Surface Modification of Cranioplasty Implants to Reduce Postoperative Cerebrospinal Fluid Collection: A Preliminary Clinical Study

Abstract

Objective

Postoperative cerebrospinal fluid (CSF) accumulation is a common complication after cranioplasty, causing wound tension, delayed healing, and infection. We developed a grid-patterned polyetheretherketone (PEEK) cranioplasty flap to enhance tissue integration and reduce dead space. In this single-center, nonrandomized pilot study, we evaluated the feasibility and safety of this approach as a preventive strategy against postoperative CSF collection.

Methods

In this study, we prospectively included patients who underwent cranioplasty with patient-specific PEEK implants between March 2024 and October 2025. Patients who provided informed consent received a surface-modified PEEK flap with a grid-lattice pattern, whereas the others received a standard flap. We defined postoperative CSF collection as subgaleal fluid on examination or imaging evidence of a persistent space between the flap and scalp at 1 month and compared the outcomes and complications between the groups.

Results

We included 36 patients in this study, of whom 20 and 16 belonged to the control and surface-modified groups, respectively. Median ages were 56.5 and 60.5 years, and the interval from craniectomy to cranioplasty(63.0 days) was shorter in the surface-modified group(103.0 days). In the control, 2 patients developed hemorrhages and 2 cases of CSF accumulation (10% each), whereas no CSF accumulation or other complications occurred in the surface-modified group. The group differences were not statistically significant, reflecting the small sample size.

Conclusion

Grid-patterned surface modification of patient-specific PEEK flaps appeared feasible and safe, potentially helping prevent CSF collection after cranioplasty. These preliminary results are hypothesis-generating and warrant confirmation in larger controlled studies.

GRAPHICAL ABSTRACT

INTRODUCTION

Postoperative cerebrospinal fluid (CSF) collection is a known complication following cranioplasty that can result in wound tension, delayed healing, and even infection. In a previous study, we demonstrated that the use of histoacryl injections under the scalp can effectively reduce CSF accumulation by reinforcing scalp adherence to the skull flap.⁹⁾ While this approach provided symptomatic relief, it remained a reactive solution to fluid collection versus a method of prevention.

To develop a more proactive strategy, we explored a novel modification of the cranioplasty flap design. Specifically, we introduced a surface grid pattern on the outer surface of the implant to enhance tissue integration and reduce the formation of potential dead space where CSF could accumulate. This study presents the clinical application of this modified implant design and evaluates its feasibility and effectiveness in preventing postoperative CSF collection.

MATERIALS AND METHODS

All patients who underwent cranioplasty at our institution between March 2024 and October 2025 were enrolled in this study. Patients were prospectively enrolled in this study. As a designated regional trauma and emergency medical center, our hospital manages a large volume of patients, and cranioplasty was performed in those deemed to require reconstruction following neurological recovery. In cases where the patient or their legal guardian provided informed consent, a surface-modified cranioplasty flap was used. If consent was not obtained, the conventional flap design was employed. Because allocation to the surface-modified implant depended on patient or caregiver consent rather than randomization, this design is susceptible to selection bias, and the results should be interpreted accordingly. Postoperative CSF collection was defined as clinically evident fluid accumulation under a scalp flap 1 month after surgery, or as a persistent space between the flap and scalp identified on postoperative computed tomography (CT) imaging. The cranial defects resulted from both traumatic brain injury and non-traumatic hemorrhagic stroke. In this cohort, 8 of 36 patients (22.2%) underwent decompressive craniectomy for spontaneous or aneurysmal hemorrhagic stroke and were subsequently reconstructed with PEEK cranioplasty. At the time of cranioplasty, none of the included patients had undergone ventriculoperitoneal shunt surgery, and no intraoperative lumbar drainage was used. All patients had undergone large decompressive craniectomy with duroplasty using artificial dura at the index surgery. Cranioplasty was performed as a first-time reconstruction in all cases; no patient had a history of prior cranioplasty or revision surgery.

The cranioplasty flaps used in both groups were provided by the same manufacturer and were made of polyetheretherketone (PEEK). PEEK is advantageous due to its excellent biocompatibility, ease of customization to patient-specific anatomy, and minimal artifact generation on CT and magnetic resonance imaging (MRI), which facilitates accurate postoperative imaging and monitoring.¹⁰⁾ In contrast, autologous bone was not used due to concerns regarding bone resorption and infection.⁸⁾ While titanium mesh is safe in terms of infection risk, its use is limited because it is difficult to achieve fine contouring during implantation.

The PEEK flap was custom-made for each patient by mirroring the contralateral side using preoperative CT images, as reported previously.⁹⁾ Subsequently, the modified cranioplasty flap required additional procedures, including the creation of a superficial lattice (grid-like) pattern by applying a regular series of grooves on the outer surface. A grid pattern was precisely machined onto the outer surface of the flap using a cutting tool to create grooves with a depth of 0.05–0.2 mm to further enhance tissue integration and reduce dead space. This design was inspired by prior observations that improved tissue adherence can help reduce fluid collection. The modification was implemented, following the specifications outlined in our patent application (FIGURE 1).

FIGURE 1. Representative images of cranioplasty implants. (A) A conventional PEEK flap without surface modification. (B) A surface-modified PEEK flap, featuring a grid-patterned lattice on the outer surface, that was designed to increase surface area and promote tissue integration.

PEEK: polyetheretherketone.

Postoperative outcomes were monitored with clinical examinations and imaging studies (CT or MRI), with particular attention to any signs of CSF collection, wound dehiscence, or infection. The results were compared with controls from our institution where conventional implants without surface modification had been used. Continuous variables were expressed as median and range and compared between groups using the Mann-Whitney U test. Categorical variables were compared using Fisher’s exact test. A p-value <0.05 was considered statistically significant. Data analysis was conducted with the Python programming language.

The study was conducted with approval from the Institutional Review Board of the Uijeongbu St. Mary’s Hospital the Catholic University of Korea, and informed consent was obtained from all participants or their legal representatives.

RESULTS

A total of 36 patients who underwent cranioplasty were analyzed, comprising 20 patients in the control group and 16 patients in the case group where surface modification was applied. Due to the small sample size, nonparametric tests were used for statistical comparisons.

The median age was 56.5 years (range: 22–72) in the control group and 60.5 years (range: 20–79) in the case group, with no significant difference (p=0.514). The sex distribution was also comparable between groups (control: 80.0% male; case: 62.5% male; p=0.285). Regarding diagnosis, trauma was the predominant cause in both group; trauma accounted for 65.0% of cases in the control group and 93.8% in the surface-modified group, whereas non-traumatic hemorrhagic stroke comprised 35.0% and 6.2%, respectively (p=0.053) The median interval from craniectomy to cranioplasty was 103.0 days (range: 39–841) in controls and 63.0 days (range: 25–1,219) in cases, with a significantly shorter interval in the surface-modified group (p=0.027).In the control group, postoperative complications included 2 cases of hemorrhage and 2 cases of CSF collection, each occurring in 10% of patients (n=20). No postoperative complications including infection, wound dehiscence, CSF collection, hemorrhage, or other complications were observed in the case group. Statistical analysis showed no significant differences in complication rates (p=1.000 for infection and p=0.492 for both CSF collection and hemorrhage). Both cases of postoperative hemorrhage were diagnosed as epidural hematomas. Immediate reoperation was performed upon confirmation, and the patients were subsequently discharged without any further complications.

No significant differences were found in age, sex or overall postoperative complications between the case and control groups. although the interval from craniectomy to cranioplasty was significantly shorter in the surface-modified group. Non-traumatic hemorrhagic stroke was more frequent in the control group (35.0% vs. 6.2%, p=0.053), reflecting a potential selection bias in underlying etiology. The limited sample size restricts our ability to draw definitive conclusions, but findings suggest that surface deformation in cranioplasty does not increase complication risk (TABLE 1).

TABLE 1. Comparison of patient demographics, surgical characteristics, and postoperative outcomes between control and surface-modified cranioplasty groups.

Variable		Control group (case 0, n=20)	Surface-modified group (case 1, n=16)	p-value
Age (years)		56.5 (23–72)	60.5 (20–79)	0.514
Sex				0.285
	Male	16 (80.0%)	10 (62.5%)
	Female	4 (20.0%)	6 (37.5%)
Diagnosis				0.053
	Trauma	13 (65.0%)	15 (93.8%)
	Stroke	7 (35.0%)	1 (6.2%)
Interval from craniectomy to cranioplasty (days)		103.0 (39–841)	63.0 (25–1,219)	0.027
Postoperative complications
	Infection	0 (0.0%)	0 (0.0%)	1.000
	CSF collection	2 (10.0%)	0 (0.0%)	0.492
	Hemorrhage	2 (10.0%)	0 (0.0%)	0.492

Values are presented as median (range) or number (%).

CSF: cerebrospinal fluid.

Notably, all statistical comparisons yielded non-significant p-values (p≥0.492), which primarily reflects the small sample size and low event rates rather than equivalence between groups.

DISCUSSION

Postoperative CSF collection, including subgaleal CSF effusion, is a well-recognized complication after cranioplasty, with reported incidence rates ranging from 5% to 37% depending on surgical technique, timing of reconstruction, and patient-specific factors such as hydrocephalus or previous infection.⁴,⁸⁾ The presence of a fluid pocket between the scalp and the implant can impair wound healing and may necessitate additional interventions. Histoacryl injection has been reported as an effective minimally invasive method for managing subgaleal CSF collection, with a high rate of resolution and minimal complications.⁹⁾ While autologous bone flaps remain the gold standard, synthetic materials like PEEK are increasingly used due to their customizability and biocompatibility. However, PEEK implants are associated with a 2.7-fold higher risk of subgaleal CSF collection compared with titanium mesh (46.2% vs. 20.5%),⁵,⁶⁾ likely due to their smoother surface topography and reduced tissue integration. This study introduces a novel grid-patterned surface modification to PEEK implants aimed at mitigating these complications.

The grid design creates space for tissue ingrowth. Previously, review articles in the field of prosthodontics have summarized studies that modified the surface of PEEK using various techniques to enhance soft tissue binding efficiency.²⁾ Similar to the present study, some of these reports demonstrated improved adhesion through alterations in surface morphology alone.¹²⁾ In addition, other approaches have employed a variety of materials and molecules to further improve shear strength at the tissue-material interface.¹,³,⁷,¹¹⁾ The grid pattern in this study likely operates on similar principles, providing mechanical interlocking points for fibroblasts while disrupting fluid accumulation pathways.

In this study, we aimed to proactively promote scalp integration by increasing the surface area of the cranioplasty flap. Although the small sample size limited statistical significance, the experimental approach demonstrates potential value as a pilot investigation. Increasing the surface area of biomedical implants to enhance tissue integration is a well-established concept in biomaterials research.

Limitations and future directions

The small cohort (n=16 modified implants) precludes definitive conclusions but aligns with preliminary studies exploring novel cranioplasty materials. Future work should integrate this surface design with bioactive or osteoconductive coatings to further enhance tissue integration and should ideally include larger, multicenter randomized or propensity-matched cohorts to more rigorously evaluate clinical efficacy.

CONCLUSION

Although this study lacks the statistical power to draw definitive conclusions, it introduces a promising design innovation aimed at reducing CSF collection after cranioplasty. In this small, non-randomized cohort, surface modification of the cranioplasty flap appeared safe and was not associated with increased complications, suggesting that this proactive strategy merits further evaluation in larger, prospective studies.