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IDEAS AND INNOVATIONS Use of Absorbable Poly (D,L) Lactic Acid Plates in Cranial-Vault Remodeling: Presentation of the First Case and Lessons Learned About Its Use HUMBERTO L. ACOSTA, M.D., F.A.C.S. ERIC J. STELNICKI, M.D., F.A.C.S. LUIS RODRIGUEZ, M.D., F.A.C.S. LISA A. SLINGBAUM, D.M.D. Objective: To present the first clinical use of a new bioabsorbable material, poly (D,L) lactic acid (PDLLA), in pediatric cranial-vault remodeling procedures. This discussion will highlight the benefits and detriments of PDLLA in comparison with currently used absorbable plating systems. Design: This was a case study documenting the first North American case in which PDLLA was used to treat craniosynostosis. Materials and Methods: Evaluation of pure PDLLA, a copolymer product of the mixture of poly L-lactic acid and its D-isomer, was used in an 8-month-old boy with a severe phenotypic expression of sagittal craniosynostosis. No signs of elevated intracranial pressure were present, and the neurological examination did not show impairments. Total cranial-vault remodeling with the ‘‘hung-span’’ technique was performed. The Resorb X system, containing 2.2mm screws and 0.6- to 1-mm-thick plates, was used to stabilize the reconstructed cranial vault. Results: No surgical complications occurred. The preoperative cranial index measured 62. The scaphocephalic appearance of the skull was eliminated, and the cranial index was normalized to 77. The screws and plates were less palpable than other plating systems. Twelve months postoperatively, none of the plates and screws were identifiable by external palpation. Conclusion: Resorb X has been successfully used in the treatment of sagittal craniosynostosis. Its rapid rate of resorption and lower profile make it an advantageous system for pediatric skull reconstruction. This represents the first use of this product in the United States for any pathology. KEY WORDS: cranial vault, craniosynostosis, PDLLA

Craniosynostosis is a complex process characterized by premature closure of one or more cranial sutures, resulting in an abnormally shaped skull. The prevalence of craniosynostosis is 1 in 2000 live births (Warren and Longaker, 2001) and is four times more predominant in males. It has a heterogeneous pathogenesis and etiology, and multiple causes of craniosynostosis have been identified, including genetic dis-

orders, chromosomal syndromes, metabolic disorders, mucopolysaccharidoses, mucolipidoses III, hematologic disorders, teratogens, and malformations (Cohen 1993). Isolated, nonsyndromic, sagittal craniosynostosis is the most common type of craniosynostosis, occurring at a rate of 1 in 5000 live births (Posnick, 2000). The condition is characterized by an increased anterior-posterior length of the skull and decreased biparietal width. This produces a long and narrow scaphocephalic shape to the skull. If the deformity remains untreated, the cranial vault will remain abnormal and may lead to increased intracranial pressure, visual defects, and developmental delay (Turvey and Gudeman, 1996; Warren and Longaker, 2001). The treatment of sagittal craniosynostosis has evolved considerably over the past 30 years. Initially, most of the bone fragments produced during a cranial-vault remodeling procedure were fixated with suture or wire. In the 1980s, wire fixation was replaced by metallic plating systems that offered

Drs. Acosta and Slingbaum are Craniofacial Fellows and Dr. Stelnecki is a Craniofacial Plastic Surgeon at Joe DiMaggio Children’s Hospital Cleft and Craniofacial Center, Hollywood, Florida, and at Nova Southeastern University, School of Dentistry, Fort Lauderdale, Florida. Dr. Rodriguez is a Neurosurgeon at Joe DiMaggio Children’s Hospital Cleft and Craniofacial Center, Hollywood, Florida. Paper presented at the Florida Cleft Palate–Craniofacial Association Winter Symposium in Orlando, Florida, January 17–19, 2003. This work was supported by a grant from KLS Martin, Jacksonville, Florida. Submitted May 2003; Accepted May 2004. Address correspondence to: Dr. Eric Stelnicki, 1150 N 35th Avenue, Suite 540, Hollywood, FL 33021. E-mail estelnicki@drstelnicki.com. 333


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FIGURE 1 The patient shows dolichocephalic head shape, with prominence of frontal bones, occipital protuberance, and anterior-posterior elongation.

greater stability to the newly constructed cranial vault. Although they were an improvement over wire, metal plates still had many disadvantages. The first was the concern that use of permanent metallic hardware may interfere with continuous growth. In addition, infections, bone atrophy, osteopenia because of stress shielding, and palpability often necessitated surgical removal (Pietrzak, 2000; Losken et al., 2001). Metallic fixation devices also interfere with therapeutic imaging and irradiation (Pietrzak, 2000). In the mid to late 1980s, metal implants were discovered to undergo a passive intraosseous translocation effect when placed on a growing skull

(Cohen et al., 2001). During this process, the growing cranial bones envelop the metal fixation hardware and translocate it to an intracranial position in contact with the dura. This position created significant concerns about the risks of longterm injury to the dura or central nervous system (Stelnicki and Hoffman, 1998). Absorbable technologies were created in response to the problems with metal fixation, based on a variety of preexisting monomers (L-lactic acid, glycolic acid, D-lactic acid). In 1996, the first absorbable product for craniofacial fixation was introduced (Lactosorb, Walter Lorenz Co., Jacksonville,

FIGURE 2 Computed tomography scans show an elongated calvarium, with poor visualization of the sagittal suture, involving regions of the coronal and lambdoid area.


Acosta et al., ABSORBABLE PDLLA PLATES IN CRANIAL-VAULT REMODELING

FIGURE 3 A: Note fused sagittal suture, with asymmetry between left and right sides. B: Note also a severe occipital bullet.

FL), and a new era began. Several advantages over metal implants were implemented, such as avoiding a second surgery to remove the metal hardware, avoiding long-term implant migration, and eliminating the potential for stress shielding after the use of metal implants. In addition, there was no interference of absorbable products with diagnostic or therapeutic radiation (Pietrzak, 2000). The initial monomers had a very slow rate of absorption. As a result, copolymers were produced that have a biphasic fashion of degradation. The implant loses its integrity in phase 1 of degradation, and the implant mass is reduced in phase 2. Therefore, although the implant is still present, it offers little in strength after the first few months (Pietrzak et al., 1997). The ideal implant for surgical use should be relatively small and made of noncrystalline (amorphous) dye-free copolymers that degrade at a moderate rate. Poly (D,L) lactic acid (PDLLA) (Resorb X, KLS Martin, Jacksonville, FL), a combination of poly L-lactic acid and its D-isomer, has many of the idealized implant features. The product is an amorphous polymer (no crystalline components), retains its mechanical properties over a period of 10 weeks, then absorbs

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FIGURE 4 A: A 3.5-cm-wide sagittal strip craniectomy was marked. Bilateral parietal flaps were also marked to be used for tongue-and-grove lateral advancement. B: Here, the coronal ridge shows the coronal suture synostosis.

until 72 weeks postimplantation. It has a low profile that allows its use in osteosynthesis carried out in non–load-bearing craniomaxillofacial regions. CASE STUDY An 8-month-old Caucasian boy presented for treatment for sagittal synostosis with significant scaphocephaly. He was noted to have a scaphocephalic head shape at birth, which worsened with age. At 8 months, his head circumference was 46 cm, with a cranial index of 62. His head had prominence of frontal bones, occipital protuberance, and anterior-posterior (AP) elongation (Fig. 1). The patient had a palpable ridge along the sagittal suture. Neither the anterior nor the posterior fontanelles were palpable. No symptoms of elevated intracranial pressure were present. Computed tomography (CT) examination showed an elongated calvarium with poor visualization of the fused sagittal suture and involvement of regions of the coronal and lambdoid area (Fig. 2). The coronal suture was displaced approximately 1 cm more posterior


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FIGURE 5 A: Note the abnormal elevation in the forehead, with the right parietal bone higher than the left; hence, the entire frontal bone flap was marked in order to be raised. B: The occipital bullet was marked as well to be removed and recontoured around the lambdoid suture.

on the left side, and the parietal bone was 1 cm higher on the left side. A severe occipital bullet was present (Fig. 3). Surgical Procedure The surgical procedure was carried out with the patient placed in the prone position. A bicoronal approach, using a zigzag incision, was utilized and intraoperative findings confirmed the diagnosis that the sagittal suture was fused. After complete exposure of the cranial vault, a 3.5-cm-wide sagittal suture strip craniectomy was performed (Fig. 4A). Bilateral parietal flaps, which would also be used for tongue and groove lateral advancement, were elevated (Fig. 4B). Because of the abnormal elevation in the patient’s forehead, an entire frontal bone flap was raised (Fig. 5A). The occipital bullet

was removed and recontoured around the lambdoid suture (Fig. 5B). The frontal bone flap height was reduced by 1.5 cm from the supraorbital rim, and the entire flap was hinged off the rim, with multiple 2.0 resorbable (PDS) sutures. Barrel stave osteotomies were performed in the parietal and temporal regions to allow for lateral widening (Fig. 6A). The barrel staves were out-fractured approximately 1.5 cm on each side by using the ‘‘hung-span’’ technique with 0.6- to 1-mm KLS Martin Resorb X absorbable plates and 2.2-mm screws to hold the osteotomies in their new position (Figs. 6B and 7A). The occipital bullet was osteotomized in a daisy-type fashion, where the central aspect was left intact within multiple radial osteotomies away from the center. These were then out-fractured to allow for complete expansion (Fig. 7A). The

FIGURE 6 Barrel stave osteotomies were performed in the parietal and into the temporal regions to allow lateral widening. A: The barrel staves were out-fractured 1.5 cm on each side. B: The hung-span technique for suspending lateral barrel stave osteotomies was performed.


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FIGURE 7 Note that the occipital bullet was osteotomized in a daisy-type fashion. The central aspect was left intact, and multiple radial osteotomies were done away from the center. A: KLS Martin Resorb X absorbable plates and screws were used. B: A close-up view of the plates is shown.

fused sagittal suture was then recontoured, osteotomized, shortened by 1.5 cm, and attached between the new occipital bullet and the frontal bone (Fig. 8A and 8B). The frontal bone was barrel stave osteotomized laterally to create bitemporal widening (Fig. 8B). The biparietal flaps were contoured with a Tessier bone bender and cut in a tongue-and-grove fashion to allow for rounding and expanding in this area. These flaps were held in place with a combination of PDS sutures and Resorb X plates (Fig. 9). Finally, burring and contouring of bones and plates were performed.

No complications occurred during surgery. The immediate postoperative result of cranial-vault remodeling is shown in Figure 10. Figure 11 shows an early postoperative CT scan image showing important changes in the cranial shape. Photographs and anthropometric measurements of the patient were taken at the follow-up visit. The cranial index at the follow-up visit was improved to 77 from 62. The patient’s head shape appeared normal, scars were not visible without moving the hair, and the plates and screws were not palpable (Fig. 12).

FIGURE 8 A, B: The fused sagittal suture was recontoured, osteotomized, and attached between the new occipital bullet and the frontal bone. B: The frontal bone was also barrel stave osteotomized laterally to create bitemporal widening.


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FIGURE 9 The biparietal bones were contoured and cut in a tongue-andgrove fashion and were held in place with a combination of PDS suture and Resorb X plates.

DISCUSSION Absorbable plating systems have emerged as the preferred method of fixation for the pediatric craniomaxillofacial skeleton. Absorbable plates have decreased the risk of growth retardation, implant migration, palpability, interference with images, and other detrimental effects of a permanent foreign body. Cranial-vault remodeling requires contourable plates and mesh panels that can match the newly remodeled bone structure. In the case of Resorb X, this can be achieved by heating the material intraoperatively to render it temporally malleable. Among absorbable materials, polylactic acid has been used for 30 years in medical products such as sutures and orthopedic pins. Heidemann et al. (2001) demonstrated that PDLLA, unlike other implants, does not decrease tissue pH by more than 1 unit. The interstitial fluid, without any adverse clinical consequence, easily buffers this minimal change in pH. During the analysis, no trace of crystallinity was detected around PDLLA implants, and only a mild foreign body reaction could be seen. This significantly reduced the itching and irritation to the scalp. Osteosynthesis plates for use in craniomaxillofacial surgery should have an initial bending strength of more than 100 N/mm2 or about 60 N/mm2 at 4-weeks postimplantation to achieve undisturbed healing of facial fragments. In animal models, PDLLA showed a constant value of 102 N/mm2 up to 4-weeks postimplantation, 90% of the initial bonding strength was measured in the sixth week, and 60% of the initial values were maintained up to the 12th week. After 16 months, PDLLA had been totally absorbed from the extracellular space (Heidemann et al., 2001). Several modifications are required to properly use this new polymer. A nonaqueous or an aqueous hot bath and a warmed instrument to cut the plates are needed for the procedure to prevent cracking of the polymer. Use of the 0.6-mm plates is limited to regions of low tension because they are not capable

FIGURE 10 Immediate postoperative result of cranial-vault remodeling.

FIGURE 11 Early postoperative CT scan image showing important changes in the cranial shape.


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FIGURE 12 Postoperative front, side, back, and top views showing normal head shape.

of supporting any bony structure that had to resist a load. In animal studies, PDLLA has been reported to have a rapid absorption rate, and the plates have a thin profile. Both features avoid palpability of plates and screws sooner after surgery. The present results indicate that PDLLA plates are safe and effective for calvarial reconstruction in either simple or multiple-suture synostosis where non–load-bearing osteotomies are required. It has a shorter period of absorption and lower profile (0.3, 0.6, and 1 mm). The cranial index was normalized to 77 from 62. The screws and plates were less palpable in the postoperative period than other plating systems. Four-months postoperatively, none of the plates and screws could be identified by external palpation. By the 12-month follow-up, excellent skull growth could be appreciated. REFERENCES Cohen MM Jr. Sutural biology and the correlates of craniosynostosis. Am J Med Genet. 1993;47:581–616.

Cohen SR, Holmes RE, Amis P, Fitchner H, Shusterman EM. Tacks: a new technique for craniofacial fixation. J Craniofac Surg. 2001;12:596–602. Heidemann W, Jeschkeit S, Ruffieux K, Fischer JH, Wagner M, Kru¨ger G, Wintermantel E, Gerlash KL. Degradation of poly (D, L) lactide implants with or without addition of calciumphosphates in vivo. Biomaterials. 2001; 22:2371–2381. Losken A, Williams JK, Burstein FD, Cohen SR, Hudgins R, Boydston W, Reisner A, Simms C. Outcome analysis for correction of single suture craniosynostosis using resorbable fixation. J Craniofac Surg. 2001;12:451–457. Pietrzak WS. Critical concepts of absorbable internal fixation. J Craniofac Surg. 2000;11:335–341. Pietrzak WS, Sarver DR, Verstynen ML. Bioabsorbable polymer science for the practicing surgeon. J Craniofac Surg. 1997;8:87–91. Posnick JC. Scaphocephaly: sagittal synostosis. In: Posnick JC, ed. Craniofacial and Maxillofacial Surgery in Children and Young Adults. Philadelphia: WB Saunders; 2000:199–230. Stelnicki EJ, Hoffman W. Intracranial migration of microplates versus wires in neonatal pigs after frontal advancement. J Craniofac Surg. 1998;9:60–64. Turvey TA, Gudeman SK. Nonsyndromic craniosynostosis. In: Turvey TA, Vig KWL, Fonseca RJ, eds. Facial Cleft and Craniosynostosis Principles and Management. Philadelphia: WB Saunders; 1996:596–629. Warren SM, Longaker MT. The pathogenesis of craniosynostosis in the fetus. Yonsei Med J. 2001;42:646–659.


Use of Absorbable Poly (D,L) Lactic Acid Plates in Cranial-Vault