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On-line version ISSN 1678-2674
Acta Cir. Bras. vol.16 no.2 São Paulo Apr./May/June 2001
4 ORIGINAL ARTICLE
AN EXPERIMENTAL MODEL IN RABBITS1
Carvalho ZM, Fagundes DJ, Rodrigues OR, Shimidht Jr A. Inciosional hernia: na experimental model in rabbits. Acta Cir Bras [serial online] 2001 Apr-Jun;16(2). Available from URL: http://www.scielo.br/acb.
ABSTRACT: The aim of this study was to develop an experimental model of incisional hernia in rabbits. Thirty seven rabbits, weighing from 2220 to 2750 g, were submitted to musculoaponeurotic and peritoneum pattern resection of the abdominal wall and distributed in groups of 10 animals according to the postoperative time of 30, 45 or 60 days. The animals were submitted to reoperation at the end of the observation period. In the three groups were observed hernias larger than 60 and 45 cm in transversal and longitudinal measures, respectively, and with volumes greater than 129 ml. Adherences to the internal abdominal wall were present in 13,3%. Seven deaths occurred due to evisceration (5), pulmonary infection (1) and diarrhea(1). There was no significant difference in the three groups studied, according to the statistical methods applied. The experimental model is feasible, and is established at the 30 days of postoperative period.
KEY WORDS: 1. Hernia, ventral. 2. Disease models. 3. Animal. 4. Postoperative complications. 5. Rabbits.
Besides the technological and scientific advances, the operations made in the abdominal wall are yet susceptible to a considerable frequency of incisional hernias1.
A few authors describe the operational procedures for the treatment of the incisional hernia, applying them initially to the experimental animals previously herniated 2,3,4,5.
Considering that there are few works about previously herniated animals in literature, and that the intentionally made acute defects on the abdominal wall and soon afterwards repaired did not really represent the physiopathologic factors of hernias, it seems appropriated the creation of a experimental model of incisional hernia in rabbits from a patterned surgical technique that makes possible the study of its morphological and functional characteristics, as well as its surgical treatment.
Animals and operations
Thirty seven New Zealand white male rabbits weighing from 2220 to 2750 grams, ages above 120 days were used in the present study.
Thirty animals were randomly distributed in groups of ten animals according the postoperative observation period of 30, 45 and 60 days. If there was a death, the cause was analyzed and the group completed.
Each rabbit was anesthetized with acepromazine maleate (1 mg/kg) and thiopental sodium 2,5% (25mg/kg). A median longitudinal abdominal incision measuring 9 cm in extension was performed. One abdominal segment of 90x20 mm was removed in longitudinal way, including the aponeurosis, muscle and peritoneum with the umbilical cicatrix in the medium point. The transverse muscle of abdomen was preserved.
The skin suture was performed with 4.0 nylon continuous stitches that not comprehended the superficial fascia of the abdomen.
When the postoperative period was completed, each rabbit was reoperated according to similar initial procedures of operation. A rectangular area of 108 cm2 (12x9 cm) of the abdominal wall was delimitated, keeping the surgical scar at the central point and removed for study of the incisional hernia.
At laparotomy and inspection of the cavity, took into consideration the adherences greater than 0,5 cm² to the internal surface of the incisional hernia. At the end of the experiment the animal was submitted to euthanasia.
Measurement of the incisional hernia
The abdominal wall segment was fixed to a rectangular metal support (15x12x10cm) by means of eight equidistant stitches. The internal surface was filled with an elastic material that after jellification produced a mold that was useful to measure the hernial anulus and to make the gypsum replica. This cavity obtained in gypsum covered with a flexible plastic film allowed the measuring of the hernia volume.
The abdominal wall taken was split in two symmetric parts according to the orientation of the scar, and fixed in 10% buffered formalin
Rupture force measurement.
In the Universal Assay Machine (EMIC Model MEM 30000; Engineering Laboratory of the University of Mogi das Cruzes), a tissue segment of 4x2 cm in the transversal way with a notch of 0,5 cm at the medium point, excluding the surgical scar and skin, was submitted to study for rupture force. A maximum force of 40 kilograms-force (kgf) at a velocity of five mm/minute was applied. The stretch graphic record was obtained until tissue rupture. The test was accounted for the study when the rupture occurred in the narrower region of the tissue segment. From statistical analysis were excluded the pieces where the rupture force could not be determined.
Longitudinal sections of 10x4 mm of tissue segment obtained excluding the surgical scar were submitted to hematoxylin-eosin staining and histological study.
The results were analyzed by means of the following tests Kruskal-Wallis analysis of variance, to compare the groups according to the values of the linear dimensions, volumetric measures and the rupture force obtained. When showed significant difference, the analysis was complemented by the multiple comparisons test. The c² test to compare the groups according to dehiscences and deaths occurred. The tests were considered significant when p<0.05.
Measures of hernia annulus in the longitudinal and transversal way were not significantly different among the groups, as shown in table 1.
Table 2 shows that there were seven deaths, five eviscerations, one pulmonary infection and one diarrhea. Weak adhesions to the internal wall were present in 13,3% without significant difference among the studied groups.
In the three groups, the histological examination revealed similar morphological aspects. There was a reduction of the cell layers of epidermis and a reduction of the number of papillae of dermis per studied field. The cicatritial tissue under dermis was mostly formed by fibroblasts and collagen fibers and poor vascularization. In proximity to peritoneal cavity, collagenous fibers and fibroblasts presented with ordered arrangement, and aligned longitudinally.
For the creation of an incisional hernia of large proportions in rabbits, limiting factors as total dehiscence of surgical scar followed by evisceration, constituted a major concern. The skin was the only anatomic layer to contain the abdominal viscera in the acute phase of healing. Due to this fact, the influence of the ischemic factor at the suture line, which could predispose to dehiscence, was avoided by the maintenance of the epigastrics vessels.
Resections of the abdominal wall smaller than the standardized sometimes did not develop incisional hernia and greater occurrence of adherences to the internal surface of the hernia was observed. Otherwise, greater resections than the described evolved total dehiscences of abdominal wall and evisceration.
The interference of greater capacity of regeneration and healing that happens in young animals, which could possibly result in absence of the hernia, was avoided by choosing animals older than 120 days 5,6.
The morphologic study and the rupture test demonstrated that the model of incisional hernia in rabbits is possible, presented stable characteristics on the thirtieth day of observation and did not change significantly with a major time of postoperative observation (45 and 60 days).
1. Karakousis CP, Volpe C, Tanski J, Colby ED, Winston J, Driscoll DL. Use of a mesh for musculoaponeurotic defects of the abdominal wall in cancer surgery and the risk of bowel fistulas. J Am Coll Surg 1995;181:11-6. [ Links ]
2. Lazaro da Silva A. Correction of longitudinal median or paramedian incisional hernia. Surg Gynecol Obstet 1979;148:579-83. [ Links ]
3. Franke A, Reding R, Tessmann D. Electrostimulation of healing abdominal incisional hernias by low frequency, bipolar, symmetrical rectangular pulses. Acta Chir Scand 1990;156:701-5. [ Links ]
4. Johnson-Nurse C, Jenkins DHR. The use of flexible carbon fibre in the repair of experimental large abdominal incisional hernias. Br J Surg 1980;67:135-7. [ Links ]
5. Tsui S, Ellis H. Healing of abdominal incisional hernia in infant rats. Br J Surg 1991;78:927-9. [ Links ]
6. Kiely E M, Spitz L. Layered versus mass closure of abdominal wounds in infants and children. Br J Surg 1985;72:739-40. [ Links ]
Carvalho ZM, Fagundes DJ, Rodrigues OR, Shimidht Jr A. Hérnia incisional: modelo experimental em coelhos. Acta Cir Bras [serial online] 2001 Abr-Jun;16(2). Disponível em URL: http://www.scielo.br/acb.
RESUMO: Com o objetivo de desenvolver e estudar um modelo experimental de hérnia incisional em coelhos foi realizado este estudo. Trinta e sete coelhos (2220 a 2750 g) foram submetidos à ressecção padronizada músculo-aponeurótica- peritoneal da parede abdominal e distribuídos em grupos de 10 animais conforme o tempo de observação pós-operatória de 30, 45 e 60 dias. Os animais ao término da observação pós-operatória foram reoperados e as hérnias incisionais desenvolvidas foram analisadas quanto a presença de aderências, dimensões lineares e de volume, força de ruptura e estudo histológico. Nos três grupos foram observadas hérnias incisionais com dimensões transversais e longitudinais que ultrapassaram 70 e 50mm respectivamente, volumes maiores que 120 ml e aderências presentes em 13,3%. Ocorreram 7 óbitos decorrentes de evisceração(5), infecção pulmonar (1) e diarréia (1). Na análise dos resultados não houve diferença significante nos três grupos estudados. Foi concluído que o modelo experimental é factível e está estabelecido aos 30 dias de observação pós-operatória.
DESCRITORES: 1. Hernia ventral. 2. Modelos animais de doenças. 3. Animal. 4. Complicações pós-operatórias. 5. Coelhos.
Conflito de interesses: nenhum
Fontes de financiamento: nenhuma
Address for correspondence:
Zuleica M. Carvalho
Av. São Paulo, 975
Mogi das Cruzes - São Paulo
Data do recebimento: 15/01/2001
Data da revisão: 23/02/2001
Data da aprovação: 12/03/2001
1. Master thesis, Post-graduate Program of Surgical Technic and Experimental Surgery of the Federal University of São Paulo - Brazil.
2. Master, Assistant Professor Department of Surgery, University Mogi das Cruzes - Brazil.
3. Master, PhD, Coordinator of the Program.
4. PhD, Head Professor of Thoracic Surgery, University Mogi das Cruzes - Brazil.
5. Resident Department of Surgery, University Mogi das Cruzes - Brazil.