no histopathologal abnormalities in the medullary cavities of the fractures and no subcortical resorption in the vertical section. Fluorochrome labelling showed regular layers. Callus developed mainly around the lateral pole and, to a much smaller extent, around the base of the medial fracture (Fig. 5). Articular surfaces appeared normal. There were no signs of resorption or necrosis of the small fragment in either group, and in all cases the proximal fragment consisted of vital bone. The extent of callus showed
Fig. 6. Fracture gap in polychrome light analysis (newly formed bone in orange), cross-section of pin in the middle (arrowed).
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during the 3-month period. New bone had formed and sporadic foreign body cells were present in areas around the pins. The ultrasound-melted polymer had infiltrated the trabecular structures of the surrounding host bone and created a consolidated fusion. Osteoids had formed at the interface. The use of ultrasound when the pins were inserted might have affected the host bone but we found no evidence of this; the polymer was surrounded by vital activated osteoblasts. Except for signs of drilling, the texture of the host bone remained intact and did not show any discontinuation of trabecular structures as signs of thermal alteration triggered by ultrasound. First signs of resorption could be detected by the dyes in the area around the pins. Early formation of lamellar bone could be seen in the fracture gap. The width of the histologically detectable fracture gap differed and ranged between 500 and 2800 m independent of group. The variance within individuals was larger than that between groups and for this reason, comparison of pin and miniscrew osteosynthesis was not significant.
Discussion This animal study showed no significant difference between pin and screw fixation for the treatment of condylar head fractures of the mandible. Both methods reduced the height by 1–2 mm. This is considered to be of minimal importance, and does not cause any clinical problems in humans. A reduction in height of up to 15 mm (in some cases more) may occur in condylar fractures that are not treated surgically, and those that heal in the wrong position may cause serious functional disturbances and irregularities in the condylar pathway.1,2 Both groups showed a considerable increase in the volume of the operated condyles (caused by the growth of callus), and there were no significant differences between the groups. In humans this has not been seen to such an extent when titanium screws were used and it may have been because it was impossible to immobilise the animals postoperatively. Humans can have intermaxillary immobilisation (actively) and a reduction in activity (passively). In our study the operated fracture was loaded a few minutes after operation so stability on exercise and full weight bearing need to be considered. Also, as a Lindemann burr and a surgical chisel had been used to create the fractures, their surfaces were smoother than those that occur naturally. This implies higher demands for the stability of the osteosynthesis material. Three-dimensional analysis showed mainly an increase in volume at the lateral pole where the pins and screws had been inserted. The fracture gap had little callus. It can be assumed that immediate postoperative movement leads to scars being formed with consequent transformation to callus. Generally, all fractures were stable after killing, but healing was not complete. It is possible that scar and callus may reduce during a longer healing period. Histological examination showed normal consolidation of the fracture gap, which
could barely be detected, and it indicated primary healing in both groups. The resorbable pin systems with expanding pins for osteosynthesis as described by Obwegeser18 could be considered precursors of SonicWeld® pins. The pins are particularly suitable for thin osseous structures and problems caused by resorbable and relatively brittle polylactides were not seen. Pistner et al.19 reported the use of pin systems in craniofacial surgery which were considered to stabilise bony fragments sufficiently. Despite the theoretical risks of SonicWeld® (the rise in temperature, pressure during insertion, and the need to resorb polylactides) vital osseous tissue formed in most cases. In our study this tissue had not been interwoven with connective tissue and there were no signs of necrosis around the pins. Pilling et al.11 have already shown that ultra short-term warming during insertion does not damage bone. In summary, we found no disadvantages of osteosynthesis with pins compared with titanium screws. Insertion and resorption of the pin material have already been examined in animal experiments and in clinical applications for different indications in humans.10–13 Advantages of the resorbable material (ability to degrade and no material to remove) predominate. Our results support the use of sonic welding for fractures of the condylar head in humans.
Conflict of interest The authors confirm they have no conflict of interest.
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