Modelos de osteomielitis experimental basados en la utilización de implantes precolonizados y/o suspensiones bacterianas / Models of experimental osteomyelitis using pre-colonized implants

Objetivo: El objetivo de este trabajo es valorar distintos modelos de osteomielitis crónica utilizando una cepa de Staphylococcus aureus productora de slime (SP) para establecer cuál de ellos resulta más efectivo en el establecimiento de la infección, así como determinar el papel que desempeña el biofilm y la suspensión bacteriana en el éxito de la infección. Diseño experimental: Un total de 32 animales fue utilizado para un estudio comparativo de modelos de osteomielitis crónica en rata basada en una cepa SP de S. aureus, tanto para formar biofilms de 12 h sobre los implantes de acero inoxidable, que se colocaban precolonizados en los animales el día de la intervención, como para preparar las suspensiones bacterianas que se inoculaban. Resultados: Ninguno de los modelos presentó septicemia transcurridos 63 días a partir de la intervención quirúrgica. Sólo con el modelo que utiliza exclusivamente un implante colonizado se alcanzó un 100 por ciento de infección en hueso e implante; en el modelo que incorporaba además la inoculación de suspensión bacteriana, también se consiguió un 100 por ciento de éxito en la infección de los implantes, pero solamente se infectaron 5 de las 8 tibias intervenidas en este grupo. Cuando se inoculó una suspensión de 106 ufc sólo se consiguieron infectar (implante y tibia) 6 de los 8 animales, y cuando se redujo a 105 ufc, tan sólo 2 implantes y 1 tibia. Conclusiones: El modelo que implica la utilización exclusiva de un implante precolonizado con S. aureus SP ha demostrado la mayor eficacia para reproducir la infección (AU)

A simple infection model using pre-colonized implants to reproduce rat chronic Staphylococcus aureus osteomyelitis and study antibiotic treatment.

Staphylococcus aureus biofilms formed on medical implants represent a serious problem, being difficult to eradicate with antibiotic therapy and leading to chronic infections. Simplified in vivo and in vitro antibiotic susceptibility assays using biofilm bacteria are needed. In this work, a novel chronic osteomyelitis infection model was developed in rats in the absence of bacterial suspension, requiring the use of only 10(6) bacteria in biofilms at the site of surgery, with a full success in reproducing infection. Stainless-steel implants pre-colonized for 12 h with a highly adherent S. aureaus isolate were introduced into the rat tibiae. In animals not submitted to antibiotic treatment, infection was found in the implants and spread to bone in all cases, indicating the high efficacy of the model to reproduce osteomyelitis. The effect of a 21-day treatment with cefuroxime, vancomycin, tobramycin or ciprofloxacin on infection was studied in this model 42 days after surgery. Bone colonization was inhibited by vancomycin and cefuroxime. Cefuroxime (the most efficient antibiotic, able to sterilize 1 out of 8 implants) reduced the number of bacteria in biofilms adhered to implants at a higher extent than vancomycin, trobramycin and ciprofloxacin. Analogous observations were made in this work in vivo and in vitro on the relative antibiotic efficacy against S. aureus biofilm bacteria. suggesting the usefulness of both tests as a potential tool to study antibiotic suceptibility, and the need for new antimicrobials against these bacteria.

Bizarre parosteal osteochondromatous proliferation. Difficulty in diagnosis.

Nora's tumor, also known as bizarre paraosteal osteochondromatous proliferation, is an exophytic outgrowth from the cortical surface that consists of a mixture of bone, cartilage, and fibrous tissue. It is a benign lesion with atypical microscopic features and a tendency to recur. Nora reported 35 cases emerging from the bones of the hands and feet. The largest published series is of 65 cases, with 17 lesions involving the long bones. With this exception, most authors report isolated cases. Age range from 8 to 74 years but most patients are between 20 and 35 years of age, and with the lesion affecting males and females in equal proportions. Usually the presenting symptoMs are due to bony mass, with a variable growth rate (months-years), and infrequent pain. In 15-20% of the cases there was trauma in the patient history: nevertheless, Fechner and Mills report no association with trauma. Radiography shows a calcified, rounded mass emerging directly from the surface of the bone. Isotope bone scans show intense tracer uptake in the lesion. With time, the appearance progresses to the more characteristic mature bone architecture.

Application of a rat osteomyelitis model to compare in vivo and in vitro the antibiotic efficacy against bacteria with high capacity to form biofilms.

A rat experimental osteomyelitis model was used to study the efficiency of antibiotics on biofilm bacteria adhered to implants in relation to the efficiency obtained in vitro. In the osteomyelitis model, 10(4) bacteria of the strain variant used for the in vitro studies (a slime-producing variant of Staphylococcus aureus) were inoculated into the rat tibia at surgery, after implanting a stainless steel canula precolonized for 12 h with this strain. After 5 weeks, a 21-day antibiotic treatment was applied (using cefuroxime, vancomycin, or tobramycin). Subsequently, implant and tibia were studied for presence of bacteria. In this osteomyelitis model, cefuroxime inhibited bone colonization and reduced the number of bacteria in metal and bone at a higher degree (P < 0.05) than vancomycin and trobramycin (the latter antibiotic did not have this reduction effect). The in vitro assay was applied using three concentrations of each antibiotic (8, 100, and 500 microg/ml) and 6-, 24-, and 48-h biofilms. Bacterial viability was evaluated by ATP-bioluminescence after 24 h of antibiotic treatment. In this in vitro assay, cefuroxime significantly (P < 0.05) reduced in all cases the number of viable bacteria in biofilms, tobramycin did not affect viability, and vancomycin affected viability except at the lowest concentration used (8 microg/ml, i.e., 8x the minimal bactericidal concentration of this antibiotic) when facing the oldest (48 h) biofilm. These results demonstrate the usefulness of the osteomyelitis model applied in providing evidence for a close correlation between the in vitro and in vivo findings on the effect of three antibiotics under study.

Adherence of Staphylococcus aureus slime-producing strain variants to biomaterials used in orthopaedic surgery.

The adherence of Staphylococcus aureus to biomaterials used in orthopaedic surgery (polymethylmethacrylate, fresh bone, steel and titanium alloys) and to glass was studied in vitro at 1, 2, 6, 24 and 48 h of incubation. Nonslime-producing strains (72, 80 and 510) and slime-producing variants of these strains were used. An automated and fast method of ATP-bioluminiscence was applied to determine bacterial viability. The lowest adherence corresponded to polymethylmethacrylate and bone, and the highest to metals. Significant adherence was detected in all cases after 6 h and was strain dependent, being lowest for strain 72. In most cases, adherence of nonslime-producing variants was not significant compared with controls, and slime-producing were more adherent than nonslime-producing variants. These differences were maximal at 6 h or 48 h, depending on the strain and the material. The findings suggest that the appearance of slime-producing cells within a given nonslime-producing bacterial population may jeopardise postoperative immune systems and antibiotic efficacy as a consequence of biofilm formation on implants and prostheses.

[Sugioka rotational osteotomy in ischemic osteonecrosis of the femoral head]. / Osteotomia di rotazione secondo Sugioka nella osteonecrosi ischemica della testa femorale.

The treatment of ischemic necrosis of the femoral head depends on the stage and the age of the patient. Sugioka's rotational osteotomy is an alternative between the different conservative techniques. We have used this technique in 12 patient and 13 hips. The mean age of the patients was 31.8 ranging from 20 to 40. In the first 4 patients we performed the classic technique, as described by Sugioka. In the rest of the patients we used a DHS to stabilize the rotation and a maleolar screw for trochanteric osteotomy. The follow-up ranged between 24 and 67 months, average 42.46 months. The main complications were: 1 embolism, 1 trochanteric pseudoarthrosis and 1 common personal nerve lesion. The radiologic study showed progression in the majority of the cases. Clinical examination was performed following Merle D'Aubigné criteria pre and post surgery. We found 1 excellent result, 3 good, 3 fair and 6 poor (four of them needed a T.H.R.). Based on our experience, we have suggested a protocol for the treatment of ischemic necrosis of the femoral head. We believe that Sugioka's osteotomy can be indicated in patients younger than 50 and with less than 200 degrees affected (Stage III). The modifications we have made may be useful to achieve a better stabilization of the osteotomy and to improve the postoperative period. We have observed an improvement in the pain and gait in 60% of the patients. The radiologic study showed a progressive deterioration but there was no correlation between the clinical and radiological findings. Sugioka's technique allows the preservation of the femoral head delaying the total hip replacement.

Intercalary bone allografts. 23 tumor cases followed for 3 years.

From 1987 to 1991, 26 patients with malignant bone tumors (osteosarcoma, Ewing's sarcoma, chondrosarcoma and malignant fibrous histiocytoma) in the diaphysis or metaphysis of long bones have been treated by chemotherapy, radiotherapy and intercalary bone allograft replacement after resection. The mean follow-up was 3 years in 23 patients, 2 died from tumors, and 1 had an amputation because of local recurrence. Allograft incorporation in 11 metaphyseal anastomoses was excellent in all cases. In the 23 diaphyseal anastomoses there were 6 non-unions. Other complications were deep infection in 3 cases, leg length discrepancy in 2 and allograft fracture in 2. Function became satisfactory in 14 cases.

Iliac allograft used for sternal reconstruction after resection of a chondrosarcoma.

We report the case of a man, aged 48 years, with a primary chondrosarcoma of the sternum which was treated by radical resection and reconstruction with an iliac allograft and musculocutaneous flaps. No complications were seen at follow up after two years.

Lymphocyte response to polymethylmethacrylate in loose total hip prostheses.

We investigated the lymphocyte-mediated immune response to polymethylmethacrylate bone cement in 26 patients who had revision surgery for aseptic loosening of cemented total hip arthroplasties, at a mean time of seven years after the first replacement. We studied eight patients with cemented total hip arthroplasties which were not loose as controls. Patch tests to polymethylmethacrylate bone cement were positive in 13 patients with loosening, and these patients had higher lymphoblast transformation values against polymethylmethacrylate bone cement patients with a negative skin reaction (p < 0.01) or those in the control group (p < 0.001). Specific monoclonal antibodies were used to assess the percentage of certain cells of the immune system according to their cluster of differentiation (CD). There was a higher number of total T and B lymphocytes (CD2 and CD22) and interleukin-2 receptor-positive lymphocytes (activated cells, CD25) in patients with loose prostheses. More CD25 lymphocytes were found in patients with positive patch tests. The activation of the lymphocyte-mediated immune response was not related to the presence or absence of aggressive granulomatous lesions at the cement-bone interface.