The use of self-reinforced biodegradable bone plates and screws in orthognathic surgery

J Oral Maxillofac Surg 60:59-65, 2002

The Use of Self-Reinforced Biodegradable Bone Plates and Screws in Orthognathic Surgery Timothy A. Turvey, DDS,* R. Bryan Bell, DDS, MD,† Tinerfe J. Tejera, DMD, MD,‡ and William R. Proffit, DDS, PhD§ Purpose:

This report describes the authors’ experience with self-reinforced biodegradable bone plates and screws to stabilize maxillary and mandibular osteotomies. Patient acceptance, demographics, types of osteotomy, means of stabilization, etiology of the deformity, complications, and patient disposition are reviewed. Patients and Methods: Seventy patients underwent 194 osteotomies of the maxilla and/or mandible. Stabilization of each osteotomy was achieved using self-reinforced polylactite bone plates and/or screws of similar size and configuration to that of titanium systems. Placement of the devices was accomplished transorally and transfacially, consistent with the osteotomy approach. Maxillomandibular elastics were used to control the position of the jaws in each patient. Results: There was good patient acceptance of the material (70/74). Stabilization was accomplished as planned in all patients. Three patients experienced problems that resulted in immediate loosening of the bone screws. The remaining 67 experienced no short-term problems (6 to 24 months), and healing progressed uneventfully. In each case, acceptable occlusion and favorable aesthetic changes were noted. Conclusions: The experience with self-reinforced polylactite bone plates and screws to stabilize maxillary and mandibular osteotomies has been favorable on short-term observation. © 2002 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 60:59-65, 2002 Just as the development of metal bone plates and screws revolutionized the conduct of oral and maxillofacial surgery, the development of biodegradable plates and screws is now poised on a similar frontier. Although bioresorbable materials have been used in surgery for decades, their principal role has been as suture material and membranes.1,2 Although biode-

gradable bone plates and screws have been used for more than a decade, reliable composition, strength, duration, presence of an inflammatory response, and proper design have been problematic.3-12 Self-reinforced polylactite polymers are currently available for use in the craniofacial skeleton, and these polymers have overcome many of the shortcomings of earlier materials.13-22 Combining adequate strength and rigidity with bioresorption has appeal for both patients and health providers. By eliminating the permanency of bone plates and screws there is less risk of infection and other long-term problems associated with metal in the body. Moreover, concerns about compatibility with future imaging needs, interference with radiation therapy, migration of the material, growth restriction, long-term palpability, and thermal sensitivity have been reduced.5,12 Polylactate, polyglycolate, and polydioxanone (polyalpha-hydroxy acids) are a few of the biodegradable materials that have undergone the scrutiny of human testing for more than 40 years. The strength, biocompatibility, and degradation process of each has been studied extensively. The products are initially hydrolyzed, then phagocytized, and finally excreted in ex-

*Professor and Chairman, Department of Oral and Maxillofacial Surgery, University of North Carolina at Chapel Hill, Chapel Hill, NC. †Chief Resident, Department of Oral and Maxillofacial Surgery, University of North Carolina at Chapel Hill, Chapel Hill, NC. ‡Fellow, Facial Plastic and Reconstructive Surgery, Carolina Surgical Arts, Greensboro, NC. §Professor and Chairman, Department of Orthodontics, University of North Carolina at Chapel Hill, Chapel Hill, NC. This study was supported by NIDR DE05215. The manufacturer provided no funds or materials for this study. Address correspondence and reprint requests to Dr Turvey: The University of North Carolina at Chapel Hill, Department of Oral and Maxillofacial Surgery, CB # 7450, Chapel Hill, NC 27599-7450. © 2002 American Association of Oral and Maxillofacial Surgeons

0278-2391/02/6001-0097$35.00/0 doi:10.1053/joms.2002.28274

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pired gas (CO2) and urine (H2O) through the Krebs cycle. When these materials are combined or when isomers of the same material are combined (copolymer), strength, absorption rates, and inflammatory response are controlled by altering the content and manufacturing process of the copolymer.12,13,21 Because all polymers (even those with the same chemical composition) are not identical, minor alterations in the formula and manufacturing process can result in profound effects on duration, strength, and inflammatory response. The manufacturing techniques are critical to the performance of the material, especially strength, degradation, and lack of inflammatory response. Polylactite exists in 2 forms: D and L isomers. Polymer engineers have determined that manufacturing polylactite plates and screws by extrusion increases the strength of the material by building molecular linkages. When these isomers are copolymerized (70L:30DL) and extruded, bone plates and screws of adequate strength, lasting 3 to 4 months and having a low inflammatory response, can be manufactured. The copolymer is able to be molded by bending with instruments and does not require heating. This is in contrast to copolymer plates and screws manufactured by injection molding or heat processing. These heat-dependent copolymers lack the strength of molecular linkage resulting from extrusion and require heat to mold into the proper configuration.19,20 The estimated length of complete biodegradation of the copolymer poly L/DL lactide is 2 to 3 years. Because of the prolonged degradation process, significant inflammation is minimized and the soft tissues are tolerant.23 This report describes the results of the use of selfreinforced polylactite bone plates and screws (poly L/DL lactide, Bionx Corp, Blue Bell, PA) in patients

undergoing osteotomies and repositioning of the maxilla and mandible.

Patients and Methods Seventy-four consecutive patients who were scheduled for osteotomies of the maxilla and/or mandible, and/or chin were offered stabilization with resorbable bone plates and screws. Offerings were made independent of age, gender, medical problems, etiology of the deformity, the type of osteotomy, the approach (oral or facial), the direction of skeletal movement, or the magnitude of skeletal movement. All patients were informed of the surgeon’s minimal experience with the system, the lack of US Food and Drug Administration approval for the use of the material in the mandible, the uncertainty of resorption, and the potential for an inflammatory response. The plates and screws were composed of a copolymer of L-lactic acid and D-lactic acid (70%:30%). The material was manufactured by the process of extrusion. The strength of this material is less than similar dimension titanium but stronger than other commercially available biodegradable plates (Fig 1). Seventy patients accepted the offer to be treated with the biodegradable materials: 49 women and 21 men, ranging in age from 5 to 53 years. Represented in this group were 6 patients with craniofacial microsomia, 3 patients with repaired cleft palate, and 4 patients with syndromes (Down, Tourette, craniofrontal dysplasia, congenital telangiectasia). One patient was an insulin-dependent diabetic, and all but 2 had not smoked for at least 3 months before surgery. The latter patients were suspected to have used tobacco during the immediate postoperative period even though they denied it. The

FIGURE 1. Comparative strength of poly L/DL lactide with another biodegradable material and titanium of similar dimension. (Information supplied by the manufacturer.)

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All sagittal osteotomies were stabilized using four 2.0-mm screws (20-mm long) placed transorally.24 In 1 patient, additional support was required from a transorally placed 2.0-mm biodegradable bone plate. In the 7 transcutaneously performed ramus osteotomies, bone plates were placed (2.0 or 2.4 mm) and, when defects were present at the osteotomy site, autogenous bone grafts were also placed (6/7). The 34 genioplasties were secured with 3 transorally placed screws that engaged both the proximal and distal segments. In 3 cases, bones plates were also necessary to adequately secure the segment. No patient was left in maxillomandibular fixation with wires. All patients used light elastics postsurgically to guide jaw movement. All patients were treated with routine antibiotic prophylaxis consisting of intravenous penicillin, cephalosporin, or clindamycin administered at induction of anesthesia and repeated every 6 hours for 24 hours. When bone grafts were placed, antibiotics were continued orally for 10 days.

Table 1. ETIOLOGY OF THE DEFORMITIES TREATED

Craniofacial microsomia Cleft lip/palate Craniofrontonasal dysplasia Down syndrome Tourette syndrome Congenital telangiectasia Developmental disorder Total

6 3 1 1 1 1 57 70

remaining patients were healthy, with typical dentofacial deformities of all varieties (Table 1). Forty-five patients underwent total maxillary osteotomies. Of these, 16 maxillas were in multiple segments. Eighty-eight intraoral sagittal osteotomies were performed, 7 other ramus osteotomies were done through transcutaneous incisions, and 34 genioplasties were completed. In addition, 2 patients underwent condylectomy at the same surgical setting. One patient had a rib graft placed for condyle reconstruction, which was stabilized with biodegradable screws. In 33 patients, simultaneous mobilization of the entire maxilla and mandible was performed; 15 of these patients also had simultaneous genioplasty (Table 2). All maxillary osteotomies were stabilized with biodegradable bone plates and screws placed through a transoral route. In most instances, 2.0-mm bone plates and screws were placed in 4 regions (pyriform aperture and zygomaticomaxillary buttress). In 2 patients, four 1.5-mm bone plates and screws were used and in 5 patients, four 2.0-mm screws alone were used to secure the maxilla. Autogenous bone grafts were used to reinforce the position of the maxilla in all patients undergoing maxillary advancement.

Results Of the 70 patients treated, all eventually healed. Three patients experienced immediate problems that resulted in loosening of the stabilization devices, and all 3 required additional surgery to reinforce the position of the segments. This included 1 patient who developed laryngospasm and required emergent reintubation. Another patient with Tourette syndrome experienced severe facial tics immediately after surgery and, as a result, the fixation in the mandible loosened. The third patient had Down syndrome, and postsurgical behavior resulted in loosening of the

Table 2. PROCEDURES PERFORMED AND MEANS OF STABILIZATION

No.

Means of Stabilization

Total maxillary osteotomy (segmental)

45 (16)

4—2.0-mm plates 4—1.5-mm plates 4—2.0-mm screws 2—2.20-mm plates and 2—2.0-mm screws

36 2 5 2

Sagittal osteotomy of mandibular ramus

88

4—2.0-mm screws 4—2.0-mm screws ⫹ 2.0-mm plate

87 1

Transcutaneous ramus osteotomy

9

2—2.0-mm plates 2—2.4-mm plates

Body osteotomy

1

Bone plate

Genioplasty Rib graft stabilization for condyle-ramus construction Simultaneous mobilization of maxillary and mandible (genioplasty)

34 1 33 (15)

3—2.0-mm screws Plate fixation Screw fixation

7 2 31 3 1

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genioplasty chen segment. One patient developed an infection at a sagittal osteotomy site 3 weeks postoperatively. The infection responded to incision, drainage, sequestrectomy, and antibiotics. The bone screws were left in place and timely union occurred. One other patient developed a nonproductive sinus tract in a sagittal osteotomy site 4 months postoperatively. Union had occurred, and no further treatment other than irrigation was done. At 15 months postsurgery, 1 patient had residual swelling (mild) and tenderness at a maxillary osteotomy site. At her request, the region was explored, and screw and plate remnants were removed. No purulence or exudate were present, and cultures were negative. Another patient with preexisting sinus symptoms underwent septoplasty and exploration of the sinus by an otolaryngologist 6 months after maxillary osteotomy. Screw ends were noted in the sinus, and the membranes were described as inflamed. No purulence or exudate were noted, and no biopsy or culture were performed. The association of these findings and the relationship to the material is obscure. Stabilization of the maxilla with biodegradable bone plates and screws was associated with greater mobility of the segments during the postsurgical phase than with of titanium systems. This mobility facilitated postsurgical adjustment of the position of segments and did not interfere with bone healing. This is considered advantageous over the more rigid titanium systems. In the 5 patients whose maxillas were stabilized with four 2.0-mm screws and in the 2 patients stabilized with four 1.5-mm plates and screws, postsurgical movement exceeded that in patients stabilized with 2.0-mm plates and screws. The movement persisted for several weeks and reduced as healing progressed. In all intraoral sagittal osteotomy sites and in the transcutaneously performed ramus osteotomy sites, stabilization with the biodegradable hardware was satisfactory and, in no instance, was mobility detected. There was no prolonged mobility, instability, or nonunion at the osteotomy sites. As of September 2001, almost all of the 70 patients completed orthodontic care with satisfactory results (Class I occlusion and improved aesthetics).

Discussion The self-reinforced polylactite system used was technically awkward and similar to the initial bone plate and screw systems made of titanium or stainless steel developed almost 2 decades ago. Plate design and the screw head to plate interface were bulky, but the surgeons were always able to manage, especially because the plates could be cut to size. The plate size (2.0 and 2.4 mm) provided adequate strength and

stabilization for use in both the maxilla and mandible, even with extensive mandibular advancements. The packaging and delivery system, as well as the instrumentation, were primitive and not user-friendly. The self-reinforced polymers made by extrusion require bending with pliers; heating is not necessary. Gamma radiation is used for sterilization, and resterilization and/or reusage are not possible. When screws broke, it was always possible to redrill and tap through the same hole. Screws of the same dimension or larger were used for replacement. The pilot hole is drilled with a power drill; the tapping system requires hand instrumentation. This is a major disadvantage because it requires more time and effort by the surgical staff, especially because some patients required more than 30 screws. In a few instances, nonthreaded but serrated tacks were used, which eliminated the need for tapping. The manufacturer has developed a springloaded pressure device that fastens the tack and bone to the plate by pressure, without the need for tapping. The use of this technologic innovation reduced the time of placement and the labor intensity and was a welcome addition to the system. Unfortunately the system is not yet available from the manufacturer. The cost of the material exceeds the cost of titanium by approximately 20%. Stabilization of sagittal osteotomies was accomplished with four 2.0-mm screws placed transorally. Either 18- or 20-mm screws were usually placed because this length permits diagonal bicortical engagement. When using transoral placement of 2-mm screws for stabilization of sagittal osteotomies, although tapping was burdensome, screw placement was easy and did not displace the segments as sometimes occurs with the self-threading metal systems. The heads of the polylactite screws were not able to be threaded into the bone. If excessive length was noted, the excess was easily removed with a batterypowered cautery loop. There is a learning curve to screw placement. If screws broke, the holes were easily retapped, and another screw of similar dimension was placed. Because the longest tack available is 8 mm, their use for stabilization of sagittal osteotomies was not possible. The strength of the material is a major concern when using biodegradable systems. When the primary author (T.A.T.) initiated the use of this system, it was with the philosophy that less foreign material is better and that transoral placement is always preferred. The material showed adequate strength to maintain bone segments during the critical bone healing phases (6 to 8 weeks), and the same quantity of material was used to support segments as was used when titanium was employed. Therefore, four 2.0-mm bone plates were used to secure most maxillas. In some instances, four 1.5-mm bone plates were

TURVEY ET AL

FIGURE 2. Tissue specimen obtained at 4 months after surgery shows fibrous tissue with no inflammation and indicates minimal biodegradation.

used and in other instances four 2.0-mm screws were used to secure the position of the maxilla. Autogenous bone grafts were always wedged into place and, in some instances, were secured with additional polylactite screws. When the 1.5-mm bone plating system and isolated screw fixation for stabilization of the maxillary segments were used, greater mobility of the maxilla was detected. For this reason, it is advised to use four 2.0-mm bone plates when stabilizing the maxilla. Adequate strength to resist displacement and prevent mobility during acute healing, followed by gradual loss of strength to permit bone maturation, are ideal characteristics of resorbable bone plates and screws used in the maxillofacial skeleton. Maintenance of adequate strength to permit jaw movement for 12 weeks, as is afforded with this polymer, permits initial bone formation. The gradual degradation of the material after 12 weeks permits transference of the masticatory forces to the immature bone, which enhances the maturation of woven bone. Light elastics were used in each patient, and complete jaw function, including chewing, was not permitted for the first 8 weeks. The diet was restricted to soft, nonchewable foods. In general, this population was highly compliant, which factored significantly in the success reported. It is doubtful if the same level of success will be observed in patients who sustain jaw fractures and are stabilized with this system. There are significant compliance differences between the trauma population and the orthognathic surgery population. Of the 3 patients who experienced immediate loosening of the polylactite bone screws, 2 were syndromic, and 1 was an 18-year-old, 240-lb male. The latter patient developed laryngospasm on extubation after simultaneous maxillary and mandibular osteotomies. The gagging and retching while in elastic traction, combined with the trauma of emergent reintu-

63 bation, loosened the maxilla. Failure occurred at the screw– bone interface and not in the plates. The mandibular fixation remained stable. The patient with Tourette syndrome underwent simultaneous maxillary and mandibular osteotomies to improve vertical maxillary excess, mandibular deficiency, and retrogenia. At the completion of surgery, the patient experienced uncontrollable facial tics and twitches. Before adequate sedation could be administered, the genioplasty segment loosened and retracted into the neck. On exploration, the screws at the genioplasty site were noted to be bent but not broken. The genial segment had fractured around each screw and muscle contraction had displaced the segment. At the sagittal osteotomy sites, the positional screws on each side had loosened, and it was decided to replace all of the hardware in the mandible with titanium bone plates and screws. Subsequently, the patient healed uneventfully. In the patient with Down syndrome, the genial segment loosened and retracted into the neck the day after surgery. Reoperation and restabilization of the segment with titanium bone screws was done. All 3 of these complications occurred in the first 20 operated patients, which is consistent with a learning curve. The authors had the opportunity to reoperate 2 patients at 2 different postsurgical time intervals. Figure 2 is a tissue sample taken from a 15 year old at the genioplasty site at 4 months after surgery. The osteotomy and bone graft sites had healed, but the bone plates and screws remained in place with minimal evidence of degradation. The histologic examination of the tissue around the bone plate revealed fibrous tissue without evidence of inflammation, which is consistent with phase 1 of the degradation process (hydrolysis). Figure 3 is a tissue sample removed from a 29-year-old woman at the lateral maxillary wall 15 months after surgery. Fibrous tissue, some giant cells, and a mild inflammatory infiltrate were observed in

FIGURE 3. A soft tissue biopsy at 15 months after surgery is consistent with phagocytosis and mild inflammation. Note the macrophages and lymphocytic infiltration. Arrow points to a remnant of a screw.

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SELF-REINFORCED BIODEGRADABLE BONE PLATES AND SCREWS

the specimen, which was consistent with phase 2 degradation (phagocytosis). In this patient, the bone, including the bone grafts, was healed and even the drill holes had filled with bone. Small remnants of the screw heads were discovered in the soft tissues over-

FIGURE 5. A, Immediate postsurgery radiograph of this 29 year old shows radiolucencies in the ramus where screws were placed. B, Fifteen months after surgery the radiolucencies persist but are smaller, suggesting incomplete bone healing in the defects.

lying the bone. The biopsy specimen included these remnants. Because the poly L/DL lactite copolymer is radiolucent, tracking degradation with radiographs is difficult. According to the manufacturer, complete elimination is expected within 2 to 3 years. In the mandible, it is possible to identify the radiolucencies of the screw holes immediately after surgery. This is not possible in the maxilla. In some patients, the mandibular screw sites were disappearing on the radiographs at 6 months. This suggests degradation of the screws and bone healing in the defects (Fig 4). In others, the screw sites remained visible on the 1-year postoperative radiograph (Fig 5). This observation suggests nonhealing of the screw holes or delayed degradation of the material. The significance of persistent radiolucencies is unknown. In no instance was bone healing at the osteotomy delayed or instability detected. These observations demand long-term scrutiny.

Addendum

FIGURE 4. A, Immediate postsurgery radiograph of this 18 year old shows radiolucencies in the ramus where screws were placed. B, Six months after surgery the radiolucencies appear to be healing with bone.

Since submission of the article, the primary author (T.A.T.) has performed orthognathic surgery on another 60 patients (35 women and 25 men from 10 to 59 years of age) using self-reinforced biodegradable bone plates and screws placed in an identical fashion. The 141 procedures included 40 Le Fort I osteotomies (21 in multiple segments), 78

TURVEY ET AL sagittal osteotomies, 16 genioplasties, 6 inverted-L ramus osteotomies, and a symphysis osteotomy. Twenty-three cases involved simultaneously performed maxillary and mandibular osteotomies. These cases have been followed up for variable periods, up to 1 year. Displacement of the osteotomy segment after surgery occurred in only 1 patient in this series. The reason was fracture of the bone at the genioplasty site and not screw breakage. Another patient developed a sterile abscess 3 months after surgery, which responded to removal of the material. Bone healing occurred uneventfully and without the need for further stabilization. Two of the patients in the initial series developed sterile abscesses at maxillary osteotomy sites approximately 18 months after surgery. These responded to debridement and did not interfere with bone healing. The total series now includes 130 patients and 336 osteotomies, supporting the usefulness of this technology in orthognathic surgery. Evaluation of the long-term fate of the material and outcome measures are in progress.

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65 10. Montag ME, Morales L, Daane S: Bioabsorbables: Their use in pediatric craniofacial surgery. J Craniofac Surg 8:97, 1997 11. Goldstein JA, Quereshy FA, Cohen AR: Early experience with biodegradable fixation for congenital pediatric craniofacial surgery. J Craniofac Surg 8:110, 1997 12. Pietrzak WS, Sarver DR, Verstynen ML: Bioabsorbable polymer science for the practicing surgeon. J Craniofac Surg 8:87, 1997 13. Tormala P: Ultra-high strength self-reinforced absorbable polymeric composites for application in different disciplines of surgery. Clin Mater 13:35, 1993 14. Haers PE, Sailer HF: Biodegradable self-reinforced poly-L/DL lactide plates and screws in bimaxillary orthognathic surgery: Short-term skeletal stability and material related failures. J Craniomaxillofac Surg 26:363, 1998 15. Haers PE, Suuronen R, Lindqvist C, et al: Biodegradable polylactide plates and screws in orthognathic surgery: Technical note. J Craniomaxillofac Surg 26:87, 1998 16. Kallela I, Laine P, Suuronen R, et al: Skeletal stability following mandibular advancement and rigid fixation with polylactide biodegradable screws. Int J Oral Maxillofac Surg 27:3, 1998 17. Kallela I, Laine P, Suuronen R, A et al: Osteotomy site healing following mandibular sagittal split osteotomy and rigid fixation with polylactide biodegradable screws. Int J Oral Maxillofac Surg 28:166, 1999 18. Suuronen R, Pohjonen T, Vasenius J, et al: Comparison of absorbable self-reinforced multiplayer poly-L-lactide and metallic plates for the fixation of the mandibular body osteotomies: An experimental study in sheep. J Oral Maxillofac Surg 60:255, 1992 19. Suuronen R, Pohjonen T, Wessman L, T et al: New Generation biodegradable plate for fracture fixation: Comparison of bending strengths of mandibular osteotomies fixed with absorbable self-reinforced multi-layer poly-L-lactide plates and metallic plates—An experimental study in sheep. Clin Mater 9:77, 1992 20. Suuronen R, Pohjonen T, Taurio R, et al: Strength retention of self-reinforced poly-L-lactide screws and plates: An in vivo and in vitro study. J Mater Sci 3:246, 1992 21. Suuronen R, Pohgonen T, Hietanen J, et al: A 5-year in vitro and in vivo study of the biodegradation of polylactide plates. J Oral Maxillofac Surg 56:604, 1998 22. Suuronen R, Manninen MJ, Pohjonen T, et al: Mandibular osteotomy fixed with biodegradable plates and screws: An animal study. Br J Oral Maxillofac Surg 25:341, 1997 23. Suuronen R, Kallela I, Lindqvist C. Bioabsorbable plates and screws: Current state to the art in facial fracture repair. J Craniomaxillofac Trauma 6:19, 2000 24. Turvey TA, Hall DJ: Intraoral self-threading screw fixation for sagittal osteotomies: Early experience. Int J Adult Orthodont Orthognath Surg 1:243, 1986