Retrospective evaluation on the outcome of perineal herniorrhaphy augmented with porcine small intestinal submucosa in dogs and cats

Abstract

The purpose of this study was to evaluate post-operative outcome in dogs and cats undergoing perineal herniorrhaphy using porcine small intestinal submucosa (PSIS) alone and with internal obturator muscle transposition augmented with PSIS (IOMT + PSIS). Medical records were retrospectively reviewed and information collected on signalment, pre-operative signs, operative details, and hospitalization. Data on post-operative outcome were obtained from medical records and survey. Eleven dogs and 3 cats had 18 perineal hernias repaired with IOMT + PSIS and 3 using PSIS alone. Surgical site infection developed following IOMT + PSIS in 1/21 hernias (5.6%). Short- and long-term postoperative complications occurred in 9/14 animals and 3/14 animals, respectively. Among the 21 perineal hernias, 3 recurred, 2 of which were repaired with IOMT + PSIS and 1 with PSIS alone. Use of PSIS alone or augmenting IOMT was acceptable for perineal herniorrhaphy and should be considered by surgeons if there are concerns about internal obturator muscle integrity.

Introduction

Perineal hernia occurs when muscular and connective tissue components of the pelvic diaphragm weaken and separate, leading to caudal displacement of intra-pelvic and abdominal structures into the subcutaneous perineal region (1–5). Prevalence in dogs has been reported to range from 0.1% to 0.4%, with limited data available on cats (2,6–8). The majority of dogs with perineal hernias are intact males between 7 and 9 y of age (4,9–11). Several factors are suspected to cause or contribute to this condition, including gonadal hormonal influences, breed conformation, neurogenic atrophy, and tenesmus from constipation, rectal disease, or prostatomegaly (2,4,6,10,11).

Internal obturator muscle transposition (IOMT) has been considered the standard of care surgical treatment for perineal herniorrhaphy, although the efficacy of this technique has varied (12–14). Recurrence rates up to 36% have been reported for IOMT for the treatment of perineal herniorrhaphy in dogs (4,14). The internal obturator muscle (IOM) is a component of the pelvic diaphragm and may undergo atrophy as part of the disease process resulting in a perineal hernia (12,15). Atrophy of the IOM could pose a challenge in the IOMT technique, which may contribute to increased failure and complication rates (3,12,14,15). To bolster repair, synthetic implants such as polypropylene mesh (PPM), peripheral autogenous grafts (fascia lata), and biomaterials have been used in an attempt to reduce herniorrhaphy failure from a compromised IOM (1,10,13,14).

Porcine small-intestinal submucosa (PSIS) is an extracellular matrix biomaterial that has been used for repair and reconstruction of the abdominal body wall, diaphragm, urinary bladder, Achilles tendon, and dura mater (16–19). Porcine small-intestinal submucosa is composed of a lattice of predominantly type I collagen fibers containing glycoproteins, proteoglycans, glycosaminoglycans, cytokines, and growth factors (20). On implantation, PSIS promotes host cell ingrowth and constructive remodelling, and results in formation of functionally and histologically similar site-specific tissue (1,20,21). Growth factors within the matrix, namely transforming growth factor-beta, vascular endothelial growth factor, and fibroblast growth factor, may facilitate this process by mediating cell migration, proliferation, differentiation, and neovascularization (20). Acellularity lends the graft immunological protection and allows host accommodation, an advantage over synthetic implants (21). While less cost-effective than autogenous grafts, use of commercial PSIS implants holds more consistent graft properties, decreases donor morbidity, and may prove to be less technically challenging (22). When compared to an autogenous tunica vaginalis graft, which has been previously proposed to be obtained following castration at time of perineal herniorrhaphy, PSIS avoids the potential for spread of undiagnosed malignancy at time of surgery and can be used in signalments other than intact males (9).

Ease of handling, absorbability, resistance to infection, and success of small intestinal submucosa (SIS) in previous reports suggest it as a promising biomaterial for use in perineal herniorrhaphy (1). Biomechanical testing of pelvic diaphragms in canine models of perineal herniorrhaphy demonstrated no significant difference in post-operative strength, elasticity, and stiffness of PSIS compared to transposed normal IOM (1). One case study described use of an SIS allograft for perineal herniorrhaphy in 2 dogs with no complications (2). The purpose of our study was to further characterize the short- and long-term outcomes of dogs undergoing perineal herniorrhaphy with PSIS alone and in combination with IOMT (IOMT + PSIS).

Materials and methods

Case selection

Medical records of all canine and feline patients that underwent perineal herniorrhaphy between January 1, 2012 and December 31, 2017 at the Ontario Veterinary College Health Sciences Centre (OVCHSC) were retrospectively reviewed. Patients were selected for the study if they had perineal herniorrhaphy with PSIS alone or IOMT + PSIS in at least 1 perineal hernia. Dogs undergoing perineal herniorrhaphy using IOMT alone or any other surgical methods were excluded. Dogs with repair of the contralateral hernia at a separate date were included, even if the hernia was repaired with surgical techniques other than PSIS alone or IOMT + PSIS. Patients with cystopexy, colopexy, or castration staged or in conjunction with perineal herniorrhaphy were also included. Animals were excluded from the study if they had perineal herniorrhaphy performed without the use of PSIS.

Data collection

Data collected included age, sex, breed, body weight (BW), body condition score (BCS), pre-operative clinical signs, physical examination findings, and comorbidities at time of presentation. Data on anesthetic protocol, surgical technique, adjuvant surgical procedures, intra-operative findings, duration of surgery, anesthesia time, and hospitalization time were also collected. Bilateral perineal herniorrhaphy was defined as repair of 2 contralateral hernias under the same anesthetic episode. Staged bilateral perineal herniorrhaphy was defined as performance of unilateral perineal herniorrhaphy at an alternate date following repair of the contralateral hernia. Cystopexy or colopexy were also considered staged if they were performed on a separate date than the herniorrhaphy. All cystopexies and colopexies were performed before perineal herniorrhaphy. Duration of operation was defined as time from first skin incision to end of skin closure. Anesthesia time was defined as time from inhalant initiation to extubation. Hospitalization time was defined as time spent in hospital from end of surgery to discharge (hours).

All patients received cefazolin (Teva Canada, Toronto, Ontario), 16.7 to 25.0 mg/kg body weight (BW), IV, or cefoxitin (Teva Canada), 14.3 to 23.9 mg/kg BW, IV, 15 min before skin incision and every 90 min until the end of skin closure.

Perineal herniorrhaphy

The patient was positioned in sternal recumbency with the tail retracted. A purse-string suture pattern was placed in the anus following packing with surgical gauze to faciliate palpation of the rectum. The surgical site was aseptically prepared. A curvilinear incision was made beginning lateral to the anus extending ventrally towards the ischium. The subcutaneous tissues were dissected and hernial sac contents were reduced into the abdomen. For perineal herniorrhaphy with PSIS alone, the procedure was performed as previously described by Stoll et al (1) with modifications depending on intraoperative findings (Figure 1). A sheet of commercially available PSIS (BioSyst; Smiths Medical, Markham, Ontario and Vet BioSIS, Cook Veterinary Products, Bloomington, Indiana, USA) was folded 3 to 4× into the shape of the perineal hernia. Sutures were placed between the PSIS and the levator ani and coccygeal muscles laterally, the IOM and ischial periosteum ventrally, and the external anal sphincter medially in a simple interrupted pattern with polydioxanone suture (PDS; Ethicon, Markham, Ontario). In perineal herniorrhaphy with IOMT + PSIS, IOMT was performed as previously described by Hardie et al (12) with modifications depending on muscle atrophy (Figure 1). A sheet of commercially available PSIS (BioSyst; Smiths Medical, and Vet BioSIS, Cook Veterinary Products) was applied over the IOMT flap and sutured to the coccygeal muscle laterally, IOM ventrally, and external anal sphincter medially in a simple interrupted pattern with PDS, Glycomer 631 (Biosyn; Medtronic, Saint-Laurent, Quebec), or polyglytone 6211 (Caprosyn; Medtronic) suture (Figure 2). The sacrotuberous ligament was incorporated or not incorporated based on surgeon preference. The wound was lavaged with saline. Subcutaneous tissue was closed in a simple continuous or interrupted pattern. A cruciate pattern using polypropylene suture (Prolene; Ethicon, and Surgipro, Medtronic) or intradermal pattern using poliglecaprone suture (Monocryl; Ethicon) was used to appose skin edges. The decision to use PSIS to augment IOMT or to use PSIS alone was made by the attending surgeon based on subjective evaluation of IOM integrity.

Figure 1.

Diagrammatic representation of perineal herniorrhaphy with porcine small intestinal submucosa (PSIS) alone and in combination with internal obturator muscle transposition (IOMT + PSIS). a — external anal sphincter muscle; b — levator ani muscle; c — coccygeus muscle; d — internal obturator muscle; e — porcine small intestinal submucosa.

Figure 2.

Intra-operative image of perineal herniorrhaphy using internal obturator muscle transposition augmented with porcine small intestinal submucosa.

Open cystopexy and colopexy

Patients were positioned in dorsal recumbency and the surgical site was aseptically prepared. A ventral midline incision was made from xyphoid to pubis. If the urinary bladder was retroflexed, cystocentesis was performed as necessary and the bladder was reduced to a normal intra-abdominal position. Serosa on the ventral aspect of the bladder was scarified with the blunt end of a scalpel blade. A partial thickness incision was made in the transversus abdominis muscle of the right abdominal wall approximately halfway between the linea alba and sublumbar musculature. Seromuscular and submucosal layers of the bladder were sutured to the abdominal wall incision in 2 rows with a simple continuous pattern. For the colopexy, colonic serosa was scarified as with the cystopexy. A partial thickness incision was made in the musculature of the left lateral abdominal wall. The colonic serosal and muscularis layers were sutured to the abdominal wall incision in a simple continuous pattern using PDS suture.

Orchiectomy

All intact patients were castrated either at the time of colopexy and cystopexy, or at the time of perineal herniorrhaphy. Canine orchiectomy was performed using an open pre-scrotal approach (23). Inguinal cryptorchid orchiectomy was performed through displacement of the testicle into the pre-scrotal region and proceeding as with the open pre-scrotal approach.

Postoperative care

Patients were monitored after surgery in the Intensive Care Unit, Intermediate Care Unit, or Wards of the OVCHSC. They were treated with injectable and/or oral analgesics such as hydromorphone (Sandoz Canada, Mississauga, Ontario), 0.025 to 0.05 mg/kg BW, IV or SQ, q4 to 6h, buprenorphine (Chiron Compounding Pharmacy, Guelph, Ontario), 0.005 to 0.02 mg/kg BW, IV, q6h, a continuous rate infusion (CRI) of fentanyl (Sandoz Canada), 2 to 6 μg/kg BW per hour, meloxicam (Metacam; Boehringer Ingelheim, Burlington, Ontario), 0.1 mg/kg BW, IV/PO, q24h, gabapentin (Auro-gabapentin; Auro, Woodbridge, Ontario), 10 mg/kg BW, PO, q8h, tramadol (Chiron), 2.8 to 5 mg/kg BW, PO, q8h. Patients were also treated with antibiotics including cefoxitin (Teva Canada), 22 to 30 mg/kg BW, IV, q8h, and amoxicillin-clavulanic acid (Clavamox; Zoetis, Kirkland, Quebec), 13.8 to 17.9 mg/kg BW, PO, q12h. Lactulose (Pharmascience, Montreal, Quebec), 0.13 to 0.25 mg/kg BW, PO, q6–12h, maropitant (Cerenia; Zoetis), 1 mg/kg BW, IV, q24h, famotidine (Pepcid AC; McNeil Consumer Healthcare, Markham, Ontario), 0.5 mg/kg BW, IV, q12–24h, metronidazole (AA Pharma, Vaughan, Ontario), 10 mg/kg BW, PO, q12h, metoclopramide (Sandoz; Boucherville, Quebec), 2 mg/kg BW/d, IV CRI, prednisone (Apo-prednisone; Apotex, Toronto, Ontario), 0.5 mg/kg BW, PO, q48h, and phenylpropanolamine (Propalin; Vétoquinol, Lavaltrie, Quebec), 1 mg/kg BW, PO, q12h, were administered on a patient-specific basis.

All patients were discharged with amoxicillin-clavulanic acid [(Clavamox; Zoetis) or (Clavaseptin; Vétoquinol)], 10.4 to 19.5 mg/kg BW, PO, q12h for 7 to 14 d, and analgesic medications [meloxicam, robenacoxib (Onsior; Elanco, Guelph, Ontario), or tramadol]. At discharge, owners received instructions for incision care, exercise restriction, use of an Elizabethan collar, and monitoring for complications. Some patients received instructions to switch to a high fiber or low residue diet, and ice the incision site. A recheck appointment was recommended at 10 to 14 d after surgery.

Outcome

Post-operative complications, as defined by Dindo et al (24), were deemed “any deviation from the ideal post-operative course” which excluded failure to cure events and inherent surgical sequelae.

Complications were graded according to the refined Accordion classification system by Kazaryam et al (25). Data on post-operative complications were collected from medical records and by telephone and e-mail survey of referring veterinarians. Telephone survey was administered in the form of a questionnaire (Table 1) on presence of common post-operative complications described in previous studies (4,10,12,14,26). If complications occurred, the dates at which complications were noted was documented and classified as short-term (< 14 d after perineal herniorrhaphy) and long term (> 14 d after perineal herniorrhaphy). Date of last follow-up and whether the animal was currently receiving medications were obtained. Follow-up time was defined as time from surgery to last examination by a veterinarian or time of owner survey. If the patient was deceased, information on cause of death was obtained. Recurrence was diagnosed based on rectal palpation performed at the referring veterinary hospital or OVCHSC. Complications of cystopexy, colopexy, or castration were not considered related to herniorrhaphy. The animal was considered lost to follow-up if the clinic had not seen the patient following surgery and the owner could not be contacted following 4 telephone calls.

Table 1.

Telephone questionnaire for referring veterinarians for post-operative outcome following perineal herniorrhaphy.

Statistical analysis

Surgical outcome was evaluated based on descriptive analysis. The post-operative complication and recurrence rates were determined with Kaplan-Meier analysis. Risk factors for development of post-operative complications and recurrence were evaluated with a logistical regression test. Values with P < 0.05 were considered significant.

Results

Pre-operative data

Fifteen animals, 12 dogs and 3 cats, that underwent perineal herniorrhaphy at the OVCHSC, performed between January 1, 2012 and December 31, 2017, met the inclusion criteria (Table 2). One dog was excluded due to lack of follow-up. Distribution of breeds was mixed breed (n = 4), papillon (n = 3), shih tzu (n = 1), Yorkshire terrier (n = 1), Havanese (n = 1), and greyhound (n = 1) for dogs and domestic shorthair (n = 2) and domestic longhair (n = 1) for cats. All 11 dogs were male, and 10 were intact on presentation, including a unilateral inguinal cryptorchid. Of the cats, 2 were spayed females and 1 was a castrated male. Median BW at time of surgery was 6.2 kg (range: 3.2 to 34.3 kg) for dogs and 5.3 kg (range: 3.7 to 6 kg) for cats. Body condition score was available for 9 patients. Mean BCS was 3.5 (range: 3 to 5) for animals scored on a 9-point scale and 3 (range: 2 to 4) for patients scored on a 5-point scale. Median age was 9.9 y (range: 5.1 to 12.0 y) for dogs and 9.0 y (range: 5.2 to 11 y) for cats.

Table 2.

Signalment, procedure, and intra-operative findings for dogs and cats with perineal herniorrhaphy using porcine small intestinal submucosa.

Patient number	Breed	Sexa	Agea (y)	Weight (kg)	Hernia sideb	Procedure	Adjunctive procedure	Staged adjunct	Herniated structures
1	Shih tzu	MI	11	6.7	Bilateral	PSIS alone	Castr	No	NA
2	Domestic shorthair	MC	12	6	Right	IOMT + PSIS	Cysto, Colo, Castr	Yes	NA
3	Yorkshire terrier	MC	6	5.4	Right	IOMT + PSIS	Cysto, Colo	No	Omental fat
4	Havanese	MI	9	6.7	Right	IOMT + PSIS	Castr	No	Omental fat
5	Papillon	MI	12	4.9	Bilateral	IOMT + PSIS	Cysto, Colo, Castr	Yes	NA
6	Domestic longhair	FS	5	3.7	Left	IOMT + PSIS	Cysto, Colo	Yes	Omental fat
7	Domestic shorthair	FS	9	5.3	Bilateral	IOMT + PSIS	NA	NA	Omental fat
8	Papillon	MI	10	4.3	Left	IOMT + PSIS	Cryptorchid Castr	No	Omental fat
9	Mixed breed	MI	10	5	Bilateral	IOMT + PSIS	Cysto, Colo, Castr	Yes	Omental fat
10	Mixed breed	MI	10	23	Bilateral	IOMT + PSIS	Castr	No	Bladder, omental fat
11	Mixed breed	MI	9	6.2	Bilateral	IOMT + PSIS	Castr	No	Omental fat
12	Papillon	MI	11	3.2	Right	PSIS alone	Cysto, Colo, Castr	Yes	Omental fat
13	Australian shepherd	MI	6	34.3	Bilateral	IOMT + PSIS	Cysto, Colo, Castr	No	Necrotic calcified fat
14	Greyhound	MC	5	32	Right	IOMT + PSIS	Cysto, Colo	No	Omental fat

^aAt time of presentation.

^bOnly hernias with PSIS alone or IOMT + PSIS perineal herniorrhaphy.

MI — Male intact; FS — Female spayed; MC — Male castrated; IOMT — Internal obturator muscle transposition; PSIS — Porcine small intestinal submucosa; Cysto — Cystopexy; Castr — Castration; NA — Not applicable.

Pre-operative clinical signs were as follows: perineal swelling (n = 9), vomiting (n = 6), tenesmus (n = 8), constipation (n = 5), inappetence (n = 5), soft stool or diarrhea (n = 4), altered mentation or lethargy (n = 2), dyschezia (n = 5), hematochezia (n = 3), stranguria (n = 2), oliguria to anuria (n = 2), firm stool (n = 1), pollakiuria (n = 1), urinary incontinence (n = 1), weight loss (n = 1), abnormal ambulation (n = 1), and hemorrhagic rectal discharge (n = 1). Hernias were diagnosed by rectal examination in 10 patients. The remaining 4 cases were diagnosed with a combination of ultrasound (n = 4), cystourethrogram (n = 1), and radiography (n = 3). Prostatic enlargement was present in 3 dogs. One of the cats had cutaneous asthenia at time of diagnosis.

The 11 dogs meeting the selection criteria had a total of 17 perineal hernias and had 14 repaired with IOMT + PSIS and 3 with PSIS alone. The 3 cats had 4 perineal hernias all repaired with IOMT + PSIS. Six dogs and 1 cat had bilateral perineal herniorrhaphy. Five dogs and 2 cats had unilateral perineal herniorrhaphy. Of these, 2 dogs had staged repair of bilateral hernias of which 1 side was repaired with IOMT alone. One dog had bilateral hernias, in which 1 side was repaired with PSIS alone while the other did not undergo perineal herniorrhaphy. One cat had unilateral IOMT performed and then unilateral PSIS alone on the contralateral side at a later date. In this case the IOMT repaired hernia was found to have recurred at the time of presentation for perineal herniorrhaphy by PSIS alone but was not subsequently repaired. Herniated structures included omental fat (n = 12), urinary bladder (n = 2), and colon (n = 1). Median surgical time for unilateral IOMT + PSIS was 125 min (range: 75 to 140 min) for dogs and 72.5 min (range: 60 to 85 min) for cats. Surgical time for bilateral IOMT + PSIS was 175 min (range: 90 to 190 min) for dogs and 105 min for the cat. Surgical time for unilateral PSIS alone was 70 min and bilateral PSIS alone was 210 min.

Two cats and 6 dogs had a colopexy and cystopexy performed. One cat and 3 dogs had staged colopexy and cystopexy before perineal herniorrhaphy. In these patients, median time between laparotomy and time of perineal herniorrhaphy was 31 d (range: 17 to 1424 d). Of the intact dogs, 6 were castrated at the time of perineal herniorrhaphy, including the unilateral cryptorchid. Three dogs were castrated concurrently with staged cystopexy and colopexy.

All procedures were performed by a Board-certified surgeon or by surgical residents under direct supervision of a Board-certified surgeon.

Post-operative data

The median hospitalization time was 46.7 h (range: 23.9 to 191.2 h). Fourteen of 15 (93%) animals were available for follow-up. Owners were surveyed in 2 cases in which the patients had not been examined since the time of surgery or re-check appointment. Post-operative outcome was analyzed for 3 cats and 11 dogs (Table 3) with 21 repaired perineal hernias (3 PSIS alone and 18 IOMT + PSIS). Median post-operative follow-up time was 621 d (range: 121 to 2090 d). Five patients were deceased at the time of study. Causes of death were all unrelated to the perineal herniorrhaphy. Median time of euthanasia from date of perineal herniorrhaphy was 971 d (range: 213 to 1724 d).

Table 3.

Complications for dogs and cats with perineal herniorrhaphy (PH) using porcine small intestinal submucosa.

Patient number	Follow-up (d)	Complication	Complication grade	Recurrence	Other
1	912	ST: diarrhea	2	No
2	575	ST: rectal prolapse, tenesmus LT: fecal impaction, tenesmus, hematochezia	2	No	IOMT of left perineal herniorrhaphy 564 d pre-IOMT + PSIS left perineal herniorrhaphy recurrence at time of right herniorrhaphy
3	2090	ST: tenesmus	0	No	IOMT of left perineal herniorrhaphy 1433 d post-IOMT + PSIS left perineal herniorrhaphy recurrence 2127 d post-IOMT + PSIS
4	1797	ST: incisional infection	2	No	Infected wound cultured Pseudomonas sp.
5	1132	None	NA	No
6	651	None	NA	No	Cutaneous asthenia, suspected dehiscence colopexy site
7	601	None	NA	No
8	681	ST: tenesmus	0	No
9	174	ST: tenesmus LT: dyschezia, tenesmus, fecal impaction	2	Yes
10	182	ST: fecal impaction, tenesmus	2	No
11	121	ST: tenesmus, dyschezia LT: dyschezia, tenesmus	2	No
12	213	ST: diarrhea, tenesmus	2	Yes	Unrepaired left perineal herniorrhaphy
13	640	None	0	No
14	584	ST: tenesmus	2	No	IOMT of left perineal herniorrhaphy 18 d post-IOMT + PSIS

ST — Short-term; LT — Long-term; NA — Not applicable; IOMT — Internal obturator muscle transposition; PSIS — Porcine small intestinal submucosa.

One patient out of 14 (7%) had a grade 1 complication, and 8 (57%) had grade 2 complications. Eight dogs and 1 cat (64%) with a total of 13 hernias had short-term post-operative complications within 7 d of surgery. Median time of onset of clinical signs was 2 d (range: 1 to 4 d). Short-term complications included tenesmus (n = 8), diarrhea (n = 2), and fecal impaction (n = 1). In 8 animals, short-term post-operative complications resolved within 26 d with medical management. Surgical site infection of 1 perineal hernia (5.6%) occurred in 1 dog. Pseudomonas sp. was cultured and the patient was treated with amoxicillin-clavulanic acid (Clavamox; Zoetis), 18.7 mg/kg BW, PO, q12h for 5 d, and enrofloxacin (Baytril; Bayer, Mississauga, Ontario), 11.2 mg/kg BW, PO, q24h for 14 d. Thirteen days following initiation of antimicrobial treatment, the incision healed and the infection resolved.

Two dogs and 1 cat with 5 IOMT + PSIS hernias had long-term post-operative complications. Clinical signs included tenesmus (n = 3), fecal impaction (n = 2), dyschezia (n = 2), and hematochezia (n = 1). Median time of long-term post-operative complication since hernia repair with IOMT + PSIS or PSIS alone was 161 d (range: 26 to 897 d). One of these dogs had bilateral recurrence of IOMT + PSIS perineal herniorrhaphy diagnosed 176 d post-operatively. The cat with long-term complications had an unrepaired hernia on the contralateral side to the repair. All animals with long-term post-operative complications had previously resolved short-term complications. These animals also all had cystopexy and colopexy performed. Cystopexy and colopexy, species, pre-operative tenesmus, unilateral or bilateral herniorrhaphy, bladder herniation, and rectal sacculation were not significantly associated with development of complications or recurrence (P > 0.05). At the time of follow-up, 6/14 patients received ongoing medical management.

Two dogs had recurrence of 3 perineal hernias with perineal herniorrhaphy using PSIS. One dog had recurrence of 2 IOMT + PSIS, diagnosed bilaterally, and 1 dog had recurrence of 1 PSIS alone repaired hernia. Median time to recurrence for individual perineal herniorrhaphys was 176 d (range: 117 to 176 d). In 2 other animals, recurrence occurred on the side of IOMT repair while the IOMT + PSIS repair remained intact. Surgical revision was not pursued for any failed hernia repairs. Reasons for not attempting surgical revision were increased anesthetic risk due to intracranial disease and owner’s concern for persistence of clinical signs following surgery from concurrent rectal sacculation. None of the cats had recurrence.

Discussion

Our report is the first to evaluate the efficacy of commercially available PSIS for augmentation of IOMT in perineal herniorrhaphy and contributes to current literature on its outcome when used alone in perineal herniorrhaphy (1,2). The canine population in our study was comparable to those in other perineal herniorrhaphy studies with the exception of having a lower median BW (4,6,10,12–14,26,27). The low body weight and BCS were representative of patients presented to the OVCHSC for perineal herniorrhaphy and may be related to frequently reported pre-operative vomiting, inappetence, and soft stool. This study shows that IOMT + PSIS and PSIS alone are acceptable methods for use in perineal herniorrhaphy in the dog and cat. Furthermore, surgeons should consider the use of IOMT + PSIS should they judge the IOM to be atrophied.

Previous reports of IOMT have described complication rates ranging from 12% to 53% (4,14,28). Most animals herein (9/14) had short-term complications. Many of these complications were Grade 2, which resolved with medical management and had good long-term clinical outcomes. Tenesmus was the most frequent short-term post-operative complication observed, as has been commonly reported for IOMT (4,14). Pain, local inflammation, and unrepaired rectal defects are possible contributing factors for development of post-operative tenesmus and are inherent to perineal herniorrhaphy (7,27). Thus, tenesmus and other transient clinical signs observed in the early post-operative period may be considered unavoidable sequelae to the procedure and not true complications (29).

Long-term outcome provides further valuable information in determining a benefit to the use of IOMT + PSIS and PSIS alone techniques (13). In our study, 3/14 animals had long-term complications, with tenesmus, fecal impaction, and dyschezia being the most common. This complication rate is consistent with previous reports on outcome following perineal herniorrhaphy in the literature. (4,6,10,12–14,26). Two animals with long-term complications either had a recurrence or a coexisting unrepaired hernia on the contralateral side. Retrospectively, we are unable to discern whether clinical signs developed first and promoted recurrence, or whether failure of repair, undiagnosed at the time, led to clinical signs. As a consequence, the present study may overestimate long-term complications occurring prior to recurrence.

Based on the results of our study, animals with bilateral perineal hernia may benefit from bilateral perineal herniorrhaphy under the same anesthetic episode as, from the authors’ experience, repair of the contralateral side is not always pursued later. One study identified evidence of contralateral hernias in all patients with unilateral disease presentation (30). These patients had a successful outcome following bilateral perineal herniorrhaphy (30). In our study, 1 animal with long-term complications had a coexisting unrepaired hernia and may have had improvement in clinical signs had bilateral perineal herniorrhaphy been performed.

Most complications in our study were classified as Grade 2 according to the Accordion classification scheme. Routinely, animals are maintained on a low-residue diet, stool softeners, analgesics, and antibiotics following perineal herniorrhaphy, independent of whether complications developed (29). As such, most patients with short-term complications had clinical signs resolve within 26 d of surgery with standard medical management. Persistent clinical signs were present in 1 patient (7.1%) and this was lower than in previous studies, in which there were observed persistent signs in 9% to 17% of patients (4,14). Fecal incontinence, a commonly noted complication in previous studies, was not observed, but may be a result of a small sample size (28).

In our study, 3/21 perineal hernias recurred following IOMT + PSIS or PSIS alone. These recurrence rates are comparable to IOMT recurrence rates reported in the literature, which ranged from 9.7% to 27.4% (4,13,14). A previous study identified post-operative tenesmus as a significant risk factor associated with recurrence and proposed it as a complication related to inadequate repair (13). This was not identified in our study although this may be due to type II error and it is certainly possible that forces exerted with tenesmus during early stages of healing affect the integrity of repair and have consequences on long-term outcome.

Perineal hernias occur rarely in cats and have been associated with conditions such as megacolon, chronic fibrosing colitis, pelvic canal stenosis, and apocrine gland anal sac adenocarcinoma (7,8). Only 1 of the 3 cats in our study had a pre-existing medical condition, namely cutaneous asthenia, which may have predisposed to perineal herniorrhaphy development. Cutaneous asthenia is a rare hereditary disorder of collagen dysplasia, characterized by thin, hyperextensible, and fragile cutaneous tissue prone to laceration (8,31). Several reports have described non-traumatic diaphragmatic, perineal, and inguinal hernias in cutaneous asthenia cases and patients with cutaneous asthenia may be prone to hernia formation (8,32). Atraumatic tissue handling is crucial in preventing inadvertent tearing (32). While delayed wound healing, dehiscence, and scarring are noted in human Ehlers-Danlos syndrome (EDS), several reports have described unremarkable primary intention wound healing in cats with cutaneous asthenia (8,32). A previous report of bilateral perineal herniorrhaphy in a cat with cutaneous asthenia described unilateral recurrence within 4 mo of IOMT (8). Regardless, the cat in our study with cutaneous asthenia had an excellent outcome following IOMT + PSIS with no recurrence, problems with wound healing, or other complications.

The infection rate in our study was 5.6%, which is comparable to previous reports for IOMT (4,12–14,26). A previous report of PPM-reinforced IOMT described a similar infection rate to our study; however, the affected patients required surgical debridement of the infected wound (3). By contrast, infection in our patient resolved following antibiotic therapy. While PSIS lacks in vitro antimicrobial properties, it has shown increased resistance against infection in contaminated sites compared to synthetic implants (15,33–35). This has been attributed to early neovascularization, which allows host defences and antibiotics to readily access the site of bacterial infection (16). While lack of degradability of synthetic implants provides a long-term substrate for bacterial colonization and poses a challenge for elimination of infection, PSIS is completely absorbable (15,35,36). Porcine small intestine submucosa was histologically indistinguishable from transposed internal obturator muscle at 12 wk following perineal herniorrhaphy (1).

This study’s retrospective nature poses several limitations on outcome assessment. The absence of a control group in this study limits our ability to compare outcomes between herniorrhaphy techniques. Inherent biases in the survey method, medical record quality, owner observational acuity, and accuracy of recollection influenced the collected data. Non-specific or minor complications may have been attributed to another cause, not reported by owners, or remained undocumented. This limited our ability to compare pre- and post-operative clinical signs to assess clinical improvement. Justification for technique selection remained largely undocumented. A previous study showed a significant reduction in herniorrhaphy recurrence with increasing surgical experience (26). The distribution of roles between residents and faculty in surgery is unknown and so the effect of experience on outcome was unaccounted for.

Our results suggest that IOMT + PSIS and PSIS alone are acceptable methods for perineal herniorrhaphy in the dog and cat and may be helpful where the IOM is atrophied. A larger prospective controlled study would be beneficial in comparing outcome to other perineal herniorrhaphy methods. CVJ