A Scoping Review to Evaluate the Clinical Ef ﬁ cacy of Indigenously Produced, Patient-Speci ﬁ c Acrylic Cranial Prosthesis in Decompressive Craniectomy in India

Background Health Technology Assessment in India assesses, evaluates, and carries out cost-effectiveness of available health technologies in the country for evidence-based decision-making. Current study carried out a scoping review to assess clinical ef ﬁ cacy of poly-methyl-methacrylate (PMMA) after decompressive craniectomy using various prototyping techniques in published literature. Methods The O ’ Malley methodology and Preferred Reporting Items for Systematic Reviews and Metanalysis for Scoping Reviews — PRISMA-ScR — checklist were used to assess published literature from year 2008 to 2023


Introduction
Decompressive craniectomy (DC) is a surgical procedure that includes removing a portion of the patient's skull without immediate restoration.2][3][4] This procedure overcomes the space constraints of the Monroe-Kelly doctrine, which dictates that maintenance of constant ICP is a prerequisite for normal functioning of the brain. 57][8] After DC, cranial defects are restored by cranioplasty to maintain normal ICP and improve aesthesis.6][17] Therefore, PMMA is reported with high tensile strength, which makes it more resistant to stress and compression. 12It is considered to be readily available, relatively inexpensive, moldable, adherent to soft tissue, nonconductive, heat resistant, and radiolucent. 16Rapid prototyping technique (RPT), like three-dimensional (3D) casting of skull mount, has become convenient and reduces surgery time and errors related to manual fabrication. 18A study used locally available material (Osteo3D Inc, Bengaluru, India) and reported a one-fifth reduction in average production cost as compared to nonmolded titanium plate. 19][22] In India, Health Technology Assessment (HTA) has been launched for assessment, evaluation, and analysis of the costeffectiveness of available health technologies in country.It is aimed to reduce OOPE and maximize the health benefits.Through its HTA India resource centers, evidence-based decision-making is done to inform national and state-level health policy.New technologies are assessed for their clinical efficacy and effectiveness with existing literature and then cost-effective analysis is carried out.Based on the result, a cost-effective technology is introduced among the population to maximize benefits. 23With this mandate, current coping review was done to assess the extent of the use of PMMA in post-DC procedures with clinical efficacy using various prototyping techniques in published literature.

Methods
The scoping review was carried out using O'Malley methodology involving standard steps like defining research question, identification of pertaining literature, selection of publications, extraction of data, data analysis, and summary. 24o report current scoping review, the Preferred Reporting Items for Systematic Reviews and Metanalysis for Scoping Reviews-PRISMA-ScR-checklist was used. 25or the purpose of current review, the framed research question was: "What is the clinical efficacy of indigenously produced, patient-specific acrylic PMMA cranial prosthesis in decompressive craniectomy (DC) in India?"It also included a specific subset of questions "What techniques are being used to place prosthesis?" and "What types of clinical criteria were used to assess for efficacy?"Inclusion criteria of studies were: studies mentioning PMMA acrylic material manufactured in India; studies carried out in India; full-text publications; published studies (original articles, case series/reports); studies published in the last 15 years (2008-2023); and publications in English language.Exclusion criteria for studies were: use of PMMA in other surgical procedures except DC; study protocols, abstracts, brief highlights, and editorials/commentaries/ communications; and other languages.We searched the Cochrane Central Register of Controlled Trials and Cochrane Database of Systematic Reviews, MEDLINE, PUBMED, Science Direct, and Google Scholar for relevant studies.The keywords used were "decompressive craniotomy," "decompressive craniectomy," "cranial implants," "India," "cranial acrylic implants," "PMMA implants," "cranioplasty," and "efficacy."In addition, widespread Internet search was applied for relevant gray literature along with manual assessment of cross-references of included studies.
Studies were assessed first with screening of abstract and then full-text evaluation was done based on laid down inclusion and exclusion criteria.It was carried out by two researchers independently with an excellent agreement rate, so third independent assessment was not done.Mendeley reference manager was used for deduplication of retrieved records.Microsoft Excel was used to extract and collect information in a structured format aligning to research question.

Results
A total of 507 records were identified after searching electronic databases and a total of 27 duplicate studies were removed.Therefore, a total of 12 studies were finally included in the current review, which focused on and described indigenously produced patient-specific acrylic implants post-DC (►Fig.1).The acrylic material widely used for cranial defect restoration was PMMA, which edges over others in being radiolucent, ease of availability, and biocompatibility.
A detailed summary of the studies included for review is mentioned in ►Table 1.A total of four studies were described as experimental and eight were case reports/series (►Table 1).The sample size of intervention studies varied between 10 and 30 patients with a mean age of 36.7 years, whereas it ranged between 8 and 74 years in case reports/series.Distribution of clinical indication for intervention was TBI and stroke, and majority were males ($80.0%).In one clinical experimental study, cranioplasty was performed for restoration of cranial defects mainly due to nonavailability of the autologous bone graft. 19A clinical experimental study compared PMMA with other materials like autologous bone grafts and titanium, 26 and another study retrospectively compared 3D technique with conventional alginate impression technique. 27In remaining two clinical experimental studies, no comparator group was chosen to assess clinical outcomes following PMMA implant with 3D technology 18,19 (►Table 1).
In a total of seven studies, cranioplasty was done by a selfmade PMMA prosthesis fabricated using a novel 3D-printed cranial model fabrication technique.One of the studies used a 3D binder jet printer and in-house software for prosthesis fabrication. 18Another one used 3D template molds created using a local start-up company, Osteo3D Inc, Bengaluru, India, using locally available acrylic material. 19Majorly, studies reported the use of RPT for the fabrication of acrylic prosthesis using 3D technology (►Table 1).
All four clinical experimental studies reported the clinical efficacy as quantitative measures.Among these, a single study mentioned postoperative Glasgow Outcome Scale (GOS) as a criterion, two studies reported improved aesthesis by analysis of cosmesis and conformity using Cranial Index of Symmetry score and Visual Analog Score for Cosmesis (VASC), two studies mentioned patient satisfaction score and Odom's score, and one study reported postoperative infection episode and need for resurgery (►Table 1).
The mean GOS score postoperatively in a patient cohort (n ¼ 10) was observed to be 4.2 AE 0.9 with a median score of 5. Similarly, cranial symmetry is considered excellent in majority (80.0%) of cases postoperatively after fabrication of the PMMA implant. 18,27The other study reported excellent median Odom's score in 52.0% of cases and good in 40.0% of cases postoperatively.The same study reported a good VASC score of 8.2 AE 1.4 in the postoperative patients. 19ne of the studies compared two techniques of PMMA fabrication, where patient satisfaction was excellent in 69.2% of cases in 3D group as compared to 23.5% in group with conventional method (alginate-based).Cranial symmetry was reported satisfactory by 92.3% (n ¼ 12) of the patient who underwent cranioplasty using 3D group compared to only 52.9% in alginate group.There was no need for resurgery in 92.3% of the patients who had PMMA implants with 3D fabrication.Further, a higher blood loss volume of 187.6 mL was observed in patients under alginate  Clinical Efficacy of Indigenously Produced Acrylic Cranial Prosthesis in DC in India Guleria et al.
group.In contrast, a lower mean blood loss volume was observed in PMMA implanted group, i.e., 158.9 mL. 27In a comparative study measuring outcomes in cranioplasty done using autograft vs. alloplastic material (PMMA vs. Titanium), it was observed that patients who underwent cranioplasty with PMMA and titanium reported infection and implant exposure postoperatively.Meanwhile, none of the complications were reported in the group with autograft implants 28 (►Table 1).
In addition to the patient-related outcomes that were observed postoperatively, one of the studies established safety profile of the self-fabricated PMMA prosthesis and compared its properties with those of other alloplastic materials as mentioned in the literature.The authors obtained good properties of casted PMMA that include hardness of 15.8 AE 0.24 Hv, tensile strength of 30.7 AE 3.9 Mpa, and elastic modulus of 1.5 AE 0.1 Gpa, which was clinically acceptable.Hence, low-cost 3D printer-based PMMA flap fabrication is an affordable option for cranioplasty in resource-constrained settings 18 (►Table 1).
Further, clinical complications were reported in 11 (12.6%)out of a total of 87 patients in 4 clinical experimental studies.After PMMA, wound infection was reported in 6 (6.9%) and fluid collection in 5 (5.7%) patients, which improved later on.In one of the patients, extradural collection post surgery required immediate reopening, evacuation of the clot, and replacement of the customized flap.In other two patients, there was a need to redo the surgery for construction of the bone flap using their previous template. 18,19,27,28here were seven case reports and one series report, which only mentioned subjective analysis of outcomes as an overall improvement in the patient aesthesis.The material used as implants in all the studies was PMMA.More than 50% of the studies used 3D technology RPT for fabricating the implant.In the rest of the studies, conventional methods of casting were described.In one study, comparison was done in two patients for prosthesis construction directly on skull and printed directly using 3D technology.None of case reports/series reported any complications after the surgery and reported satisfactory/ improved/good/excellent aesthesis [29][30][31][32][33][34][35][36] (►Table 1).

Discussion
The current literature review suggests PMMA acrylic material as one of the potential candidates that can be recommended for fabrication of the cranial defects post-DC.It edges over other materials in being less expensive and has produced good clinical outcomes regarding patients' overall aesthetics and satisfaction.Limited evidence from India suggests that the use of 3D RPT is growing.It is likely to reduce time and errors in the fabrication of the prosthesis, improve technical efficiency, reduce surgery time, and provide good aesthetics as compared to manual fabrication of the implant using conventional techniques.PMMA observed hardness and better cranial symmetry when 3D technique was used to cast the graft. 18,19,27Accessibility to locally produced 3D technology and PMMA material is expected to reduce production costs (up to 80.0%). 19In all intervention studies, postoperative complications were observed among 11 (12.6%)out of a total of 87 patients in 4 clinical experimental studies.After PMMA, wound infection was reported in 6 (6.9%) and fluid collection in 5 (5.7%) patients.Complications like implant exposure were observed in three patients whereas two patients required redo surgery.None of the case reports/series reported postoperative complications.All patients in case reports/series were assessed clinically and observed with satisfactory clinical aesthetics.
Clinical outcomes to assess intracranial function were limited, as one study 18 reported a mean GOS of 4.2, which can be considered favorable. 37Odom's criteria, 38 a 4-point scale to assess patient's satisfaction, were used in one study where it was excellent in half of the patients. 19Same study observed a Visual Analogue Scale to assess clinical wounds and also showed excellent results. 39Assessment for clinical symmetry was also done along with blood loss and average surgery time in one study.These indicators favored PMMA with 3D as compared to conventional alginate impression and wax elimination cranioplasty technique. 27atient dissatisfaction due to cranial deformity after DC is a common reason for placing grafts.In a study, not from India, in which retrospective analysis was done on 108 patients, 18.0% underwent primary/secondary surgical intervention to recorrect temporal deformity.In one patient, an altered mental state due to mass effect was observed and urgent recontouring of PMMA was done.A review of 25 studies reported that complications were not reported in patients with alloplastic material, autologous bone, and free tissue transfer.Catastrophic complications like stroke, pulmonary embolism, and death were not observed with the use of alloplastic material as a graft, whereas it was observed to be associated with fat augmentation and dermal filler. 40omputer-aided manufacturing was adopted where autologous bone grafts cannot be used.A systematic review of 36 articles showed that 3D printing was used in various other fields along with neurosurgery for surgical planning, simulation and training, tissue-engineered implants, and secondary devices. 41The use of desktop 3D printers led to the production of patient-specific implants with excellent cosmesis.It can be done intraoperatively for various cranial discontinuities.This evidence reported with cost of Canadian dollar (CAD) 50-100 per case with expected annual savings of CAD 685,000 in Canada. 42

Limitations of Study
As a limitation, quality assessment of studies in scoping reviews is not explicit.For current review, studies from India and those that used PMMA implant as a post-DC procedure, irrespective of clinical condition, were studied.It was more specific as to a research question.Studies reported were extracted using online platforms with crosschecking of references.It is limited to numerical summary and reporting of results.Next steps like stakeholders' consultations and additional considerations to support applications and advancements of scoping review were not done in current study. 43

Conclusion
We think that in the Indian context, this study gives a good idea that suggests usage of PMMA material with 3D printing technology.Selection of study period was considered wide to include all available evidence and it suggests that it is recently becoming in use due to availability of affordable technology.PMMA is safe, with satisfactory aesthetic and low complication rate favoring its more use in coming times.This review suggests a large scope of PMMA and computeraided technology in post-DC procedure.Affordable and quality manufacturing of PMMA and 3D printers with standardized training protocols will be beneficial to patients.

A Way Forward
However, there is negligible evidence to support the clinical efficacy of acrylic material over other alloplastic materials.Studies highlighting the outcomes have inadequate sample sizes with differential results.Most of them are focused around visual inspection of improved aesthesis pre and post surgery, which might not be valid study designs to assess clinical efficacy.The current review suggested scarce evidence to support the use of clinical effectiveness of PMMA in DC.It would have been prudent to use interventional study with a comparator/control group with high study power to assess PMMA in DC.Patients requiring DC should be as per the prior laid inclusion and exclusion criteria.Standardization of interventions (PMMA technology and surgical protocols) and clinical outcome measures like Glasgow Coma Scale (GCS), aesthetics, patient satisfaction, and postoperative complications should be clearly defined.Due to limited and varying study participants in one health institute, a multicentric study with standardized protocols could be planned to reach out required sample size.

Fig. 1
Fig. 1 PRISMA-Preferred Reporting Items for Systematic Reviews and Metanalysis-flowchart to report clinical efficacy of indigenously produced, patient-specific acrylic cranial prosthesis in decompressive craniectomy in India.

Table 1
Characteristics of the Indian studies included for search related to usage of acrylic implants post decompressive craniotomyClinical Efficacy of Indigenously Produced Acrylic Cranial Prosthesis in DC in India Guleria et al.
Indian Journal of Neurosurgery © 2023.The Author(s).