The “springform” technique in cranioplasty: custom made 3D-printed templates for intraoperative modelling of polymethylmethacrylate cranial implants

Abstract

Background Manual moulding of cranioplasty implants after craniectomy is feasible, but does not always yield satisfying cosmetic results. In contrast, 3D printing can provide precise templates for intraoperative moulding of polymethylmethacrylate (PMMA) implants in cranioplasty. Here, we present a novel and easily implementable 3D printing workflow to produce patient-specific, sterilisable templates for PMMA implant moulding in cranioplastic neurosurgery. Methods 3D printable templates of patients with large skull defects before and after craniectomy were designed virtually from cranial CT scans. Both templates — a mould to reconstruct the outer skull shape and a ring representing the craniectomy defect margins — were printed on a desktop 3D printer with biocompatible photopolymer resins and sterilised after curing. Implant moulding and implantation were then performed intraoperatively using the templates. Clinical and radiological data were retrospectively analysed. Results Sixteen PMMA implants were performed on 14 consecutive patients within a time span of 10 months. The median defect size was 83.4 cm2 (range 57.8–120.1 cm2). Median age was 51 (range 21–80) years, and median operating time was 82.5 (range 52–152) min. No intraoperative complications occurred; PMMA moulding was uneventful and all implants fitted well into craniectomy defects. Excellent skull reconstruction could be confirmed in all postoperative computed tomography (CT) scans. In three (21.4%) patients with distinct risk factors for postoperative haematoma, revision surgery for epidural haematoma had to be performed. No surgery-related mortality or new and permanent neurologic deficits were recorded. Conclusion Our novel 3D printing-aided moulding workflow for elective cranioplasty with patient-specific PMMA implants proved to be an easily implementable alternative to solely manual implant moulding. The “springform” principle, focusing on reconstruction of the precraniectomy skull shape and perfect closure of the craniectomy defect, was feasible and showed excellent cosmetic results. The proposed method combines the precision and cosmetic advantages of computer-aided design (CAD) implants with the cost-effectiveness of manually moulded PMMA implants.

Clinical and patient-reported outcome after patient-specific 3D printer-assisted cranioplasty

“…These factors could have predisposed to the development of an epidural hematoma. This is comparable to published data where postoperative epidural hematoma, which had to be evacuated by revision surgery, occurred in 21.4% of patients [ 11 ]. The second most common complication in our case series was an infection in 12.9% of patients.…”

“…Based on the method of cost calculation, the costs for 3D printer-assisted cranioplasty mentioned in the literature vary between 260 and 2780 USD [ 11 , 25 , 26 ]. One of the main reasons for the low cost calculation in the literature is that labor and licensing costs are often not considered.…”

“…However, possible secondary costs from revision surgeries due to inadequate cosmesis are not considered. The costs for autologous bone flap consist mainly of the cost of cryoconservation of approximately 600 USD, while costs for potential revision surgery in case of bone resorption were not considered [ 11 ]. Industrially manufactured PSIs made of titanium, PEEK, cost approximately 5000–10,000 USD [ 12 , 25 ].…”

Endoscopic transorbital and transcranial multiportal resection of a sphenoorbital meningiomas with custom bone 3D printing reconstruction: Case report

“…CAD/CAM usually implies industrial manufacturing with an associated increased cost and time of production 24 . Intraoperative modeling of formable thermoplastic polymers, such as PMMA, allows to overcome the limits of industrial CAD/CAM, although it may result inferior from a cosmetic standpoint 25–27 . Although commonly used for cranioplasty due to its biocompatibility, availability, low cost, and strength, PMMA free‐hand molding during polymerization can be difficult in the presence of large and irregular bony loss with respect to the size, shape, and curvature of the defect itself 18,26,27 .…”

Low-Cost Cranioplasty—A Systematic Review of 3D Printing in Medicine

“…Out of those, the three patients who bore clinically relevant coagulation-related risk factors required revision surgery due to a postoperative hematoma. Apart from that, no other complications have been recorded [ 67 ]. The analogous method was used by da Silva Junior, where a polycarbonate-made SLA-printed two-piece mold accompanied an intraoperative PMMA final implant formation, achieving satisfying results without any complications on a 3–26-month follow-up [ 68 ].…”