Susceptibility to local infection in biological internal fixation. Experimental study of open vs minimally invasive plate osteosynthesis in rabbits

Experimental In Vitro Microfluidic Calorimetric Chip Data towards the Early Detection of Infection on Implant Surfaces

Heat flux measurement shows potential for the early detection of infectious growth. Our research is motivated by the possibility of using heat flux sensors for the early detection of infection on aortic vascular grafts by measuring the onset of bacterial growth. Applying heat flux measurement as an infectious marker on implant surfaces is yet to be experimentally explored. We have previously shown the measurement of the exponential growth curve of a bacterial population in a thermally stabilized laboratory environment. In this work, we further explore the limits of the microcalorimetric measurements via heat flux sensors in a microfluidic chip in a thermally fluctuating environment.

A Journey into Animal Models of Human Osteomyelitis: A Review

Osteomyelitis is an infection of the bone characterized by progressive inflammatory destruction and apposition of new bone that can spread via the hematogenous route (hematogenous osteomyelitis (HO)), contiguous spread (contiguous osteomyelitis (CO)), and direct inoculation (osteomyelitis associated with peripheral vascular insufficiency (PVI)). Given the significant financial burden posed by osteomyelitis patient management, the development of new preventive and treatment methods is warranted. To achieve this objective, implementing animal models (AMs) of infection such as rats, mice, rabbits, avians, dogs, sheep, goats, and pigs might be of the essence. This review provides a literature analysis of the AMs developed and used to study osteomyelitis. Historical relevance and clinical applicability were taken into account to choose the best AMs, and some study methods are briefly described. Furthermore, the most significant strengths and limitations of each species as AM are discussed, as no single model incorporates all features of osteomyelitis. HO’s clinical manifestation results in extreme variability between patients due to multiple variables (e.g., age, sex, route of infection, anatomical location, and concomitant diseases) that could alter clinical studies. However, these variables can be controlled and tested through different animal models.

Use of the Minimally Invasive Reduction Instrumentation System for Facilitating Alignment and Reduction When Performing Minimally Invasive Plate Osteosynthesis in Three Dogs

The Minimally Invasive Reduction Instrumentation System (MIRIS) was utilized to facilitate minimally invasive plate osteosynthesis (MIPO) of distal limb diaphyseal comminuted fractures (2 crural, 1 antebrachial) in three dogs. The MIRIS facilitated efficient MIPO in all three fractures. Radial and tibial lengths were restored within 2% of the length of the intact bone and postoperative frontal and sagittal plane angulation were within 3° of the normal contralateral limb for each of the fractures. Fixation failed in one of the tibial fractures when the plates bent a week following surgery. The implants were removed and the fracture was restabilized via MIPO facilitated by the MIRIS. Inappropriate implant selection was considered the primary reason for implant failure. All three fractures achieved union by 10 weeks following surgery. The dog that underwent revision surgery developed a surgical site infection 5 months following revision surgery, which necessitated implant removal. All three dogs had excellent limb function at the time of the final evaluation. This system resulted in reductions that were near anatomic, with acceptable restoration of length and alignment and excellent limb function.

Feline pantarsal arthrodesis using pre-contoured dorsal plates applied according to the principles of percutaneous plate arthrodesis

Objective: To describe the surgical technique for pantarsal arthrodesis (PTA) in cats according to the principles of percutaneous plate arthrodesis with application of a pre-contoured dorsal plate, without external coaptation and to report the long-term clinical outcome.

Materials and methods: Retrospective review was performed of all cats treated by percutaneous plate application using a new pre-contoured dorsal plate for PTA between 2008 and 2011. Inclusion criteria were clinical and radiographic records plus clinical follow-up to at least six weeks. Data recorded included signalment, indication for surgery, postoperative care, and complications encountered. Radiographs were assessed for arthrodesis progression and complications. Outcome was assessed using an owner questionnaire.

Results: Eleven cats were treated for tarsal injuries and met the inclusion criteria. Mean age was 86 ± 45 months, weight 4.50 ± 0.92 kg. The only major short-term complication encountered was wound dehiscence requiring sedation and re-suturing. In the medium-term (23.3 months ± 11.6 months) eight out of nine cats returned to normal activity and one cat showed intermittent lameness. Long-term (34.3 months ±17.5 months) radiographic evaluation was performed in seven out of nine cats; six manifested complete arthrodesis and one sustained plate breakage. Based on owner questionnaire, all nine cats returned to normal activity in the long-term, even the case with plate breakage.

Conclusion: Based on our results, PTA using a custom pre-contoured dorsal plate is a suitable salvage surgery for treatment of severe tarsal injuries in cats.

A rabbit model of implant-related osteomyelitis inoculated with biofilm after open femoral fracture

Currently, animal models used in research on implant-associated osteomyelitis primarily use intramedullary fixation and initial inoculum of planktonic bacterial cells. However, these techniques have certain limitations, including lack of rotational stability and instable inoculation. To improve these models, the present study aimed to establish a novel rabbit model of implant-associated osteomyelitis using biofilm as the initial inoculum following plate fixation of the femoral fracture. A total of 24 New Zealand White rabbits were randomly divided into two equal groups. Osteotomy was performed at the right femoral shaft using a wire saw following fixation with a 5-hole stainless steel plate. The plates were not colonized with bacteria in group 1, but colonized with a biofilm of Staphylococcus aureus (American Type Culture Collection, 25923) in group 2. All the rabbits were sacrificed after 21 days for clinical, X-ray, micro-computed tomography and histological assessments of the severity of osteomyelitis. Scanning electron microscopy and confocal laser scanning microscopy were used for biofilm assessment. In group 2, pus formation, periosteal reaction, cortical destruction and absorption were observed in all the rabbits and biofilm formation was observed on all the plates. However, no pus formation was observed except for a slight inflammatory response and all the plates appeared clean without infection in group 1. The differences between the two groups were statistically significant regarding histologic scores and semi-quantification of the bacteria on the plates (P<0.001). In the present study, a novel rabbit model of infection following internal plate fixation of open fracture was successfully established, providing a novel tool for the study of implant-associated osteomyelitis.

Outcome and complications in dogs with appendicular primary bone tumors treated with stereotactic radiotherapy and concurrent surgical stabilization

OBJECTIVE

To document the outcome of dogs with appendicular primary bone tumors treated with stereotactic radiotherapy (SRT) and concurrent stabilization.

STUDY DESIGN

Multi-institutional retrospective case series.

ANIMALS

Eighteen dogs with presumptive or definitive diagnosis of appendicular osteosarcoma.

METHODS

Medical records of dogs with appendicular primary bone tumors treated with SRT and stabilization were reviewed for signalment, preoperative staging and diagnostics, radiation dose, stabilization method, and outcome.

RESULTS

The distal radius was affected in 13/18 cases. Osteosarcoma or sarcoma was confirmed cytologically or histologically in 15/18 cases. Seven dogs were diagnosed with a pathological fracture at the time of treatment, and 11 were considered at high risk for pathological fracture. Dogs received a single dose (n = 5) or 3 doses (n = 13) of SRT. Surgical stabilization was performed under the same anesthetic event as the final dose of SRT in 10 dogs. Stabilization was achieved with a bone plate (n = 15) or interlocking nail (n = 3). Seventeen dogs received adjuvant chemotherapy. Complications occurred in 16/17 dogs, 15/17 of those being considered major complications. Four dogs experienced more than one complication. Infection was the most common complication, diagnosed in 15/17 cases, and considered as a major complication in 13/15 cases. Postoperative fracture was recorded as a major complication in 3 cases. Nine dogs were amputated at a median of 152 days. The median survival time was 344 days.

CONCLUSION

Treatment of bone tumors with SRT and concurrent stabilization was associated with a prohibitively high complication rate in dogs. Alternative methods for limb salvage should be considered for dogs at risk for pathologic fracture.

Minimally invasive internal fixation of distal femur fractures

Fractures of the distal femur remain a daunting challenge. Since 1970, operative treatment has been recommended. Unfortunately, it is fraught with complications, and techniques have been developed to limit incidence of non-union, infection and stiffness. A soft-tissue friendly approach is the key point, with minimally invasive surgery as the ultimate goal: its biological and anatomical advantages have been demonstrated, but clinical studies have been less convincing, being based on historical series. At present, retrograde nailing and minimally invasive percutaneous plate osteosynthesis (ideally by locking plate) are the two main techniques. Unfortunately, reports tend to compare implants rather than operative techniques, hindering solid conclusions. Lastly, the delineation of "distal femur fracture" is quite variable, sometimes situated well above the AO epiphyseal square. Meta-analyses find almost no difference between the two implants in minimally invasive procedures. The main advantage of the plate is its versatility, whereas nailing can be impossible in case of certain hip or knee prostheses, compound articular fracture or medullary canal obstruction by fixation material (nail, stem, screw, etc.). The role of arthroscopy is limited. Only a few case reports describe its use in reduction of epiphyseal fracture. In the last analysis, the surgeon's experience is more relevant to outcome than any particular implant.

Infection after fracture osteosynthesis - Part I

Bone and surgical site infections after osteosynthesis are notoriously difficult to manage and pose a tremendous burden in fracture management. In this article, we use the term osteosynthesis-associated infection (OAI) to refer to this clinical entity. While relatively few surgically treated fractures become infected, it is challenging to perform a rapid diagnosis. Optimal management strategies are complex and highly customized to each scenario and take into consideration the status of fracture union, the presence of hardware and the degree of mechanical stability. At present, a high level of relevant evidence is unavailable; most findings presented in the literature are based on laboratory work and non-randomized clinical studies. We present this overview of OAI in two parts: an examination of recent literature concerning OAI pathogenesis, diagnosis and classification and a review of treatment options.

A new model of implant-related osteomyelitis in the metaphysis of rat tibiae

Background

Animal models serve as an important tool to understand peri-implant infection. Most of the models use high bacterial loads (>10⁴ colony forming units, CFU) to provide high infection rates. Therefore these animals evolve rather similarly, making comparison between groups and statistical analysis possible. On the other hand, to mimic clinical constellation of surgery-related infections the use of low amounts of bacteria would be more advantageous.

Methods

We developed a metaphyseal rat model of peri-implant bone infection with low amount of bacterial loads (10² and 10³ CFU of Staphylococcus aureus) and investigated osseointegration of the implants coated with hydroxyapatite (HA) and low-dosed HA-silver (HA-Ag). Non-infected implants served as controls. After 6 weeks rats were sacrificed and implants evaluated for osseointegration and infection.

Results

Infection of implanted devices was reliably induced, independently whether 10² or 10³ CFU of S. aureus were inoculated and HA or HA-Ag coated implants were used. No systemic infection was present in any of the animals at the time of sacrifice, and no animal developed acute infection requiring premature sacrifice. All CFU counts of the implant and the bone at sacrifice were significantly higher than the inoculated load (p < .05). All sterilely inserted implants showed excellent osseointegration and no infection.

Conclusions

Our present study of a rat tibia model reliably induced osteomyelitis in the metaphysis with low-doses of bacteria. The addition of low-dosed Ag to the implant coating was not able to reduce the infection rates. The results demonstrate that it is possible to develop a model of implant-related osteomyelitis in rats with low amounts of bacteria to better mimic clinical constellations. No other promoters of infection besides insertion of the screw implant were used in this model.

A systematic review of animal models for Staphylococcus aureus osteomyelitis

Staphylococcus aureus (S. aureus) osteomyelitis is a significant complication for orthopaedic patients undergoing surgery, particularly with fracture fixation and arthroplasty. Given the difficulty in studying S. aureus infections in human subjects, animal models serve an integral role in exploring the pathogenesis of osteomyelitis, and aid in determining the efficacy of prophylactic and therapeutic treatments. Animal models should mimic the clinical scenarios seen in patients as closely as possible to permit the experimental results to be translated to the corresponding clinical care. To help understand existing animal models of S. aureus, we conducted a systematic search of PubMed and Ovid MEDLINE to identify in vivo animal experiments that have investigated the management of S. aureus osteomyelitis in the context of fractures and metallic implants. In this review, experimental studies are categorised by animal species and are further classified by the setting of the infection. Study methods are summarised and the relevant advantages and disadvantages of each species and model are discussed. While no ideal animal model exists, the understanding of a model's strengths and limitations should assist clinicians and researchers to appropriately select an animal model to translate the conclusions to the clinical setting.

A model of implant-associated infection in the tibial metaphysis of rats

OBJECTIVE

Implant-associated infections remain serious complications in orthopaedic and trauma surgery. A main scientific focus has thus been drawn to the development of anti-infective implant coatings. Animal models of implant-associated infections are considered helpful in the in vivo testing of new anti-infective implant coatings. The aim of the present study was to evaluate a novel animal model for generation of implant-associated infections in the tibial metaphysis of rats.

MATERIALS AND METHODS

A custom-made conical implant made of Ti6Al4V was inserted bilaterally at the medial proximal tibia of 26 female Sprague-Dawley rats. Staphylococcus aureus in amounts spanning four orders of magnitude and each suspended in 15  μ l phosphate buffered saline (PBS) was inoculated into the inner cavity of the implant after the implantation into the defined position. Controls were treated accordingly with PBS alone. Animals were then followed for six weeks until sacrifice. Implant-associated infection was evaluated by microbiological investigation using swabs and determination of viable bacteria in the bone around the implant and the biofilm on the implants after sonification.

RESULTS

Irrespective of the initial inoculum, all animals in the various groups harbored viable bacteria in the intraoperative swabs as well as the sonication fluid of the implant and the bone samples. No correlation could be established between initially inoculated CFU and population sizes on implant surfaces at sacrifice. However, a significantly higher viable count was observed from peri-implant bone samples for animals inoculated with 10(6) CFU. Macroscopic signs of animal infection (pus and abscess formation) were only observed for implants inoculated with at least 10(5) CFU S. aureus.

DISCUSSION/CONCLUSION

The results demonstrate the feasibility of this novel animal model to induce an implant-associated infection in the metaphysis of rats, even with comparatively low bacterial inocula. The specific design of the implant allows an application of bacteria in reproducible numbers at well-defined contact sites to the animal bone.

Orthopedics and biofilm--what do we know? A review

Bacteria have been found to grow predominantly in biofilms. The initial stage includes the attachment of bacteria to the substratum. Bacterial growth and division then leads to the colonization of the surrounding area and the formation of the biofilm. The environment in a biofilm is not homogeneous; the bacteria in a multispecies biofilm are not randomly distributed, but rather are organized to best meet their needs.

Although there is an initial understanding on the mechanisms of biofilm-associated antimicrobial resistance, this topic is still under investigation. A variety of approaches are being explored to overcome biofilm-associated antimicrobial resistance. A greater understanding of biofilm processes should lead to novel, effective control strategies for biofilm control and a resulting improvement in patient management.

Biplanar fixation of a locking plate in the diaphysis improves construct strength

BACKGROUND

Elevation of a locking plate over the bone surface not only supports biological fixation, but also decreases the torsional strength of the fixation construct. Biplanar fixation by means of a staggered screw hole arrangement may combat this decreased torsional strength caused by plate elevation. This biomechanical study evaluated the effect of biplanar fixation on the torsional strength of locking plate fixation in the femoral diaphysis.

METHODS

Custom titanium plates were manufactured with either a linear or staggered hole pattern to evaluate planar and biplanar fixation, respectively. Fixation strength under torsional loading was evaluated in surrogates of the femoral diaphysis representative of osteoporotic and non-osteoporotic bone. Furthermore, fixation strength was determined for plate fixation with unicortical or bicortical locking screws. Five specimens per configuration were loaded to failure in torsion to determine their strength, stiffness, and failure mode.

FINDINGS

In osteoporotic bone, biplanar fixation was 32% stronger (P=0.01) than planar fixation when unicortical screws were used and 9% stronger (P=0.02) when bicortical screws were used. In non-osteoporotic bone, biplanar fixation was 55% stronger (P<0.001) than planar fixation when unicortical screws were used and 42% (P<0.001) stronger when bicortical screws were used.

INTERPRETATION

A biplanar screw configuration improves the torsional strength of diaphyseal plate fixation relative to a planar configuration in both osteoporotic and normal bone. With biplanar fixation, unicortical screws provide the same fixation strength as bicortical screws in non-osteoporotic bone.

[Diabetic osteoarthropathy: problems and complications in foot surgery]

Charcot neuroarthropathy is one of the most serious manifestations of the diabetic foot syndrome and the multifaceted disease pattern requires interdisciplinary cooperation. Problems may arise even if the diagnosis is made early and lack of pain may mislead to the assumption of an infectious or traumatic event. With respect to operative therapy the characteristics of polyneuropathy and altered bone metabolism have to be taken into account. Rehabilitation, in particular, differs from the guidelines for trauma patients. In the face of high complication risks substantial improvement of function must be the goal for operative treatment.

Influence of bacteria on spinal implant-centered infection: an in vitro and in vivo experimental comparison between Staphylococcus aureus and mycobacterium tuberculosis

STUDY DESIGN

an in vitro and in vivo experimental study.

OBJECTIVE

this study was undertaken to evaluate differences in the capability of inducing an implant-centered infection between Staphylococcus aureus and Mycobacterium tuberculosis.

SUMMARY OF BACKGROUND DATA

bacterial infection is still one of the most serious and devastating complications after orthopedic implant surgery despite the advent of new antibiotics and treatment methods.

METHODS

S. aureus and M. tuberculosis were separately cultured with titanium plates. The bacteria colonized on the plates were isolated and cultured on culture medium. They were evaluated and compared by colony-forming units enumeration. Scanning electron microscopy was used to evaluate the difference in the colonization features of the 2 pathogens. In the in vivo experiment, 22 dogs were used to assess the susceptibility to infection after a local bacterial challenge with either S. aureus or M. tuberculosis.

RESULTS

S. aureus showed heavy adhesion and multiplication on the surface of titanium plates in vitro, whereas M. tuberculosis rarely adhered to the surface of the plates. Under scanning electron microscopy, S. aureus colonization was observed: the coccoid was widespread on the surface of the plates but only a few M. tuberculosis cells scattered on the surface of the plates. In in vivo test, the infection rateforthe S. aureus inoculation was higher than that for the M. tuberculosis challenge. The infection rate for the entire test population (n = 44 sites) was 39.58% (19/48). The infection rates were 54.17% (13/24) for the S. aureus challenge and 25% (6/24) for the M. tuberculosis challenge, respectively (P < 0.05).

CONCLUSION

it is less likely for M. tuberculosis to adhere and form a biofilm on an implant surface than S. aureus. Under otherwise identical conditions, M. tuberculosis contamination following instrumented spine surgery might lead to less occurrence of infection than S. aureus contamination.

Internal pedal amputations

Internal pedal amputation consists of resection of the metatarsals, midtarsal bones, or talus with preservation of the toes and soft-tissue envelope. Although used in the past for the treatment of tuberculosis within the pedal skeleton, internal pedal amputations have become almost forgotten, historical procedures. However, following internal pedal amputations of a diabetic patient, the foot undergoes significant contracture that results in a stable, functional, foreshortened residual foot capable of being protected in custom-molded shoe gear with external or in-shoe orthoses. The author presents the surgical approach and postoperative treatment regime for each form of internal pedal amputation, as well as "pearls" for success.

Submuscular plating after distraction osteogenesis in children

Although distraction osteogenesis has solved limb length discrepancies, many complications are inevitable from long duration of external fixation. Use of intramedullary nails for early removal of fixators has its own challenges especially in pediatric age group. To facilitate early removal of external fixators in children, we tried a novel method of submuscular plating over the distraction callus, which is described, and the results and complications of this technique are presented. In eight children (four girls and four boys), of limb lengthening (four cases) and bone transport (four cases) done in three femurs and five tibiae with external fixators (five Ilizarov ring fixators and three monofixators), submuscular plating was done over the distraction callus. The causes of limb length discrepancy included traumatic and septic growth arrest, congenital pseudoarthrosis of tibia, fibular hemimelia, tumor salvage, and Perthes' disease. The purpose of plating was to remove the external fixator earlier after achieving the target length. Mean age of plating procedure was 11.62 years, and mean amount of distraction was 5.47 cm. In all patients, the distraction callus healed on maintaining its length or correcting into the original alignment. The mean external fixation index was 26.93 days/cm and healing index was 52.01 days/cm. One complication of superficial pin-track infection occurred, which resolved completely with conservative treatment. None of the patients developed deep infection or implant failures. The mean follow-up after plating was 28 months (range, 18-62 months). Submuscular plating over the distraction callus may be a successful method that permits early removal of fixator with fewer complications. This method can be a useful alternative in children or when nailing is difficult.

Comparison of open versus percutaneous pedicle screw insertion in a sheep model

Minimally invasive surgery has become more and more important for the treatment of traumatic spine fractures. Besides, some clinical studies, objective data regarding the possible lower damage to the surrounding tissue of the spine is still missing. Here we report a sheep model where we compared a percutaneous versus an open approach for dorsal instrumentation with pedicle screws to the spine. Twelve skeletally mature sheep underwent bilateral pedicle screw fixation at the L4-L6 level. Forty-eight pedicle screws were bilaterally inserted into the pedicles and connected with rods using either an open dorsal standard or a percutaneous approach. Operation time, blood flow, compartment pressure, radiation time, loss of blood, laboratory findings and EMG were evaluated to objectify possible advantages for the percutaneous operation technique. Loss of blood and the distribution of CK-MM as a marker for muscle damage were significantly lower in the percutaneous group. However, radiation time was significantly longer in the percutaneous group. Other parameters like compartment pressure, blood flow and also measurement of the EMG at different time points did not reveal significant differences. Based on the results we found in the present study, percutaneous screw insertion can bring moderate advantages but it should be noted that essential functional deficits to the muscle could not be detected.

Local application of basic fibroblast growth factor increases the risk of local infection after trauma: an in-vitro and in-vivo study in rats

INTRODUCTION

Local application of growth factors to stimulate wound and fracture healing is attracting increasing interest. We studied the effect of local application of a potent angiogenic growth factor, basic fibroblast growth factor (bFGF), on resistance to local infection after soft tissue trauma.

METHODS

For in-vitro and in-vivo experiments, we used recombinant human bFGF. The in-vitro investigations were performed by isolation of human leukocyte fractions, cytokine analysis, phagocytosis assay, flow cytometry, and LDH assay. For the in-vivo investigation, a paired comparison of infection rates was carried out on Sprague-Dawley rats after standardized, closed soft tissue trauma and local, percutaneous bacterial inoculation of different concentrations of Staphylococcus aureus (2 x 10(4) to 2 x 10(7) colony-forming units (cfu)). The lower leg was treated with 1, 10 or 100 ng bFGF (16 animals for each concentration) and without bFGF (16 animals).

RESULTS

Cytotoxic reactions due to the concentrations of bFGF used could be excluded in the in-vitro tests since incubations of isolated peripheral blood mononuclear cells (PBMCs) with increasing concentrations of bFGF for 24 h did not lead to an increase in the release of lactate dehydrogenase in the culture supernatants compared to corresponding control incubations without any bFGF added. A significant increase in cytokine release was observed after the co-incubation of PBMCs with 100 or 200 ng of the same bFGF that was used for the animal experiments. Furthermore, the capacity of phagocytes in whole blood to phagocytose bacteria was suppressed in the presence of 100 ng exogenously added bFGF. We found continuously reduced granulocytic phagocytosis in FGF-supplemented blood compared to non-supplemented blood. In the in-vivo investigation, the infection rate for the group without bFGF was 0.25. In the groups with 1, 10 and 100 ng bFGF, the infection rates were 0.5, 0.7 and 0.8, respectively. A dose-dependent increase in infection rate was observed after local application of bFGF, compared to the untreated control group. The difference in infection rates for the groups in which 10 and 100 ng bFGF was used, relative to the group without bFGF, was statistically significant.

INTERPRETATION

If these initial results are confirmed for other potent angiogenic growth factors, then the local use of growth factors for stimulation of wound and bone healing--a main focus of current research in traumatology--will have to be reconsidered and preceded with a strict evaluation of the risks and benefits.

Antimicrobial agents in orthopaedic surgery: Prophylaxis and treatment

The pathogenesis of implant-associated infection involves interaction between the microorganisms (biofilm formation), the implant and the host. Despite improvement of perioperative prophylaxis, orthopaedic implants still remain highly susceptible to bacterial or fungal contamination, generally resulting in persistent implant-associated infection. Therefore, perioperative and life-long prevention of infection is important. For perioperative prophylaxis, a first- or second-generation cephalosporin is recommended, which should be administered between 60 and 30 minutes before incision. The duration of prophylaxis should not exceed 1 day. In centres with a low incidence of infection, a single dose is sufficient. Treatment of infections associated with orthopaedic devices usually requires appropriate surgical intervention combined with prolonged antimicrobial therapy. The choice of the antimicrobial regimen depends on the duration and pathogenesis of infection, stability of the implant, antimicrobial susceptibility of the pathogen and condition of the surrounding soft tissue. The role of rifampicin (rifampin), which has excellent activity on adherent staphylococci, in combination with beta-lactams, glycopeptides, fluoroquinolones, minocycline, cotrimoxazole or fusidic acid, in the treatment of staphylococcal infections is outlined. Increasing antimicrobial resistance requires the use of alternative agents, such as quinupristin/dalfopristin, linezolid and daptomycin, but results of clinical trials with these agents are limited. Also reviewed are potential new antimicrobial agents currently undergoing investigation, such as the novel oxazolidinone RWJ-416457, the new glycopeptide dalbavancin, the glycylcycline compound tigecycline, the new carbacephem BP-102 and novel rifamycin derivatives. Vaccination against Staphylococcus aureus with StaphVAX induced specific antibodies potentially preventing bacteraemia; however, there are no studies on efficacy in the prophylaxis of device-associated infections with this vaccine.

Effect on infection resistance of a local antiseptic and antibiotic coating on osteosynthesis implants: an in vitro and in vivo study

The purpose of this study was to acquire information about the effect of an antibacterial and biodegradable poly-L-lactide (PLLA) coated titanium plate osteosynthesis on local infection resistance. For our in vitro and in vivo experiments, we used six-hole AO DC minifragment titanium plates. The implants were coated with biodegradable, semiamorphous PLLA (coating about 30 microm thick). This acted as a carrier substance to which either antibiotics or antiseptics were added. The antibiotic we applied was a combination of Rifampicin and fusidic acid; the antiseptic was a combination of Octenidin and Irgasan. This produced the following groups: Group I: six-hole AO DC minifragment titanium plate without PLLA; Group II: six-hole AO DC minifragment titanium plate with PLLA without antibiotics/antiseptics; Group III: six-hole AO DC minifragment titanium plate with PLLA + 3% Rifampicin and 7% fusidic acid; Group IV: six-hole AO DC minifragment titanium plate with PLLA + 2% Octenidin and 8% Irgasan. In vitro, we investigated the degradation and the release of the PLLA coating over a period of 6 weeks, the bactericidal efficacy of antibiotics/antiseptics after their release from the coating and the bacterial adhesion of Staphylococcus aureus to the implants. In vivo, we compared the infection rates in white New Zealand rabbits after titanium plate osteosynthesis of the tibia with or without antibacterial coating after local percutaneous bacterial inoculations at different concentrations (2 x 10(5)-2 x 10(8)): The plate, the contaminated soft tissues and the underlying bone were removed under sterile conditions after 28 days and quantitatively evaluated for bacterial growth. A stepwise experimental design with an "up-and-down" dosage technique was used to adjust the bacterial challenge in the area of the ID50 (50% infection dose). Statistical evaluation of the differences between the infection rates of both groups was performed using the two-sided Fisher exact test (p < 0.05). Over a period of 6 weeks, a continuous degradation of the PLLA coating of 13%, on average, was seen in vitro in 0.9% NaCl solution. The elution tests on titanium implants with antibiotic or antiseptic coatings produced average release values of 60% of the incorporated antibiotic or 62% of the incorporated antiseptic within the first 60 min. This was followed by a much slower, but nevertheless continuous, release of the incorporated antibiotic and antiseptic over days and weeks. At the end of the test period of 42 days, 20% of the incorporated antibiotic and 15% of the incorporated antiseptic had not yet been released from the coating. The antibacterial effect of the antibiotic/antiseptic is not lost by integrating it into the PLLA coating. The overall infection rate in the in vivo investigation was 50%. For Groups I and II the infection rate was both 83% (10 of 12 animals). In Groups III and IV with antibacterial coating, the infection rate was both 17% (2 of 12 animals). The ID50 in the antibacterial coated Groups III and IV was recorded as 1 x 10(8) CFU, whereas the ID50 values in the Groups I and II without antibacterial coating were a hundred times lower at 1 x 10(6) CFU, respectively. The difference between the groups with and without antibacterial coating was statistically significant (p = 0.033). Using an antibacterial biodegradable PLLA coating on titanium plates, a significant reduction of infection rate in an in vitro and in vivo investigation could be demonstrated. For the first time, to our knowledge, we were able to show, under standardized and reproducible conditions, that an antiseptic coating leads to the same reduction in infection rate as an antibiotic coating. Taking the problem of antibiotic-induced bacterial resistance into consideration, we thus regard the antiseptic coating, which shows the same level of effectiveness, as advantageous.

Minimally invasive plate fixation of lower limb injury in horses: 32 cases (1999-2003)

REASONS FOR PERFORMING STUDY

Complications of osteosynthesis including superficial and deep infections continue to affect adversely outcome in equine surgery of the lower limb.

OBJECTIVE

To describe a technique for minimally invasive plate fixation in horses and evaluate clinical results of the technique.

HYPOTHESIS

Lower complication rates would occur in horses treated with a minimally invasive approach compared with conventional techniques.

METHODS

Cases of minimally invasive plate fixation from January 1999 to December 2003 were evaluated. Case records, radiographs and race records for horses that sustained distal third metacarpal/metatarsal (Mc/tIII) condylar fractures were assessed. Follow-up information was obtained and results analysed. In addition, results for horses that received arthrodesis by a conventional, open approach during the same period were evaluated and statistical analysis was performed.

RESULTS

Thirty-two cases of minimally invasive plate fixation were identified (22 incomplete distal Mc/tIII condylar fractures with a spiralling or diaphyseal component, 10 metacarpophalangeal arthrodeses and 4 pastern arthrodeses). For both types of arthrodesis, surgery times and infection rates were lower and survival rates higher in the minimally invasive group, but no statistical difference was found. Spiralling condylar fractures were successfully managed, without catastrophic fracture.

CONCLUSIONS AND POTENTIAL RELEVANCE

Minimally invasive percutaneous plate osteosynthesis (MIPPO) can be successfully used for select applications in horses, and may reduce morbidity and mortality in equine fracture repair.

Diagnosis and treatment of infections associated with fracture-fixation devices

The pathogenesis of infections associated with fracture-fixation devices is related to microorganisms growing in biofilms, which render these infections difficult to treat. These infections are classified as early (<2 weeks), delayed (2-10 weeks) or late infections (>10 weeks) according to the implant surgery. Most infections are caused by staphylococci and are acquired during trauma (in penetrating injuries) or subsequent fracture-fixation procedures. A combination of clinical, laboratory, histopathology, microbiology, and imaging studies are usually needed to accurately diagnose infection. Magnetic resonance imaging (MRI) and computed tomography (CT) scans are often used to diagnose infection and plan surgical treatment. Positron emission tomography (PET) and PET-CT are promising new tools for diagnosing implant-associated osteomyelitis. The treatment goal is achieving bone consolidation and avoiding development of chronic osteomyelitis. Successful treatment requires adequate surgical procedures combined with 6-12 weeks of antimicrobial therapy acting on adhering stationary-phase microorganisms. In chronic osteomyelitis, orthopedic and plastic- reconstructive surgery is combined in the same procedure or within a short time span. In this article, pathogenesis, classification, diagnosis, and treatment of infections associated with intramedullary nails, external-fixation pins, plates, and screws are reviewed.

Infection resistance of unreamed solid, hollow slotted and cannulated intramedullary nails: an in-vivo experimental comparison

Infection continues to be a problematic complication of fracture treatment, particularly in severe open fractures. The implant design and material as well as implantation technique play an important role in the pathogenesis of local infection. The aim of our study was to determine if the local resistance to infection of a cannulated IM nail is less than that of a solid nail and more similar to that of a hollow nail. In 65 female White Zealand rabbits, the intramedullary cavity was inoculated with matching concentrations of Staphylococcus aureus, and one of the three nails was inserted. The solid nail had a greater than twofold higher resistance to infection (23%) compared to that of the other two nails (hollow, 65%; cannulated, 61%) which was statistically significant (p<0.02). No difference in infection resistance was detected between the hollow slotted and cannulated nail designs (p=1). Although these experimental results may be clinically considered, direct extrapolation to clinical infection rates is ill advised.

Percutaneous plating for unstable tibial fractures

Twenty-four unstable tibial fractures were stabilized with a narrow limited contact-dynamic compression plate inserted using a percutaneous plating technique under fluoroscopic guidance. The major indication for this technique was a tibial fracture for which intramedullary nailing would be difficult. There were 16 proximal or distal metaphyseal fractures and 5 segmental fractures in adults and 3 mid-shaft fractures in adolescents who still had an open physis. Of the 24 fractures, 22 healed without a second procedure; the two failures included one that required an early bone graft for severe comminution and another with a superficial infection that healed after early removal of the plate. There were no other infections. There were three cases of screw breakage, but they did not require a further procedure. At the final follow-up, one patient had healed with 5 degrees varus alignment and another with 10 degrees external rotation. All the patients had good knee or ankle function. We are confident that the percutaneous plating technique to treat unstable tibial fractures for which intramedullary nailing would be difficult will prove to be an alternative stabilization method, as it avoids the risk of infection or soft tissue compromise.

Influence of a standardized closed soft tissue trauma on resistance to local infection. An experimental study in rats

PURPOSE

The etiology of local posttraumatic infection in the locomotor system depends on the amount, virulence and pathogenicity of the inoculated microorganisms and the local/systemic host damage due to the type and extent of the accident or iatrogenic trauma. The relative effect of these factors remains unclear. In particular, it is still unclear today whether--in presence of microorganisms--soft tissue damage and its pathophysiological consequences lead to infection after soft tissue trauma, or whether the bacterial contamination is the primarily cause for posttraumatic infection. The aim of the project was to gain information on the consequences of a soft tissue injury in terms of resistance to local infection. Since clinical populations are too heterogeneous, the problem was investigated in a standardized, reduced (no surgery or implants) experimental in vivo model.

METHOD

In female Sprague-Dawley-rats with a standardized closed soft tissue trauma to the tibialis anterior muscle (group I: n=13) or without (group II: n=13), we compared the incidence of local infection after a pairwise local, percutaneously injected bacterial challenge with various concentrations of Staphylococcus aureus (2 x 10(4)-2 x 10(6) colony forming units, CFU). The standardized closed soft tissue trauma was created by application of a specially designed, computer controlled impact device. The contaminated soft tissue and the underlying bone were removed under sterile conditions after five days and quantitatively evaluated for bacterial growths. Infection was defined as positive bacterial growth at the soft tissue and/or bone. A stepwise experimental design with an "up-and-down" dosage technique was used to adjust the bacterial challenge in the area of the ID50 (50% infection dose). Statistical evaluation of the difference between the infection rates of both groups was performed by two-sided fisher exact test (p<0.05).

RESULTS

The overall infection rate was 46%. For the group with soft tissue trauma the ID50 was 1.32 x 10(5) CFU and 1.05 x 10(6) CFU for the group without soft tissue trauma. The infection rate was 69% (9 of 13 animals) for the group with soft tissue trauma and 23% (3 of 13 animals) for the group without soft tissue trauma. This difference is statistically significant (p=0.047).

CONCLUSIONS

The infection rate after a standardized closed soft tissue injury was significantly higher and the ID50 lower than without soft tissue trauma. Our results demonstrate that in presence of microorganisms it is not primarily the bacterial contamination but rather the soft tissue damage and its pathophysiological consequences resulting in decreased infection resistance that secondarily lead to infection.

Distal tibia metaphyseal fractures treated by percutaneous plate osteosynthesis

Twenty-one patients with fractures of the distal tibial metaphysis, some with minimal displacement in the ankle, were treated by percutaneous plate osteosynthesis with a narrow limited contact-dynamic compression plate. Using the classification by the Arbeitsgemeinschaft für Osteosynthesefragen and Orthopaedic Trauma Association, 17 fractures had no articular involvement, whereas four included intraarticular extension. At final followup (mean, 20 months), all the fractures healed without second procedures and the mean union time was 15.2 weeks. One patient had malalignment of the limb with 10 degrees internal rotation, but there were no angular deformities greater than 5 degrees or any shortening greater than 1 cm. All patients had excellent or satisfactory ankle function. There were no infections or any soft tissue compromise. Percutaneous plate osteosynthesis is a safe and worthwhile method of managing such fractures, which avoids some of the complications associated with conventional open plating methods.

Endoscopic-assisted, minimally invasive anterior pelvic ring stabilization: a new technique and case report

This report describes the technique of endoscopic-assisted reduction and stabilization of the anterior pelvic ring with endoscopic visualization of all critical bone and soft tissue structures. Compared with the conventional ilioinguinal approach of Letournel, the endoscopic technique facilitates a reliable internal fixation of anterior pelvic ring fractures with minimal soft tissue trauma. Thus, the use of the endoscope enables us to apply the concept of minimal invasive plate osteosynthesis to the pelvis. We recommend the described technique for complex anterior pelvic ring fractures, in which the anterior stabilization has to be achieved with a plate from the symphyseal region to the iliac wing.