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Outcomes of Cranioplasty with Synthetic Materials and Autologous Bone Grafts Jaakko M. Piitulainen1,3, Tommi Kauko4, Kalle M. J. Aitasalo1,3, Ville Vuorinen2, Pekka K. Vallittu3, Jussi P. Posti2
OBJECTIVE: Using current surgical methods, cranioplasty is associated with a high complication rate. We analyzed if there are preexisting medical conditions associated with complications and compared the effect of different implant materials on the degree of complications.
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METHODS: A retrospective review of the medical records of all patients who underwent cranioplasty for cranial bone defects during the period 2002e2012 was conducted, and 100 consecutive cranioplasty procedures that met eligibility criteria were identified. Patients were analyzed in 4 groups, which were created based on the cranioplasty material: autograft (n [ 20), bioactive fiberereinforced composite (n [ 20), hydroxyapatite (n [ 31), and other synthetic materials (n [ 29). Survival estimates were constructed with Kaplan-Meier curves, and the differences between categorical variable levels were determined using a log-rank test. Multiple comparisons were adjusted using a Sidák correction.
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RESULTS: During a median follow-up time of 14 months (interquartile range 3e39 months), 32 of 100 patients (32.0%) developed at least 1 complication. A minor complication occurred in 13 patients (13.0%), whereas 19 patients (19.0%) developed a major complication, which required reoperation or removal of the implant. In the autograft subgroup, 40.0% of patients required removal of the cranioplasty. The 3-year survival of the autograft subgroup was lower compared with other subgroups of synthetic materials. In hydroxyapatite and bioactive fiberereinforced composite
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Key words Autograft - Bioactive glass - Bioglass - Biomaterials - Craniectomy - Cranioplasty - Fiber-reinforced composite - FRC - Skull bone defect -
Abbreviations and Acronyms BG: Bioactive glass FRC: Fiber-reinforced composite HA: Hydroxyapatite PE: Polyethylene PEEK: Polyetheretherketone
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groups, fewer complications were observed compared with the autograft group. CONCLUSIONS: Based on these results, synthetic materials for cranial bone defect reconstruction exhibit more promising outcomes compared with autograft. There were differences in survival rates among synthetic materials.
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INTRODUCTION
I
n modern neurosurgical practice, craniectomy is a common procedure that may be needed secondary to a traumatic skull bone fracture, tumor infiltration of the skull bone, a malignant middle cerebral artery infarction, or severe infection. The objective of cranioplasty—reconstruction of a skull bone defect— is to diminish the complications of a craniectomy. These complications include herniation of the cortex through the bone defect, subdural effusion, seizures, and syndrome of the trephined (13, 15). Other objectives are to restore the earlier contour of skull bone and to protect the underlying brain. Cranioplasty is associated with a high complication rate with present surgical methods (23, 32). A postoperative complication rate of 10%e40% has been reported in large cranioplasty series (2, 6, 17, 35). Frozen autologous bone graft is traditionally used for primary reconstruction because it is readily available. However, more recent reports suggest that problems after cranioplasty with frozen bone may be more common than was thought previously (12, 18). Polymethyl methacrylate (PMMA) is used as bone cement (i.e., polymerized in situ from methyl methacrylate monomer and
PMMA: Polymethyl methacrylate SSI: Surgical site infection From the Departments of 1OtorhinolaryngologyeHead and Neck Surgery, Division of Surgery and Cancer Diseases, and 2Neurosurgery, Division of Clinical Neurosciences, Turku University Hospital; and 3Turku Clinical Biomaterials Centre, Institute of Dentistry, and 4Department of Biostatistics, University of Turku, Turku, Finland To whom correspondence should be addressed: Jaakko M. Piitulainen, M.D. [E-mail:
[email protected]] Citation: World Neurosurg. (2015). http://dx.doi.org/10.1016/j.wneu.2015.01.014 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2015 Elsevier Inc. All rights reserved.
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polymer powder mixture) and as a bulk polymer implant material. PMMA, when used in bulk polymer form, is considered a reliable and inexpensive implant material (14), which showed better longterm outcomes compared with frozen autograft (22). PMMA, when used as bone cement, causes local toxic reactions, and the material becomes encapsulated by fibrous tissues. Other commercially available materials include hydroxyapatite (HA); titanium; polyethylene (PE); polyetheretherketone (PEEK) (19); and glass fiberereinforced composite (FRC), which is loaded with particulates of bioactive glass (BG). Meta-analyses of available data are scarce (9, 28, 29). The optimal timing of cranioplasty and numerous associated risk factors predicting complications are unknown. In the present study, we investigated whether preexisting medical conditions are associated with complications after cranioplasty and compared the degree of complication with different surgical materials. A 10-year consecutive retrospective study was performed to analyze these after cranioplasty. MATERIALS AND METHODS Selection Criteria and Study Population We reviewed electronic medical records from all patients who underwent a skull bone defect (>4 cm2) reconstruction during a 10-year period at our tertiary care institution, which has Neurosurgical and Head and Neck surgery departments that are responsible for craniofacial reconstructive surgery of people living in Southwest Finland, Satakunta, and Åland Islands areas (combined population of 725,000). A database was generated by querying procedures with the current procedural terminology codes for cranioplasty from June 2002 through December 2012. We excluded patients who had not undergone cranioplasty for previous craniectomy, but rather some other related procedure (i.e., operation for craniosynostosis or a maxillofacial reconstruction). After these exclusion criteria were applied, 84 consecutive patients who underwent 100 cranioplasty procedures were identified to be eligible and were entered into the database. The medical records were reviewed for the following variables: age, gender, presenting diagnosis, material used for skull bone defect reconstruction, time interval between craniectomy and reconstruction, defect size, and anatomic location. Preexisting conditions considered were the following: diabetes, abuse of intoxicants, immunosuppressive medication, smoking, radiation therapy, infection, and body mass index. The definition of infection included intracranial infection before cranioplasty and infection of the previously implanted material. Follow-up outcome was measured at the following time points: 1 month, 6 months, 12 months, and 36 months. Outcome was defined as normal when no wound healing problems or other complications were observed. We defined complications as major when revision surgery was needed and as minor when conservative treatment was sufficient. The following events after cranioplasty were recorded: superficial incisional surgical site infection (SSI), deep incisional SSI, epidural hematoma, cerebrospinal fluid leak, hydrocephalus, exposure of implant, resorption, implant breakage, implant migration, and cosmetic appearance. The location and the size of each defect were documented from preoperative computed tomography images. The cranial bone defects were classified into 3
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groups based on the size of the defect according to the classification by Uygur et al. (34). Autogenous bone flaps were stored at 80 C under sterile conditions until reimplantation. A swab sample was taken before storage. If bacterial growth was seen, the bone flap was discarded. Intraabdominal placements were not performed at our institution. Cranioplasty Materials During the study period, numerous different materials were used for skull bone reconstruction, including autogenous bone, fiberreinforced composite (FRC) containing particles of BG S53P4 (1), HA bone cement paste, PMMA as a moldable bone cement mass, porous PMMA scaffold coated with BG granules (24), titanium mesh and solid titanium, PEEK, and PE. The autogenous bone flaps were secured with titanium miniplates (Craniofix, Aesculap; B. Braun Melsungen AG, Melsungen, Germany). Alloplasts were fixed in place with titanium screws (Matrix; Synthes, Inc., West Chester, Pennsylvania, USA) or titanium miniplates and occasionally with biodegradable screws. Infection prophylaxis with intravenous antibiotics was given according to departmentspecific protocols (cefuroxime 3 g preoperatively and 1.5 g 3 times daily for 3 days after cranioplasty). The 100 cranioplasties were divided into 4 subgroups for subgroup analysis: autograft (n ¼ 20), FRC (n ¼ 20), HA (n ¼ 31), and other synthetic materials (n ¼ 29). We merged PMMA, PMMA-BG, PEEK, titanium, and PE into 1 subgroup (other synthetic material) because these alloplasts are less commonly used at our institution. As in any retrospective study, there was some paucity in the follow-up data. Of 100 patients, 38 (38.0%) had follow-up data at the time point of 3 years. However, if a normal healing pattern was observed at the last follow-up visit, the healing was defined as normal up to the time point of 3 years. This estimate was based on the fact that our institute is responsible for serving the whole population of the area, and if problems had arisen, the patients would have contacted our hospital. The follow-up times of each subgroup are presented in Tables 1 and 2. Statistical Analysis Patients were analyzed in 4 groups, which were based on the cranioplasty material used. Survival estimates were constructed with Kaplan-Meier curves, and the differences among categorical variable levels were determined using a log-rank test. Multiple comparisons were adjusted using a Sidák correction. Interactions among groups and each continuous independent variable were checked with Cox regression. The confidence level was set at 95%. All analyses were performed using SAS System for Windows, version 9.4 (SAS Institute Inc., Cary, North Carolina, USA), and all figures were drawn using R, version 3.0.2 (R Foundation for Statistical Computing, Vienna, Austria). RESULTS Description of Sample Altogether 100 cranioplasties (84 individual patients) with sufficient complete data were included. Of these 100 cranioplasty procedures, there were 81 primary, 16 secondary, 2 tertiary, and 1 fourth reconstruction during the period 2002e2012. A cranioplasty was performed in 34 female patients (34.0%) and 66 male patients
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FORUM
0
0
0
1 (25.0%)
Number (%)
Mean
SD
Range
105.2
87.5
4.0e420.0
Age (years)
42.1
17.4
3.0e79.0
BMI
26.5
5.1
17.3e40.8
390.4
463.1
0e3815
0
0 2 (100%)
0 0
Male
66 (66.0)
Female
34 (34.0)
Defect site Temporal
65 (65.0)
Occipital
5 (5.0)
Parietal
17 (17.0)
Frontal
13 (13.0)
0
0 1 (100%) 0
0 1 (7.1%)
0 3 (75.0%)
13 (92.9%) 2 (10.5%)
Table 2. Descriptive Statistics
Gender
1 (20.0%)
0 0 7 (100%) 1 (6.3%)
1 (10.0%) 0 9 (90.0%) 2 (14.3%)
Minor Compl.
CRANIOPLASTY OUTCOMES WITH SYNTHETIC MATERIALS AND AUTOGRAFTS
0
0
0
0
Compl., complications; FRC, fiber-reinforced composite; HA, hydroxyapatite; PMMA, polymethyl methacrylate; PEEK, polyetheretherketone; PE, polyethylene.
0
5 (100%) 0
0 0
0 6 (100%)
5 (100%) 0
0 0
0 9 (100%)
7 (100%) 7 (7.0%)
9 (9.0%) Titanium
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PE
1 (100%) 0 2 (2.0%) PEEK
2 (100%)
0
0
1 (100%)
0
4 (80.0%)
1 (5.3%) 16 (84.2%) 2 (7.1%)
3 (30.0%) 0 7 (70.0%) 1 (9.1%)
2 (6.5%) 4 (22.9%)
1 (9.1%) 9 (81.8%)
25 (80.7%) 31 (31.0%)
11 (11.0%) PMMA
HA 3
4
25 (89.3%)
1 (3.6%)
0 15 (93.8%) 1 (5.6%) 20 (20.0%) 2
Bioactive FRC
17 (85.0%)
3 (15.0%)
0
16 (88.9%)
1 (5.6%)
1 (7.1%) 11 (78.6%) 3 (18.8%) 0 20 (20.0%) 1
Autograft
14 (70.0%)
2 (10.0%)
4 (20.0%)
13 (81.3%)
Normal Healing Normal Healing Major Compl. Minor Compl. Normal Healing Overall Material Subgroup
Benign tumor
20 (20.0)
Malignant tumor
Major Compl.
Minor Compl.
Diagnosis
Minor Compl.
12 Months 6 Months 1 Month
Table 1. Number and Percentage of Patients with Complications and with Normal Healing with Different Implant Materials
Major Compl.
Normal Healing
36 Months
Major Compl.
JAAKKO M. PIITULAINEN ET AL.
3 (3.0)
Trauma
35 (35.0)
Infection
28 (28.0)
Intracranial hemorrhage
2 (2.0)
Intracranial ischemia
2 (2.0)
Implant made intraoperatively
36 (36.0)
Abuse of intoxicants
13 (13.0)
Diabetes
1 (1.0)
Smoking
27 (27.0)
Bone defects 200 cm
16 (16.0%)
2
Defect size (cm2)
Time between cranioplasty and craniectomy (days)
Time between cranioplasty and major complication (days) Autograft
8 (40.0%)
318
192
122e648
HA
4 (12.9%)
318
241
0e580
FRC
2 (10.0%)
402
347
156e647
Other
5 (16.1%)
267
199
0e542
Time between cranioplasty and last follow-up visit when normal progressive healing was observed (days) Autograft
12 (60.0%)
164
154
0e531
HA
27 (87.1%)
445
381
0e1466
FRC
18 (90.0%)
682
834
0e3815
Other
24 (82.8%)
284
297
0e1165
BMI, body mass index; HA, hydroxyapatite; FRC, fiber-reinforced composite.
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(66.0%) with an average age of 42.1 years (range, 3e79 years). The average body mass index was 26.5 (range, 17.3e40.8). The average defect size was 105.2 cm2 (range, 4.0e420.0 cm2). The HA subgroup had an average defect size of 49.9 cm2; in the autograft, FRC, and other subgroups, the averages were 137.1 cm2, 107.0 cm2, and 137.3 cm2. The temporal area was the most common defect site (65.0%). Leading causes for skull bone defects were trauma in 35 cases (35.0%), benign tumor in 20 cases (20.0%), and infection in 28 cases (28.0%). The cause for craniectomy was malignant tumor in 3 cases (3.0%), and intracranial ischemia or intracranial hemorrhage in 2 cases (2.0%). Descriptive data are presented in detail in Table 2. An autologous bone flap was used for reconstruction in 20 patients (20.0%). A cranioplasty with FRC was used in 20 patients (20.0%); 15 primary, 3 secondary, and, in 1 patient, a third and a fourth reconstruction were performed. HA bone cement was the material of choice in 27 primary and 4 secondary reconstructions and altogether in 31 cases (31.0%). PMMA cranioplasty was performed for 11 patients (11.0%): 5 primary, 5 secondary, and 1 tertiary reconstruction. Titanium and PE were used in cranioplasties in 9 and 7 patients (9.0% and 7.0%), respectively, and PEEK was used in 2 cranioplasties (2.0%). Time Interval Between Craniectomy and Cranioplasty In this study, cranioplasty was defined as “early” when performed 3 months. On average, the time interval between craniectomy and cranioplasty was 417.5 days. Of 21 patients who underwent early cranioplasty, 4 (19.0%) major complications were observed. There were 79 late cranioplasties performed, and 15 of these patients (19.0%) needed revision surgery. In this study, the timing of cranioplasty did not have a statistically significant effect on the major complication rate (P ¼ 0.1885). Survival Analysis The 3-year survival of the autograft subgroup was lower compared with other synthetic material subgroups (Figure 1). The HA and FRC groups showed the best outcomes, but statistical significance was not observed with the set confidence level compared with the autograft group (P ¼ 0.0505 and P ¼ 0.1346, respectively). Preexisting Conditions In this study, body mass index, radiation therapy or infection of the operative site before cranioplasty, abuse of intoxicants, smoking, diabetes, and immunosuppressive medication seemed to have no statistically significant effect. Defect Size and Anatomic Location Cranial bone defects were classified into 3 groups according to the size of the defect. The small-sized group included defects 200 cm2. The anatomic location or the defect size did not have a statistically significant effect on the major complication rate (Table 3). Complications Requiring Reoperations Altogether 100 cranioplasty outcomes were evaluated. In 13 of 84 patients (15.5%), a second, third, or fourth reconstruction was
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Figure 1. The 3-year survival of cranial bone defect reconstruction material in 4 subgroups: autograft, hydroxyapatite, fiber-reinforced composite (FRC), and other synthetic materials.
necessary. The overall complication rate was 32% (13.0% for minor complications and 19.0% for major complications). The complications in the 4 subgroups are listed in Table 4. In patients with a cryopreserved autograft reimplanted, healing was complicated in 60.0%, and in 40.0% of cases (8 of 20), the bone flap needed to be removed. Of these 8 patients with major complications, 5 presented with SSI, and 3 presented with resorption. In the autograft subgroup, the infection rate was 25.0%, and the resorption rate was 15.0%. Revision surgery was needed in 2 patients (10.0%) in the FRC subgroup. Both of these patients had primary reconstruction performed with a FRC implant. One patient presented with superficial incisional SSI, and the other patient presented with cerebrospinal leak. Both patients had secondary reconstruction performed with a FRC implant. In the HA subgroup, 4 (of 31) patients needed reoperation, 2 because of infections (6.5%) and 2 because of implant displacements (6.5%). In the subgroup of other synthetic material, 5 complications warranted implant removal: 3 deep incisional SSIs and 2 implant displacements. All of these were PMMA bone cement mass cranioplasties (5 of 11; 45.5%).With titanium, PE, and PEEK, normal progressive healing was observed in all cases. DISCUSSION The main finding of this study was that after skull bone reconstruction with autogenous bone, the implanted bone flap needed to be removed in 40.0% of cases. Leading causes for complication and removal of the autograft were infection and resorption (25.0% and 15.0%, respectively). Survival analysis of autograft, HA, FRC, and other alloplast subgroups showed the best survival in HA and FRC groups; however, the difference compared with the autograft group was not statistically significant. At our institution, we found that the HA bone cement paste was mainly used in reconstruction of small-sized to medium-sized
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Table 3. Log-Rank Tests in Subgroups Autograft
Bioactive FRC
HA
Other
c2
P
c2
P
c2
P
c2
P
1.0386
0.7709
0.9221
0.8067
0.4255
0.9443
0.1900
0.9871
6.8405
0.1714
0.2438
1.0000
0.9971
0.9997
Gender Female vs. male Defect site Frontal vs. occipital Frontal vs. parietal
8.1349
0.0873
0.2940
1.0000
0.0749
1.0000
0.4247
1.0000
Frontal vs. temporal
0.0092
1.0000
0.1230
1.0000
0.0107
1.0000
3.9932
0.6254
Occipital vs. parietal
0.4192
1.0000
0.00297
1.0000
0.1987
1.0000
Occipital vs. temporal
3.2859
0.7815
0.0112
1.0000
Parietal vs. temporal
2.9829
0.8421
0.00534
1.0000
3.1692
0.2086
10.1097
0.0059*
0.4034
0.0992
0.9963
3.3251
0.7733
0.0951
1.0000
3.4857
0.7386
3.0830
0.2191
1.1618
0.6285
0.9492
0.8822
0.8189
1.5903
0.6051
0.00102
1.0000
0.4242
0.9446
1.0862
0.7562
0.2732
0.9994
0.00063
1.0000
1.4788
0.8685
0.1177
1.0000
12.0945
0.0040*
0.1139
1.0000
7.4241
0.0503
3.1463
0.2114
4.0852
0.1242
1.1562
0.6303
0.6961
0.8739
0.1096
0.9955
0.2561
0.9775
0.6456
0.8066
1.4029
0.5545
0.8875
0.7205
Implant made intraoperatively No vs. yes Abuse of intoxicants No vs. yes Smoking No vs. yes Bone defects 25e200 cm2 vs. 200 cm 2
2
1.0026
0.9525
200 cm2 Age 65 years BMI 30
7.2660
0.0278*
Previous infection No vs. yes FRC, fiber-reinforced composite; HA, hydroxyapatite; BMI, body mass index. *< .05.
cranial bone defects with an average defect size of 49.9 cm2. The easy shaping of the HA bone cement paste during surgery is a major advantage for craniofacial surgeons. In general, for larger defects, when autograft was unavailable for reconstruction, a patient-specific implant was used. There is a growing interest in bioactive implants with porous structure that enable bone ingrowth (8). The osseointegration potential of HA and FRC may be a reason for the positive cranioplasty outcomes observed in this study. If a biomaterial, whether an autologous bone flap or a synthetic material, is not osseointegrated with the skull bone, it may be a reason for the inferior performance. HA and FRC are porous biomaterials with a suggested osseointegration capacity. The osseointegration potential of FRC has been demonstrated in rabbit models (33). However, the HA bone cement paste did not demonstrate as
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significant bone ingrowth as the ceramic form of HA in an adult sheep model (11). Also, HA bone cement paste could not be used in treatment of large bone defects because of its low mechanical strength, which is opposite to FRC with its known high strength and toughness. The presence of BG particles in FRC implants may have a positive effect in reducing periprosthetic infections. BG S53P4 is known to be an antimicrobial material, and it has an indication of use, for example, in the treatment of osteomyelitis (20). The present study revealed that even with large defect sizes, survival of FRC implants did not differ from survival of smaller defects with HA bone cement. In this consecutive retrospective study, 10-year outcomes of cranioplasty in 2 departments of 1 government institution are presented with standardized outcome and prognostic variables. The institution serves a population of approximately 725,000. The
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Table 4. Surgery-Associated Complications in Cranioplasty with Autologous Bone Flap, Hydroxyapatite, Bioactive Fibere Reinforced Composite, and Other Synthetic Materials Complication
Autograft Bioactive FRC
Total
12 (60%)
Superficial incisional SSI
HA
Other
3 (15%)
9 (29%) 8 (28%)
1 (5%)
3 (9.7%)
Deep incisional SSI
5 (25%)
Epidural hematoma
1 (5%)
1 (5%)
1 (3.2%) 3 (10%) 1 (3.5%)
CSF leak
2 (10%)
1 (5%)
2 (6.5%) 1 (3.5%)
Exposure of implant
1 (5%)
Resorption
3 (15%)
Implant migration
2 (6.5%) 2 (6.9%)
Cosmetic result Need for reoperation
1 (3.2%) 1 (3.5%) 8 (40%)
2 (10%)
4 (13%) 5 (17%)
All values are number and percentage. FRC, fiber-reinforced composite; HA, hydroxyapatite; SSI, surgical site infection; CSF, cerebrospinal fluid.
advantage of this study is that if a patient has not moved away from the district area, the problems related to skull bone reconstruction are treated at our institution. Postulating from this presumption, we determined the 3-year survival analysis. However, as in any retrospective study, there is a paucity in follow-up data; not all patients visited the hospital after progressive healing was observed. With most patients, the follow-up check-up was 2 months postoperatively and afterward only when needed. However, many of the patients visited the hospital for other reasons (e.g., neurologic rehabilitation), and these visits to the physician were taken into account as follow-up time points when generating the database. These assets of our study eliminate typical biases found in a retrospective study. However, as in any retrospective analysis of cranioplasty outcomes, this study has several limitations. The subgroups of patients have different pathologies. During the studied time period, the surgical technique evolved in terms of the introduction of patient-specific onlay grafts, which shortened the operative times. Autologous bone flap was the material of choice when possible. However, there may have been a selection bias in that all operations in the FRC subgroup were performed in a prospective clinical study setting that has been ongoing since 2007 at our institution, as described earlier. Cranioplasty has traditionally been considered a basic neurosurgical procedure. In the first decade of the new millennium, reports of high rates of complications with statistical significance emerged, but it was concurrently observed that scarce data exist in larger cranial repair study samples (4, 10). Reimplantation of a patient’s own cryopreserved or abdominally preserved bone is a classically preferred practice with a presumption that the procedure has a superior quality in terms of low risk of immunorejection and beneficial ossification and revascularization properties (3). In the present study, after cranioplasty was performed with autograft, 40.0% of patients needed removal of the implanted material.
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This rate is parallel to more recent publications (12, 21) and it is considerably higher compared with earlier studies (7, 30). In the present study, 45.5% (5 of 11) of cranioplasties performed with PMMA bone cement were to be removed; 3 patients presented with SSI, and 2 patients presented with displaced alloplast. At our institution, the use of PMMA bone cement in cranial bone defect reconstruction has diminished as other options have become available. PMMA is used in 2 ways: as bone cement and as bulk polymer implant material. “Bone cement reaction” caused by toxicity of methyl methacrylate monomers and exothermic polymerization reaction is one cause for reduced survival. Less is known regarding whether ex vivo polymerized bulk PMMA would differ biologically from that of other bulk polymers, such as PEEK and PE. In earlier studies, the optimal timing of cranioplasty was debated. Traditionally, cranioplasty has been defined as “early” when the time interval between craniectomy and cranioplasty is 3 months. Findings supporting early timing of cranioplasty after craniectomy have been presented (4, 5, 26). However, a more recent metaanalysis showed contradictory findings, which suggest that early surgery has no effect on the rate of cranioplasty infections (25, 36). After decompressive craniectomy, the optimal time frame between 2 and 6 months was suggested by Schuss et al. (31). In this study, the analysis of 100 cranioplasty procedures showed that the timing of cranioplasty seemed not to have an effect on the outcome. In this study, cranioplasties performed with synthetic materials showed a limited number of complications. However, this finding did not reach statistical significance. Klinger et al. (16) reported parallel findings, whereas Reddy et al. (27) observed a higher infection rate among patients who had an alloplast reconstruction performed. This finding is contradictory to our series. Also, our results did not suggest preoperative infection as a predisposing factor for alloplast material extrusion. In their meta-analysis of 18 studies, Yadla et al. (36) concluded that implant material has no effect on the cranioplasty infection rate or overall complication rate. Taking into consideration the small sample size and retrospective nature of this study, it is not within the scope of this study to draw conclusions of the best performing currently available material. Cryopreserved bone is readily available and remains the first-choice method for many surgeons. However, the question arises whether using some other biomaterial in the first place would reduce the number of subsequent cranioplasties needed after failure of the primary reconstruction material. CONCLUSIONS Based on the results of the present study, synthetic cranioplasty materials show more promising outcomes compared with autograft. Even with large defect sizes, survival of FRC implants did not differ from survival of smaller defects with HA bone cement. A prospective study comparing autograft with synthetic materials is warranted to reach more in-depth conclusions. ACKNOWLEDGMENT Robert M. Badeau, Ph.D., of Aura Professional English Consulting, Ltd. (www.auraenglish.com), is acknowledged for the language content editing of the manuscript.
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Conflict of interest statement: This research was funded by the Emil Aaltonen Foundation and Turku University Hospital. The principal financing partners of the FRC implant research are Tekes (the Finnish Agency for Technology and Innovation), Academy of Finland, and European Commission (Grant No. NEWBONE NMP3-CT-006-026279-2). J.M.P., J.P.P., and V.V. have received financial support in the form of a congress fee and travel expenses from Skulle Implants Corporation. K.M.J.A. and P.K.V. are board members and shareholders of the start-up company Skulle Implants Corporation, which is aiming to commercialize FRC implants. T.K. does not have any conflicts of interest to declare. Citation: World Neurosurg. (2015). http://dx.doi.org/10.1016/j.wneu.2015.01.014 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2015 Elsevier Inc. All rights reserved.
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