Controversias en Cirugía Oral y Maxilofacial: Parte II

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Maxillofacial osteosynthesis with resorbable material
Osteosíntesis maxilofacial con materiales reabsorbibles

 

J.L. López-Cedrún Cembranos

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Abstract: Resorbable plates and screws composed of polylactic and polyglycolic acid, as internal fixation devices have gained widespread use during recent years in pediatric and also adult patients. Although these materials show some disadvantages when compared with titanium plates, such as discomfort and economical cost, accumulated experience shows that resorbable ostheosynthesis is a reliable alternative to the titanium osteosynthesis used in most clinical cases. In this paper we analyze the main characteristics of resorbable materials used in maxillofacial osteosynthesis. We discuss the advantages and disadvantages of both types of osteosynthesis and the indications for resorbable ostheosynthesis at the present time, based on our experience and on a revision of the literature. Key words: Resorbable osteosynthesis; Polylactic acid; Polyglycolic acid; Osteotomy.

Resumen: La popularización de la combinación de ácidos poliláctico y poliglicólico ha hecho que estos nuevos materiales se utilicen cada vez más en la osteosíntesis maxilofacial, no solo en su aplicación pediátrica, sino también en adultos. Aunque todavía presentan algunas desventajas en relación con el titanio, como la mayor incomodidad de uso y el coste económico, la experiencia acumulada demuestra que es una alternativa válida a la osteosíntesis con titanio en la mayoría de las situaciones clínicas. En este artículo se analizan las características y cualidades de los materiales reabsorbibles empleados en osteosíntesis maxilofacial. Así mismo, se discuten las ventajas y desventajas de ambos tipos de osteosíntesis y se documentan las indicaciones actuales de la osteosíntesis reabsorbible basándonos en nuestra experiencia y en la revisión de la literatura. Palabras clave: Osteosíntesis reabsorbible; Acido poliláctico; Acido poliglicólico; Osteotomía.

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Jefe de Servicio.
Servicio de Cirugía Oral y Maxilofacial.
Complejo Hospitalario Universitario Juan Canalejo, La Coruña, España

Correspondencia:
Complejo Hospitalario Universitario Juan Canalejo
C/ Xubias de Arriba, 84
15006 A Coruña
E-mail: lopezcedrun@centromaxilofacial.com

 

Introduction

Rigid osteosynthesis has supposed one of the greatest advances in the field of modern maxillofacial surgery. Titanium has demonstrated excellent qualities over 25 years. However, the appearance and widespread use of combinations of polylactic and polyglycolic acids has meant that these new material are used more frequently. Few doubts remain as to its application in pedriatrics, but there is still some controversy as to its use in maxillofacial surgery in adults. And we should therefore ask. Can resorbable osteosynthesis at the moment replace titanium in craniomaxillofacial bone fixation in adult patients?

In order to answer this question we first have to stress that, in addition to the inherent advantages of osteosynthesis with titanium, disadvantages have been attributed to it including; unacceptable palpability, intraoral exposure, passive migration of the screws and plates,1 and the distortion of future NMR and CT² images, in addition to interferences with radiotherapy treatment^.3 Titanium particle deposits and migration to soft tissue and lymphatic nodes has also been described.⁴

The first reference to resorbable osteosynthesis was by Kulkarni and cols,⁵ who in 1966 proposed the use of polylactic acid as a surgical implant. The first publication on the use of absorbable materials for fixing the facial skeleton belongs to Cutright and cols⁶ and it was an experimental study, although in that era biomaterials were not commercialized. In the 80s experiments were carried out with PLLA plates and screws with promising results and which lead to various clinical trials.^7-10

The bioresorbable materials that have been used most in craniomaxillofacial surgery are poly-alpha-hydroxy acids that have a high molecular weight: polylactic acid (PLA), polyglycolic acid (PGA), polydioxane (PDS) and their copolymers. These acids are degraded through simple hydrolysis in the aqueous medium of living tissue. They are first dissolved in small fragments, which are phagocytosed by macrophages and by giant cells. The resulting products of the PLA and PGA degradation are metabolized in carbon dioxide and water and they are eliminated through repiration.^1,9 The products of PDS are excreted primarily in the urine. Complete resorption varies between 6 months and 4 years depending on the composition, although tension is lost several months before.^1,11

The object of this work is to analyze the qualities of the resorbable materials used in maxillofacial osteosynthesis, to discuss their advantages and disadvantages with regard to titanium, and to document the current indications for resorbable osteosynthesis based on our experience and a revision of the literature.

Characteristics of resorbable materials

Most of the resorbable osteosynthesis material is composed of two resorbable copolymers (polylactic acid and polyglycolic acid) in a variable proportion, which will condition resistance as opposed to resorption time, according to which one dominates. Degradation occurs in two phases, first through hydrolysis and then through phagocytosis of the fragments by macrophages that converts the rest of the polymers in water and carbon dioxide. Some of the factors that influence the rate of degradation are, the chemical identity of the polymer, its molecular weight, the crystalline/amorphous proportion, and the size and form of the implant.^1,12 By changing the properties of the copolymers through adequate selection of the identity and proportion of the monomers, the behavioral characteristics of the implant can be manipulated increasing its resistance (L-lactic), absorption (glycolic), or malleability (D-lactic).^1,7,12

Some companies also add trimethylene carbonate to the composition, which gives the plate more malleability and improves their handling properties (www.inion.com unpublished data). This compound has been used in the composition of the Maxon resorbable suture,⁸ which is formed by a copolymer of glycolic, and trimethylene carbonate, the latter representing 32.5% of its weight.¹³

Next, we will sum up the characteristics that stand out of the polymers used in the composition of resorbable plates and screws.^1,9,10,14

Polylactic acid (PLA). It has two enantiomers: L-lactic acid and D-lactic acid. It is used clinically as pure poly-L-lactic acid and as a copolymer of poly-D, L-lactic acid (PDLLA). The racemic PDLLA contains 50% of both enantiomers (50L:50D) and it demonstrates a moderate mechanical force.

Poly-L-lactic acid (PLLA). This has the best properties regarding strength, and it is the polymer which is most used. Its strength is lost slowly, only 25% during the first three months and 100% after a year, but its complete biodegradation requires 4-5 years. It has been shown to be very biocompatible in clinical trials, although inflammation is frequently produced due to high crystallinity.¹⁵

Poly- DL/L-Lactic acid (P(L/DL)LA). Currently the use of the copolymers L-lactic acid and D-lactic acid is preferred to pure PLLA, as they have adequate mechanical properties (mechanical resistance for more than 3-4 months) and are amorphous. Degradation occurs in two phases and in this way tissue tolerance is not exceeded.

Polyglycolic acid (PGA). Self-reinforced polyglycolic [acid] has been demonstrated as having the best properties for initial resistance, similar to stainless steel, which is lost at 6 weeks, and reabsorbed completely in under a year.¹⁶ However, in more than 60% of cases adverse reactions appear due to the rapid production of polymer remains that exceeds tissue capacity.¹⁷

Due to adverse reactions, pure PGA and the PLLA are not used and copolymers of both of them are preferred in different proportions in pediatric patients as no adverse reactions appear. They are available commercially in a ratio of 82:18 (Lactosorb) and 80:20 (Biosorb PDX). It is amorphous, conserving 70% of its initial resistance for 6-8 weeks and it degrades after a year.¹¹ It can produce discrete inflammation in adults caused by the PGA that is not detected in children.

Trimethylene carbonate (TMC). It provides malleability. It also has advantages for plate manipulation, as it can be molded on cooling after being heated initially, as the heating device requires less temperature. (55º).

Other resorbable components. Caprolactone (CL) and Polydioxanone (PDS). Even though its use has been described, it has not been used in the composition of the latest plates. Polydioxane has modest mechanical properties as it degrades at 6 months. Adverse reactions have not been described in soft tissue, although transient osteolytic reactions may occur.

Self-reinforced polymers. Törmälä¹⁸ developed self-reinforcing techniques for the manufacture of biodegradable techniques. Self-reinforcement represents an important improvement in the mechanical properties of resorbable materials, as one part of the polymer structure is transformed into reinforced fibers during the manufacturing process. Serlo and cols¹⁹ verified that the SR-PLLA plates have an elasticity similar to that of bone; metal ones were, on the contrary, 5-10 times greater.

In experimental studies²⁰, these polymers have shown their superiority over other materials. In addition they can be sterilized with gamma rays. Clinical experience with these polymers has shown good results for more than 10 years.²¹

Table 1 gives a summary of the principal characteristics of resorbable osteosynthesis material commercially available in Spain. The majority are combinations of poly D-lactic, or polyglycolic with poly-l-lactic combinations. This reduces crystallization, which makes resorption slower and is the principal cause of the adverse reactions that were first documented.

Current indications for resorbable osteosynthesis

The three basic applications for maxillofacial osteosynthesis are: Traumatology, Orthognathic surgery and Craniofacial surgery. Our experience to date of resorbable osteosynthesis is based on a series of 80 operated patients having craniofacial surgery (29 patients), orthognathic surgery (31 patients) and craniofacial trauma (20 patients). Perhaps the fractures that are ideal for comparing metallic osteosynthesis using titanium, with resorbable osteosynthesis are those that occur as a result of osteotomies performed in orthognathic surgery; these are standard fractures lines that are reproduced in all patients.

The osteotomies performed correspond to Le Fort 1 (in one fragment or segment, or in two or four fragments), sagittal osteotomies of the mandible and mentoplasties. More than half the patients correspond to bimaxillary surgery. In the maxilla we have used 4 2.0 miniplates (4 L shaped or sometimes 2 L shaped and 2 straight ones); in the mandible 3 or 4 2.4 or 2.8 screws in each side, and 1.5 miniplates for the chin (Figs. 1-3).

One of the most controversial aspects regarding the use of resorbable osteosynthesis is stability, as cases requiring surgical reintervention in order to stabilize the maxilla have been published.²² Clinically, it is evident that there is less fixation than with titanium and, in this respect, in segmental maxillary osteotomies the maxilla is movable, and the osteosynthesis is thus semi-rigid; other than this, mobility of the segmented mandible has not been observed in any of the cases. In our series no patient needed reintervention; during the first 3-4 weeks postsurgery the maxilla has a certain amount of mobility when segmented, and it is more sensitive to the traction forces of the elastics. This movement is a worry at first during the learning curve, but in the long term, however, we have not observed any problems regarding stability. Moreover, we believe that this reduced resistance of the maxilla to the elastic forces facilitates, in some cases, postoperative orthodontic work. The cases that are most difficult to handle in this sense, are maxillary expansions, which we had already experienced with titanium osteosynthesis. With regard to intermaxillary wiring, we do not include it in our surgical protocol for orthognathic surgery, and on no occasion has it been necessary for those cases in which fixation was carried out with resorbable material.

Other variables that should be compared, in addition to stability, are surgical time, procedure simplicity, hospital stay, postoperative inflammation and complications. The most important problems arise initially on placing the plates, as these are less malleable and easy to use than those of titanium, and this requires some training. On the other hand, in the operative field, most systems require the heating of the miniplates before insertion. Some systems have a pistol that can take up to ten screws and, as a diestock is not required, insertion is very easy, meaning that operative time is reduced considerably. Mandibular screws require diestocks (Fig. 4), although this procedure does not delay the surgery more than 2-3 minutes. In our series, operative time with both methods is similar (titanium or resorbable) when 4 miniplates are placed; when only 2 preformed plates are used of titanium (in the resorbable system these do not exist) with resorbable material, the surgery take 10 to 15 minutes longer.

The larger the size of the plate, the more cumbersome placing it is, and the more obvious they are. In this sense, in two patients it was possible to feel the plate under the infraorbital rim, although extraction was not necessary (Fig. 5). We are currently cutting the last hole of the plates in an L shape so that they do not reach the infraorbital rim and we check that they are not palpable before screwing them.

Postoperative inflammation has not been any different to that experienced in osteosynthesis with titanium. Neither has hospital stay varied.

No cases of infection were observed among the complications. We observed one case of exposure of osteosynthesis material in the maxillary cavity 9 months after surgery, corresponding to a miniplate fragment from the segment of the maxilla that had been advanced, which was removed using a mini incision (Fig. 6).

In pediatric craniofacial surgery the only material that is used is resorbable, and the results therefore cannot be compared with titanium (Figs. 7 and 8).

In adult facial trauma we do not use resorbable material in a routine way and, as we do not have a long-term follow- up in our series, we cannot compare stability in the long term. If we make an exception of fracture cases having significant comminution and fractures that are severely displaced where the use of resorbable plates is not advised, we have not observed problems of stability in the short term nor complications (Figs. 9-11). We should, however, point out that osteosynthesis of fragment fractures in some facial localizations, result more cumbersome.

Discussion

The use of resorbable plates in pediatric craniofacial surgery is currently routine, as titanium has been displaced because of its adverse effects. Metallic material is not ideal because it can produce growth alterations in the cranial vault and some authors recommend removing them.²³ On the other hand their use in the skulls of [infants] under the age of six months is very difficult because of weakness.

Documented cases include; palpable plates and screws in areas of fine skin; occasional extrusion through the skin; infrequent cases of secondary infection because of foreign body reaction. However, of most concern is the significant percentage of plate migration through the dura mater, which is more frequent in the temporal region and in syndromic cases.²⁴

On the other hand, permanent rigid fixation in a growing cranium can lead in itself to the appearance of residual deformities.²⁵ Numerous publications support the use and positive results of resorbable miniplates in this type of patient.^{26- 30}

In craniofacial trauma the use of resorbable plates has been less documented than in craniofacial surgery for deformity, but it is sufficient to justify its use. Eppley and Prevel³¹ published in 1997 their experience in midface fractures with the use of Lactosorb in 30 patients. The follow-up period was of more than a year, and adequate healing with no adverse reactions was observed, although the authors did not recommend their use in small or fine fracture fragments. Similar results were published by Enislidis and cols.³² in a series of 27 maxillomalar fractures.

Ylikontiola and cols³³ have used resorbable plates for the osteosynthesis of parasymphyseal fractures in 10 adults, with good results (one patient suffered intraoral exposure of a plate, which required partial extirpation). These authors recommend adequate soft tissue cover in order to avoid plate exposure. Other authors³⁴ have also published good results for mandibular fractures.

Tams and cols,³⁵ in an experimental study, confirmed that mandibular angle fractures could be treated efficiently with 2 resorbable plates placed on the external oblique ridge and half way up the height of the mandible respectively.

Hoffmann and cols³⁶ used the PDLLA (Resorb X) plates in 22 patients treated for craniofacial trauma, Le Fort 1 osteotomy and craniofacial syndromes, with no complications being observed in healing (neither clinically nor radiologically). Suuronen and cols,¹ in a retrospective study of more than 200 patients treated with resorbable fixation in various applications of craniomaxillofacial surgery over 7 years, maintain that resorbable plates can be used routinely in maxillofacial osteosynthesis.

The other considerable application of resorbable plates is in orthognathic surgery. In this field the literature increases constantly, with numerous documented articles as to their application. Haers and cols.³⁷ published in 1998 the first case of simultaneous bimaxillary surgery and mentoplasty fixed exclusively with resorbable material. Turvey and cols.38 published their experience with 70 patients in orthognathic bimaxillary surgery with a short-term follow-up (6-24 months). Three patients had problems with screw loss, but stability and occlusion were adequate in all patients.

Norholt and cols.³⁹ have compared the use of Lactosorb resorbable plates and titanium plates in Le Fort 1 osteosynthesis, in a randomized prospective study of 60 patients, in relation with stability and morbidity. These authors³⁹ observed an average postoperative vertical change of 0.6 mm at 6 weeks in the resorbable group (a significant statistical change carried out with metallic implants placed in the bone), but they did not find significant changes in the titanium group. There was no clinically apparent change, nor did any appear in the following radiological evaluations, bone consolidation having taken place satisfactorily in all patients. There were 2 cases of wound infection and dehiscence with the resorbable plates while, in the titanium group, the plates were more frequently palpated 6-12 months later, and 3 cases required removal.

Matthew and cols12 studied the stability of the SR-PLLA resorbable screws in osteosynthesis for sagittal split mandibular advancement osteotomies in 11 patients, compared with a cohort of 11 patients submitted to the same osteotomies fixed with titanium. They did not find significant differences between both groups on comparing cephalometric stability during a follow-up period of one year. Other studies of Le Fort 1 osteotomies and mandibular sagittal osteotomies have shown the absence of complications.^40-43

Ferretti and Reyneke⁴⁴ have published a prospective comparative study of ⁴⁰ patients with class II malocclusion who underwent sagittal split osteotomies of the mandible, in which long-term stability was compared with the complications [arising] from the fixation with titanium screws and with P(L/DL)LA 82:18 screws, with no significant differences being found between both groups.

The Helsinki group demonstrated their 8-year experience in orthognathic surgery together with a follow-up of more than 5 years, with excellent results.^1,14 Recently they published their experience in orthognathic surgery during a 10- year period (1991-2001) in a retrospective study of 163 patients and 329 osteotomies.⁴⁵ Patient acceptance was excellent and the incidence of complications observed was minor, with no cases influencing the final result: 8.6% with minor complications, 0.6% (one case) of infection and 1.8% (3 cases) of postoperative open bite, which occurred with the older devices in the first phase of the study.

Fuente del Campo⁴⁶ has recently published his experiences in a multicentric study of maxillofacial osteosynthesis with resorbable material (SR-PLLA) in 208 cases, of which 142 corresponded to orthognathic surgery, with a maximum following of 8 years. This author46 observed a complication rate of 7.9%: 2 cases of maxillary instability because of bad technique, 6 cases of granuloma, 4 cases of plate exposure and another 4 of displacement. Most of these complications were attributed to technique and not to the material used. It seems clear that, for orthognathic surgery, resorbable material is an absolutely valid alternative to titanium.

Advantages and disadvantages to resorbable osteosynthesis

The literature revised shows that, in general, resorbable plates are a valid alternative to titanium in most craniomaxillofacial osteosynthesis. Larger rates of complications are published in small series that tend to correspond to the first application phase of these materials. Some problems remain unresolved, such as prolonged biodegradation.⁴⁷ Another problem concerns the plates being palpable. Gerlach⁴⁸, using resorbable plates for the treatment of malar fractures, observed that these could be palpated through the skin after two years. He also observed that of 15 patients treated, two presented a non-infectious inflammatory reaction after 30 months. On the other hand, Bergsma and cols¹⁵ observed a series in which all patients developed foreign body reaction in the operated area three years later. Fragments of LPLA fragments were found during the surgical examination as much as 5.7 years later.

It should be stressed that these publications correspond to the initial phases in which resorbable osteosynthesis was used. The ideal resorbable material should be able to support bone fragments during the healing period, and it should be able to reabsorb itself completely after this without the resulting metabolites causing any local or systemic alterations.¹² These characteristics provide undoubted advantages, particularly as they do not have to be extracted. It has been published that 11.1% of patients required the extraction of titanium plates in orthognathic surgery and 11.5% in mandibular fractures.⁵⁰ On the other hand, it is of particular advantage in countries in which osteosynthesis material is removed postoperatively, which entails general anesthesia, morbidity and economic cost. The interferences that titanium can produce regarding radiological procedures² and thermal sensitivity are avoided⁵¹.

Analysis of the disadvantages of osteosynthesis with resorbable material

• Physical properties. One of the inconveniences is the thickness of the plates. For the same resistance a greater thickness of resorbable plate is needed. This is an inconvenience in some localizations and specific situations. Another problem is the difficult application in comminuted fractures and very fine bones. In these conditions, adapting these plates is very difficult, which could be a contraindication. If they are bent too many times, some authors⁵² indicate that the heating procedure can make them lose their mechanical properties although this also poses a problem with titanium.

• Learning curve. Handling and adapting these plates is more cumbersome than what we are used to with titanium, so initially operative time is longer. This is due to the heating process and the need for adjustments to the orifice that most systems require; the development of shooters for introducing the screws into the holes without the need for a diestock has meant that operative time is reduced without prejudicing the mechanical properties. This has been demonstrated in experimental⁵³ as well as clinical⁵⁴ studies. However, its use in fine bones is difficult because of the possibility of fracturing them.⁵⁵ This requires an initial training curve for familiarization with the material,⁴⁵ although the ease of handling is still today lower than with titanium; however, this does not compromise the end result.

• Handling in orthognathic surgery. For a sagittal mandibular osteotomy the screws are inserted in the same way in both the titanium and resorbable systems, only a few more seconds are required for adjustments to the orifices. In the maxilla, the initial mobility during 4-5 weeks may be of concern, especially in segmental osteotomies, but in actual fact it is not, and there is no problem regarding stability at the end of this period.⁴⁵ Another aspect entailing some difficulty is the placing of miniplates in the premaxilla for segmental Le Fort osteotomies. Currently the development of resorbable pre-formed plates is being worked on for (Lindorf or Prebent type) maxilla advancement; this will make placing maxillary osteosynthesis as simple as titanium. One aspect that we have already mentioned is the palpation of the plates in the infraorbital rim, which is not currently a problem.

• Non-visualization of screws in the radiographic film. This can sometimes make diagnosis difficult when there are consolidation problems, etc.⁴⁵

• Adequate protection is needed of soft tissue so that there is no plate exposure, as the degradation process can be altered. In these cases their removal after the consolidation period is necessary.

• Versatility of miniplates. Some companies only dispose of a single system that is not valid for all osteotomies. Generally, these systems are not indicated for mandibular osteosynthesis or for situations requiring greater resistance. Thus. Dolanmaz and cols⁵⁶ recommend intermaxillary wiring in the immediate postoperative period, following an experimental comparison in sheep the stability of resorbable plates PLLA-PGA 82:18 with titanium in the osteosynthesis of the sagittal osteotomies of the mandible, with an advance of 5 mm.

• Cost. Currently the cost of resorbable osteosynthesis is 2- 3 times higher that titanium osteosynthesis. However, if we bear in mind the cost of extracting the titanium, which is a far from negligible percentage, and that in some countries removal is routine, it is evidently cheaper than titanium. Moreover, in some countries, and soon in the rest of the EEC, the supply of titanium osteosynthesis material will be the same as resorbable material. That is to say, they will be packaged in one or several units, (and not in a general package) which will make the product more expensive. It is to be hoped that, with the widespread use of resorbable material, the price will fall.

Conclusions

The use of resorbable plates and screws in craniofacial osteosynthesis is more frequent every day. The literature has demonstrated that it is a valid alternative to titanium osteosynthesis in most clinical situations. There are still some disadvantages compared with titanium, such as more cumbersome handling and the economic cost. If we exclude fine fracture fragments and comminuted fractures, and some specific situations, resorbable material can substitute titanium in current craniomaxillofacial osteosynthesis. Experience is the only thing needed in order to surmount the initial learning curve that makes its use more cumbersome. Moreover, studies are needed in order to compare the different resorbable systems as the compositions, and as a result their characteristics, vary from one to another.

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