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Arquivo Brasileiro de Medicina Veterinária e Zootecnia

Print version ISSN 0102-0935On-line version ISSN 1678-4162

Arq. Bras. Med. Vet. Zootec. vol.53 no.4 Belo Horizonte Aug. 2001 

External skeletal fixation in dogs: clinical and microbiological evaluation

[Fixação esquelética externa em cães: avaliação clínica e microbiológica]


L.P. Carneiro1, C.M.F. Rezende2*, C.A. Silva1, M.G. Laranjeira1,
M.A.R. Carvalho3, L.M. Farias3.

1Estudante de Pos-Graduação - Escola de Veterinária - UFMG
Escola de Veterinária - UFMG
Caixa Postal 567
30123-970 - Belo Horizonte, MG
Instituto de Ciências Biológicas - UFMG


Recebido para publicação em 31 de maio de 2000.
*Autor para correspondência




Eleven dogs, of both sexes, average weight of 12kg, with ages ranging from two to five years were used with the objective of evaluating two treatments of skin wounds produced after percutaneous bone transfixation of the tibia. In six animals, cotton swabs embedded in 0.2% iodine-alcohol were used to clean the areas of pin perforations. In five dogs, a 0.9% sodium chloride solution, under approximate 30 psi pulse pressure, was used. In both cases, and treatments were carried out every three to four days, during four weeks. Clinical specimens were collected under anaerobic conditions, immediately before the treatments, and on days 3, 7, 14 and 28 after surgery. Samples were cultured in specific media in order to allow isolation of aerobic and anaerobic bacteria and yeast. Dogs treated with sodium chloride solution showed little purulent exudation, while dogs treated with iodine-alcohol presented dry skin wounds with minimum blood-serous to serous exudation. The microbiological evaluation revealed predominance of Staphylococcus spp, but no differences were observed between the two treatments. The results allowed to conclude that both methods are efficient for post-surgical treatments of bone percutaneous transfixation in dogs.

Keywords: Dog, external skeletal fixation, post-surgical complication



Foram utilizados 11 cães de ambos os sexos, sem raça definida, clinicamente sadios, com média de peso de 12kg e idade entre dois e cinco anos, para avaliação de dois métodos de tratamento da ferida cutânea produzida pela transfixação óssea percutânea da tíbia íntegra. Em seis animais empregou-se haste de polipropileno com ponta de algodão embebida em álcool iodado a 0,2% para limpeza dos orifícios de penetração dos pinos. Em cinco cães usou-se soro fisiológico sob pressão pulsátil (± 30 psi). Em ambos os casos, os tratamentos eram repetidos a cada três a quatro dias, por um período de quatro semanas. Espécimes clínicos foram colhidos em anaerobiose após 3, 7, 14 e 28 dias da cirurgia, imediatamente antes dos tratamentos, semeados em meios de cultura específicos para isolamento de bactérias anaeróbias, aeróbias e leveduras. Os cães do grupo tratado com soro fisiológico apresentaram diminuta exsudação purulenta, enquanto que nos tratados com álcool iodado a ferida apresentou-se seca ou com diminuta exsudação de serosanguinolenta a serosa. A avaliação microbiológica revelou predomínio de Staphylococcus spp. Não houve diferença entre os tratamentosn quanto à avaliação microbiológica. Os resultados permitiram concluir que ambos os métodos foram eficientes no pós-operatório da transfixação percutânea.

Palavras-chave: Cão, fixação esquelética externa, complicação pós-operatória




The post-surgical complications related to external skeletal fixation in dogs might affect the healing of bones and soft tissues and, very often, determine changes in the treatment protocols. One of the most common complications in fracture reduction with percutaneous fixation refers to the drainage of the pin perforation sites, associated or not to pin loosening (Egger, 1991).

With the insertion of percutaneuos pins, the tegument, which constitutes the primary defense barrier against bacterial invasion, is broken, exposing the medullar channel to potential pathogens, present on the skin around the pins (Aron & Dewey, 1992; Clary & Roe, 1995). Penetration of microorganisms into the skin lesion, at least at superficial levels, is inevitable. However, the presence of bacteria is not necessarily incompatible with wound healing, as long as the host defense mechanisms are able to compete with the virulence of the invaders (Sucena, 1982; Muir et al., 1987).

The infection at the pin perforation sites is caused, in most cases, by bacteria living on the skin (Staphylococcus spp.), and present around the pins (Harari, 1992). The bacteria recovered from the skin are classified as permanent, such as Staphylococcus spp. (positive and negative coagulase), a-hemolytic Streptococcus, Micrococcus spp., Acinetobacter spp., or temporary, such as Bacillus spp., Escherichia coli, Proteus mirabilis, Corynebacterium spp. and Pseudomonas spp. The latter have little importance, unless they are part of a pathological process as secondary invaders (Scott, 1990).

Several protocols have been proposed for post-surgical treatments of external skeletal fixation, however there are controversies regarding their adequacy (Toombs, 1991). Some authors recommend to clean the skin around the pin orifices with swabs soaked in diluted chlorhexidine (0.05%) or in warm water (Harari et al., 1996). Others recommend the use of 0.9% sodium chloride solution (Harari, 1992), hydrogen peroxide (Aron & Dewey, 1992) or water and soap, twice a day to remove crusts (Green, 1983). There is even recommendation for a minimum handling around the pin orifices, in order to allow crusts to seal the sites of perforation (Egger, 1991). Another suggestion for treatment is a daily hydrotherapy using a manual shower to massage and clean the area around the pins (Aron & Dewey, 1992).

According to Stashak (1990), the solutions used for cleaning act more efficiently if applied under a minimum pressure of 7 psi (pounds per square inch). This pulse pressure can be achieved with the use of a "water pik".

Cleaning of wounds with high pressure is efficient in reducing the number of bacteria and the wound débridement, however the flush should clean the wounds without causing additional lesion to the tissue (Griego et al., 1995). The recommended fluid should be osmotically and ionically as similar as possible to the intracellular fluid. Sodium chloride and Ringer Lactate are the most appropriate solutions, the latter being the one that did not cause significant degenerative alterations (Buffa et al., 1997).

It is also possible to clean the wounds with iodine compounds, of broad spectrum of activity against vegetative forms, fungi, virus, protoza and yeast. This action is directly related to the concentration of free-iodine; however the solution should be diluted at a concentration ranging from 0.1% to 1%, in order to minimize its cytotoxic action (Lozier, 1993).

The objective of this study was to evaluate, through a clinical monitoring and microbiological analyses, the post-surgical treatment of external skeletal fixation in dogs, using either iodine-alcohol or sodium chloride to clean the areas of pin perforations.



Eleven dogs, of both sexes, average weight of 12kg, with ages ranging from two to five years were used in this study.

After a 15-day period of adaptation, the animals were submitted to clinical and laboratory examinations, vaccinations and anti-parasitic treatments (Defensor Vaccines (anti-rabies) and Vanguard HTLP 5/CV-L (óctupla) - Pfizer Laboratories/Brazil), (Endal Plus Schering-Plough Veterinária - Ind. Quím. Farm. Shering-Plough S.A., RJ), and to radiography of the right tibia at the craniocaudal and mediolateral positions.

The dogs were dipped in water and coconut soap, dried and housed in individual cages on the day preceding the surgery. They were randomly divided into two groups of six and five animals.

Under general anesthesia, each animal was placed in dorsal decubitus, keeping the right pelvic limb vertically suspense, attached to a support, following the routine procedures for orthopedic interventions, using povidine and iodine alcohol at 0.3% for antisepsis.

The surgical procedure comprised the bilateral-uniplanar external skeletal fixation - type II. Four Steinmann pins were introduced into the right tibia, medium-laterally oriented, equidistant, keeping an approximate angle of 70o in relation to the bone. At the entry and exitus of the pins, 0.5cm-skin incisions were made and the pins were immediately introduced using a pneumatic orthopedic perforator (Mini-Driver II K200 ; 3M (0 - 1100 RPM), SP), under constant irrigation with a 0.9% sodium chloride solution. The diameter of the pins ranged from 2.5mm to 3.0mm, achieving at maximum 20% of the diameter of the bone. The pins were then curved and fixed with autopolymerable acrylic resin (Jet - Clássico Ind. Brasileira, SP), keeping an approximate distance of two centimeters from the skin.

After cooling the resin with sodium chloride solution, sterile gauze was placed around the pins filing up the spaces between the skin and the resin. The apparatus was then externally covered with a bandage. Neither topic nor parenteral antibiotictherapy was given to the animals. After recovering from anesthesia, all animals received an Elizabethan collar, which was kept through out the post-surgical period.

Treatments begun after the first clinical specimens were taken, three days after the surgical procedure, and were carried out every three to four days, during 28 days. In six animals of group I, the skin and pins were cleaned with swabs soaked into a 0.2% iodine-alcohol solution. This was followed by the wrapping up of pins with sterile gauze, filling the spaces between the skin and the resin. Gauze was humidified with sodium chloride solution. In five animals of group II, the skin and pins were cleaned with approximately two liters of a 0.9% sodium chloride solution. Cleaning was carried out perpendicularly to the pins, under pulse pressure (approximately 30 psi), using a "water pik" (Teledyne Water Pik - Colorado, USA). Pins were then covered with sterile dry gauze.

In both groups, after cleaning and covering of pins, the apparatus was covered with a bandage.

Clinical specimens were taken on days 3, 7, 14 and 28 after the surgical procedure, always immediately before the treatment. Sterile absorbent paper cones (Tanari - Tanariman Industrial Ltda. – Brazil) were introduced and kept for one minute inside the pin orifices, using sterile nippers. The cones were then soaked into two milliliters of Ringer "pre-reduced anaerobically sterilized" (PRAS) solution (Sutter et al., 1980), under CO2 flow.

The clinical specimens were placed into an anaerobic chamber, under a 5%CO2, 10%H2, 85%N2 atmosphere. Samples were seeded in plates containing either supplemented tryptic soy agar (TSA) culture medium (Sutter et al., 1980), for anaerobic bacteria, or in TSA for aerobic bacteria. Plates were incubated, under anaerobic or aerobic conditions, at 37oC, for 48 hours. MacConkey agar was used for isolation of enterobacteria (Kooneman) and Sabouraud agar (Van Der Walt & Yarrow, 1984) was used for isolation of yeast. In the first case incubation was carried out under aerobiosis at 37oC, for 48 hours and in the second case plates were kept at room temperature up to 21 days (Dixon & Fromtling, 1995).

After incubation, the colonies produced were counted and were morphologically characterized, for subsequent establishment and identification of pure colonies. Approximately three colonies of each morphological type were subcultured in blood agar, with no supplementation, when under aerobiosis and in supplemented blood agar, when under anaerobiosis. The respiratory test was carried out after growth of pure cultures under anaerobiosis.

All tests for bacterial identification used pure cultures, which had been subcultured in TSA 24 hours before. Based on morphological and staining features and on catalase production, other tests were carried out. Staphylococcus-like colonies were tested for coagulase, manitol fermentation under aerobiosis and anaerobiosis, termonuclease and sensitivity to novobiocin or to polymixin. In some cases, the identification was based on biochemical and physiological features, determined through manual systems (commercial kits (Bio Mérieux, S.A., Marcy L’etoile, France)): API Staph, API 20 Strep (Holdeman et al., 1977). Gram negative rods were identified by IAL (Culture medium produced by the Laboratory of Microbiology - Fundação Ezequiel Dias, Belo Horizonte, MG, Brazil).

The results were analyzed using the non-parametric Kruskal-Wallis test, with a significance of 5%, following the procedure described by Sampaio (1998).



Eight animals (73%) sustained the limp soon after recovering from anesthesia and three animals (27%) did it between the second and the fifth day after the surgery. Among them, one had the bandage inadequately placed, affecting the sustenance of the member, but this was solved after its replacement. In the other two animals, in the moment of the first treatment, an intense pressure was observed on the skin. This was probably due to the excess of gauze around the pins. Consequently, the color of the surrounding skin was altered, but this was also solved after the treatment.

The medical care taken during the surgical procedure, regarding the skin incision, tissue divulsion, selection of pins, contributed to minimize post-surgical complications. General post-surgical care related to the speed of pin introduction, to the distance between the resin bar and the skin and restriction of skin movements over the pin were also important in avoiding complications (Egger, 1991; Aron & Dewey, 1992; Harari, 1992). There was no loosening of pins and the drained exudate was minimum and only superficial.

The use of Elizabethan collars did not prevent the animal to interfere in the surgical sites, as illustrated in Table 1. Since treatments were carried out at pre-defined intervals (three and four days), it was not possible to clean the sites immediately after animal interference. Cleaning was carried out only 12 to 24 hours later, in the moment of the following treatment. During that period, the apparatus was protected only with the bandage, until the next cleaning. Animal interference was probably due to the inadequate size of the collar and was related to its fragility, which allowed excessive flexibility. Under the conditions in which the present experiment was carried out, the ideal interval between treatments appeared to be 48 hours.



The microbiological evaluation showed that most cases of interference resulted in increased bacterium counts (Figs. 1 and 2). This was probably related to the animal immune response against bacterial infections, and due to the local bacterial concentration or even to a lack of contamination during licking.





Individual inflammatory reactions were observed and varied according to the quantity of muscular mass transfixed, to the skin movement over the pin and to the animal interference. Such reactions were, at some extent, expected and occurred in all animals in the moment of the first treatment. They were observed through out the experimental period, particularly at the proximal lateral pin sites, where muscular masses were larger, and consequently, more tissue had been transfixed. In two dogs, that removed gauze around the pins (allowing skin movements), the tissue was edematous and reddish. These factors, as reported by Green (1983), Aron & Dewey (1992) and Harari et al. (1996) accelerate the inflammatory process and facilitate local infections. Thus, maintenance of an appropriate wound dressing enables a better post-surgical result.

During the experimental period, all animals presented a type of exudation, which varied according to the location of pin perforations, independently of the treatment.

There was a thickness at the edge of the pin site, which persisted through out the period of iodine-alcohol treatment, with four among six animals presenting a reddish and bright coloration of skin. This result might be related to the irritating action of the alcohol or to the cytotoxic effect of the iodine (Huber, 1992). However, the concentration of iodine used was compatible to that recommended in the literature to minimize its cytotoxic activity (Lozier, 1993). Taking into account the microbiological results, the iodine-alcohol solution was efficient in controlling contamination in the sites of pin penetration.

Animals in group II showed a similar evolution, however they presented more sites with little purulent exudation.

In all animals, from both groups, the volume of exudation was minimum (<0.1ml). The apparatus was in the right position, in the moment of its removal, and the radiographic evaluation did not show any sign of infection along the pin trajectory. Only a discrete bone growth was observed in the cortical area adjacent to the pin. Cutaneous healing was observed after the apparatus removal.

Cleaning using sodium chloride solution leaded to the removal of crusts and generated a reddish color of the skin around the pins, due to an increased local blood supply, as reported by Stashak (1990). In all these cases there was epitelization surrounding the pins, through out the treatment. On the other hand, a light compression in this area allowed a discrete serous-purulent exudation without discomfort for the animal. According to Green (1983) and Harari et al. (1996), such reaction could be considered a mild infection, taking into account the small quantity of exudation.

Bacteria were isolated in almost every sample taken, with predominance of the genus Staphylococcus (Fig.3).



Microorganisms were detected in the exudate from 43 (98%) among the 44 samples taken from the 11 animals. It was not possible to recover microorganisms from the sample taken from one animal (n 10). In its case, bacterial growth was only possible in tioglicolate medium, but in small quantities. Although bacteria were present in the exudate of 91% of the animals in the moment of the first sampling, the clinical aspect did not suggest infection, according to the classification proposed by Green (1983). Infection may occur due to the rupture of the external tegument, which is the primary defense against bacterium penetration (Clary & Roe, 1995). Contamination of skin is inevitable during pin introduction (Aron & Dewey, 1992). However, infection does not necessarily interfere with wound healing, provided that the animal defense is able to compete with the bacterial challenge, taking into account the number and virulence of the invaders (Sucena et al., 1982; Muir et al., 1987). Thus, the establishment and the severity of infection are dependent, in principle, on the microorganism features, on its concentration and on host immune response. In general, the quantity of microorganisms required for the establishment of infection is related to its virulence (Sucena et al., 1982; Muir et al., 1987).

The microbiological evaluation revealed presence of bacteria, in relatively low numbers, during all four moments of evaluation, and these were apparently compatible with the host defense system. These results were supported by the similarity between the bacteriological findings (Figs 1 and 2), in 98% of the cases, in different moments. It is important to highlight that the methodology used in the present study was standardized and the results were representative from a pool of specimens taken from eight different surgical sites. This allowed a coherent and reproducible semi-quantitative analysis. Bacterial count in one animal was over the critical limit (106 bacteria/ml of fluid), but due to the fact that each specimen represented the sum of eight sites (media of 10 cones), the bacterium concentration in this animal was under the limit proposed by Stashak (1990). The greatest discrepancy observed corresponded to data from the last sampling from one animal (n 8). Its treatment suffered a lot of interference, particularly preceding the final sampling and this probably affected the representation of that clinical specimen (Fig. 2).

The results indicate that data from both post-surgical treatments were equivalent.

Although there was an increased cellular count at the final evaluation of animal n 8, the number of cells and the type of bacteria found in animals in group II were inferior to those obtained from animals treated with iodine-alcohol solution (Figs. 1 e 2). Griego et al. (1995) report that cleaning of wounds under pressure is efficient in reducing the number of bacteria and wound débridement. However, this procedure should not cause any additional damage to the animal.

The microbiological results showed no statistically difference between the two methods. There was a predominance of the genus Staphylococcus. Other bacteria found were: Streptococcus spp., Bacillus spp., Peptostreptococcus spp., Alcaligenes spp. and Proteus mirabilis. According to Harari (1992) and Seguin et al. (1997), the infection at the pin perforation sites is caused, in most cases, by bacteria present on the skin surrounding the pin, particularly Staphylococcus spp. According to Scott (1990), bacteria are classified as permanent, such as Staphylococcus spp., (positive and negative coagulase), a-hemolytic Streptococcus, Micrococcus spp. and Acinetobacter spp., or transitory, such as Bacillus spp., Escherichia coli, Proteus mirabilis, Corynebacterium spp. and Pseudomonas spp., as the case of Streptococcus spp., Bacillus spp. and Proteus mirabilis in the present study. Peptostreptococcus spp. and Alcaligenes spp. were isolated only from one animal that interfered in the treatment since the first day of evaluation. This contamination was probably from oral origin.

Although there was contamination in the sites of pin perforation, no premature loosening of pins was observed, and this is one of most important post-surgical complications (Egger, 1991). This fact was possibly due to care taken during the apparatus introduction, as well as to the lack of infection in deep layers. As reported by several authors (Green, 1983; Aron & Dewey, 1992; Harari et al., 1996), contamination justifies the need for strict care during the post-surgical period. Contamination may lead to a focal osteomyelitis and annular sequestration. The results allowed to conclude that both methods are efficient for post-surgical treatments of bone percutaneous transfixation in dogs.



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