Clinical Anatomy and Surgical Repair of Prepubic Hernia in Dogs and Cats
Prepubic hernia is a traumatic hernia in small animals, most often associated with severe trauma to the caudal abdomen. Common causes include vehicular trauma, dog fights, and kicks by large animals. Rupture of the prepubic tendon in dogs and of its equivalent in cats results in a ventral abdominal hernia. Due to the traumatic nature of the injury, concurrent injuries are frequently seen. Clinical signs of herniation are often nonspecific, and the resultant hernia may not be readily apparent during routine physical examination. This being so, diagnosis is often based on a thorough physical examination in conjunction with abdominal radiography and, possibly, abdominal ultrasonography. Multiple methods of repair of prepubic hernia have been reported, and survival rates are quite good if concurrent injuries are not severe.
Introduction
In the dog, the prepubic tendon is a dense mass of collagenous tissue that attaches the ventral abdominal muscles to the cranial border of the pubis. In the cat, no distinct prepubic tendon exists; rather, the abdominal muscles attach directly to the pelvic brim. Rupture of the prepubic tendon in dogs and its equivalent in cats occurs from blunt force to the abdomen and results in a ventral abdominal hernia. The incidence of prepubic hernia is lower than other types of traumatic hernias, such as lateral paralumbar hernias, and often the diagnosis can be challenging.1 In this article, prepubic tendon anatomy, clinical signs associated with rupture, and surgical correction of the resulting defect are reviewed.
Anatomy
The prepubic tendon, which has also been called the cranial pubic ligament, serves as a point of attachment for the ventral abdominal musculature onto the pelvis. In this capacity, the prepubic tendon aids in the action of the abdominal press that makes possible the acts of urination, defecation, exhalation, and parturition.2 The prepubic tendon has been described in the dog, but a homologous structure has not been reported in the cat.3 In preparation for this review, dissection of the inguinal region was performed in several canine and feline cadavers. Results of these dissections differed from previously reported anatomical findings and have been recently published.4
The prepubic tendon in the dog is stated to be composed of the combined fibers of the rectus abdominis and pectineus muscles as well as the attachments of the abdominal oblique and transversus abdominis muscles.3 However, according to our previously published findings, the attachments of the prepubic tendon are somewhat more complicated than previously reported.2–4 The transversus abdominis muscle does not attach to the prepubic tendon, as previously reported. The caudal border of the transversus abdominis muscle, called the linea arcuata, ends cranial to the pecten of pubis. Furthermore, the medial portion of the muscular fibers of the rectus abdominis muscle attaches to the ventral pubic tubercle, while the lateral portion of the rectus abdominis muscle and the aponeuroses of the two abdominal oblique muscles attach to the pecten of pubis [Figure 1]. The lateral part of the rectus abdominis muscle has an elliptically shaped aponeurosis with fibers that pass over and under the prepubic tendon. The two crura of the superficial inguinal ring (from the external abdominal oblique muscle) firmly attach to the prepubic tendon and the pectineus muscle [Figures 2A, 2B].4 Additionally, the prepubic tendon extends from the pecten to the iliopubic eminence on either side [Figure 1], with minimal crossover of fibers.2 The iliopubic cartilage is intercalated in the pectineus tendon.3
The abdominal and pectineus muscles in the cat have separate attachments to the pubis, and, thus, a prepubic tendon does not exist.2 However, the two crura of the superficial inguinal ring firmly attach on the cranial border of pubis on both sides of the iliopubic eminence, where the pectineus muscle inserts.4 Furthermore, the aponeurosis of the external abdominal oblique muscle sends strong attachments to the medial aspect of the thigh, in addition to the femoral lamina.4 We speculate that in the cat, the strong attachments of the crura of superficial inguinal ring and external abdominal oblique muscle aponeurosis serve the same function as the prepubic tendon in the dog [Figure 3].
Etiology
Prepubic hernia is usually attributable to blunt trauma. In most cases, prepubic hernia happens as the result of the animal being struck by a car, but other causes (such as dog fight injury or kicks by large animals) are possible.
Clinical Findings
Any trauma severe enough to cause rupture of the prepubic tendon has the potential to damage surrounding structures both within and outside the abdomen. Often either partial or complete avulsion of the tendinous attachments from the iliopubic eminence occurs, resulting in a defect in the ventral abdominal wall. Although less common, the tear could occur at the musculotendinous junction.5 In some cases, concurrently acquired femoral and/or inguinal hernias are seen as a result of injury to the arcus inguinalis, a structure formerly known as the inguinal ligament.6 The most recent literature reports that 44% of animals suffering from traumatic abdominal hernias also have serious concurrent injuries.3 Concurrent orthopedic injuries, especially to the pelvis, are seen commonly; however, soft tissue injuries involving the respiratory, gastrointestinal, and genitourinary systems are also seen frequently.5,7,8 As with any traumatic injury, initial efforts should be aimed at identification and stabilization of life-threatening injuries.
Diagnosis of Prepubic Hernia
Clinical findings specifically associated with prepubic hernia are somewhat vague and nonspecific. Other injuries may contribute to an animal’s clinical state at presentation, causing a prepubic hernia to be overlooked initially. Abdominal palpation, abdominal radiography, and possibly ultrasonography are necessary for diagnosing prepubic hernia. Abdominal examination and palpation may reveal bruising, edema, pain, and/or subcutaneous intestinal loops; however, in some cases, intestinal loops may not be palpated until several days after trauma.8 In most cases, abdominal radiographs will provide more useful information than abdominal palpation alone. Radiographic findings include loss of the ventral abdominal stripe and evidence of subcutaneous intestinal loops [Figure 4]; however, these findings are not specific for prepubic hernia. Ultrasonography [Figures 5A, 5B] and contrast peritoneograms have also been suggested when other methods of diagnosis are inconclusive.5 In some cases, the diagnosis of prepubic hernia may not be made until surgery is performed for exploration and repair of other associated injuries.
Timing of Repair
Timing of repair of prepubic hernias is dependent upon several factors, including overall status of the animal and severity of associated injuries. Stabilization of the animal and treatment of life-threatening injuries should always take precedence over hernia repair. Repair can be delayed several days, if necessary, as prepubic ruptures most often result in large abdominal wall defects; thus, the incidence of visceral incarceration and strangulation is quite low.5
Methods of Repair
Multiple methods of repair have been reported in the literature.5,6,8 The most common method is described in detail here, and others are highlighted below. Regardless of the method of repair, proper positioning of the animal during surgery is vital to provide a tension-free repair. We prefer the position of standard dorsal recumbence, in which the pelvic limbs are pulled caudally; however, this position results in significant tension at the surgical site during surgery. Therefore, some surgeons prefer a modified dorsal recumbence in which the pelvic limbs are flexed and pulled cranially to create truncal ventroflexion. This position reduces the size of the defect and decreases tension during suture placement.5 The surgeon must remember that natural body positions in an awake animal, compared to modified dorsal recumbence, may place greater stress on the surgical site.
Repair of a prepubic hernia begins with a ventral midline incision and exploration of the abdomen. The regional anatomy should be reviewed before any repair is undertaken. Vascular and neural structures found within the femoral triangle (i.e., the femoral artery and vein and genitofemoral nerve) should be noted and protected.5 Assessment and repair of traumatized organs should be undertaken prior to herniorrhaphy. Common concurrent surgical findings include subcutaneously located abdominal organs, soft tissue damage, adhesions, and cranial retraction of the rectus abdominus muscles.6 Crushed or damaged soft tissues should be handled carefully to prevent further trauma to the vascular supply. In dogs, the prepubic tendon should be carefully dissected such that the lateral margins are visible for inspection. In cats, it is important to inspect the crura of the superficial inguinal ring as well as the aponeurosis of the external abdominal oblique muscle, as these are commonly affected in feline prepubic hernias. The lateral margins should then be closely inspected for evidence of concurrently acquired femoral or inguinal hernias. If an inguinal or femoral hernia is present, reattachment of the prepubic tendon to the pubis should be performed first for proper anatomical alignment of tissues.
Reattachment to the Pubis
As with any herniorrhaphy, proper suture selection and placement are key to successful repair. Substantial bites of tissue should be taken using a tension-relieving pattern, such as cruciate or mattress sutures. Care should be taken to avoid incorporation of intrapelvic structures, such as the urethra, during suture placement. Synthetic monofilament absorbable or nonabsorbable sutures have been used; however, we prefer a nonabsorbable suture, such as polypropylene, because muscle fascia takes approximately 3 weeks to reach 20% of its original strength after injury and up to a year to regain 80% of its original strength.5,9 Selected suture material must be capable of supporting tissues until adequate healing has occurred. Absorbable sutures such as polyglactin 910 and poliglecaprone 25 lose most of their tensile strength within 2 to 3 weeks.10 Even polydioxianone, which can reliably provide wound support for up to 6 weeks, may not retain enough tensile strength to support healing of prepubic tendon repair.10 Nonabsorbable sutures such as monofilament nylon and polypropylene are preferred for repair of prepubic hernias, because they provide long-lasting support to tissues. Nylon retains 81% of its tensile strength at 1 year and 72% of its strength at 2 years.10 Polypropylene is not significantly degraded in the body, and thus it can maintain nearly all of its tensile strength at 2 years.10
The surgeon must remain cognizant of some potential disadvantages of nonabsorbable sutures, including long-term local tissue reaction and formation of a nidus for infection.10 Although we prefer to use synthetic, nonabsorbable suture, absorbable suture has reportedly resulted in successful repair.7 This is further illustrated by the case of an adult, mixed-breed cat that sustained a prepubic hernia after being hit by a car [Figure 6A]. The hernia was repaired with a synthetic absorbable suture (specific type not recorded). The cat was euthanized 8 months postoperatively for unrelated problems, and postmortem dissection revealed the healed musculoskeletal attachment [Figure 6B].
Our preferred repair method involves holes predrilled in the cranial brim of the pubis for passage of the suture. Placement of suture through predrilled holes in the pubis provides a stable repair with minimal dissection of soft tissues. Holes are drilled in the pubis, and sutures are preplaced through the avulsed portion of the tendon (or fascia of the external abdominal oblique in the cat) and through the holes in the pubis. Once all of the sutures have been placed, an assistant can manipulate sutures to decrease overall tension as each suture is tied. After preplaced sutures are tied, the linea alba is closed. In rare cases, enough tendon is still attached to the pelvis to allow apposition of prepubic tendon tissues; however, recommendations are for sutures to still be placed in the pubis for proper fixation.5 The holding strength of the injured tendon is questionable, and failure of the repair could result.
Other repair techniques reported in the literature include the obturator foramen suture placement method and use of a cranial sartorius flap. The obturator foramen suture placement method involves passage of the suture through both obturator foramina rather than through predrilled holes in the pubis. In this method of repair, it is imperative that the suture be placed directly adjacent to bone. If sutures are placed over soft tissue, the fixation could loosen as the suture cuts through underlying muscle.8 While this technique requires more careful dissection and suture placement, no drilling of bone is necessary; thus, the risk of iatrogenic fracture and damage to abdominal organs is low.
The cranial sartorius flap is described for repair of femoral hernias in the dog, but it can be modified for use in prepubic hernia repair.11 The cranial portion of the muscle is separated from its caudal belly and the quadriceps femoris muscle. The cranial portion of the muscle is then transected at its distal insertion on the medial aspect of the patella and elevated to the level of the proximal vascular pedicle [Figure 7]. The flap is rotated 180° to the defect and secured in a simple interrupted fashion.11 While this technique is useful in cases with little viable prepubic tendon to reconstruct, the risk of devitalization of the flap must be considered.
Repair of associated inguinal or femoral hernias can be accomplished using the cranial sartorius flap described above; or, if tissue damage is minimal, anatomical reconstruction can be performed. In most cases of femoral hernias, the arcus inguinalis is ruptured. Repair usually involves placing sutures between the external abdominal oblique aponeurosis and muscles of the proximal medial thigh. Care should be taken to avoid damage to vascular and neural structures in the area, including the femoral artery and vein as well as the genitofemoral nerve. Additionally, entrapment of the urethra in the repair should be avoided by performing careful tissue dissection, placing sutures carefully, and catheterizing the urethra prior to surgery for ease of identification.
When excessive tension is present at the suture line, repair using synthetic mesh may be necessary. Synthetic mesh may be used to augment repair and relieve tension when using one of the techniques described above. In these cases, a mesh cuff or double-layer mesh can be incorporated into the repair.5 Alternatively, the mesh can be used to gap the entire defect in cases where minimal tissue is available for anatomical reconstruction. To augment repairs, swine intestinal submucosa may also be used, as it has been applied to perineal herniorraphy.12 Swine intestinal submucosa is reported to possess valuable properties for use as a biological graft material; it provides resistance to infection, predictable activity in situ, and biocompatibility in most tissue environments.12
Although some authors have suggested drain placement during wound closure after prepubic hernia repair,5,6 drains may be unnecessary in many cases and may promote a number of complications including wound dehiscence, infection, abscessation, and/or erosion into nearby hollow organs.13 Careful consideration should be taken prior to placement of a drain to ensure that potential benefits out-weigh the risks.
Aftercare/Prognosis
Postoperative needs are dependent upon concurrent injuries and the animal’s status. Vital parameters and pain levels should be monitored carefully and treated accordingly. Exercise restriction is recommended for at least 4 to 6 weeks postoperatively, especially in cases where the repair necessitated use of a synthetic mesh.
Very few complications are seen that relate directly to prepubic hernia or repair. Urethral entrapment can occur during suture placement;8 however, catheterization of the urethra preoperatively can decrease the risk of this occurring by allowing easy intraoperative identification of the urethra. Other complications reported include wound infection and skin sloughing.1,6 Failure of prepubic tendon repair occurs in approximately 15% of cases, with the defect becoming evident within 1 month postoperatively.5 Factors contributing to failure include excessive tension at the surgical site, self-traumatization, and dehiscence. Most causes of morbidity and mortality in cases of prepubic hernia are related to intra-abdominal or orthopedic injuries. Prognosis is generally quite good, with reports of 80% to 90% survival rates.5
Medical Management
Few cases of medical management of prepubic hernia have been reported. Two cases of prepubic hernia in cats could not be immediately surgically corrected because of overlying tissue damage and contamination. Follow-up examination of these cats several weeks later revealed that scar tissue had formed to support the defect.7 Despite the positive outcomes in these cases, one should be cognizant of the potential for complications following medical management, including visceral strangulation and incarceration.5 In both of the cases reported, the animal was hospitalized at least 1 week for wound management and thus could be carefully observed for evidence of complications related to the prepubic hernia. We recommend surgical correction whenever possible.
Acknowledgments
The authors thank Howard Wilson and Phillip Snow for their contributions and assistance with image editing.
Citation: Journal of the American Animal Hospital Association 45, 6; 10.5326/0450284
Citation: Journal of the American Animal Hospital Association 45, 6; 10.5326/0450284
Citation: Journal of the American Animal Hospital Association 45, 6; 10.5326/0450284
Citation: Journal of the American Animal Hospital Association 45, 6; 10.5326/0450284
Citation: Journal of the American Animal Hospital Association 45, 6; 10.5326/0450284
Citation: Journal of the American Animal Hospital Association 45, 6; 10.5326/0450284
Citation: Journal of the American Animal Hospital Association 45, 6; 10.5326/0450284
Canine pelvis, illustrating the attachments of the rectus abdominis muscle, abdominal oblique muscles, and prepubic tendon. The medial portion of the muscular fibers of the rectus abdominis muscle attaches to the ventral pubic tubercle (1), while the lateral portion of the rectus abdominis muscle and the aponeuroses of the two abdominal oblique muscles attach to the pecten of pubis (2). The prepubic tendon attaches to the brim of the pubis from one iliopubic eminence (3) to the other.
Normal anatomy of the prepubic tendon in the dog (A), illustrating the combined fibers of the rectus abdominis, internal abdominal oblique, and external abdominal oblique muscles. (B) The two crura of the superficial inguinal ring firmly attach to the prepubic tendon and the pectineus muscle.
Normal anatomy of the prepubic musculature attachments in the cat. The strong attachments of the crura of the superficial inguinal ring and aponeurosis of the external abdominal oblique muscle replace the prepubic tendon in the cat. The two crura of the superficial inguinal ring firmly attach on the cranial border of pubis on both sides of the iliopubic eminence where the pectineus muscle inserts.
Radiograph of a 10-year-old, castrated male, domestic longhaired cat that was hit by a car. Radiographic findings associated with prepubic hernia include loss of the ventral abdominal stripe and evidence of subcutaneous intestinal loops.
Ultrasound images of prepubic hernia in a 2-year-old, castrated male, American Staffordshire terrier that was hit by a car. (A) Image of intact prepubic tendon on the dog’s right side. Note the homogeneous longitudinal fibers running along the top of the image (arrows). (B) Image of the ruptured prepubic tendon on the dog’s left side. An approximately 1-cm area with heterogeneous echogenicity and a focus of hyperechogenicity with distal acoustic shadowing interrupts the prepubic tendon, just cranial to the pubis (arrow). This area represents rupture of the prepubic tendon with possible avulsion of a portion of the ventral pubic tubercle.
Intraoperative and follow-up views of prepubic hernia repair in an adult, mixed-breed cat that was hit by a car. (A) Note severe bruising of the bladder. The abdominal musculature has been reattached to the pubis with suture. (B) Postmortem dissection 8 months after surgery, showing the healed prepubic hernia repair. Death was unrelated to original injuries. The (1) pubis and (2) insertion of the abdominal musculature are noted.
Prepubic hernia repair using a sartorius muscle flap. The cranial portion of the sartorius muscle is transected distally at its insertion on the medial aspect of the patella and is elevated to the level of the proximal vascular pedicle. The flap is then rotated to the area to be repaired.
