Comparative evaluation of the diffusion of tobramycin and cefotaxime out of antibiotic-impregnated polymethylmethacrylate beads

Local Administration of Antibiotics in Orthopedics and Traumatology

2022 marks the 50th anniversary of the development of the antibiotic loaded PMMA chain. The loading of bone cements with antibiotics was a major advance in the treatment of musculoskeletal infections and is still a proven standard today. The research and use of novel antibiotic carriers continues to be an important part of research in the context of musculoskeletal infections. The article provides an overview of the various local antibiotics available and their specifics. In addition, current adapted treatment concepts are discussed.

Local Fixation of Colistin With Fibrin Spray: An in vivo Animal Study for the Therapy of Skin and Soft Tissue Infections

Objective

Skin and soft tissue infections (SSTI) are a commonly known entity of diseases associated with difficult treatment procedures. The current gold standard when there is a rapidly progressing infection of soft tissues with a risk of sepsis is radical surgical debridement accompanied by systemic antibiotic therapy. In clinical settings, local antibiotics alone or formulated within carrier material are commonly used alongside this therapy regimen. One possibility of local antibiotic application is the fixation of colistin with fibrin glue spray. It is not yet sufficiently researched how the local antibiotic concentrations remain as high as possible over time.

Methods

We conducted an animal study including 29 male Wistar rats inducing sterile back sores reaching the muscle fascia. We sprayed only colistin, simultaneously or consecutively, with fibrin glue in different groups in order to measure the tissue concentration of the antibiotic applied locally.

Results

After liquid chromatography and quadrupole mass spectrometry analysis, it could be demonstrated that in comparison to the colistin group, tissue concentrations of colistin stayed significantly higher in the wound tissue when it was fixed with fibrin glue. This was observed in both groups, the simultaneous as well as in the consecutively fibrin glue sprayed groups after colistin application.

Conclusion

The fixation of colistin with the fibrin-glue-spray technique as a carrier for local antibiotic therapy is an easy and inexpensive method and shows promising potential for the treatment of SSTI.

Negative pressure wound therapy does not diminish efficacy of topical antibiotic powder in a preclinical contaminated wound model

AIMS

High-energy injuries can result in multiple complications, the most prevalent being infection. Vancomycin powder has been used with increasing frequency in orthopaedic trauma given its success in reducing infection following spine surgery. Additionally, large, traumatic injuries require wound coverage and management by dressings such as negative pressure wound therapy (NPWT). NPWT has been shown to decrease the ability of antibiotic cement beads to reduce infection, but its effect on antibiotic powder is not known. The goal of this study was to determine if NPWT reduces the efficacy of topically applied antibiotic powder.

METHODS

Complex musculoskeletal wounds were created in goats and inoculated with a strain of Staphylococcus aureus modified to emit light. Six hours after contaminating the wounds, imaging, irrigation, and debridement and treatment application were performed. Animals received either vancomycin powder with a wound pouch dressing or vancomycin powder with NPWT.

RESULTS

There were no differences in eradication of bacteria when vancomycin powder was used in combination with NPWT (4.5% of baseline) compared to vancomycin powder with a wound pouch dressing (1.7% of baseline) (p = 0.986), even though approximately 50% of the vancomycin was recovered in the NPWT exudate canister.

CONCLUSION

The antimicrobial efficacy of the vancomycin powder was not diminished by the application of NPWT. These topical and locally applied therapies are potentially effective tools that can provide quick, simple treatments to prevent infection while providing coverage. By reducing the occurrence of infection, the recovery is shortened, leading to an overall improvement in quality of life. Cite this article: Bone Joint Res 2021;10(2):149-155.

An In Vitro Comparison of PMMA and Calcium Sulfate as Carriers for the Local Delivery of Gallium(III) Nitrate to Staphylococcal Infected Surgical Sites

Antibiotic-loaded bone cements, including poly(methyl methacrylate) (PMMA) and calcium sulfate (CaSO₄), are often used for treatment of orthopaedic infections involving Staphylococcus spp., although the effectiveness of this treatment modality may be limited due to the emergence of antimicrobial resistance and/or the development of biofilms within surgical sites. Gallium(III) is an iron analog capable of inhibiting essential iron-dependent pathways, exerting broad antimicrobial activity against multiple microorganisms, including Staphylococcus spp. Herein, we evaluated PMMA and CaSO₄ as carriers for delivery of gallium(III) nitrate (Ga(NO₃)₃) to infected surgical sites by assessing the release kinetics subsequent to incorporation and antimicrobial activity against S. aureus and S. epidermidis. PMMA and to a lesser extent CaSO₄ were observed to be compatible as carriers for Ga(NO₃)₃, eluting concentrations with antimicrobial activity against planktonic bacteria, inhibiting bacterial growth, and preventing bacterial colonization of beads, and effective against established bacterial biofilms of S. aureus and S. epidermidis. Collectively, our in vitro results indicate that PMMA is a more suitable carrier compared to CaSO₄ for delivery of Ga(NO₃)₃; moreover they provide evidence for the potential use of Ga(NO₃)₃ with PMMA as a strategy for the prevention and/or treatment for orthopaedic infections.

Applications of Local Antibiotics in Orthopedic Trauma

Local antibiotics have a role in orthopedic trauma for both infection prophylaxis and treatment. They provide the advantage of high local antibiotic concentration without excessive systemic levels. Nonabsorbable polymethylmethacrylate (PMMA) is a popular antibiotic carrier, but absorbable options including bone graft, bone graft substitutes, and polymers have gained acceptance. Simple aqueous antibiotic solutions continue to be investigated and appear to be clinically effective. For established infections, such as osteomyelitis, a combination of surgical debridement with local and systemic antibiotics seems to represent the most effective treatment at this time. Further investigation of more effective local antibiotic utilization is ongoing.

Antibiotic-loaded synthetic calcium sulfate beads for prevention of bacterial colonization and biofilm formation in periprosthetic infections

Periprosthetic infection (PI) causes significant morbidity and mortality after fixation and joint arthroplasty and has been extensively linked to the formation of bacterial biofilms. Poly(methyl methacrylate) (PMMA), as a cement or as beads, is commonly used for antibiotic release to the site of infection but displays variable elution kinetics and also represents a potential nidus for infection, therefore requiring surgical removal once antibiotics have eluted. Absorbable cements have shown improved elution of a wider range of antibiotics and, crucially, complete biodegradation, but limited data exist as to their antimicrobial and antibiofilm efficacy. Synthetic calcium sulfate beads loaded with tobramycin, vancomycin, or vancomycin-tobramycin dual treatment (in a 1:0.24 [wt/wt] ratio) were assessed for their abilities to eradicate planktonic methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis relative to that of PMMA beads. The ability of the calcium sulfate beads to prevent biofilm formation over multiple days and to eradicate preformed biofilms was studied using a combination of viable cell counts, confocal microscopy, and scanning electron microscopy of the bead surface. Biofilm bacteria displayed a greater tolerance to the antibiotics than their planktonic counterparts. Antibiotic-loaded beads were able to kill planktonic cultures of 10(6) CFU/ml, prevent bacterial colonization, and significantly reduce biofilm formation over multiple days. However, established biofilms were harder to eradicate. These data further demonstrate the difficulty in clearing established biofilms; therefore, early preventive measures are key to reducing the risk of PI. Synthetic calcium sulfate loaded with antibiotics has the potential to reduce or eliminate biofilm formation on adjacent periprosthetic tissue and prosthesis material and, thus, to reduce the rates of periprosthetic infection.

Comparing PMMA and calcium sulfate as carriers for the local delivery of antibiotics to infected surgical sites

Antibiotic-loaded bone cement is a primary option for treatment of orthopedic infections. Poly(methyl methacrylate) (PMMA) is a widely used cement that, when loaded with antibiotics in spacer or bead form, has been shown to reduce infection rates. However, PMMA is not resorbable and requires a second surgery for removal, while also acting as a potential foreign body for bacterial colonization. Alternatively, resorbable bone cements, such as calcium sulfate, have been proposed and present the advantage of being completely reabsorbed. It is unknown whether the antibiotic elution characteristics of absorbable bone cements are similar to PMMA. This study (1) characterized antibiotic elution from synthetic, highly purified calcium sulfate cement beads of varying sizes against pathogenic bacteria both in liquid culture and seeded on agar plates, (2) tested calcium sulfate beads against PMMA beads loaded with the same antibiotics, and (3) analyzed the structural differences between how PMMA and calcium sulfate bind to antibiotics. In every assay, the calcium sulfate beads performed as well as, or better than, the PMMA beads in inhibition of bacterial growth and elution of vancomycin in vitro with complete elution observed from calcium sulfate within three days. These data suggest that calcium sulfate, functions, as well as PMMA in the patient setting for infection control.

Size and composition of synthetic calcium sulfate beads influence dissolution and elution rates in vitro

Treatments of osteomyelitis lag behind bacterial resistance to antibiotics. We tested different-sized calcium sulfate beads and their ability to elute multiple antibiotics in vitro as a possible method to improve the therapeutic delivery in patients. Two sizes of calcium sulfate beads (4.8 and 3.0 mm diameter) that contained vancomycin, tobramycin, or both were dissolved in phosphate-buffered saline, and the rate of dissolution by weight and antibiotic elution by the disc diffusion assay and high-pressure liquid chromatography were measured. The 4.8 mm beads showed significantly higher dissolution rates relative to the 3.0 mm beads (2.3 mg/day vs. 1.3 mg/day). While the vancomycin-loaded 4.8 mm beads eluted for a longer time relative to the 3.0 mm beads (20 days vs. 10 days), the smaller beads had threefold higher elution for the first 2 days, before dropping to near zero elution by day 4. The presence of tobramycin extended the elution of the vancomycin to day 40, which closely matches the recommended 6 weeks to treat orthopedic staphylococcus infections. These data suggest that size and content of the bead are variables that could affect their clinical success, and both could be exploited to tailor treatments of specific infections and injuries.

Cortical bone fenestrations with continuous antibiotic irrigation to mediate hematogenous tibial osteomyelitis in children

The objective of this study was to evaluate the results of drainage and continuous antibiotic irrigation of the medullary canal to mediate hematogenous osteomyelitis of the tibia in children. Data were analyzed from 376 patients (388 tibiae) treated from January 1982 to December 2004. The average age at the time of surgery was 5 years and 9 months. The diagnosis of mediate hematogenous osteomyelitis was based on clinical examination, plain radiographs, scintigraphy, ultrasound, and bacterial cultures. Treatment included two groups: (i) group I [from January 1981 to September 1984 in 108 patients (112 tibiae)] who were operated on according to traditional surgical procedure (pus drainage), (ii) group II [from October 1984 to December 2004 in 268 patients (276 tibiae)] who were operated on according to cortical bone fenestrations with continuous antibiotic irrigation. Postoperative antibiotic(s) with the intravenous antibiotic therapy were administered for 2 weeks and oral antibiotic therapy for 4 weeks. The total time of antibiotic therapy was 6 weeks. There were 152 (40.4%) female and 224 (59.6%) male patients. Unilateral involvement was the most common, with the left tibia affected in 119 (31.6%) patients, and the right in 245 (65.2%). Both tibiae were involved in 12 (3.2%) patients. The average age at the time of operation was 5 years 9 months (range: 22 days-13 years, 7 months). All patients were classified as having a mediate stage of osteomyelitis. We attained good results in 50.9% of the patients in the group I, fair results in 7.1%, and poor results in 42% with pathologic fracture in eight tibiae. In group II, there were good results in 77.9%, fair results in 21.4%, and poor results in 0.7% tibiae with the development of chronic osteomyelitis and without pathologic fracture. In conclusion, this technique is generally safe and effective. We suggest that similar management might also be applied for hematogenous osteomyelitis of femur and humerus.

A prospective, randomized clinical trial comparing an antibiotic-impregnated bioabsorbable bone substitute with standard antibiotic-impregnated cement beads in the treatment of chronic osteomyelitis and infected nonunion

OBJECTIVES

We sought to compare the effectiveness of an antibiotic-impregnated bioabsorbable bone substitute (BBS, tobramycin-impregnated medical-grade calcium sulfate) with antibiotic-impregnated polymethylmethacrylate (PMMA) cement beads after surgical débridement in patients with chronic nonhematogenous osteomyelitis and/or infected nonunion.

DESIGN

A prospective, randomized clinical trial.

SETTING

A university-affiliated teaching hospital.

PATIENTS/PARTICIPANTS

Thirty patients requiring surgical treatment for chronic long bone infection or infected nonunion were included: BBS (15 patients, mean age 44.1 years) PMMA (15 patients, mean age 45.6 years).

INTERVENTION

Patients were randomized to receive either BBS or PMMA to the bone void created by surgical débridement.

MAIN OUTCOME MEASUREMENTS

Eradication of infection, new bone growth, rate of union, repeat operative procedures complications.

RESULTS

Patients were followed for a mean 38 months (range, 24-60 months). One patient was lost to follow-up in each group. In the BBS group, infection was eradicated in 86% (12 of 14) of patients. Seven of eight patients achieved union of their nonunion, and five patients underwent seven further surgical procedures. In the PMMA group, infection was eradicated in 86% (12 of 14) of patients. Six of eight patients achieved union of their nonunion, and nine patients required 15 further surgical procedures. There were more reoperations in the PMMA group (15 versus seven, P = 0.04), and these procedures tended to be of greater magnitude.

CONCLUSIONS

The results of this preliminary study suggest that, in the treatment of chronic osteomyelitis and infected nonunion, the use of an antibiotic-impregnated BBS is equivalent to standard surgical therapy in eradicating infection and that it may reduce the number of subsequent surgical procedures. A larger, definitive study on this topic is required.

Treatment recommendations and strategies for the management of bone and joint infections

Bone and joint infections are a cause of rising concern, mainly owing to the increasing number of traumatic accidents, the appearance of new groups of patients at risk, the widespread use of prosthetic devices and the emergence of new patterns of antimicrobial resistance. Treatment guidelines and particular strategies for the management of such infections are reviewed. Decisions regarding the best therapeutic modality can be challenging and take into account the factors involved in infection staging, along with a better knowledge of the bacterial biofilm status. Surgery and antibiotic therapy are the keystones of the management, but overall the timing and length of treatment and follow-up should be posed to obtain the best quality of life for the patient. These infections are characteristically intriguing and sometimes need multiple surgical interventions and several courses of therapy. A multi-disciplinary approach is worthwhile in each institution. The collaboration of a specialized team composed by surgeons, pathologists, microbiologists and clinicians will permit diagnostic and therapeutic protocol-guided decisions.

Management of medullary osteomyelitis of the humerus

Osteomyelitis is a severe infection of bone and is particularly challenging to treat when involving long bones. Osteomyelitis of the humerus is an uncommon but difficult problem, and the guidelines of treatment have been drawn from the literature on the treatment of tibial and femoral osteomyelitis. We present our technique for treating adult hematogenous medullary osteomyelitis of the humerus. Steps include the following: (1) a deltopectoral approach to the humerus, (2) formation of a cortical window in the proximal humerus, (3) biopsy and reaming of the intramedullary canal from proximal to distal under fluoroscopy, (4) lavage of the intramedullary canal, (5) placement of antibiotic-impregnated antibiotic beads on a stainless steel wire into the canal, and (6) long-term antibiotics and laboratory monitoring of white blood cell count and erythrocyte sedimentation rates levels. Preliminary clinical results with at least 12 months' follow-up have resulted in excellent results without complications. We recommend this technique for the treatment of osteomyelitis of the humerus, for it affords a reliable and familiar approach to the treatment of a difficult infection of the humerus.

Osteomyelitis in Horses

Much has been learned in the past decade about osteomyelitis. The inhibitory mechanisms of the "biofilm slime" layer that is formed by bacterial extracapsular exopolysaccharides and binds to bone, joints, and implants are now better understood than in the past. The surface colonization of bacteria that occurs within these biofilms is a biologic phenomenon that is somewhat unique to orthopedic infections. This survival strategy of bacteria is effective, and it is important for veterinarians who treat osteomyelitis to be aware of current diagnostic and therapeutic treatment modalities. The practitioner should be aware of the most common bacteria associated with osteomyelitis and the traditional treatments that are still used. Current therapeutic treatment modalities, such as antibiotic- impregnated polymethylmethacrylate, antibiotic-impregnated plaster of Paris, and regional perfusion, have become routine, however, and have been responsible for improving the prevention and outcome of osteomyelitis in the horse. It is the intent of this article to make equine veterinarians aware of current information as well as the future treatments of osteomyelitis.

Adult osteomyelitis

Adult osteomyelitis remains difficult to treat, with considerable morbidity and costs to the health care system. Bacteria reach bone through the bloodstream, from a contiguous focus of infection, from penetrating trauma, or from operative intervention. Bone necrosis begins early, limiting the possibility of eradicating the pathogens, and leading to a chronic condition. Appropriate treatment includes culture-directed antibiotic therapy and operative debridement of all necrotic bone and soft tissue. Treatment often involves a combination of antibiotics. Operative treatment is often staged and includes debridement, dead space management, soft tissue coverage, restoration of blood supply, and stabilization. Clinicians and patients must share a clear understanding of the goals of treatment and the difficulties that may persist after the initial course of therapy or surgical intervention. Chronic pain and recurrence of infection still remain possible even when the acute symptoms of adult osteomyelitis have resolved.

Local Delivery of Vancomycin for the Prophylaxis of Prosthetic Device-Related Infections

PURPOSE

To evaluate the in vivo efficacy and pharmacokinetics of vancomycin delivered from glycerylmonostearate (GMS) implants in a prosthetic-device based biofilm infection model.

METHODS

A biofilm infection model was developed in male Sprague-Dawley rats by implanting a vascular graft on the dorsal side of each rat and infecting it with 1.5 x 10(8) cfu/ml Staphylococcus epidermidis. The rats were divided into 3 groups of 6 rats each: 1) the control group that received no antibiotics, 2) the IM group that received multiple IM injections of vancomycin at a dose of 25 mg/kg every 6 h for a total of 12 doses, and 3) the implant group that received GMS implants designed to deliver vancomycin at a total dose of 300 mg/kg for a period of 4 days. The pharmacokinetics of vancomycin was determined from IM and implant groups by analyzing for vancomycin in blood using HPLC. In vivo efficacy was studied by evaluation of the wound site and the prosthetic device upon excision, for evidence of infection in the form of purulent discharge at the wound site and yellowish discoloration of the prosthetic device and inflammation as sign of biofilm formation. Microbiological evaluation on the wound site and the prosthetic device was performed by culturing the swabs at the wound site and the prosthetic device in sterile tryptic soy broth for 36-48 h at 37 degrees C.

RESULTS

Vancomycin was successfully delivered in a sustained manner for 100 h from GMS implants and the resulting plasma profile showed that the concentrations, after an initial burst, plateaued at about of 4.77 +/- 1.43 mug/ml with less fluctuations than the IM group in which the plasma concentrations fluctuated between 2.73 +/- 0.94 mug/ml and 19.26 +/- 3.67 mug/ml. Upon excision of the wound site, all the animals in the control group developed infection in the form of purulent discharge and yellowish discoloration of the prosthetic device. However, none of the rats in the implant group showed evidence of infection clearly demonstrating the efficacy of the local delivery system in preventing infection. Systemically delivered vancomycin by IM injections failed to prevent infection in four out of six rats. Microbiological evaluation of the wound site and prosthetic device resulted in isolation of biofilm-producing organisms such as Staphylococcus epidermidis, Enterococcus faecalis, and Staphylococcus aureus. These organisms were isolated in greater number of animals in the control group compared to the IM and implant groups.

CONCLUSIONS

The GMS implants as a delivery system for vancomycin were successful in preventing infection in all the animals compared to the IM and control groups demonstrating the efficacy of a local delivery system in a prosthetic device related biofilm infection model.

Osteomyelitis in long bones

Osteomyelitis in long bones remains challenging and expensive to treat, despite advances in antibiotics and new operative techniques. Plain radiographs still provide the best screening for acute and chronic osteomyelitis. Other imaging techniques may be used to determine diagnosis and aid in treatment decisions. The decision to use oral or parenteral antibiotics should be based on results regarding microorganism sensitivity, patient compliance, infectious disease consultation, and the surgeon's experience. A suppressive antibiotic regimen should be directed by the results of cultures. Standard operative treatment is not feasible for all patients because of the functional impairment caused by the disease, the reconstructive operations, and the metabolic consequences of an aggressive therapy regimen. Operative treatment includes debridement, obliteration of dead space, restoration of blood supply, adequate soft-tissue coverage, stabilization, and reconstruction.

Elution of metronidazole and gentamicin from polymethylmethacrylate beads

OBJECTIVE

To characterize the elution and bioactivity of metronidazole and gentamicin sulfate polymerized, individually and in combination, with polymethylmethacrylate (PMMA).

STUDY DESIGN

In vitro experimental study.

METHODS

PMMA beads containing metronidazole (3 concentrations), gentamicin sulfate, or metronidazole and gentamicin sulfate were immersed in 5 mL of phosphate-buffered saline in triplicate. Eluent was replaced at specified time intervals for 1 or 21 days, and antibiotic concentrations were measured by high-performance liquid chromatography. Changes in antibiotic bioactivity attributable to polymerization or copolymerization of the antibiotics with PMMA, ethylene oxide sterilization, and storage of AIPMMA beads containing metronidazole were evaluated.

RESULTS

Antibiotic elution patterns were similar for all groups. Day 1 elution for groups containing metronidazole or gentamicin individually represented a mean 63%-66% and 79%, respectively, of the 21-day total. Approximately 50% of the day 1 elution occurred during the first hour. The elution of metronidazole was dose dependent. The elution of metronidazole (day 3-21) and gentamicin (all days) was significantly greater when metronidazole and gentamicin were combined (P <.05). The addition of metronidazole delayed polymerization of PMMA. Neither polymerization nor copolymerization of metronidazole and gentamicin with PMMA, gas sterilization, or 2-month storage of beads containing metronidazole significantly affected antimicrobial bioactivity.

CONCLUSIONS

Metronidazole elution from PMMA was dose dependent. Copolymerization of metronidazole and gentamicin sulfate in PMMA resulted in increased rates of elution. Intraoperative preparation of metronidazole-impregnated PMMA beads is not practical, but sterilization and storage for 2 months should not affect efficacy.

CLINICAL RELEVANCE

The local delivery of biologically active metronidazole and gentamicin by elution from PMMA is feasible.

Antimicrobial release kinetics from polymethylmethacrylate in a novel continuous flow chamber

Polymethylmethacrylate is used for local delivery of antimicrobials in the treatment of musculoskeletal infections. A novel continuous flow chamber system was designed to measure in vitro antimicrobial release. Three-millimeter beads containing amikacin, gentamicin, tobramycin, or vancomycin [concentration of 7.5% (weight per weight)] were placed individually in a continuous flow chamber with a total volume of 1 mL Kreb's Ringer buffer flowing at 1 mL/hour. Effluent was sampled hourly for 24 hours and then every 2 hours up to 48 hours; antimicrobial concentrations were measured in triplicate by bioassay. The mean peak concentrations were 40.9, 30.1, 30.0, and 19.1 microg/mL; the mean areas under the concentration time curves (Time 0 to infinity) were 263, 327, 110, and 180 hours x microg/mL of antibiotic; and the mean percentages of initial amount of antimicrobial released were 11.7%, 14.5%, 6.6%, and 10.9% for tobramycin, gentamicin, amikacin, and vancomycin, respectively. The results for each polymethylmethacrylate-antimicrobial agent combination were reproducible. In contrast to other in vitro elution systems, this novel system operates under the premise that there is dynamic flow surrounding polymethylmethacrylate in vivo and permits rapid in vitro comparison of the relative release of antimicrobial agents from polymethylmethacrylate.

The use of an antibiotic-impregnated, osteoconductive, bioabsorbable bone substitute in the treatment of infected long bone defects: early results of a prospective trial

OBJECTIVE

We sought to evaluate the use of a bioabsorbable, tobramycin-impregnated bone graft substitute (calcium sulfate alpha-hemihydrate pellets) in the treatment of patients with infected bony defects and nonunions.

STUDY DESIGN/METHODS

Twenty-five patients (15 male and 10 female, mean age 43 years (range 27-69 years) requiring surgical debridement of culture-positive long bone infection (16 with associated nonunion) were entered into an ongoing consecutive, prospective clinical trial. Involved bones included the tibia ( 15), femur ( 6), ulna ( 3), and humerus ( 1). All defects were posttraumatic in origin, and each patient had had previous surgery at the involved site (mean 4.3 surgeries; range 1-8 surgeries). The duration of infection ranged from 4 months to 20 years (mean 43 months). According to the Cierny-Mader classification system, there was 1 stage I (medullary osteomyelitis), 6 stage III (localized osteomyelitis), and 18 stage IV (diffuse osteomyelitis) lesions. There were 4 normal (A) hosts and 21 locally and/or systemically compromised (B) hosts. Mean bone defect/void was 30.5 cm (range 3-192 cm ).

RESULTS

Mean follow-up was 28 months (range 20-38 months). Radiographically, pellets were resorbed at a mean of 2.7 months postoperatively. Infection was eradicated in 23 of 25 patients (92%). Isolated bony defects healed in all nine patients without further treatment. Fourteen of 16 patients with nonunion achieved union, although nine required autogenous bone grafting. Union was achieved in five of seven nonunion patients treated with bone graft substitute in isolation. Complications included refracture (three), recurrence of infection (two), persistent nonunion (two), and superficial wound necrosis (one). Eight patients developed sterile draining sinuses that healed upon radiographic resorption of the pellets.

CONCLUSIONS

In patients with posttraumatic osteomyelitis, the bone graft substitute was effective in eradicating bone infection in 23 of 25 patients. Isolated bony defects healed reliably (nine of nine) following addition of bone graft substitute alone. The role of the bone graft substitute in isolation in the treatment of nonunion is unclear at present.

Experimental osteomyelitis treatment with antibiotic-impregnated hydroxyapatite

A calcium hydroxyapatite antibiotic implant was evaluated to determine its efficacy as an antibiotic delivery system in a localized osteomyelitis rabbit model. Localized rabbit tibial osteomyelitis was developed with an intramedullary injection of methicillin resistant Staphylococcus aureus. Infected rabbits were randomized and divided into eight groups depending on treatment with or without debridement, systemic antibiotics, antibiotic-impregnated polymethylmethacrylate beads, or calcium hydroxyapatite implants with and without antibiotic impregnation. All treatments began 2 weeks after infection. After 4 weeks of therapy, the involved bones were cultured for concentrations of Staphylococcus aureus per gram of bone. Rabbits (n = 11) that had calcium hydroxyapatite (impregnated with vancomycin) implanted into the dead space after the debridement surgery had an 81.8% infection clearance after treatment. Rabbits (n = 10) that had polymethylmethacrylate beads (impregnated with vancomycin) implanted into the dead space after debridement surgery had a 70% clearance rate. All other treatment modalities resulted in less than 50% clearance rates. Calcium hydroxyapatite may be an effective alternative to polymethylmethacrylate for providing local antibiotic therapy in cases of methicillin resistant Staphylococcus aureus osteomyelitis.

Impregnation of vancomycin, gentamicin, and cefotaxime in a cement spacer for two-stage cementless reconstruction in infected total hip arthroplasty

Twenty-two patients with infected total hip arthroplasty were treated with 2-stage arthroplasty, using a cement spacer impregnated with a combination of 3 thermostable antibiotics (vancomycin, gentamicin, and cefotaxime). Initially, implants were removed, and a spacer was inserted. Six to 12 weeks later, the spacer was removed, and the patients underwent reconstruction using cementless components. The patients were followed for an average of 41 months. One patient had a recurrence of infection and was treated with resection arthroplasty. The remaining 21 patients (95%) had no evidence of infection at the final follow-up. We recommend using the combination of these 3 antibiotics in the cement spacer for 2-stage reconstruction in infected hip arthroplasty when the causative organism is not identified in the culture of preoperative aspiration.

Questions and Answers from the F.I.X./• Digibind in Chronic Digoxin Dosing /• Fosphenytoin (Cerebyx) Use in Dialysis Patients/ • MMR vs MR/ • Insulin Drip Protocol/ • Tobramycin Powder Alternatives

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Antibiotic beads in the treatment of diabetic pedal osteomyelitis

Antibiotic-impregnated polymethylmethacrylate (PMMA) beads have improved the outcome of osteomyelitis treatment in both experimental models and clinical trials. The primary benefit of antibiotic-impregnated PMMA beads is that they provide high local concentrations of antibiotic while systemic levels of antibiotic remain low. Little has been written about the specific use of antibiotic-impregnated PMMA beads in the treatment of diabetic pedal osteomyelitis. The authors review antibiotic-impregnated PMMA beads and provide examples of their use in the treatment of diabetic pedal osteomyelitis.

Bone and joint infections in the elderly: practical treatment guidelines

Two types of haematogenous osteomyelitis that are seen in the elderly are vertebral and long bone osteomyelitis. Osteomyelitis secondary to contiguous foci of infection can occur in older adults without vascular insufficiency (secondary to pressure ulcers) or with vascular insufficiency due to diabetes mellitus or peripheral vascular disease from atherosclerosis. Most cases of osteomyelitis can be reasonably treated with adequate drainage, thorough debridement, obliteration of dead space, wound protection, and antimicrobial therapy. Patients are initially given a broad spectrum antimicrobial that is changed to specific antimicrobial therapy based on meticulous bone cultures taken at debridement surgery or from deep bone biopsies. Surgical management is often required in the treatment of osteomyelitis and includes adequate drainage, extensive debridement of all necrotic tissue, obliteration of dead spaces, stabilisation, adequate soft tissue coverage, and restoration of an effective blood supply. Bone repair and bone mineral density may be significantly retarded and may be corrected by eliminating risk factors, supplementing the diet with calcium, bisphosphonates, and/or vitamin D, and treating with testosterone and/or estrogen when deficient. Sodium fluoride treatment and anabolic steroids may be used as alternatives. Septic arthritis is a medical emergency, and prompt recognition and rapid and aggressive treatment are critical to ensuring a good prognosis. The treatment of septic arthritis includes appropriate antimicrobial therapy and joint drainage. Adverse effects of prescribed antibacterials occur more often in the elderly patient than in young adults. The physician can help to minimise the incidence of adverse effects and improve outcomes by being aware of the principles of clinical pharmacology, the characteristics of specific drugs, and the special physical, psychological and social needs of older patients.

Adult posttraumatic osteomyelitis of the tibia

Posttraumatic tibial osteomyelitis results from trauma or nosocomial infection from the treatment of trauma that allows organisms to enter bone, proliferate in traumatized tissue, and cause subsequent bone infection. The resulting infection is usually polymicrobial. The patient may be classified using the May and the Cierny-Mader classification systems. The diagnosis is based on the isolation of the pathogen(s) from the bone, or blood cultures. Appropriate therapy of posttraumatic tibial osteomyelitis includes adequate drainage, thorough debridement, obliteration of dead space, stabilization when necessary, wound protection, and specific antimicrobial therapy.

Treatment of infected left ventricular assist device using antibiotic-impregnated beads

There is no well-established therapy for treating infections of heart-assist or artificial heart devices, a serious problem with life-threatening consequences. We used a promising new approach in which antibiotic-impregnated polymethylmethacrylate beads were placed around an implanted left ventricular assist device to control an external blood pump infection in a bridge-to-transplant patient. In this case report, we describe the potential of antimicrobial-impregnated polymethylmethacrylate beads for in situ control of infections involving external surfaces of cardiovascular devices.

Management of femoral diaphyseal infected nonunion with antibiotic beads local therapy, external skeletal fixation, and staged bone grafting

BACKGROUND

Fifteen patients with femoral shaft fractures complicated by infected nonunions were treated with a two-stage protocol.

METHODS

In the first stage, radical debridement was performed along with antibiotic bead chains local therapy and external skeletal fixation. In the second stage, the debrided nonunion site was repaired with bone grafting and the external skeletal fixator was used until bony union was achieved. The time between the first and second stages of treatment was 2 to 6 weeks. The debrided bone defects ranged from 0.5 to 15 cm. Autogenous iliac cancellous bone grafting was performed in 11 patients, and microvascularized osteoseptocutaneous fibular transfer was performed in 4 patients.

RESULTS

Wound healing and bone union were achieved in all 15 cases. The duration of external fixation of these patients ranged from 7 to 15 months, with an average of 9 months. Minor pin-track infection was seen in seven patients. Postoperative infection after the second-stage bone grafting occurred in three patients. These three infections were arrested by limited debridement along with 2 to 4 weeks of parenteral antibiotic therapy. In one case, stress fracture occurred at 11 months after microvascularized fibular transfer; this was managed with another 5 months of external skeletal fixation. With an aggressive physical therapy program, 10 patients achieved nearly full range of knee motion and 5 patients had relevant knee flexion deficits. The follow-up averaged 58 months (range, 40-76 months); no recurrence of osteomyelitis was observed even at 76 months.

CONCLUSION

We have found that our two-stage treatment with antibiotic beads local therapy, definitive external skeletal fixation, and staged bone grafting is an acceptable treatment protocol for the management of femoral diaphyseal infected nonunion. It results in rapid recovery from osteomyelitis and a predictable recovery from nonunion.

Management of small infected tibial defects with antibiotic-impregnated autogenic cancellous bone grafting

Between January of 1991 and December of 1993, 36 patients who had tibia fractures complicated by small infected tibia defects were treated at the authors' service. The group included 30 men and 6 women whose average age was 36.5 years (range, 18-72 years). The average follow-up period was 3.7 years. By using the Cierney-Mader staging classification of chronic osteomyelitis, 26 of 36 patients (72%) were stage 4A and 10 of 36 patients (28%) were stage 4B. Ten patients required muscle transfer. All patients were treated with a two-stage protocol. In the first stage, antibiotic-impregnated polymethylmethacrylate bead chains were used to obliterate the debrided osseous defect. In the second stage, the beads were removed, and the defects were reconstructed with antibiotic-impregnated autogenic cancellous bone graft. The time between the first and second stage was 2 to 8 weeks for patients without muscle transfer and 8 to 12 weeks for the patients with muscle transfer. The bone defects ranged from 2 to 4 cm. Wound healing and bony union were achieved in all patients. Only two patients had recurrent infections. The infection arrest rate was 94.4%. Minor pin tract infection of the external skeletal fixation was seen in two patients. Two patients developed skin rashes secondary to antibiotic therapy. Radiographs at an average follow-up of 3.7 years showed good consolidation and hypertrophy of grafted bones in all patients. After 3 to 5 years of follow-up, our results suggest that the use of impregnating antibiotics have no adverse effects on autogenic cancellous bone graft incorporation and may help to eliminate infection. This treatment protocol provided rapid recovery from osteomyelitis. The use of antibiotic-impregnated autogenic bone graft seems to be an effective and safe method for the management of small infected tibial defects.

Management of large infected tibial defects with antibiotic beads local therapy and staged fibular osteoseptocutaneous free transfer

Fifteen patients with tibial fractures complicated by large infected tibial defects were treated with a two-stage protocol. In the first stage, antibiotic-impregnated polymethylmethacrylate bead chains were used to obliterate the debrided osseous defect, and a meshed porcine skin was used for temporary wound coverage. In the second stage, the bead chains were removed, and the defects were reconstructed with a microvascularized fibular osteoseptocutaneous free transfer. The time between the first and second stages of treatment was 2 to 6 weeks. The bone defects ranged from 6 to 16 cm, and the skin defect areas ranged from 10 to 82 cm2. Wound healing and bony union were achieved in all 15 cases. An additional muscle flap or skin graft was required for only three patients with a large skin defect. Minor pin tract infections were seen in two patients. Stress fractures in three cases were successfully managed with bracing, external skeletal fixation or plating, and cancellous bone grafting. All of the most recent roentgenograms showed good consolidation and hypertrophy of grafted fibular bones. No recurrence of osteomyelitis was observed during an average follow-up period of 50 months (range, 36-86 months). We therefore conclude that this treatment protocol provides rapid recovery from osteomyelitis. The fibular osteoseptocutaneous graft is a useful method for the reconstruction of a large tibial defect, and it also offers the unique advantage of simultaneously reconstructing a moderate skin defect.

In vitro evaluation of antibiotic diffusion from antibiotic-impregnated biodegradable beads and polymethylmethacrylate beads

Antibiotic-impregnated beads are used in the dead bone space following debridement surgery to deliver local, high concentrations of antibiotics. Polymethylmethacrylate (PMMA), 2,000-molecular-weight (MW) polylactic acid (PLA), Poly(DL-lactide)-coglycolide (PL:CG; 90:10, 80:20, and 70:30), and the combination 2,000-MW PLA-70:20 PL:CG were individually mixed with clindamycin, tobramycin, or vancomycin. Beads were placed in 1 ml of phosphate-buffered saline (PBS) and incubated at 37 degrees C. The PBS was changed daily, and the removed PBS samples were stored at -70 degrees C until the antibiotic in each sample was determined by microbiological disk diffusion assay. Nondissolving PMMA beads with tobramycin and clindamycin had concentrations well above breakpoint sensitivity concentrations (i.e., the antibiotic concentrations at the transition point between bacterial killing and resistance to the antibiotic) for more than 90 days, but vancomycin concentrations dropped by day 12. ALl PLA, PL:CG, and the 2,000-MW PLA-70:30 PL:CG biodegradable beads release high concentrations of all the antibiotics in vitro for the period of time needed to treat bone infections (i.e., 4 to 8 weeks). Antibiotic-loaded PLA and PL:CG beads have the advantage of better antibiotic elution and the ability to biodegradable (thereby averting the need for secondary surgery for bead removal) compared to the PMMA beads presently used in the clinical setting.

Elution characteristics of vancomycin and tobramycin combined in acrylic bone-cement

Combining two antibiotics in antibiotic-loaded bone-cement is common in clinical practice. As the effect this has on elution characteristics is unknown, an in vitro quantitative elution study was carried out. Three groups of five antibiotic-loaded cement disks were prepared and placed in individual saline baths for 5 weeks. The elution of tobramycin from the disks in the study group (containing 2.4 g tobramycin and 1.0 g vancomycin per 40-g packet of Palacos-R cement powder [Smith & Nephew Orthopaedics, Memphis, TN]) was increased by 68% over that of the tobramycin control disks (2.4 g tobramycin only) (P = .024). The release of vancomycin from the study group disks was increased by 103% over the vancomycin control disks (1.0 g vancomycin only) (P = .007). Combining two antibiotics in bone-cement improves elution of both antibiotics in vitro and may translate into enhanced elution in vivo.

Management of large infected tibial defects with radical debridement and staged double-rib composite free transfer

Seven patients with tibial fractures complicated by large infected tibial defects were treated with a two-stage protocol. In the first stage, antibiotic-impregnated polymethylmethacrylate (PMMA) bead chains were used to obliterate the debrided osseous defect, and a meshed porcine skin was used for temporary wound coverage. In the second stage, the bead chains were removed, and the defects were reconstructed with a microvascularized double-rib and serratus anterior muscle composite free transfer. The interval between the first and second operations was 2 to 4 weeks. The bone defects ranged from 6 to 9 cm, and the skin defect areas ranged from 20 to 40 cm2. Wound healing and bony union was achieved in all seven cases. Minor pin track infection was seen in one patient. Stress fractures in two cases were successfully managed with patellar tendon short-leg bracing for 6 months in one case and a plate internal fixation in the other case. Within 2 years, all seven patients returned to light work without any external support, and all of their most recent radiographs showed good consolidation and hypertrophy of grafted rib bones. No occurrence of osteomyelitis was observed during an average follow-up of 37 months (out of a range of 24 to 50 months). We conclude that this treatment protocol provides rapid recovery from osteomyelitis and the double-rib graft is a useful, durable alternative for large tibial defect management.