The Autoclaving of Autologous Bone is a Risk Factor for Surgical Site Infection After Cranioplasty

Biomaterials for Regenerative Cranioplasty: Current State of Clinical Application and Future Challenges

Acquired cranial defects are a prevalent condition in neurosurgery and call for cranioplasty, where the missing or defective cranium is replaced by an implant. Nevertheless, the biomaterials in current clinical applications are hardly exempt from long-term safety and comfort concerns. An appealing solution is regenerative cranioplasty, where biomaterials with/without cells and bioactive molecules are applied to induce the regeneration of the cranium and ultimately repair the cranial defects. This review examines the current state of research, development, and translational application of regenerative cranioplasty biomaterials and discusses the efforts required in future research. The first section briefly introduced the regenerative capacity of the cranium, including the spontaneous bone regeneration bioactivities and the presence of pluripotent skeletal stem cells in the cranial suture. Then, three major types of biomaterials for regenerative cranioplasty, namely the calcium phosphate/titanium (CaP/Ti) composites, mineralised collagen, and 3D-printed polycaprolactone (PCL) composites, are reviewed for their composition, material properties, and findings from clinical trials. The third part discusses perspectives on future research and development of regenerative cranioplasty biomaterials, with a considerable portion based on issues identified in clinical trials. This review aims to facilitate the development of biomaterials that ultimately contribute to a safer and more effective healing of cranial defects.

Comparison of Perioperative and Long-term Outcomes Following PEEK and Autologous Cranioplasty: A Single Institution Experience and Review of the Literature

OBJECTIVE

Three-dimensionally (3D) printed polyether-ether-ketone (PEEK) implants are a relatively novel option for cranioplasty that have recently gained popularity. However, there is ongoing debate with respect to material efficacy and safety compared to autologous bone grafts. The purpose of this study was to offer our institution's experience and add to the growing body of literature.

METHODS

A single-institution retrospective analysis of patients undergoing cranioplasties between 2016 and 2021. Patients were divided into PEEK and autologous cranioplasty cohorts. Parameters of interest included patient demographics as well as perioperative (<3 months postoperative) and long-term outcomes (>3 months postoperative). A P value < 0.05 was considered statistically significant.

RESULTS

A total of 31 patients met inclusion criteria (PEEK: 15, Autologous: 16). Mean age of total cohort was 48.9 years (range 19-82 years). Modified Frailty Index (mFI) revealed greater rate of comorbidities among the Autologous group (P = 0.073), which was accounted for in statistical analyses. Multiple logistic regression model revealed significantly higher rate of surgical site infection in the Autologous cohort (31.3% vs. 0%, P = 0.011). Minor complications were similar between groups, while the Autologous group experienced significantly more major postoperative complications (50%) versus PEEK (13.3%) (P = 0.0291). Otherwise perioperative and long term complication profiles were similar between groups. Additionally, generalized linear model demonstrated both cohorts had similar mean hospital length of stay (LoS) (Autologous: 16.1 vs. PEEK: 10.7 days).

CONCLUSIONS

PEEK cranioplasty implants may offer more favorable perioperative complication profiles with similar long-term complication rates and hospital LoS compared to autologous bone implants. Future studies are warranted to confirm our findings in larger series, and further examine the utility of PEEK in cranioplasty.

Effect of microorganisms isolated by preoperative osseous sampling on surgical site infection after autologous cranioplasty: A single-center experience

PURPOSE

The most frequent postoperative complication in autologous cranioplasty (AC) is infection. European recommendations include osseous sampling before cryogenic storage of a bone flap. We evaluated the clinical impact of this sampling.

METHODS

All patients who underwent decompressive craniectomy (DC) and AC in our center between November 2010 and September 2021 were reviewed. The main outcome was the rate of reoperation for infection of the cranioplasty. We evaluated risk factors for bone flap infection, rate of reoperation for any reason (hematoma, skin erosion, cosmetic request, or bone resorption), and radiological evidence of bone flap resorption.

RESULTS

A total of 195 patients with a median age of 50 (interquartile range: 38.0-57.0) years underwent DC and AC between 2010 and 2021. Of the 195 bone flaps, 54 (27.7%) had a positive culture, including 48 (88.9%) with Cutibacterium acnes. Of the 14 patients who underwent reoperation for bone flap re-removal for infection, 5 and 9 had positive and negative bacteriological cultures, respectively. Of patients who did not have bone flap infection, 49 and 132 had positive and negative bacteriological cultures, respectively. There were no significant differences between patients with and without positive bacteriological culture of bone flaps in the rates of late bone necrosis and reoperation for bone flap infection.

CONCLUSIONS

A positive culture of intraoperative osseous sampling during DC is not associated with a higher risk of re-intervention after AC.

Infection-related failure of autologous versus allogenic cranioplasty after decompressive hemicraniectomy - A systematic review and meta-analysis

Introduction

Cranioplasty is required after decompressive craniectomy (DC) to restore brain protection and cosmetic appearance, as well as to optimize rehabilitation potential from underlying disease. Although the procedure is straightforward, complications either caused by bone flap resorption (BFR) or graft infection (GI), contribute to relevant comorbidity and increasing health care cost. Synthetic calvarial implants (allogenic cranioplasty) are not susceptible to resorption and cumulative failure rates (BFR and GI) tend therefore to be lower in comparison with autologous bone. The aim of this review and meta-analysis is to pool existing evidence of infection-related cranioplasty failure in autologous versus allogenic cranioplasty, when bone resorption is removed from the equation.

Materials and methods

A systematic literature search in PubMed, EMBASE, and ISI Web of Science medical databases was performed on three time points (2018, 2020 and 2022). All clinical studies published between January 2010 and December 2022, in which autologous and allogenic cranioplasty was performed after DC, were considered for inclusion. Studies including non-DC cranioplasty and cranioplasty in children were excluded. The cranioplasty failure rate based on GI in both autologous and allogenic groups was noted. Data were extracted by means of standardized tables and all included studies were subjected to a risk of bias (RoB) assessment using the Newcastle-Ottawa assessment tool.

Results

A total of 411 articles were identified and screened. After duplicate removal, 106 full-texts were analyzed. Eventually, 14 studies fulfilled the defined inclusion criteria including one randomized controlled trial, one prospective and 12 retrospective cohort studies. All but one study were rated as of poor quality based on the RoB analysis, mainly due to lacking disclosure why which material (autologous vs. allogenic) was chosen and how GI was defined. The infection-related cranioplasty failure rate was 6.9% (125/1808) for autologous and 8.3% (63/761) for allogenic implants resulting in an OR 0.81, 95% CI 0.58 to 1.13 (Z ​= ​1.24; p ​= ​0.22).

Conclusion

In respect to infection-related cranioplasty failure, autologous cranioplasty after decompressive craniectomy does not underperform compared to synthetic implants. This result must be interpreted in light of limitations of existing studies. Risk of graft infection does not seem a valid argument to prefer one implant material over the other. Offering an economically superior, biocompatible and perfect fitting cranioplasty implant, autologous cranioplasty can still have a role as the first option in patients with low risk of developing osteolysis or for whom BFR might not be of major concern.

Trial registration

This systematic review was registered in the international prospective register of systematic reviews. PROSPERO: CRD42018081720.

Microbiological profile and infection potential of different cryopreserved skull flaps after decompressive hemicraniectomy. Is cryopreservation at - 80 ℃ better?

OBJECTIVE

Patterns of cryopreservation of explanted skull bone flaps have long been a matter of debate, in particular the appropriate temperature of storage. To the best of our knowledge no study to date has compared the microbiological profile and the infection potential of skull bone flaps cryostored at the same institution at disparate degrees for neurosurgical purposes. In the context of our clinical trial DRKS00023283, we performed a bacterial culture of explanted skull bone flaps, which were cryopreserved lege artis at a temperature of either - 23 °C or - 80 °C after a decompressive hemicraniectomy. In a further step, we contaminated the bone fragments in a s uspension with specific pathogens (S. aureus, S. epidermidis and C. acnes, Colony forming unit CFU 103/ml) over 24 h and conducted a second culture.

RESULTS

A total of 17 cryopreserved skull flaps (8: - 23 °C; 9: - 80 °C) explanted during decompressive hemicraniectomies performed between 2019 and 2020 as well as 2 computer-aided-designed skulls (1 vancomycin-soaked) were analyzed. Median duration of cryopreservation was 10.5 months (2-17 months). No microorganisms were detected at the normal bacterial culture. After active contamination of our skull flaps, all samples showed similar bacterial growth of above-mentioned pathogens; thus, our study did not reveal an influence of the storage temperature upon infectious dynamic of the skulls.

Management of infected hydroxyapatite cranioplasty: Is salvage feasible?

Introduction

The use of hydroxyapatite cranioplasties has grown progressively over the past few decades. The peculiar biological properties of this material make it particularly suitable for patients with decompressive craniectomy where bone reintegration is a primary objective. However, hydroxyapatite infection rates are similar to those of other reconstructive materials.

Research question

We investigated if infected hydroxyapatite implants could be saved or not.

Materials and methods

We present a consecutive series over a 10-year period of nine patients treated for hydroxyapatite cranioplasty infection. Clinical and radiological data from admission and follow-up, photo and video material documenting the different phases of infection assessment and treatment, and final outcomes were retrospectively reviewed in an attempt to identify the best options and possible pitfalls in a case-by-case decision-making process.

Results

Five unilateral and four bifrontal implants became infected. Wound rupture with cranioplasty exposure was the most common presentation. At revision, all implants were ossified, requiring a new craniotomy to clean the purulent epidural collections. The cranioplasty was fully saved in one hemispheric and 2 bifrontal implants and partially saved in the remaining 2 bifrontal implants. A complete cranioplasty removal was needed in the other 4 cases, but immediate cranial reconstruction was possible in 2. Skin defects were covered by free flaps in 3 cases. Four patients underwent adjunctive hyperbaric therapy, which was effective in one case.

Discussion and conclusion

In our experience, infected hydroxyapatite cranioplasty management is complex and requires a multidisciplinary approach. Salvage of a hydroxyapatite implant is possible under specific circumstances.

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We present a series of 9 patients treated for hydroxyapatite cranioplasty infection.

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One hemispheric and 2 bifrontal implants were fully saved, 2 bifrontal only partially.

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A complete removal was needed in 4 cases, but immediate cranial reconstruction was possible in 2.

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Infected hydroxyapatite cranioplasties salvage is complex, but possible under specific circumstances.

Predictive Value of Swab Cultures for Cryopreserved Flaps During Delayed Cranioplasties

OBJECTIVE

To assess the predictive value of swab cultures of cryopreserved skull flaps during cranioplasties for surgical site infections (SSIs).

METHODS

A retrospective review was conducted of consecutive patients who underwent delayed cranioplasties with cryopreserved autografts between 2009 and 2017. The results of cultures obtained from swabs and infected surgical sites were assessed. The accuracy, sensitivity, and specificity of swab cultures for SSIs were evaluated.

RESULTS

The study included 422 patients categorized into two groups, swab and nonswab, depending on whether swab cultures were implemented during cranioplasties. The overall infection rate was 7.58%. No difference was seen in infection rates between groups. There were 18 false-positive and no true-positive swab culture results. All bacteria between swab cultures and SSI cultures were discordant. Meanwhile, there were 19 false-negative swab cultures. The results showed high specificity but low sensitivity for swab cultures to predict SSI occurrence and the pathogens.

CONCLUSIONS

Owing to low accuracy and sensitivity, swab cultures of cryopreserved autografts should not be routinely performed during delayed cranioplasties.

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.

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.

Reduction in the infection rate of cranioplasty with a tailored antibiotic prophylaxis: a nonrandomized study

BACKGROUND

Cranioplasty carries a high risk of surgical site infections (SSIs) for a scheduled procedure, particularly with antibiotic-resistant bacteria.

METHODS

The goal of this retrospective study was to measure the effect of tailored antibiotic prophylaxis on SSIs resulting from cranioplasties. The authors collected a prospective database of cranioplasties from 2009 to 2018. Risk factors for SSI were registered, as well as infection occurring during the first year postoperatively. A new protocol was initiated in 2016 consisting of antibiotic prophylaxis tailored to the colonizing flora of the skin of the scalp and decolonization of patients who were nasal carriers of methicillin-resistant S. aureus (MRSA); infection rates were compared.

RESULTS

One hundred nine cranioplasties were identified, 64 in the old protocol and 45 in the new protocol. Of the 109 cranioplasties, 16 (14.7%) suffered an infection, 14 (21.9%) in the old protocol group and 2 (4.4%) in the new protocol group (OR for the new protocol 0.166, 95% CI 0.036-0.772). Multiple surgeries (OR 3.44), Barthel ≤ 70 (OR 3.53), and previous infection (OR 3.9) were risk factors for SSI. Of the bacteria identified in the skin of the scalp, 22.2% were resistant to routine prophylaxis (cefazoline). Only one patient was identified as a nasal carrier of MRSA and was decolonized.

CONCLUSIONS

A high percentage of bacteria resistant to routine prophylaxis (cefazoline) was identified in the skin of these patients' scalps. The use of tailored antibiotic prophylaxis reduced significantly the infection rate in this particular set of patients.

Presence of Propionibacterium acnes in patients with aseptic bone graft resorption after cranioplasty: preliminary evidence for low-grade infection

OBJECTIVE

Autologous bone graft reimplantation remains the standard treatment after decompressive hemicraniectomy. Unfortunately, some patients present with signs of bone resorption without any visible signs of infection; the reasons remain unknown. Contamination with Propionibacterium acnes has been discussed as a potential source of the osteolytic process. The aim of this study was to investigate the microbial spectrum detected in samples of grafts from patients with aseptic bone resorption and compare them to septic bone graft infections in order to identify P. acnes as the specific pathogen of aseptic bone resorption.

METHODS

The authors retrospectively reviewed all patients treated for aseptic bone resorption between 2012 and 2017 in their neurosurgical department. Septic infections were used as a control group to gain information on the present bacterial spectrum. Perioperative data such as demographics, number of surgeries, and complications were assessed and compared with the microbiological analyses conducted in order to detect differences and potential sources for aseptic bone resorption and possible differences in bacterial contamination in septic and aseptic bone infection.

RESULTS

In total, 38 patients underwent surgery between 2012 and 2017 for septic bone infection-14 for aseptic bone resorption. In 100% of the septic bone infection cases in which bone flap removal was needed, bacteria could be isolated from the removed bone flap (55% Staphylococcus aureus, 13.2% Enterococcus faecalis, and 18.4% Staphylococcus epidermidis). The microbial spectrum from samples of aseptic bone flaps with resorption was examined in 10 of 14 patients and revealed contamination with P. acnes in 40% (n = 4, the other 6 bone grafts were sterile), especially in sonication analysis, whereas visible septic bone infection was mainly caused by S. aureus without detection of P. acnes.

CONCLUSIONS

Aseptic bone resorption may be caused by low-grade infections with P. acnes. However, further analysis needs to be conducted in order to understand its clinical relevance and treatment perspective.

Cranioplasty with Titanium Might Be Suitable for Adult Epilepsy Surgery After Subdural Placement Surgery To Avoid Surgical Site Infection

BACKGROUND

The purpose of the present study was to compare the surgical site infection (SSI) rates between resorbable plates and titanium plates used for adult patients with intractable epilepsy who had undergone epilepsy surgery after subdural electrode placement.

METHODS

We performed subdural electrode surgery, followed by epilepsy surgery, for 87 adult patients with intractable epilepsy. The epilepsy surgery included 75 focus resections and 12 corpus callosotomies. We compared the SSI rates between patients who had undergone cranioplasty with titanium and resorbable plates after epilepsy surgery.

RESULTS

Of the 87 patients, 43 had undergone cranioplasty with resorbable plates (group A) and 44 had undergone cranioplasty with titanium plates (group B). The frequency of SSI was significantly greater in group A (7 patients; 16.3%) than in group B (1 patient; 2.3%; P = 0.03, Fisher's exact test). Univariate regression analysis also showed a significantly greater infection rate with the resorbable plates (P = 0.024).

CONCLUSION

For epilepsy surgery of adult patients after subdural electrode placement surgery, the SSI rate for cranioplasty was greater with resorbable plates than with titanium plates.

Factors related to failure of autologous cranial reconstructions after decompressive craniectomy

PURPOSE

Cranioplasty is customary after decompressive craniectomy. Many different materials have been developed and used for this procedure. The ideal material does not yet exist, while complication rates in cranioplasties remain high. This study aimed to determine factors related to autologous bone flap failure.

MATERIALS AND METHODS

In this two-center retrospective cohort study, 276 patients underwent autologous bone cranioplasty after initial decompressive craniectomy between 2004 and 2014. Medical records were reviewed regarding patient characteristics and factors potentially related to bone flap failure. Data were analyzed using univariable and multivariable regression analysis.

RESULTS

Independent factors related to overall bone flap failure were: duration of hospitalization after decompressive craniectomy [OR: 1.012 (95%CI: 1.003-1.022); p = 0.012], time interval between decompressive craniectomy and cranioplasty [OR: 1.018 (95%CI: 1.004-1.032); p = 0.013], and follow-up duration [OR: 1.034 (95%CI: 1.020-1.047); p < 0.001]. In patients with bone flap infection, neoplasm as initial diagnosis occurred significantly more often (29.2% vs. 7.8%; RD 21.3%; 95%CI 8.4 -38.3%; NNH 5; 95%CI 3 -12) and duration of hospitalization after decompressive craniectomy tended to be longer (means 54 vs. 28 days, MD 26.2 days, 95%CI -8.6 to 60.9 days). Patients with bone flap resorption were significantly younger (35 vs. 43 years, MD 7.7 years, 95%CI 0.8-14.6 years) and their cranial defect size tended to be wider than in patients without bone flap resorption (mean circumference 39 vs. 37 cm; MD 2.4 cm, 95% CI -0.43-5.2 cm) and follow-up duration was significantly longer (44 vs. 14 months, MD 29 months, 95%CI 17-42 months).

CONCLUSION

A neoplasm as initial diagnosis, longer hospitalization after decompressive craniectomy, larger time interval between decompressive craniectomy and cranioplasty, and longer follow-up duration are associated with a higher risk of failure of autologous bone flaps for cranioplasty. Patients with these risk factors may be better served with an early recovery program after decompressive surgery or an alloplastic material for cranioplasty.

Calcium and phosphorus loss from laying hen bones autoclaved for tissue removal

Standard procedure for most conventional bone assays rely on bones being free of attached muscle or integumentary tissue. Use of an autoclave for bone cleaning is advantageous, as parts may be cleaned afterward by peeling the muscle away as opposed to tediously scrapping muscle tissue from the bone by hand. However, autoclave use for tissue removal has not been validated and published studies typically do not specify the cleaning method. One concern is that autoclave usage could cause mineral leaching out of the bone. The objective was to determine any change in bone mineral content as a result of autoclaving bone samples to remove muscle tissue. Ten pairs of frozen chicken legs were randomly selected and thawed from 72-wk-old W36 hens. Right legs were autoclaved at 121°C for 25 min in individual trays. Left legs were thawed and cleaned by hand. The tibia, meat, and exudate were collected from each leg. Cleaned bones were placed in a soxhlet to extract the fat for 30 h and ashed at 600°C for 8 h. Bone and muscle samples underwent microwave digestion in 10 mL of 70% nitric acid. Digested samples were analyzed for calcium using a flame atomic absorption spectrophotometer. Phosphorus was determined by a colorimetric assay measuring phosphate ion complexes. Statistical analysis was completed by paired t-tests. We found no significant calcium (P = 0.6319) or phosphorus (P = 0.1698) loss from bones autoclaved as compared with bones that were hand cleaned. This study provides evidence that affirms that the use of the autoclave on bones is a suitable method for tissue removal from the leg bones of adult laying hens.

The safety of simultaneous cranioplasty and shunt implantation

BACKGROUND

A large cranial defect combined with hydrocephalus is a frequent sequela of decompressive craniectomy (DC) performed to treat malignant intracranial hypertension. Currently, many neurosurgeons perform simultaneous cranioplasty and shunt implantation on such patients, but the safety of this combined procedure remains controversial.

METHODS

We retrospectively evaluated 58 patients treated via cranioplasty and shunt implantation after DC. Twenty patients underwent simultaneous procedures (simultaneous operation group) and 38 underwent staged procedures (staged operation group). We collected and analysed demographic data, information on disease histories, and clinical findings.

RESULTS

The overall complication rate was 19%. The two groups did not significantly differ regarding the all-complication (30% vs. 13%), bleeding complication (0% vs. 5%), or treatment failure (15% vs. 3%) rates. However, the rate of surgical site infection/incision healing problems (25% vs. 3%) and the re-operation rate (20% vs. 3%) were significantly higher in the simultaneous operation group.

CONCLUSION

Patients undergoing simultaneous cranioplasty/shunt implantation may be at a higher risk of infectious complications than those undergoing staged operations.

Never say never again: A bone graft infection due to a hornet sting, thirty-nine years after cranioplasty

Background:

Cranioplasty (CP) is a widespread surgical procedure aimed to restore skull integrity and physiological cerebral hemodynamics, to improve neurological functions and to protect the underlying brain after a life-saving decompressive craniectomy (DC). Nevertheless, CP is still burdened by surgical complications, among which early or late graft infections are the most common outcome-threatening ones.

Case Description:

We report the case of 48-year-old man admitted to our neurosurgical unit because of a painful right frontal swelling and 1-week purulent discharge from a cutaneous fistula. He had been undergone frontal CP because of severe traumatic brain injury (TBI) when he was 9-year-old. Since then, his medical history has been being unremarkable without any surgical or infective complication of the graft for 39 years, until he was accidentally stung by a hornet in the frontal region. After the CT scan and laboratory findings had evidenced a probable infection of the graft, the patient was treated by vancomycin and cefepime before he underwent surgical revision of its former CP, with the removal of the graft and the debridement of the surgical field. Subsequent bacteriological tests revealed Staphylococcus aureus as causal agent of that infection.

Conclusion:

This case illustrates an anecdotal example of very late CP infection, due to an unpredictable accident. Due to lack of consensus on risk factors and on conservative or surgical strategy in case of graft infection, we aimed to share our surgical experience.

Cryostored autologous skull bone for cranioplasty? A study on cranial bone flaps' viability and microbial contamination after deep-frozen storage at -80°C

Craniectomy is a life-saving procedure. Subsequent cranioplasty with autologous skull bone has a bone resorption rate from 4% to 22.8% and an infection rate from 3.3% to 26%. There are concerns with their viability and the potential microbial contamination as they were explanted for a long period of time. Eighteen cranial bone flaps stored at Prince of Wales Hospital Skull Bone Bank during the period from June 2011 to March 2016 were identified. Ethics approval was obtained. Bone chips and deep bone swabs were collected for osteoblast culture and microbial culture. Skull Bone Bank was kept at -80°C under strict aseptic technique during the study period. The storage period ranged from 4months to 55months. For the osteoblast culture, all eighteen bone flaps had no viable osteoblast growth. For the bacterial culture, five had positive bacteria growth (27.8%). Three were Pasteurella multocida and two were Methicillin-resistant Staphylococcus aureus. The mean duration of storage of the infected bone flap was 32.9months (±15.1months) versus 19.9months (±17.9months) of those bone flaps with no bacterial growth (p=0.1716). The mean size of the infected versus non-infected bone flaps was 117.7cm² (±44.96cm²) versus 76.8cm² (±50.24cm²) respectively (p=0.1318). Although in this study statistical significance was not reached, it was postulated that infected bone flaps tended to be larger in size and had a longer duration of storage. In conclusion, cryostored skull bone flaps beyond four months showed no viable osteoblasts. Bacterial contamination rate of bone flaps was 27.8% in this study.