Microbiological cultures of allografts of the femoral head just before transplantation

Allogenic bone grafts and postoperative surgical site infection: are positive intraoperative swab cultures predictive for a higher infectious risk?

In spine surgery, allogenic bone grafts are often required to ensure bone fusion, however, the main concern regarding their use is the infection risk: therefore, an intraoperative swab for culture test is performed. The cost-effectiveness of these swabs and their influence on the patients' postoperative course have often been questioned. This study aims at determining whether positive spine allograft culture results are predictive of an increased risk of surgical site infection and whether they influence the surgeon's choices in postoperative management. The records of 340 patients who received allogenic bone graft during spinal fusion surgery in our institution were reviewed, for a total of 677 allografts. Each graft was swabbed intraoperatively. All patients were followed clinically for postoperative complications. Infection was diagnosed based on clinical data, blood tests and radiographic images, all assessed by an infectious disease specialist. Only 4 of the 677 allografts used (0.6%) resulted positive at the intraoperative swab culture. Three cultures were positive for Staphylococcus epidermidis and one culture for S. warneri. No clinical infection occurred in any of these patients. Twenty-eight of the 340 patients (8.2%) developed an infection, but none of them had a positive intraoperative swab culture. The most common microbiologic pathogen isolated from this cohort was S. aureus. According to our series, intraoperative swab culture results were not predictive for higher risk of infection and did not affect the clinical behavior of the surgeons in postoperative management.

Bacterial contamination of bone allografts in the tissue banks: a systematic review and meta-analysis

BACKGROUND

Bone allografts are harvested and transplanted under sterile conditions. However, the risk of bacterial contamination of grafts during these processes is a health concern. Bioburden testing and bacterial contamination detection are conducted to ensure allograft sterility.

AIM

The present study aimed to determine the incidence of bacterial contamination in bone allografts based on different classifications.

METHODS

PROSPERO registration number was received for the study. Systematic searches were conducted in PubMed and EMBASE databases with relevant keywords from January 2000 to March 2021. After choosing related studies according to the PRISMA flow diagram, Stata software was used for data analysis. We considered I² ˃ 50% as heterogeneity between studies.

FINDINGS

The overall incidence of bacterial contamination was 12.6% (95% CI 0.100, 0.152) among 19,805 bone allografts of 17 studies. The bacterial contamination rate among bone allografts was 10.8% before 2010 and 14.7% in 2010-March 2021. The contamination frequency in Asia, Europe, and Australia was 11.5%, 14.3%, and 5.2%, respectively. Bone contamination rates were higher in cadaver donors (19.9%), retrieval time sampling (13.5%), and swab samples (13.2%) compared to those in living donors (7.5%), implantation time sampling (6.9%), and bone fragments cultures (6.3%). Bacterial contamination was recovered 24.4%, 19.7%, 13.2%, and 21% from tibia, fibula, femoral, and other bones, respectively. Staphylococcus spp. was the predominant isolated bacteria from bones (63.2% of all isolated genera), followed by Propionibacterium spp. (10.6%).

CONCLUSION

The high contamination of bone allografts is a health concern, indicating the need for more health monitoring and improvement of standards.

The quality assessment of the University hospital bone bank in Central Serbia: the second audit after fourteen years

We analyzed the prevalence and predisposing factors for the overall rejection rate after retrieval of 267 fresh femoral head allografts over the past 7 years. The present study aimed to assess the quality system of institutional bone banking that can provide high-standard allografts with a low infection rate. Retrospective analysis of bone banking from June 2013 to December 2019 was conducted on 267 donors and 153 recipients. Of the 267 donated femoral heads, 74 were rejected, giving an overall rejection rate of 27.71%. The leading cause of allograft rejection was the inability to perform serology tests due to donor death; the absence of serological tests itself, and the donor refusal to perform the serology 6-month retest in 42 donors (15.72%). At retrieval, 12 allografts were positive, giving an overall contamination rate of 4.49%. Seven (2.62%) of the 267 allografts failed the blood screening tests. Thirteen allografts (4.86%) were discarded because of suspected damage to the packaging or disuse during surgery. An infection rate of 1.30% was found following transplantation. Over the past 7 years of bone banking, our results show that the overall rejection rate and the allograft-related infection rate correlate with international standards. The leading cause of allograft rejection was the inability to perform serology tests due to donor death and their refusal to perform the serology retests. Besides stringent aseptic allograft handling, donor motivation to participate in bone banking is extremely important for its efficient functioning.

[A clinical radiological score for femoral head grafts : Establishment of the Tabea FK score to ensure the quality of human femoral head grafts]

INTRODUCTION

Transplantation of cancellous tissue from human femoral heads (FK) is an established method in the reconstruction of bony defects in orthopedic and trauma surgery. Standardized rating systems with respect to the morphological quality of this tissue are not available.

MATERIALS AND METHODS

In 91/105 patients who had been a regular, clinically-indicated surgery (arthroplasty of the hip joint) the respective femoral head (FK) was taken under standardized conditions. Using a checklist defined clinical and radiological criteria of FK are judged in terms of their quality (cysts, necrosis, calcification, deformities, osteoporosis) and divided by the Tabea FK score into three classes (best/middle/poor quality). This was followed by a blinded repeated scoring, now as macroscopic assessment of three sawed layers from the same femoral head. The femoral heads are examined by peripheral quantitative computed tomography (pQCT) and a standardized histological examination of the bony tissue. We evaluated the accordance of the Tabea FK score with complementary assessments by calculation of sensitivity and specificity.

RESULTS

Femoral heads from 91/105 patients (ages: 68.4 ± 9.9 , n = 60 women, n = 31 men) were explanted and included in the study. The correlation between the primary radiologic clinical score (Tabea FK score) and the macroscopic second review of the sawn FK with respect to middle/best and poor/middle quality was classified as good (sensitivity 77% and 81%, respectively; specificity 76% and 84%, respectively). The correlation of histology and macroscopic second review was worse and in relation to discrimination of middle/best and poor/middle quality had a sensitivity of 85% and 54%, respectively, and a specificity of 66% and 97%, respectively. The pQCT showed a sensitivity of 82% only in discrimination of middle/best, while sensitivity in discrimination of poor/middle and poor/middle + best, respectively, was <10%.

DISCUSSION

The corresponding correlation between the primary and the second clinical score was evaluated as good. This emphasizes the long-standing skills of operationally active orthopedic surgeons to classify the quality of cancellous bone correctly already on the basis of X‑ray images and intraoperative findings. In this respect, the introduction of the Tabea FK score as a quality assurance tool in the routines of bone banks can be recommended.

Comparative evaluation of bioburden and sterility of indigenously prepared bone allograft with and without gentamicin

During bone allograft processing, despite stringent donor screening and use of aseptic techniques, microbial invasion may occur due to the porous nature of the graft and cause potentially fatal infections. The aim of the present study was to prepare bone allograft with and without gentamicin and to compare bioburden and sterility in the obtained grafts to evaluate the role of antibiotic in enhancing graft safety. Fifty samples of demineralized freeze-dried bone allograft were prepared from suitable donors according to international standards. Randomly selected 25 samples were placed in 8 mg gentamicin/gram bone solution for 1 h. Packaging and sealing was done to ensure no microbial ingress during transportation. 40 samples were selected for bioburden testing. Remaining 10 were subjected to 25 kGy gamma radiation and tested for sterility. Microbiological evaluation revealed no evidence of colony forming units in all the samples of both the groups (Bioburden = 0). Post-radiation sterility testing also revealed no bacterial colony in the tested samples from both the groups. Favorable results validate the processing protocol while comparable results in both groups indicate no additive benefit of gentamicin addition. Nil bioburden may be used in further studies to determine a lower radiation dose to achieve adequate sterility and minimize the disadvantages of radiation like collagen cross-linking and decreased osteoinductive capacity.

Successful disinfection of femoral head bone graft using high hydrostatic pressure

The current standard for sterilization of potentially infected bone graft by gamma irradiation and thermal or chemical inactivation potentially deteriorates the biomechanical properties of the graft. We performed an in vitro experiment to evaluate the use of high hydrostatic pressure (HHP); which is widely used as a disinfection process in the food processing industry, to sterilize bone grafts. Four femoral heads were divided into five parts each, of which 16 were contaminated (in duplicate) with 10⁵–10⁷ CFU/ml of Staphylococcus epidermidis, Bacillus cereus, or Pseudomonas aeruginosa or Candida albicans, respectively. Of each duplicate, one sample was untreated and stored similarly as the treated sample. The remaining four parts were included as sterile control and non-infected control. The 16 parts underwent HHP at the high-pressure value of 600 MPa. After HHP, serial dilutions were made and cultured on selective media and into enrichment media to recover low amounts of microorganism and spores. Three additional complete femoral heads were treated with 0, 300 and 600 MPa HHP respectively for histological evaluation. None of the negative-control bone fragments contained microorganisms. The measured colony counts in the positive-control samples correlated excellent with the expected colony count. None of the HHP treated bone fragments grew on culture plates or enrichment media. Histological examination of three untreated femoral heads showed that the bone structure remained unchanged after HHP. Sterilizing bone grafts by high hydrostatic pressure was successful and is a promising technique with the possible advantage of retaining biomechanical properties of bone tissue.

Intraoperative culture positive allograft bone and subsequent postoperative infections: a retrospective review

BACKGROUND

Obtaining intraoperative cultures of allograft bone just before use in orthopedic procedures is standard practice in many centres; however, the association between positive cultures and subsequent surgical infections is unknown. Our study had 3 goals: to determine the prevalence of positive intraoperative allograft culture and subsequent infection; to determine if, in cases of subsequent infection, organisms isolated at reoperation were the same as those cultured from the allograft at the time of the index procedure; and to assess the costs associated with performing intraoperative allograft cultures.

METHODS

In this retrospective case series, we obtained data on patients receiving allograft bone between 2009 and 2012. Patients receiving allograft with positive cultures were reviewed to identify cases of significant infection. Organisms isolated at reoperation were compared with the allograft culture taken at the time of implantation, and we performed a cost assessment.

RESULTS

Of the 996 allograft bone grafts used, 43 (4.3%) had positive intraoperative cultures and significant postoperative infections developed in 2, requiring reoperation. Antibiotics based on culture results were prescribed in 24% of cases. Organisms cultured at the time of reoperation differed from those isolated initially. The cost of performing 996 allograft cultures was $169 320.

CONCLUSION

This series suggests that rates of positive intraoperative bone allograft culture are low, and subsequent infection is rare. In cases of postoperative infection, primary allograft culture and secondary tissue cultures isolated different organisms. Costs associated with performing cultures are high. Eliminating initial culture testing could save $42 500 per year in our health region.

Staphylococcal biofilm formation on the surface of three different calcium phosphate bone grafts: a qualitative and quantitative in vivo analysis

Differences in physico-chemical characteristics of bone grafts to fill bone defects have been demonstrated to influence in vitro bacterial biofilm formation. Aim of the study was to investigate in vivo staphylococcal biofilm formation on different calcium phosphate bone substitutes. A foreign-body guinea-pig infection model was used. Teflon cages prefilled with β-tricalcium phosphate, calcium-deficient hydroxyapatite, or dicalcium phosphate (DCP) scaffold were implanted subcutaneously. Scaffolds were infected with 2 × 10(3) colony-forming unit of Staphylococcus aureus (two strains) or S. epidermidis and explanted after 3, 24 or 72 h of biofilm formation. Quantitative and qualitative biofilm analysis was performed by sonication followed by viable counts, and microcalorimetry, respectively. Independently of the material, S. aureus formed increasing amounts of biofilm on the surface of all scaffolds over time as determined by both methods. For S. epidermidis, the biofilm amount decreased over time, and no biofilm was detected by microcalorimetry on the DCP scaffolds after 72 h of infection. However, when using a higher S. epidermidis inoculum, increasing amounts of biofilm were formed on all scaffolds as determined by microcalorimetry. No significant variation in staphylococcal in vivo biofilm formation was observed between the different materials tested. This study highlights the importance of in vivo studies, in addition to in vitro studies, when investigating biofilm formation of bone grafts.

Microbiological culture findings of the femoral heads as a prognostic factor in the total hip replacement surgery

Background

In primary total hip replacements (THRs), the dissected femoral heads (FHs) are commonly used to make the bone-chips for the reconstruction in the orthopaedic surgery. The donated FHs are routinely microbiologically cultured to identify and contaminated FHs are discarded. This study examines whether a positive FH culture predicts an infection and prosthetic failure after primary THR.

Methods

The study sampled 274 donated FHs from patients with osteonecrosis (ON), hip joint osteoarthritis (OA), and femoral neck fracture (FNF) in THR to culture the microbes. The FH contamination rates were analyzed for ON, OA, and FNF groups. Proportion of the postoperative infection or prosthetic failure in the group of donors with a positive FH culture were compared to the proportion in the group of donors with a negative FH culture.

Results

The rates of the positive culture in the ON, OA, and FNF groups were 7.1%, 3.8%, and 4.0%, respectively. The infection rate was found to be non-significantly greater in the ON group than in the OA and FNF groups. In the negative culture group, one patient (0.63%) had a postoperative superficial infection, and five patients (3.2%) experienced additional surgeries including a fixation for a periprosthetic fracture, within a minimum follow-up of two years. However, no postoperative infection was encountered, and no revision surgery was required in the positive culture group.

Conclusions

A positive FH culture is not always associated with elevated risks of infection or prosthetic failure after THR. Therefore, such finding cannot be used as a prognostic factor of THR. The FHs that return a positive culture may not lead to the orthopaedic assessment of an infection or other postoperative complication risks in primary THR.

Culture methods of allograft musculoskeletal tissue samples in Australian bacteriology laboratories

Samples of allograft musculoskeletal tissue are cultured by bacteriology laboratories to determine the presence of bacteria and fungi. In Australia, this testing is performed by 6 TGA-licensed clinical bacteriology laboratories with samples received from 10 tissue banks. Culture methods of swab and tissue samples employ a combination of solid agar and/or broth media to enhance micro-organism growth and maximise recovery. All six Australian laboratories receive Amies transport swabs and, except for one laboratory, a corresponding biopsy sample for testing. Three of the 6 laboratories culture at least one allograft sample directly onto solid agar. Only one laboratory did not use a broth culture for any sample received. An international literature review found that a similar combination of musculoskeletal tissue samples were cultured onto solid agar and/or broth media. Although variations of allograft musculoskeletal tissue samples, culture media and methods are used in Australian and international bacteriology laboratories, validation studies and method evaluations have challenged and supported their use in recovering fungi and aerobic and anaerobic bacteria.

Long-term outcome of total hip replacement in patients with or without femoral head contamination

PURPOSE

To compare long-term outcomes of total hip replacement (THR) in patients with or without contamination of the femoral head.

METHODS

After a mean period of 12 (range, 8-17) years, 104 female and 71 male THR patients aged 47 to 96 (mean, 77) years were reassessed via a self-administered questionnaire, and 25 other THR patients were reassessed by review of case notes. The questionnaires comprised the 12-item Oxford hip score and the European Quality Of Life (EuroQOL). 87 and 88 patients had positive and negative cultures in the donated femoral heads, respectively. The 2 groups were compared with respect to the Oxford hip score, the EuroQOL, and rates of complication and revision surgery.

RESULTS

Long-term outcomes of THR patients with or without femoral head contamination were not significantly different. Respectively, the mean Oxford hip scores were 36 and 39 (p=0.4); 16 and 14 patients had the maximum score of 48; 2 and 3 patients scored <10 (mostly owing to aseptic loosening). The respective mean visual analogue scale score of the EuroQOL were 65 and 73 (p=0.07); only the dimension of self care was significantly different between groups (p=0.04). Respectively, 14 and 12 patients had complications (16% vs. 15%, χ²=0.05, p=0.8), whereas 11 and 5 patients had revision surgery (13% vs. 6%, χ²=2.2, p>0.1).

CONCLUSION

Microbiological screening of donated femoral heads plays no role in predicting long-term failure of THR in the donors.

The concentration of antibiotic in fresh-frozen bone graft

We investigated the antibiotic concentration in fresh-frozen femoral head allografts harvested from two groups of living donors. Ten samples were collected from patients with osteoarthritis of the hip and ten from those with a fracture of the neck of the femur scheduled for primary arthroplasty. Cefazolin (1 g) was administered as a pre-operative prophylactic antibiotic. After storage at -80 degrees C for two weeks the pattern of release of cefazolin from morsellised femoral heads was evaluated by an in vitro broth elution assay using high-performance liquid chromatography. The bioactivity of the bone was further determined with an agar disc diffusion and standardised tube dilution bioassay. The results indicated that the fresh-frozen femoral heads contained cefazolin. The morsellised bone released cefazolin for up to four days. The concentration of cefazolin was significantly higher in the heads from patients with osteoarthritis of the hip than in those with a fracture.Also, in bioassays the bone showed inhibitory effects against bacteria.We concluded that allografts of morsellised bone from the femoral head harvested from patients undergoing arthroplasty of the hip contained cefazolin, which had been administered pre-operatively and they exhibited inhibitory effects against bacteria in vitro.