Clinical Features in Patients with Delayed Exposure of Titanium Plates and Meshes after Cranioplasty

Abstract

Titanium plates and meshes are frequently used to secure bone flaps or to reconstruct defects after craniectomy. Although generally effective, they are occasionally associated with delayed skin complications. This study aimed to identify clinical features of delayed exposure of titanium implants. We retrospectively reviewed 29 patients with titanium implant exposure ≥1 year after cranioplasty or craniotomy (12 with titanium meshes and 17 with titanium plates) treated at our institution between January 2000 and December 2021. Patient characteristics (age, sex, initial disease, multiple surgeries, radiation therapy, diabetes mellitus, body mass index, and interval from the most recent surgery to implant exposure) were compared in the 2 groups. The relationship among the location of skin complications, implant placement, and original surgical incision line was also evaluated. Implant exposure was more frequent in female patients (82.8%). The median interval was significantly shorter in the mesh group than in the plate group (3.9 years vs. 12.0 years, respectively); 82.4% of plate-related exposures were located directly under previous incision, whereas mesh-related exposures tended to occur away from incisions. In both groups, more than 90% of lesions developed in areas lacking muscle coverage; 47.1% of titanium plate exposure was found over the linea temporalis and directly beneath incision lines. In conclusion, titanium implants―particularly in female patients and in those placed beneath incision lines or in areas lacking muscle coverage―are associated with an elevated risk of delayed exposure. Surgical planning should carefully consider implant positioning to reduce long-term complications.

Introduction

Titanium implants are frequently used to secure free bone flaps after craniotomy or to provide cranial protection in areas with bone defects after decompressive surgery.¹⁾ Although complications eventually develop in some patients―such as skin thinning, ulceration, implant exposure, and infection―the underlying mechanisms remain poorly understood.^2-6) This uncertainty is partly attributable to the rarity of these events, which occur in approximately 0.5% of cases annually, and their tendency to manifest long after the initial procedure.⁷⁾

A recent large-scale survey in Japan reported that most postoperative wound infections occur early in the postoperative period, suggesting that late-onset complications, such as implant exposure, may result from distinct etiological factors.⁷⁾ Consequently, from a surgical perspective, it is essential to identify anatomical or patient-specific factors that predispose individuals to implant exposure. However, few studies have provided definitive insights into this clinical issue.

The present study focused on cases in which complications related to titanium implants emerged ≥1 year after the most recent craniotomy. A detailed evaluation of the anatomical characteristics of the implantation sites and overlying skin lesions was conducted, and we discussed strategies to prevent localized skin ulceration and implant exposure at the site of titanium implant placement. Given the known differences between titanium plates and titanium mesh in terms of the timing and anatomical distribution of postoperative complications, we also performed a comparative analysis of the 2 implant types.

Methods

Study design and patient population

Eligible patients were identified through a retrospective review of the institutional surgical database, covering the period from January 2000 to December 2021. Inclusion criteria were delayed onset (≥1 year) of skin ulceration, exposure, or infection localized to the implant site (Fig. 1). Regarding management, exposure of titanium plates often occurs directly beneath the original surgical incision. In these cases, the wound is typically reopened to fully expose the plate, followed by simple closure after elevating the surrounding periosteum. In contrast, exposure of titanium mesh frequently presents with more extensive skin defects or significant thinning of the overlying skin, making simple closure infeasible. Consequently, reconstruction using a vascularized flap is commonly required for mesh exposure. However, treatment strategies for mesh-related implant exposure were not evaluated in this study.

Fig. 1.

Study flowchart.

Demographic and clinical data were collected retrospectively from medical records. Variables included sex, age at initial surgery, initial surgical indication, number of prior craniotomies, radiation therapy, diabetes mellitus, body mass index at the time of implant removal, interval from the most recent surgery to reoperation, implant type (titanium mesh or titanium plates), plate shape (wheel, I-shape, or rectangle/double-Y-shape), and anatomical features of the complication site. Particular attention was given to the relationship between the lesion and previous skin incisions, skull defect location, and presence or absence of muscular coverage. Statistical analyses were conducted to compare variables in the titanium mesh and titanium plate groups. Categorical variables were analyzed using Fisher's exact test, whereas continuous variables were analyzed using the Mann-Whitney U test. A p < 0.05 was considered statistically significant; a p < 0.1 was interpreted as indicating a trend. All statistical analyses were performed using JMP Student Edition, version 18.0.

This study was approved by the institutional review board of Kyoto University Hospital (Institutional Review Board Number R2088). The requirement for informed consent was waived owing to the retrospective nature of the study. All procedures were conducted in accordance with the Declaration of Helsinki.

Results

Demographic data (Table 1)

Table 1.

Patient Demographics

	All cohort (n=29)	Titanium mesh (n=12)	Titanium plate (n=17)	p Value
Sex (female)	24 (82.8%)*	9 (75.0%)	15 (88.2%)	0.62†
Age at initial surgery	52 (35-63)	60 (34–69)	51 (38–59)	0.32‡
median, years old (25-75%ile)
Initial disease
Vascular	11	2	9
Tumor	16	8	8	N.A.
Trauma	1	1	0
Function	1	1	0
Infection after initial surgery	3 (10.3%)	3 (25.0%)	0 (0%)	0.060†
Multiple surgeries	13 (44.8%)	9 (75.0%)	4 (24.0%)	0.010†
Radiation therapy	6 (20.7%)	3 (25.0%)	3 (17.7%)	0.67†
Diabetes mellitus	2 (6.9%)	1 (8.3%)	1 (5.9%)	1.0†
Body mass index median (25–75%ile)	21.3 (19.0-23.6)	21.8 (19.0-23.7)	21.2 (18.4-23.0)	0.47‡
Interval since most recent surgery years; median (25–75%ile)	7.9 (3.9-15.8)	3.9 (2.0–11.5)	12.0 (5.8–16.9)	0.042‡

*As a reference, 55.6% of the craniotomy cases at our hospital (2018-2021) were in female patients.

^†Fisher’s exact test.

^‡Mann–Whitney U test.

N.A.: not applicable

Between January 2000 and December 2021, 33 patients required surgical removal of artificial cranial implants ≥1 year after their most recent craniotomy owing to implant-related skin ulcers or infections at our institution. Among these, 5 patients initially underwent primary cranioplasty at other hospitals and were later treated at our institution for delayed implant exposure. Of the 33 cases, 29 patients (87.9%) experienced implant exposure specifically associated with titanium-based materials: 12 with titanium mesh and 17 with titanium plates. Of the 29 patients, 24 (82.8%) were female and 5 (17.2%) were male. By comparison, 55.6% of all craniotomy cases at our institution between 2018 and 2021 involved female patients. The median age at the time of initial surgery was 52 years (interquartile range [IQR], 35-63), with a median age of 60 years (IQR, 34-69) in the mesh group and 51 years (IQR, 38-59) in the plate group. The initial diagnoses prompting cranioplasty included vascular lesions (n = 11), tumors (n = 16), trauma (n = 1), and functional disorders (n = 1). Multiple surgeries were performed in 13 patients (44.8%), with a significantly higher proportion in the mesh group (9/12, 75.0%) than in the plate group (4/17, 24.0%) (p = 0.01).

Radiation therapy was administered in 6 patients (20.7%), with comparable distribution in groups. Postoperative infection after initial treatment was noted only in the mesh group (25%). The prevalence of diabetes mellitus and body mass index values were similar in the 2 groups. The median interval from the most recent cranioplasty to implant exposure was 7.9 years (IQR, 3.9-15.8) for the entire cohort. The mesh group had a significantly shorter median interval (3.9 years [IQR, 2.0-11.5]) than the plate group (12.0 years [IQR, 5.8-16.9]) (p = 0.042).

Characteristics of anatomical distribution of implant exposure (Table 2)

Table 2.

Exposure Site and Titanium Implantation Shape Characteristics

	All cohort (n=29)	Titanium mesh (n=12)	Titanium plate (n=17)	p Value
Directly beneath skin incision	16 (55.2%)	2 (16.7%)	14 (82.4%)	<0.001*
Directly above bone defect	6 (20.7%)	5 (41.7%)	1 (5.8%)	0.056*
Without muscle coverage	27 (93.1%)	11 (91.7%)	16 (94.1%)	1.0*
Anatomical site
Frontal	8 (27.6%)	3	5
Parietal-Occipital	6 (20.7%)	4	2
Temporal	2 (6.9%)	1	1	N.A.
Above linea temporalis	10 (34.5%)	2	8
Mastoid/posterior fossa	3 (10.3%)	2	1
Titanium implantation shape
3D reconstructed mesh		3 (25.0%)
Malleable mesh plate		9 (75.0%)
“Wheel”-shaped plate			14 (82.4%)#	N.A.
“I”-shaped plate			1 (5.9%)#
“Double Y” or “rectangle” plate			2 (11.8%)#

*Fisher’s exact test.

# As a reference, of the titanium plates used at our hospital (2018-2021), 49.6% were wheel-shaped; 45.2% were I-shaped; and 5.2% were either rectangular or double-Y–shaped.

3D: 3-dimensional; N.A.: not applicable

Implant exposure occurred directly beneath the initial skin incision in 16 patients (55.2%), including 2 (16.7%) in the mesh group and 14 (82.4%) in the plate group (Figs. 2A and 3A). This rate was significantly higher in the plate group (p < 0.001). Exposure directly over the bone defect was observed in 6 cases (20.7%): 5 (41.7%) in the mesh group and 1 (5.8%) in the plate group, showing a trend toward greater frequency in the mesh group (p = 0.056). In cases when the implant was placed without muscle coverage or positioned over the linea temporalis, exposure consistently occurred on the side lacking muscular protection. Overall, 27 patients (93.1%) had implant exposure at sites without muscle coverage, including 11 (91.7%) in the mesh group and 16 (94.1%) in the plate group. Anatomical sites of exposure included the frontal region (n = 7), parietal (n = 3), occipital (n = 3), temporal (n = 2), over the linea temporalis (n = 11), and mastoid/posterior fossa (n = 3). In the mesh group, malleable mesh plates were used in 9 cases (75.0%) and 3-dimensionally reconstructed meshes in 3 cases (25.0%) (Fig. 2B). In the plate group, wheel-shaped plates were used in 14 cases (82.4%), I-shaped plates in 1 case (5.9%), and double-Y or rectangular plates in 2 cases (11.8%) (Fig. 3B). For reference, among all titanium plates used at our institution between 2018 and 2021, 49.6% were wheel-shaped, 45.2% I-shaped, and 5.2% either rectangular or double-Y-shaped.

Fig. 2.

Locations and types of titanium mesh implants with delayed exposure. (A) Schematic illustration showing the distribution of titanium mesh implants on the skull in cases with delayed exposure. The numbers within the circles and the size of each circle represent the number of exposures at each site. Implants located directly beneath the prior skin incision line are labeled “Under incision.” (B) Representative illustrations of a 3D titanium mesh and a titanium mesh plate.

3D: 3-dimensional

Fig. 3.

Anatomical distribution and types of titanium plates with delayed exposure. (A) Schematic illustration depicting the anatomical locations and types of titanium plates with delayed exposure. The numbers within the circles represent the number of exposed plates, and circle size reflects frequency. Implants located directly beneath the previous skin incision line are labeled “Under incision.” (B) Representative categories of plate shapes: wheel-shape, I-shape, double-Y–shape, and rectangular-shape.

Discussion

Titanium implants are widely used owing to their ability to provide rigid cranial fixation and yield favorable cosmetic outcomes, particularly with 3-dimensional meshes or malleable mesh plates for cranial defects. Titanium mesh has also been reported to exhibit lower susceptibility to Staphylococcus epidermidis adhesion and greater resistance to infection than does stainless steel,⁸⁾ supporting its use for immediate reconstruction at the time of autologous bone flap removal in infected cases. This approach may prevent postoperative cranial defects and eliminate the need for additional surgeries. However, recent studies have shown that titanium mesh is associated with progressive thinning of the overlying skin and a risk of delayed implant exposure, which may necessitate complex reconstructive procedures, such as vascularized or adipofascial flaps.⁹⁾ Both previous reports and our present findings indicate that titanium mesh is more frequently selected in patients with compromised skin conditions, including those requiring multiple surgeries or after infection. Although this selection bias may partly explain the poorer long-term outcomes associated with titanium mesh, the frequency of such complications has led to its complete discontinuation at our institution.

Titanium plates, by contrast, are routinely used in most neurosurgical procedures and are associated with a lower incidence of complications than are mesh implants. Nonetheless, implant exposure is occasionally encountered owing to their widespread use. These exposures typically occur ≥10 years after the initial surgery and are often managed by a different surgeon, potentially limiting awareness of this delayed risk. Accordingly, we investigated the association among titanium implant type, anatomical location, and the risk of late exposure.

In our study, both titanium mesh and titanium plate implants were more frequently associated with delayed exposure in female patients. However, 55.6% of the patients who underwent craniotomy or cranioplasty at our institution between 2018 and 2021 were female, indicating minimal sex bias in the overall cohort. This finding suggests a higher predisposition to titanium exposure in female patients. In contrast, previous large-scale studies from head and neck surgery centers investigating titanium mesh exposure have reported a slight male predominance.¹⁰⁾ However, those studies included a significant proportion of patients with head and neck cancers who had undergone radiation therapy, and the mesh exposure rate exceeded 70%. These differences likely reflect distinct patient population characteristics. Although several neurosurgical studies have reported a slightly higher implant infection risk in male patients.^7,11) However, many of these studies included a substantial number of cases with early postoperative complications following cranioplasty or cranial fixation. In contrast, our study included only cases in which ≥1 year had elapsed since the initial procedure, which may explain the differing results. Despite the limited sample size, studies involving patient populations similar to ours have also reported a predominance of female patients (6/8, 75.0%), supporting this trend.¹²⁾ Although our analysis included patients who did not undergo their initial treatment at our institution, and given the prolonged time to exposure in some cases, we were unable to include all patients treated during the same period. Moreover, titanium mesh cases more frequently involved multiple initial craniotomies, suggesting compromised skin quality from the outset, which may have contributed to shorter latency to exposure. Previous research has focused primarily on the material properties of cranioplasty implants, whereas factors such as anatomical location, incision technique, and implant type remain underexplored as potential exposure risks.⁷⁾ This study aimed to address that gap by evaluating not only implant materials but also the specific types and usage patterns of titanium plates used at our institution.

Our findings indicate that in both titanium mesh and titanium plate groups, delayed exposure occurred in areas without muscle coverage in >90% of cases. Titanium mesh was significantly more likely than titanium plate to undergo thinning and exposure at locations unrelated to the original skin incision, with approximately half of these exposures occurring at the center of the cranial defect. This observation supports the hypothesis proposed by Yoshioka et al.,²⁾ who suggested that the pressure gradient between atmospheric and intracranial pressure across the mesh may draw subcutaneous tissue into the mesh, causing ischemia and subsequent thinning. In contrast, 82.4% of titanium plate exposures occurred directly beneath the initial surgical incision. In half of these cases, exposure was localized to the intersection of the linea temporalis and incision. Detailed analysis revealed that all such exposures occurred above the linea temporalis, an area lacking muscle coverage. Moreover, at the level of the linea temporalis, the calvarial curvature is relatively steep. When a flat, wheel-shaped titanium plate is used for fixation in this region, the superior corner of the plate inevitably tends to lift away from the skull, which may increase the risk of skin injury. Therefore, it is preferable to avoid burr holes in this area whenever possible. If plate placement in this region is unavoidable, the titanium plate should be contoured to match the local curvature of the skull before fixation.

Furthermore, 82.4% of the exposed plates were of the wheel type. Between 2018 and 2021, wheel-type plates accounted for 49.6% of all plates used at our institution, whereas I-type and rectangular/double-Y plates accounted for 45.2% and 5.2%, respectively. This suggests a trend toward higher exposure risk with larger plates. Because wheel-type plates are frequently used to cover burr holes created during craniotomy, our findings indicate that burr holes positioned at the intersection of the linea temporalis and skin incision should be avoided. When unavoidable, it is essential to contour the plate carefully to match the curvature of the linea temporalis to ensure proper adaptation. These insights emphasize the importance of not only selecting appropriate materials but also conducting thorough preoperative planning regarding implant placement and incision design. Burr holes should be placed in regions with muscle coverage or away from the incision line to minimize the risk of delayed implant exposure.

Study limitations

This single-center retrospective study focused on cases involving titanium implant exposure; therefore, we could not assess the overall incidence of implant exposure among all patients who underwent craniotomy or cranioplasty. The limited number of cases and incomplete information in medical records also prevented assessment of potential confounding factors, such as patients' nutritional status after the initial surgery, which may have influenced skin integrity. Moreover, owing to the nature of our institution, most initial procedures involved brain tumor resection or prophylactic cerebrovascular interventions, with relatively few trauma cases. As a result, the case mix may differ from that of other neurosurgical centers. Nonetheless, this study offers valuable insights into long-term complications of titanium implants, which are widely used in craniotomy and cranioplasty, and we believe these findings hold clinical significance.

Conclusions

Titanium implants, especially in female patients and those placed beneath incision lines or in areas lacking muscle coverage, are associated with a high risk of delayed implant exposure. Titanium meshes may lead to more diffuse skin thinning away from the incision and earlier exposure than titanium plates. Preventing delayed implant exposure requires attention to not only the type and shape of the implant but also the placement of burr holes during craniotomy.

Disclaimer

Author Yoshiki Arakawa is one of the Editorial Board members of the Journal. This author was not involved in the peer-review or decision-making process for this paper.

Conflicts of Interest Disclosure

Yoshiki Arakawa reports grants from Philips, Otsuka, Chugai, Nihon Medi-Physics, Daiichi Sankyo, Stryker, Eisai, Japan Blood Products Organization, Ono Pharmaceutical, Taiho Pharma, Sumitomo Dainippon Pharma, Astellas Pharma, Incyte Biosciences, Servier, and personal fees from Nippon Kayaku, Novocure, UCB Japan, Ono Pharmaceutical, Brainlab, Merck, Chugai, Eisai, Daiichi Sankyo, Carl Zeiss, Nihon Medi-Physics, and Stryker. All other authors report no conflict of interest.