Use of Polypropylene Mesh in Addition to Internal Obturator Transposition: A Review of 59 Cases (2000–2004)
Fifty-nine dogs with a total of 69 perineal hernias that were repaired by internal obturator transposition and polypropylene mesh reinforcement were reviewed. Thirty-six dogs were available for follow-up at a mean of 29.4 months postoperatively. Six dogs had complications within the first 60 days of surgery, such as perineal swelling, persistent tenesmus, and incisional infections. Twenty-two dogs had excellent outcomes; seven dogs needed continued medical treatment after surgery; and seven dogs had poor outcomes. Hernias recurred in five dogs. The incisional infection rate was 5.6%; the recurrence rate was 12.5%; and the overall success rate was 80.5% for the 36 dogs with long-term follow-up.
Introduction
Perineal hernias result from a weakness, separation, and eventual failure of the muscles of the pelvic diaphragm, with subsequent displacement of pelvic and occasionally abdominal contents into the perineal area.1–3 The standard surgical repair for perineal hernias involves the use of nonabsorbable sutures to reappose the muscles of the pelvic diaphragm.1–4 Hernia recurrence with this technique ranges from 10% to 50%, owing to the difficulty of repairing the ventral portion of the pelvic diaphragm, especially in large-breed dogs or when the muscles are atrophied.5 A number of alternative surgical techniques have been developed to strengthen the hernia repair and decrease the recurrence rate. Internal obturator transposition is currently the preferred surgical treatment (recurrence rates of only 2.4% to 19%), but if the internal obturator muscle is atrophied, repair can be difficult.6–9 Postoperative complications such as rectal prolapse, fecal incontinence, and wound abscessation and infection can occur regardless of the surgical technique used.3,5–10
Current advances in perineal hernia repair in dogs involve the use of synthetic and bioactive implants.11–13 Biomaterials such as porcine small intestinal submucosa and porcine dermal collagen are implanted over the hernia and degrade after inducing in-growth of site-specific tissues to repair the defect. Synthetic implants remain in place for the life of the animal. Polypropylene mesha is the preferred synthetic implant because of its strength and ease of handling.14 The use of polypropylene mesh to strengthen perineal hernia repair was first described in animals in 1966; but since then, reports have been sparse.15 The increased use of synthetic implants in hernia repair in humans has been associated with higher rates of postoperative infections, and many reports describe abscess development months to years after repair of abdominal wall hernias. 16,17 Because of the location of perineal hernias, incisional infection rates associated with hernia repair in dogs (even without the use of synthetic implants) have been as high as 45%.3,6–8,10,18 The purposes of this study are to review the use of polypropylene mesh in addition to internal obturator transposition for the repair of perineal hernias in dogs and to report the type and severity of postoperative complications.
Materials and Methods
Inclusion Criteria
The medical records of all dogs admitted to the Dallas Veterinary Surgical Center for perineal herniorrhaphy from January 2000 to December 2004 were reviewed. Dogs were selected for the study if they had an internal obturator transposition with polypropylene mesh placement at the time of surgery. Data pertaining to signalment, clinical signs, related medical conditions, anesthetic protocol, surgical findings, postoperative care, immediate and long-term complications, and histopathological results were recorded. Immediate complications were defined as those occurring ≤60 days postoperatively, and delayed complications were defined as those occurring >60 days.
Follow-up
Owners of dogs included in the study were contacted by telephone and asked a series of questions from a prewritten questionnaire. The outcome was considered excellent if the dog had no further clinical signs; good if the dog had mild clinical signs that were manageable with medical treatment; and poor if clinical signs were unmanageable with medical treatment. A dog was diagnosed with hernia recurrence if both clinical signs and perineal swelling were present at follow- up. An incisional infection was diagnosed if swelling or discharge from the incision was present and an aerobic culture of a swab of the surgical wound was positive for bacterial growth.
Results
Signalment and Clinical Findings
Fifty-nine dogs with a total of 69 perineal hernias met the criteria for inclusion in the study. Table 1 lists the affected breeds. Age at presentation ranged from 4 to 15 years (mean 9.4 years, median 9.0 years). Fifty-seven dogs were male (20 castrated), and two were female. Two dogs were castrated <6 months prior to presentation for prostatomegaly. One female dog was spayed, and the other was intact but had an enlarged clitoris and a history of male sexual behavior. The latter dog was diagnosed as a female pseudohermaphrodite based on histopathology of ovariohysterectomized tissue.
Clinical signs are listed in Table 2. Thirty-two dogs had two or more signs. The duration of clinical signs ranged from 0.5 to 104 weeks (mean 17.1 weeks, median 8.0 weeks). Twenty-four dogs had right-sided perineal hernias, 14 had left-sided, and 21 had bilateral hernias. The opposite side had a palpable weakening of the pelvic diaphragm in 11 dogs that had unilateral hernias. The bladder was present in the perineal area in five dogs, and two dogs had a palpable mass in the perineal region on rectal examination. Histopathology of the masses following excisional biopsy at the time of the perineal hernia repair revealed granulomatous cellulitis in one dog and a perianal gland adenoma in the other.
Surgical Technique
All dogs were premedicated with hydromorphoneb (0.2 mg/kg intramuscularly [IM]) and acepromazinec (0.02 mg/kg IM). Anesthesia was induced with propofold (4 mg/kg intravenously [IV]) and maintained with isoflurane.e All dogs received an epidural injection of morphinef (0.1 mg/kg) and 0.5% bupivicaineg (0.5 mg/kg). Perioperative cefazolinh (22 mg/kg IV) was administered to all dogs at induction and every 90 minutes during the surgical procedure.
A prescrotal, closed castration was performed on all intact male dogs. The five dogs that had bladder entrapment also had a ductus deferens pexy performed before perineal herniorrhaphy during the same anesthesia period.19 An internal obturator transposition was then performed on all dogs.10 At surgery, the jejunum was present in the perineal hernia in three dogs and in the prostate in one. All 69 perineal hernias contained pelvic fat and serous fluid.
Following the internal obturator transposition, a single layer of polypropylene mesha was cut to a size that over-lapped the transposed internal obturator muscle by approximately 0.25 cm on all sides. Several simple interrupted sutures of polypropylenei were used to attach the mesh to the anal sphincter medially, the transposed internal obturator dorsally and ventrally, and the levator ani laterally [see Figure]. The subcutaneous tissues were closed over the mesh using absorbable suture (e.g., polydioxanonej or poliglecaprone 25k). Skin sutures were placed in all dogs. If the perineal hernia was bilateral, the second side was repaired within 2 to 6 weeks.
Postoperative Care
All dogs received hydromorphone (0.2 mg/kg IV q 6 hours) for the first 24 hours postoperatively. Carprofenl (2.2 mg/kg per os [PO] q 12 hours) was administered after surgery for 10 days. The dogs were administered ampicillinm (22 mg/kg IV q 12 hours) while in the hospital and were sent home on amoxicillinn (22 mg/kg PO q 12 hours) for 10 days. At discharge, all owners were advised to feed a low-residue dieto or fiber supplementp for the first 14 days. If the surgical wound was contaminated with feces postoperatively, the perineal area was cleaned with a cloth and warm water. Owners were encouraged to continue to clean the perineal area at home if feces accumulated around the incision. Skin sutures were removed 14 days postoperatively.
Immediate Complications
Immediate postoperative complications occurred after six surgeries for an overall complication rate of 8.7%. Three dogs had minor perineal swelling for 3 to 14 days that resolved with warm compresses. One dog had continued tenesmus that resolved on a low-residue diet within 10 days.
Two dogs developed incisional infections. One dog developed an Escherichia (E.) coli infection 3 days postoperatively that required the incision to be surgically opened and lavaged. The dog was then given enrofloxacinq (10 mg/kg PO q 24 hours) and amoxicillin (22 mg/kg PO q 12 hours) for 14 days. The wound was completely healed by 11 days after surgery. The second dog was reoperated 5 days postoperatively (i.e., lavage and debridement of the surgical wound) after a purulent discharge developed at the incision. At surgery, a devitalized and perforated segment of jejunum had herniated through a rent in the internal obturator transposition, and it was trapped under the ventral border of the polypropylene mesh. An intestinal resection and anastamosis, as well as colopexy were performed. The perineal area was debrided, the polypropylene mesh was removed, and the pelvic muscles were reapposed with polypropylene sutures. The dog was also placed on enrofloxacin (10 mg/kg PO q 24 hours) and amoxicillin (22 mg/kg q 12 hours) for 14 days. The perineal incision was partially closed to allow drainage, and by 14 days after surgery, the remainder of the perineal incision was healing by second intention. Culture of the purulent discharge was positive for E. coli. The dog was euthanized 3 months postoperatively while in septic shock, and it was unknown whether the acute condition was related to the dog’s surgical complications. The postoperative infection rate was 5.6% for the dogs with available follow-up.
Long-term Follow-up
Follow-up of >60 days was available for 36 dogs, with a total of 40 perineal herniorrhaphies. Time to follow-up ranged from 3 to 54 months (mean 29.4 months, median 26.0 months). Twenty-two dogs had excellent outcomes, and seven had good outcomes. Six of 14 dogs with bilateral perineal hernias that had only one side repaired had excellent outcomes, and four had good outcomes. All dogs with good outcomes were on continuous medical treatment consisting of a low-residue diet, a fiber supplement, or a stool softener.r
Seven dogs had poor outcomes [Table 3]. One dog with bilateral hernias, but with only one side repaired, had continued bouts of tenesmus that were unmanageable with medical therapy for 28 months postoperatively. Another dog died 2 weeks after surgery from congestive heart failure, which was thought to be precipitated by intraoperative IV fluid overload. Although this complication was unrelated to the perineal hernia repair, the case was classified as a poor surgical outcome.
Five of the poor outcomes were associated with hernia recurrence, with the time to recurrence ranging from 3 to 24 months. None of the dogs underwent a second herniorrhaphy. One dog with a recurrence was euthanized for unrelated reasons, and one was on a daily fiber supplement and stool softener. One dog with tenesmus and perineal swelling was diagnosed with a recurrence of the hernia via rectal palpation 24 months postoperatively. Upon rectal examination, a rent was palpable between the rectal wall and the polypropylene mesh. The owner declined treatment, and upon follow-up 32 months after surgery, the dog still had occasional tenesmus. The recurrence rate for all 36 dogs with available follow-up was 12.5%.
Discussion
Polypropylene mesh has been used in the closure of thoracic and abdominal walls, the skull, and perineal, diaphragmatic, and tracheal defects in dogs; yet few studies have evaluated the long-term complications associated with implantation of the mesh.14 A study by Bowman et al. of 16 dogs and three cats with polypropylene mesh implanted to repair large chest or abdominal resections and one perineal hernia reported an immediate postoperative complication rate of 50%, with the most severe complications being an incisional infection and seroma formation.14 Many of the immediate complications in the present study were also minor and resolved with warm compresses or a low-residue diet.
The most frequent postoperative complications in dogs after perineal hernia repair techniques not involving the use of mesh were wound breakdown and infection, with occurrences ranging from 6.4% to 45%.3,7–8,10 Use of synthetic implants can further increase the risk of infection by increasing the number of bacteria in the surgical incision necessary to produce an infection.20 The greater surface area of multifilament synthetic mesh has been shown to promote the persistence of bacteria in the implant bed.16 The present study had an infection rate of 5.6% with use of polypropylene mesh, which was consistent with previously published infection rates without the use of mesh.3,7–8,10 Polypropylene mesh is a network of nonabsorbable, polypropylene monofilaments; these are thought to prevent bacteria from being trapped within the fibers, making this mesh less likely than other synthetic meshes to become infected.14,20–22 Studies in humans have shown that synthetic mesh can be used in clean-contaminated and contaminated operative fields with minimal wound-related morbidity and mortality.23 However, a number of long-term studies in humans have reported fistula formation and mesh extrusion months to years later, with all types of mesh.17 Only two dogs in the study reported here developed incisional infections, which occurred within the first 7 days postoperatively. The most severe complication in the present study occurred in the dog with the incisional infection that resulted in wound dehiscence and a perforated jejunum. A necropsy was not performed at the time of death; therefore, it was unknown whether the sepsis occurred from the dog’s inability to completely eliminate the postoperative peritonitis, a failure of the intestinal resection and anastamosis, or an unrelated disease process. One previous study of 17 dogs with perineal hernias repaired with polypropylene mesh reported no incisional infections at follow-up 4 years postoperatively.11
During the current study, prophylactic antibiotics were used and cleaning of the perineal region with warm water was routinely performed, owing to the high incidence of fecal contamination in the perineal area; however, no studies exist that suggest such measures decrease the incidence of infection. In fact, studies have shown that postoperative antibiotics are not needed in clean-contaminated procedures if proper aseptic technique is used and risk factors for wound infection are minimized.1,25 One study actually reported an increase in postoperative infection rates in animals that underwent clean surgical procedures and received postoperative antibiotics compared to those that received no antibiotics.25 Cleaning around surgical wounds may also disrupt wound healing. Because no studies validate the efficacy of either treatment, recommendations cannot be made regarding their routine use.
Recurrence is the most common long-term complication of perineal hernia repair.5 Two important factors that contribute to recurrence are the status of the perineal tissues and degree of atrophy of the muscles of the pelvic diaphragm at the time of repair.5 Previous studies have also reported that recurrence was higher when either standard herniorrhaphy or internal obturator transposition was performed by less experienced surgeons; however, when follow-up was >12 months, it was suggested that recurrence was more associated with continued deterioration of the perineal tissue than with surgeon inexperience.3,7 One study demonstrated that recurrence was lower when surgical gut rather than steel wire, nylon, or silk suture was used during standard herniorrhaphy, possibly from the inflammation and scar tissue formation that occurred as the surgical gut was absorbed.3
Polypropylene mesh reinforces the pelvic diaphragm by stimulating fibrous tissue development over the internal obturator transposition. The design of the polypropylene knit creates uneven pore sizes ranging from 200 to 800 μm.21 It has been shown experimentally that pore sizes >100 μm are required for ingrowth of vascularized connective tissue.24 The pore sizes of polypropylene are large compared to other synthetic meshes, and the mesh is rapidly infiltrated by capillaries and fibroblasts.24 Agranulation bed around the mesh is expected to form in 4 to 6 weeks.21,25 Histopathology performed up to 6 months after implantation of polypropylene in experimental animals showed the mesh was uniformly infiltrated by fibrous tissue with minimal foreign body reaction.26 In the study reported here, the recurrence rate of 12.5% was consistent with previously published reports of recurrence rates between 2.4% and 19% with internal obturator transposition alone and with follow-up times >12 months.6–9
A larger number of cases available for follow-up may have made the recurrence rate more significant. The additional cost of polypropylene mesh may also be a limiting factor to its routine use. Further studies are warranted to determine the benefits of mesh, particularly when atrophy of the muscles of the pelvic diaphragm exists.
Hernia recurrence in this study was based on owner observation of perineal swelling and the presence of clinical signs such as tenesmus. Recurrence was difficult to accurately determine if no associated clinical signs were noted after owners observed perineal swelling. A previous study found that failure of reformation of the ventral portion of the pelvic diaphragm during surgery did not necessarily result in clinical signs.7 In the study reported here, surgery was declined in the dogs diagnosed with hernia recurrence, because the dogs improved on medical therapy. Thirteen of the 22 dogs diagnosed with bilateral perineal hernias had the more severe side repaired at the time of diagnosis, but they did not return for the second staged repair. Six of the 13 dogs had excellent results, and three had occasional tenesmus that resolved on a low-residue diet. These findings suggested that many dogs with perineal hernias may have subclinical or mild clinical signs responsive to medical treatment. More studies are warranted to evaluate the overall efficacy of medical management in dogs with perineal hernias of varying severity.
Conclusion
Fifty-nine dogs (69 hernias) that underwent an internal obturator transposition with polypropylene mesh reinforcement had an overall success rate of 80.5%. Complications occurred after surgery in 13 dogs. All complications except hernia recurrence occurred within 14 postoperative days. The most severe complications were an incisional infection and resultant wound dehiscence. The low incidence of postoperative complications and hernia recurrence suggests that polypropylene mesh can be used in addition to internal obturator transposition. Further controlled studies are warranted to determine the benefits of the use of polypropylene mesh compared to internal obturator transposition alone.
Marlex mesh; Bard Pharmaceuticals, Philadelphia, PA 19104
Dilaudid; Knoll Laboratories, Mount Olive, NJ 07828
PromAce; Fort Dodge Animal Health, Fort Dodge, IA 50501
Rapinovet; Schering Plough Animal Health, Union, NJ 07083
Isoflo; Abbott Laboratories, Abbott Park, IL 60064
Duramorph; Elkins-Sinn Inc., Cherry Hill, NJ 08003
Marcaine; Abbott Laboratories, Abbott Park, IL 60064
Cefazolin; Marsam Pharmaceuticals, Cherry Hill, NJ 08003
Prolene; Ethicon Inc., Somerville, NJ 08876
PDS II; Ethicon Inc., Somerville, NJ 08876
Monocryl; Ethicon Inc., Somerville, NJ 08876
Rimadyl; Pfizer Animal Health, Exton, PA 19341
Ampicillin Sodium; Marsam Pharmaceuticals, Cherry Hill, NJ 08003
Amoxi-Tabs; Smith-Kline Beecham, Research Triangle Park, NC 27709
Low-Residue Puppy Dry Formula; Iams, Dayton, OH 45414
Metamucil powder; Procter and Gamble, Cincinnati, OH 45202
Baytril; Bayer Corporation, Shawnee Mission, KS 66203
Cephulac; Merrell Dow Pharmaceuticals, Cincinnati, OH 45202
Citation: Journal of the American Animal Hospital Association 43, 3; 10.5326/0430136
Intraoperative photograph of an 8-year-old, male German shepherd dog with a right-sided perineal hernia. The dog is in sternal recumbency. The anus is not visible but is on the left side of the image. The polypropylene mesh is placed over the transposed internal obturator muscle and sutured in place with polypropylene suture.
