Aseptic Bone Flap Resorption after Cranioplasty with Autologous Bone: Incidence, Risk Factors, and Clinical Implications

Autologous Cranioplasty with Bone Flap Preserved in Conventional Freezers: An Adequate Option in Low Resource Settings

BACKGROUND

Autologous cranioplasty has been used for decades and is the gold standard treatment in patients who underwent decompressive craniectomy (DC). One of the most common methods to store the cranial bone flap is cryopreservation at very low temperatures (-70 to -80°). The only way to achieve these low temperatures is by using special freezers which are not always available in all medical facilities, especially in low-resource centers. This paper describes our experience with the storage of cranial bone flaps in freezers of conventional refrigerators.

METHODS

This retrospective study included patients treated with autologous cranioplasty, operated between 2015 and 2020. The cranial bone flap was stored at -18°C in the freezer of conventional refrigerators. Complications and outcomes were analyzed and compared with reports of patients in whom ultra-low temperature freezers were used for bone flap preservation.

RESULTS

Twenty-five patients were included. The average follow-up period was 33 months. Trauma was the most common cause of DC, followed by stroke. The mean age was 36.7. Aseptic bone flap resorption was observed in 4 cases (16%). No cases of infection were observed.

CONCLUSIONS

The use of freezers from conventional refrigerators may be an acceptable alternative for the preservation of the cranial bone flap in facilities where special freezers are not available. The rate of aseptic bone necrosis and infections observed in this paper was similar to the incidence of these complications reported in studies where ultra-low temperatures were used.

Bone Flap Resorption After Cranioplasty: Risk Factors and Proposal of the Flap Integrity Score

BACKGROUND

Bone flap resorption is a known complication of postdecompressive autologous cranioplasty. Although several potential etiopathogenetic factors have been investigated, their role is still under discussion. To further complicate things, resorption is not an all-or-nothing event, patients frequently presenting with different degrees of flap remodeling. Focus of this paper was to describe the elaboration of a score quantifying bone resorption according to a set of clinical and radiological criteria, hopefully allowing prompt identification of patients needing resurgery before the development of adverse events.

METHODS

In a 10-year period, 281 autologous cranioplasties were performed at our institution following decompressive craniectomy. Pertinent clinical and radiological information was registered. A set of 3 clinical and 3 radiological parameters was established to score the degree of resorption, identified under the acronym FIS (Flap Integrity Score). Three groups of patients emerged, respectively showing no (208), partial (32), and advanced (41) resorption.

RESULTS

An overall 14.6% incidence of advanced bone resorption was found in our series. Younger age, bone multifragmentation, higher postcranioplasty Glasgow Outcome Scale scores, <2 cm distance of medial craniectomy border from the midline, and cause leading to decompressive craniectomy were associated to a statistically significant higher risk of developing a relevant bone flap resorption. The first three variables were confirmed as risk factors in multivariate analysis. Flap Integrity Score well discriminated the 3 different groups.

CONCLUSIONS

Autologous bone repositioning is still a valuable, low-cost, cosmetically and functionally satisfactory procedure. Nonetheless, although resorption affects a minor percentage of patients, its early identification and treatment can improve long-term results.

Risk Factor Analysis of Cryopreserved Autologous Bone Flap Resorption in Adult Patients Undergoing Cranioplasty with Volumetry Measurement Using Conventional Statistics and Machine-Learning Technique

OBJECTIVE

Decompressive craniectomy (DC) with duroplasty is one of the common surgical treatments for life-threatening increased intracranial pressure (ICP). Once ICP is controlled, cranioplasty (CP) with reinsertion of the cryopreserved autologous bone flap or a synthetic implant is considered for protection and esthetics. Although with the risk of autologous bone flap resorption (BFR), cryopreserved autologous bone flap for CP is one of the important material due to its cost effectiveness. In this article, we performed conventional statistical analysis and the machine learning technique understand the risk factors for BFR.

METHODS

Patients aged >18 years who underwent autologous bone CP between January 2015 and December 2021 were reviewed. Demographic data, medical records, and volumetric measurements of the autologous bone flap volume from 94 patients were collected. BFR was defined with absolute quantitative method (BFR-A) and relative quantitative method (BFR%). Conventional statistical analysis and random forest with hyper-ensemble approach (RF with HEA) was performed. And overlapped partial dependence plots (PDP) were generated.

RESULTS

Conventional statistical analysis showed that only the initial autologous bone flap volume was statistically significant on BFR-A. RF with HEA showed that the initial autologous bone flap volume, interval between DC and CP, and bone quality were the factors with most contribution to BFR-A, while, trauma, bone quality, and initial autologous bone flap volume were the factors with most contribution to BFR%. Overlapped PDPs of the initial autologous bone flap volume on the BRF-A crossed at approximately 60 mL, and a relatively clear separation was found between the non-BFR and BFR groups. Therefore, the initial autologous bone flap of over 60 mL could be a possible risk factor for BFR.

CONCLUSION

From the present study, BFR in patients who underwent CP with autologous bone flap might be inevitable. However, the degree of BFR may differ from one to another. Therefore, considering artificial bone flaps as implants for patients with large DC could be reasonable. Still, the risk factors for BFR are not clearly understood. Therefore, chronological analysis and pathophysiologic studies are needed.

A Comparative Study of Titanium Cranioplasty for Extensive Calvarial Bone Defects: Three-Dimensionally Printed Titanium Implants Versus Premolded Titanium Mesh

OBJECTIVE

This study compared the complications and symmetry outcomes between 3-dimensionally printed titanium implants and premolded titanium mesh in patients with extensive calvarial bone defects.

METHODS

This retrospective analysis included patients with calvarial defects >50 cm2 undergoing cranioplasty who received either a 3-dimensionally printed titanium implant manufactured by selective laser melting techniques (N = 12) or a premolded titanium mesh customized onto a 3-dimensionally printed skull template (N = 23). Complications including intracranial infection, hardware extrusion, wound dehiscence, and cerebrospinal fluid leaks were investigated. Predictive factors affecting complications were investigated to identify the odds ratios in univariate and multivariate analyses. The symmetry was assessed by calculating the root mean square deviation, which showed the morphological deviation of the selected area compared with the mirrored image of the contralateral region.

RESULTS

The overall complication rate was 26.1% (6/23 patients) in the premolded titanium group and 16.7% (2/12 patients) in the 3-dimensionally printed group. The reoperation rates did not differ significantly between the 2 groups (3-dimensionally printed group, 16.7%, versus premolded group, 21.7%). In multivariate analysis, only the number of previous cranial operation was significantly associated with the complication rate (odds ratio, 2.42; 95% confidence interval, 1.037-5.649; P = 0.041). The mean ± SD of the root mean square deviation was significantly smaller in the 3-dimensionally printed group (2.58 ± 0.93 versus 4.82 ± 1.31 mm, P < 0.001).

CONCLUSIONS

The 3-dimensionally printed titanium implant manufactured by the selective laser melting technique showed comparable stability and improved symmetry outcomes compared with the conventional titanium mesh in the reconstruction of extensive calvarial defects.

Use of adhesive cranial bone flap fixation without hardware to improve mechanical strength, resist cerebrospinal fluid leakage, and maintain anatomical alignment: a laboratory study

OBJECTIVE

Titanium plates and screws (TPS) are the current standard of care for fixation of cranial bone flaps. These materials have been used for decades but have known potential complications, including flap migration, bone resorption/incomplete osseous union, hardware protrusion, cosmetic deformity, wound infection/dehiscence, and cerebrospinal fluid (CSF) leakage. This study evaluated the efficacy of a novel mineral-organic bone adhesive (Tetranite) for cranial bone flap fixation.

METHODS

Craniotomy bone flaps created in human cadaveric skulls were tested under quasistatic and impact loading in the following conditions: 1) uncut skull; 2) bone flaps fixated with TPS alone; and 3) bone flaps fixated with bone adhesive alone. All fixative surgical procedures were performed by a group of 16 neurosurgeons in a simulated surgical environment. The position of adhesive-fixated cranial bone flaps was measured using computed tomography and compared with their original native location. The resistance of adhesive-fixated cranial bone flaps to simulated CSF leakage was also evaluated. Because there was a gap around the circumference of the TPS-fixated specimens that was visible to the naked eye, pressurized CSF leak testing was not attempted on them.

RESULTS

Adhesive-fixated bone flaps showed significantly stiffer and stronger quasistatic responses than TPS-fixated specimens. The strength and stiffness of the adhesive-fixated specimens were not significantly different from those of the uncut native skulls. Total and plastic deflections under 6-J impact were significantly less for adhesive-fixed bone flaps than TPS. There were no significant differences in any subthreshold impact metrics between the adhesive-fixed and native specimens at both 6-J and 12-J impact levels, with 1 exception. Plastic deflection at 6-J impact was significantly less in adhesive-fixated bone flaps than in native specimens. The energy to failure of the adhesive-fixated specimens was not significantly different from that of the native specimens. Time since fixation (20 minutes vs 10 days) did not significantly affect the impact failure properties of the adhesive-fixated specimens. Of the 16 adhesive-fixated craniotomy specimens tested, 14 did not leak at pressures as high as 40 mm Hg.

CONCLUSIONS

The neurosurgeons in this study had no prior exposure or experience with the bone adhesive. Despite this, improved resistance to CSF egress, superior mechanical properties, and better cosmetic outcomes were demonstrated with bone adhesive compared with TPS.

Development of a Prediction Model for Cranioplasty Implant Survival Following Craniectomy

BACKGROUND

Cranioplasty after craniectomy can result in high rates of postoperative complications. Although determinants of postoperative outcomes have been identified, a prediction model for predicting cranioplasty implant survival does not exist. Thus, we sought to develop a prediction model for cranioplasty implant survival after craniectomy.

METHODS

We performed a retrospective cohort study of patients who underwent cranioplasty following craniectomy between 2014 and 2020. Missing data were imputed using multiple imputation. For model development, multivariable Cox proportional hazards regression analysis was performed. To test whether candidate determinants contributed to the model, we performed backward selection using the Akaike information criterion. We corrected for overfitting using bootstrapping techniques. The performance of the model was assessed using discrimination and calibration.

RESULTS

A total of 182 patients were included (mean age, 43.0 ± 19.7 years). Independent determinants of cranioplasty implant survival included the indication for craniectomy (compared with trauma-vascular disease: hazard ratio [HR], 0.65 [95% confidence interval (CI), 0.36-1.17]; infection: HR, 0.76 [95% CI, 0.32-1.80]; tumor: HR, 1.40 [95% CI, 0.29-6.79]), cranial defect size (HR, 1.01 per cm2 [95% CI, 0.73-1.38]), use of an autologous bone flap (HR, 1.63 [95% CI, 0.82-3.24]), and skin closure using staples (HR, 1.42 [95% CI, 0.79-2.56]). The concordance index of the model was 0.60 (95% CI, 0.47-0.73).

CONCLUSIONS

We have developed the first prediction model for cranioplasty implant survival after craniectomy. The findings from our study require external validation and deserve further exploration in future studies.

Post-traumatic hydrocephalus may be associated with autologous cranioplasty failure, independent of ventriculoperitoneal shunt placement: a retrospective analysis

PURPOSE

Decompressive craniectomy (DC) is a common procedure used for the treatment of intracranial hypertension. Once brain swelling has subsided, a cranioplasty is performed to restore cosmesis and protection to the brain. While using the patient's autologous bone flap is often the first choice in cranioplasty, this procedure is frequently complicated by bone flap resorption and infection. This study seeks to identify predictors of autologous cranioplasty failure.

METHODS

A retrospective analysis was conducted on patients who underwent decompressive craniectomy and autologous cranioplasty. Patient demographics and factors related to both surgeries and failure rates were recorded from patient records. Logistic regressions were conducted to determine which factors were implicated in autologous cranioplasty failure.

RESULTS

In our cohort, 127 patients underwent autologous cranioplasty. Overall, 18 (14.2%) patients experienced autologous cranioplasty failure. Regression analysis identified development of post-traumatic hydrocephalus (PTH) following DC (OR: 3.26, p = 0.043), presence of neurological deficits following DC (OR: 4.88, p = 0.025), and reoperation prior to CP (OR 3.0, p = 0.049) as significant predictors of autologous cranioplasty failure. Of the 16 patients who developed PTH following DC, 9 received a VP shunt. The rate of flap failure was similar across the 9 PTH patients who received a shunt and the 7 PTH patients who did not receive a shunt (33% vs. 57% failure rate, respectively, p = 0.341).

CONCLUSION

Autologous cranioplasty is a reasonably successful procedure with a flap failure rate of 14.2%. We identified PTH, persistent neurological deficits, and reoperation prior to cranioplasty as significant predictors of autologous cranioplasty failure. Interestingly, the presence of VP shunt did not impact the odds of flap failure.

Favourable long-term recovery after decompressive craniectomy: the Northern Finland experience with a predominantly adolescent patient cohort

PURPOSE

Decompressive craniectomy (DC) is an effective treatment of intracranial hypertension. Correspondingly, the procedure is increasingly utilised worldwide. The number of patients rendered vegetative following surgery has been a concern-a matter especially important in children, due to long anticipated lifetime. Here, we report the long-term outcomes of all paediatric DC patients from an 11-year period in a tertiary-level centre that geographically serves half of Finland.

METHODS

We identified all patients younger than 18 years who underwent DC in the Oulu University Hospital between the years 2009 and 2019. Outcomes and clinicoradiological variables were extracted from the patient records.

RESULTS

Mean yearly prevalence of brain injury requiring DC was 1.34/100 000 children-twenty-four patients underwent DC during the study period and 21 (88%) survived. The median age of the patients was 16.0 years, and the median preoperative GCS was 5.0 (IQR 5.0). Fifteen patients (63%) had made a good recovery (Extended Glasgow Outcome Scale ≥ 7). Of the surviving patients, two (9.5%) had not returned to school. After traumatic brain injury (n = 20), the Rotterdam CT score (mean 3.0, range 1 to 5) was not associated with mortality, poor recovery or inability to continue school (p = 0.13, p = 0.41, p = 0.43, respectively). Absent basal cisterns were associated with mortality (p = 0.005), but not with poor recovery if the patient survived DC (p = 0.81). Hydrocephalus was associated with poor recovery and inability to continue school (p = 0.01 and p = 0.03, respectively).

CONCLUSION

Most of our patients made a favourable recovery and were able to continue school. No late mortality was observed. Thus, even in clinically and radiologically severely brain-injured children, decompressive craniectomy appears to yield favourable outcomes.

Complications of Cranioplasty in Relation to Material: Systematic Review, Network Meta-Analysis and Meta-Regression

BACKGROUND

Cranioplasty is a ubiquitous neurosurgical procedure consisting of reconstruction of a pre-existing calvarial defect. Many materials are available, including polymethylmethacrylate in hand-moulded (hPMMA) and prefabricated (pPMMA) form, hydroxyapatite (HA), polyetheretherketone (PEEK) and titanium (Ti).

OBJECTIVE

To perform a network meta-analysis (NMA) to assess the relationship between materials and complications of cranioplasty.

METHODS

PubMed/MEDLINE, Google Scholar, EMBASE, Scopus, and The Cochrane Library were searched from January 1, 1990 to February 14, 2021. Studies detailing rates of any of infections, implant exposure, or revision surgery were included. A frequentist NMA was performed for each complication. Risk ratios (RRs) with 95% CIs were calculated for each material pair.

RESULTS

A total of 3620 abstracts were screened and 31 full papers were included. Surgical revision was reported in 18 studies and occurred in 316/2032 cases (14%; 95% CI 11-17). PEEK had the lowest risk of re-operation with a rate of 8/157 (5%; 95% CI 0-11) in 5 studies, superior to autografts (RR 0.20; 95% CI 0.07-0.57), hPMMA (RR 0.20; 95% CI 0.07-0.60), Ti (RR 0.39; 95% CI 0.17-0.92), and pPMMA (RR 0.14; 95% CI 0.04-0.51). Revision rate was 131/684 (19%; 95% CI 13-25; 10 studies) in autografts, 61/317 (18%; 95%CI 9-28; 7 studies) in hPMMA, 84/599 (13%; 95% CI 7-19; 11 studies) in Ti, 7/59 (9%; 95% CI 1-23; 3 studies) in pPMMA, and 25/216 (12%; 95% CI 4-24; 4 studies) in HA. Infection occurred in 463/4667 (8%; 95% CI 6-11) and implant exposure in 120/1651 (6%; 95% CI 4-9).

CONCLUSION

PEEK appears to have the lowest risk of cranioplasty revision, but further research is required to determine the optimal material.

Complications of cranioplasty following decompressive craniectomy for traumatic brain injury: systematic review and meta-analysis

BACKGROUND

Decompressive craniectomy (DC) is a common neurosurgical intervention for severe traumatic brain injury (TBI), as well as malignant stroke, malignancy and infection. DC necessitates subsequent cranioplasty. There are significant demographic differences between TBI and non-TBI patients undergoing cranioplasty, which may influence their relative risk profiles for infection, aseptic bone flap resorption (aBFR) and re-operation.

OBJECTIVE

Perform a meta-analysis to determine the relative infection, aBFR and re-operation risk profiles of TBI patients as compared to other indications for DC.

METHODS

A systematic review and meta-analysis was performed in accordance with the PRISMA guidelines. PubMed, MEDLINE, EMBASE and Google Scholar were searched until 26/11/2020. Studies detailing rates of infection, re-operation and/or aBFR in specific materials and the post-TBI population were included, while studies in paediatrics or craniosynostosis repair were excluded.

RESULTS

Twenty-six studies were included. There was no difference in relative risk of infection between TBI and non-TBI cohorts (RR 0.81, 95% CI 0.57-1.17), with insignificant heterogeneity (I² = 33%). TBI was a risk factor for aBFR (RR 1.54, 95% CI 1.25-1.89), with no significant heterogeneity (I² = 13%). TBI was a risk factor for re-operation in the autologous sub-group (RR 1.49, 95% CI 1.05-2.11) but not in the alloplastic sub-group (RR = 0.86, 95% CI 0.34-2.18). Heterogeneity was insignificant (I² = 11%).

CONCLUSION

TBI is a risk factor for aBFR and re-operation following cranioplasty. Use of an alloplastic graft for primary cranioplasty in these patients may partially mitigate this increased risk.

Cranioplasty with Autologous Bone Flaps Cryopreserved with Dimethylsulphoxide: Does Tissue Processing Matter

OBJECTIVE

The aim of this article was to study the outcome of patients who underwent cranioplasty with cryopreserved autologous bone after decompressive craniectomy.

METHODS

Data from 74 patients were retrospectively analyzed. They were divided into groups according to the storage time and the age at cranioplasty. To assess the predictive potential for complication, factors were related to successive stages (preoperative, craniectomy, tissue processing, cranioplasty, and postoperative). Cooling and warming rates applied on bone flap were calculated. The ability to inhibit microbial growth was determined exposing bone fragments to a panel of microorganisms. The concentration of antibiotics eluted from the bone was also determined. A bone explant culture method was used to detect living cells in the thawed cranial bone.

RESULTS

Hydrocephalus was significantly more frequent in pediatric patients (26.7%) than in adults (5.1%). The overall rate of bone flap resorption was 21.6% (43.7% of which required reoperation). Surgical site infection after cranioplasty was detected in 6.8% of patients. There was no correlation between infection as a postoperative complication and previous microbiological-positive culture during processing. The cause of craniectomy did not influence the risk of bone flap contamination. Vancomycin was the only antibiotic detected in the supernatant where the bone was incubated. Outgrowth from bone explants was observed in 36.8% of thawed skulls. An early start of bone flap processing at the tissue bank had a positive effect on cell viability.

CONCLUSIONS

The outcome after autologous cranioplasty is a multifactorial process, which is modulated by patient-related, surgery-related, and bone-related factors.

The storage of skull bone flaps for autologous cranioplasty: literature review

The use of autologous bone flap for cranioplasty after decompressive craniectomy is a widely used strategy that allows alleviating health expenses. When the patient has recovered from the primary insult, the cranioplasty restores protection and cosmesis, recovering fluid dynamics and improving neurological status. During this time, the bone flap must be stored, but there is a lack of standardization of tissue banking practices for this aim. In this work, we have reviewed the literature on tissue processing and storage practices. Most of the published articles are focused from a strictly clinical and surgical point of view, paying less attention to issues related to tissue manipulation. When bone resorption is avoided and the risk of infection is controlled, the autograft represents the most efficient choice, with the lowest risk of complication. Otherwise, depending on the degree of involvement, the patient may have to undergo new surgery, assuming further risks and higher healthcare costs. Therefore, tissue banks must implement protocols to provide products with the highest possible clinical effectiveness, without compromising safety. With a centralised management of tissue banking practices there may be a more uniform approach, thus facilitating the standardization of procedures and guidelines.

Cranial bone flap resorption-pathological features and their implications for clinical treatment

Cranioplasty following decompressive craniectomy (DC) has a primary complication when using the autologous bone: aseptic bone resorption (ABR). So far, risk factors such as age, number of fragments, and hydrocephalus have been identified but a thorough understanding of the underlying pathophysiology is still missing. The aim of this osteopathological investigation was to gain a better understanding of the underlying processes. Clinical data of patients who underwent surgical revision due to ABR was collected. Demographics, the time interval between craniectomy and cranioplasty, and endocrine serum parameters affecting bone metabolism were collected. Removed specimens underwent qualitative and quantitative histological examination. Two grafts without ABR were examined as controls. Compared to the controls, the typical layering of the cortical and cancellous bone was largely eliminated in the grafts. Histological investigations revealed the coexistence of osteolytic and osteoblastic activity within the necrosis. Bone appositions were distributed over the entire graft area. Remaining marrow spaces were predominantly fibrotic or necrotic. In areas with marrow cavity fibrosis, hardly any new bone tissue was found in the adjacent bone, while there were increased signs of osteoclastic resorption. Insufficient reintegration of the flap may be due to residual fatty bone marrow contained in the bone flap which seems to act as a barrier for osteogenesis. This may obstruct the reorganization of the bone structure, inducing aseptic bone necrosis. Following a path already taken in orthopedic surgery, thorough lavage of the implant to remove the bone marrow may be a possibility, but will need further investigation.

Risk factors for bone flap resorption after autologous bone cranioplasty: Protocol for a systematic review and meta-analysis

BACKGROUND

One of the most common complications following autologous cranioplasty is bone flap resorption (BFR). Severe BFR can lead to revision surgery with implantation of synthetic bone flap and also necessarily lead to higher hospital expenses. This study aims to perform a meta-analysis to summarize available evidence regarding risk factors of BFR requiring a second surgery in patients with autologous cranioplasty.

METHODS

Cohort, case-control, and cross-sectional studies that report the incidence and risk factors of BFR among patients with autologous cranioplasty, published in English, will be considered for selection. Three databases from inception to May 2020 will be searched. The process of data selection, quality assessment, and data extraction will be assessed by 2 authors independently. The study quality will be assessed by Newcastle-Ottawa Scale (NOS) and Agency for Healthcare Research and Quality checklist.The statistical analysis of this meta-analysis will be calculated by Review manager version 5.3.

RESULTS

The results of this systematic review and meta-analysis will be disseminated through academic conferences and expected to publish in a peer-reviewed journal CONCLUSION:: This study will offer high-quality evidence about risk factors for BFR after autologous cranioplasty.

REGISTRATION NUMBER

INPLASY202050063.

Clinical and radiological risk factors of autograft cranioplasty resorption after decompressive craniectomy for traumatic brain injury

OBJECTIVE

The repositioning of an autologous bone flap after decompressive craniectomy (DC) for traumatic intracranial hypertension remains the first-line treatment for cranial reconstruction. Aseptic autologous bone flap resorption (BFR) is the most frequent complication. The identification of possible predictive parameters for BFR would help to improve the management of these patients.

PATIENTS AND METHODS

Three hundred and nine patients undergoing autologous bone flap repositioning after previous DC for TBI between September 2003 and September 2017 were included in the study.

RESULTS

BFR was identified in 76 (24,59 %) of the 309 patients undergoing autologous CP. Age of ≤ 45 years and CP bone fragmentation were seen to be significant independent risk factors for BFR (p =  0.001 and p =  0.018, respectively) using multivariate logistic regression analysis. Of the radiologic predictors, CP size and the gap between CP and the skull defect were independently associated with BFR (p =  0.034 and p =  0.0003, respectively). The Youden index and ROC curve analysis were used to estimate the cut-off values for the continuous parameters and determine the sensitivity and specificity of the radiologic risk factors. The cut-off value for these two factors was found to be 114,98 cm2 and ≥ 578,5 mm2, respectively. The area under the ROC curve was 0.627 for bone flap size and 0.758 for the DC-CP gap. The DC-CP gap had greater sensitivity and specificity as a predictor of BFR, compared to bone flap size (p = 0.079 and p = ≤ 0.001, respectively).

CONCLUSIONS

In this large cohort of patients with autologous cranioplasty, younger age, fragmented autologous bone flap and a wide gap between CP and cranial defect were predictive of bone flap resorption.

Bone Flap Resorption Associated with Indolent Propionibacterium acnes Infection After Cranioplasty: Case Report with Pathological Analysis

BACKGROUND

Autologous bone resorption is a frequent complication of cranioplasty, often necessitating reoperation. The etiology of this phenomenon is unknown, although it has recently been associated with indolent Propionibacterium acnes infection.

CASE DESCRIPTION

A 59-year-old man initially presented with a traumatic acute subdural hematoma treated with emergent decompressive hemicraniectomy and hematoma evacuation. His bone flap was cryopreserved. He underwent cranioplasty with autologous bone 3 months later. Over the subsequent 14 months, serial imaging demonstrated progressive bone flap resorption, ultimately requiring repeat cranioplasty with a custom allograft. Although there was no evidence of infection at the time of repeat cranioplasty, routine culture swabs were taken and grew P. acnes after the patient had been discharged home. Pathologic analysis of the fragments of the original bone flap that were removed demonstrated osteonecrosis with marrow fibrosis but no evidence of inflammation or infection. He was treated with 6 weeks of intravenous antibiotics and had no evidence of infection at 8-month follow-up.

CONCLUSIONS

Indolent P. acnes infection can precipitate autologous bone flap resorption. While the mechanism of this is unknown, pathologic analysis of a partially resorbed bone flap in the setting of an indolent P. acnes infection found no evidence of an infectious process or inflammation within the bone. Further studies are needed to elucidate the mechanism of action of P. acnes in bone flap resorption.

Aseptic bone-flap resorption after cranioplasty - incidence and risk factors

Objective

One of the common complications occurring after cranioplasty (CP) is aseptic bone-flap resorption (ABFR). Reoperation necessary because of the development of ABFR can lead to unfavorable complications during subsequent surgery using a synthetic skull implant, and also necessarily leads to higher costs. The aim of this study is to identify prognostic factors that may help to predict the development of ABFR.

Methods

In this study, 303 CP surgeries performed between 2002 and 2017 were examined retrospectively to identify factors predicting the occurrence of ABFR. A number of these factors (e.g., time lapse between decompressive craniectomy (DC) and CP, bone-flap size, specific laboratory signs, and the reason for the original DC) were analyzed as possibly influencing the risk of developing ABFR.

Results

ABFR of an autologous bone flap that subsequently required a CP with synthetic skull implants occurred in 10 of 303 patients (3.0%). CP timing and patients' Karnofsky Performance Scores (KPS) (p = 0.008; p = 0.012) were identified as significant factors with an impact on the development of ABRF. Age did not reveal a significant value, but statistical analysis shows a clear trend. The younger the age, the more likely it was that an ABFR would develop.

Conclusion

The risk of ABFR lessens the longer the period of time elapsed between DC and CP. Age does not reveal a significant value, but statistical analysis shows that there is a clear trend.

Deformation of cranioplasty titanium mesh in a paediatric patient following head trauma

Decompressive craniectomy is a life-saving procedure performed to treat intracranial hypertension caused by a variety of conditions. Subsequent cranioplasty reconstruction is needed for brain protection. Different alloplastic materials with different advantages and disadvantages are available for cranial reconstruction. We present the first case of a deformed titanium cranioplasty mesh in a paediatric patient following head trauma. Children who have undergone cranioplasty reconstruction should be counselled to wear a protective helmet when involved in contact sports or activities that may put their implant at risk of trauma.

Classification of bone flap resorption after cranioplasty: a proposal for a computed tomography-based scoring system

Background

Bone flap resorption (BFR) is the most prevalent complication resulting in autologous cranioplasty failure, but no consensus on the definition of BFR or between the radiological signs and relevance of BFR has been established. We set out to develop an easy-to-use scoring system intended to standardize the interpretation of radiological BFR findings.

Methods

All 45 autologous cranioplasty patients operated on at Oulu University Hospital from 2004 to 2014 were identified, and the bone flap status of all the available patients was evaluated using the new scoring system. Derived from previous literature, a three-variable score for the detection of BFR changes is proposed. The variables “Extent” (estimated remaining bone volume), “Severity” (possible perforations and their measured diameter), and “Focus” (the number of BFR foci within the flap) are scored from 0 to 3 individually. Using the sum of these scores, a score of 0–9 is assigned to describe the degree of BFR. Additionally, independent neurosurgeons assessed the presence and relevance of BFR from the same data set. These assessments were compared to the BFR scores in order to find a score limit for relevant BFR.

Results

BFR was considered relevant by the neurosurgeons in 11 (26.8%) cases. The agreement on the relevance of BFR demonstrated substantial strength (κ 0.64, 95%CI 0.36 to 0.91). The minimum resorption score in cases of relevant BFR was 5. Thus, BFR with a resorption score ≥ 5 was defined relevant (grades II and III). With this definition, grade II or III BFR was found in 15 (36.6%) of our patients. No risk factors were found to predict relevant BFR.

Conclusions

The score was proven to be easy to use and we recommend that only cases with grades II and III BFR undergo neurosurgical consultation. However, general applicability can only be claimed after validation in independent cohorts.

Bone resorption in autologous cryopreserved cranioplasty: quantitative evaluation, semiquantitative score and clinical significance

BACKGROUND

Changes after reimplantation of the autologous bone have been largely described. However, the rate and the extent of resorption in cranial grafts have not been clearly defined. Aim of our study is to evaluate the bone flap resorption (BFR) after cryopreservation.

METHODS

We retrospectively reviewed 27 patients, aged 18 years or older, subjected to cranioplasty (CP) adopting autologous cryopreserved flap. The BFR was derived from the percentage of decrease in flap volume (BFR%), comparing the first post-operative computed tomography (CT) and the last one available (performed at least 1 year after surgery). We also proposed a semiquantitative scoring system, based on CT, to define a clinically workable BFR classification.

RESULTS

After a mean ± SE follow-up of 32.5 ± 2.4 months, the bone flap volume decreased significantly (p < 0.0001). The mean BFR% was 31.7 ± 3.8% and correlated with CT-score (p < 0.001). Three BFR classes were described: mild (14.8% of cases) consisting in minimal bone remodelling, CT-score ≤ 6, mean BFR% = 3.5 ± 0.7%; moderate (51.9% of cases) corresponding to satisfactory cerebral protection, CT-score < 13, mean BFR% = 25.6 ± 2.2%; severe (33.3% of cases) consisting in loss of cerebral protection, CT-score ≥ 13, mean BFR% = 54.2 ± 3.9%. Females had higher BFR% than males (p = 0.022). BFR classes and new reconstructive surgery were not related (p = 0.58).

CONCLUSIONS

BFR was moderate or severe in 85.2% of re-implanted cryopreserved flaps. The proposed CT-score is an easy and reproducible tool to define resorption extent.

Bone Flap Necrosis due to Low Grade Infection with Propionibacterium Acnes

Osteonecrosis of bone flaps after cranioplasty with autologeous cryo-conserved bone flaps is a common phenomenon. The exact reason for it remains unknown. We present a case of a 67-year old patient who had a bone flap necrosis after elective craniotomy and underwent secondary cranioplasty. A low-grade infection with Propionibacterium acnes was detected in microbiological samples from the bone flap as cause of the lysis. We discuss similarities with aseptic implant loosening and present recent evidence that low-grade infections might be the underlying reason in several cases. We conclude that low-grade infections play an underestimated role in bone flap necrosis after cranioplasty as well and encourage routine microbiological sampling (extended culture and PCR) to rule out infection in all similar cases and suggest a routine antibiotic therapy until final microbiological results.