Discussion

Anatomy and Challenges in repairing
Subxiphoid hernias generally occur in the midline and are inferior to the tip of the xiphoid. According to the European Hernia Society classification, SIH occurs within 3 cm of the xiphoid and are terms midline (M)1 hernias. (6) Subxiphoid incisional hernias can occur either on or off the midline although in the midline is more common. (7)
SIH repair presents several challenges. Firstly, the shearing forces generated by the muscular attachments results in high intra-abdominal pressures. (2) This tension is further enhanced by an anatomical variant bifid xiphoid process or by dividing the xiphisternum surgically. The high pressure in the subxiphoid region makes repair under minimal tension and approximation of the medial borders of the anterior sheath difficult and increases the risk of dehiscence. (8, 9) Secondly, the close proximity of the ribs, diaphragm and central tendon make securing a mesh more difficult compared with other types of hernia repair. (10) This is made more challenging if a hypoplastic xiphoid process is present as there is only a small retro-xiphoid space available. (11) Lastly, the xiphoid process has vascular supply from the xiphoid artery, a terminal branch of the internal thoracic artery, and from a branch of the superior epigastric artery. Blood supply may be compromised to this area if damage occurs to the internal thoracic or superior epigastric arteries so care must be taken during surgery. (7)

Incidence

An incisional hernia is a common complication of abdominal operations, affecting 10–26% of patients. (2) However, incisional hernias following a median sternotomy are less well reported than their abdominal counterparts. The incidence of subxiphoid incisional hernias has been reported ranged between 1% to 4.2%, (1, 2, 4, 12) although most agreed that the true incidence is unknown due to the asymptomatic nature. (5)
Risk Factors
There is a variety in the reported risk factors for developing incisional hernias following a median sternotomy. The most commonly reported are obesity, wound infection, male sex, left-sided heart failure, long incisions (specifically >18cm), and repeat operations. (5, 10, 12-14) Other, less reported, suggestions include a history of chronic obstructive pulmonary disease (COPD), diabetes mellitus, a positive smoking history, and postoperative bleeding (1, 13, 14) - specifically, a transfusion requirement within 24 hours of cardiac procedure was identified as an independent risk factor specifically for subxiphoid incisional hernia development. (3) A retrospective review suggested that a history of hernias could be a risk factor for developing further hernias, claiming that “hernias beget hernias”, so there is potentially cause for caution when operating on patients with a history of hernias. (3)

Prevention of Incisional Hernias

Barner reported a technical modification of median sternotomy to reduce the incidence of SIH. It emphasises a slightly shorter incision and avoids opening the linea alba by diverting the midline incision at the tip of the xiphoid process and connecting it with a stab wound made in the left xiphoidcostal angle, shown in Figure 1.(15) Barner reported his experience in 2,500 operations with no recorded incidence of subxiphoid or paraxiphoid incisional hernias.
Barner’s technical modification has been acknowledged and developed by multiple studies, suggesting that paraxiphoid extension of the sternotomy, reinforcement near the xiphoid end of the incision, optimizing closure of the distal sternotomy and the linea alba, and non-absorbable aponeurotic suturing of the epigastrium may further improve the closure’s stability. (3, 11, 15)

Management of subxiphoid incisional hernias

Several approaches have been reported to manage SIH. The treatment of the hernia follows basic principles that emphasise tension-free repair and all methods were performed under general anaesthetic using appropriate prophylactic antibiotics.

Open, suture repair with tissue approximation

Davidson and Bailey reported their experience in managing SIH in 1987. Their management was based on the size of the defect. For large subxiphoid hernias (>10cm in diameter), Davidson and Bailey reported their experience using a double door flap, \soutand applied to the subxiphoid defect area. His method was a modification of the Wells procedures. (16) After the hernia sac was reduced, the flap was created based on the linea alba. The left flap created was mobilised and sutured to the right margin of the defect and vice versa, give a double-layered repair. On the other hand, for small defects (<4cm in diameter), a standard direct closure of the defect with non-absorbable sutures were used instead.
Open repair with mesh
Cohen et al reported the first open repair of a subxiphoid hernia with a mesh in 1985. (9) Dissection was done entirely extra-peritoneal, to develop a plane between the posterior surface of the musculofascial layer and the peritoneum. It is worth noting that the peritoneum was only entered to free adhesions if necessary. The bifid xiphoid process was excised in the majority of patients. A polypropylene mesh was then placed and secured with sutures on the posterior rectus sheath deep to the rectus abdominus. The anterior sheath was then closed over the mesh with absorbable continuous sutures. A similar technique has been reported by Boulliout et al. (15)
De Mesquita reported a new repair technique in 2017. (5) Instead of suturing the mesh between the posterior rectus sheath and the rectus abdominus muscle, they closed the rectus sheath using a continuous, non-absorbable suture. The mesh was then applied was applied anteriorly with continuous suture around the edge.

Laparoscopic Repair

Laparoscopic approach for SIH repair has been reported on three occasions. (2, 3, 10) Landau et al. reported the first laparoscopic repair of subxiphoid hernia in 2001. A similar technique was reported by Mackey et al and Eisenberg et al. After adhesiolysis, the mesh was fixated \souteither using sutures into the peritoneal cavity.

Comparisons of repair techniques and outcomes

The consistent outcome measure reported from the various methods for subxiphoid is the recurrence rate.
Recurrence of subxiphoid incisional hernias following surgical repair have been reported at various incidences, ranging from 0%-80%. (5, 9) Multiple factors can influence the risk of recurrence, particularly the surgical technique used for the primary repair; the recurrence in techniques using exclusively sutures for a repair ranged from 0%-80%, whereas the use of mesh lowered the recurrence rate to 0%-33%. (5, 12, 17). A laparoscopic approach yields very similar results for the rate of recurrence 0 - 30%. (2, 3, 10)
In addition to a lower recurrence rate, laparoscopic repair reported a reduced post-operative stay, and need for pain control. (2) This is likely due to the advantage in subfascial visualisation of the epigastrium and edges of the defect, enabling the surgeon to circumferentially cover the defect, avoidance of the previous incision and minimal tissue trauma. (3, 10) A major disadvantage of the laparoscopic approach is the steep learning curve that it presents which may attribute to a higher rate of recurrence prior mastering the technique. (10)

Risk Factors for Recurrence

Aside from surgical technique, other risk factors for a hernia recurrence include sternal wound infections, with reports of 75% of patients developing recurrent hernias (3) \soutBesides, reference has also been made to patients who are immunocompromised - notably transplant patients - due to their reduced capacity for wound healing and therefore increased risk of infection (3)
Limitations
There are several limitations to this literature study. First and most important, the available literature in the research field on SIH remains limited. This is most likely due to its asymptomatic nature and, hence underreporting. In addition to small sample size, all 8 studies included limited pre, intra and post-operative variables. For example, the post-operative follow-up period varies leading to a variation of recurrence rate. outcome measured cannot be compared directly.
Conclusion
In conclusion, SIH post median sternotomy are rare, however, difficult to repair and have a high risk of reoccurring. (1-3) The true incidence remains poorly understood due to their asymptomatic nature (17) Risk factors, preventions, and several management techniques were discussed in this article.
1. Kim HS, Kim KB, Hwang HY, Chang HW, Park KJ. Subxiphoid incisional hernia development after coronary artery bypass grafting. Korean J Thorac Cardiovasc Surg. 2012;45(3):161-5.
2. Landau O, Raziel A, Matz A, Kyzer S, Haruzi I. Laparoscopic repair of poststernotomy subxiphoid epigastric hernia. Surg Endosc. 2001;15(11):1313-4.
3. Mackey RA, Brody FJ, Berber E, Chand B, Henderson JM. Subxiphoid incisional hernias after median sternotomy. J Am Coll Surg. 2005;201(1):71-6.
4. Davidson BR, Bailey JS. Incisional herniae following median sternotomy incisions: their incidence and aetiology. Br J Surg. 1986;73(12):995-6.
5. de Mesquita GHA, Iuamoto LR, Suguita FY, Essu FF, Oliveira LT, Torsani MB, et al. Simple technique of subxiphoid hernia correction carries a low rate of early recurrence: A retrospective study. BMC Surg. 2017;17(1):51.
6. Muysoms FE, Miserez M, Berrevoet F, Campanelli G, Champault GG, Chelala E, et al. Classification of primary and incisional abdominal wall hernias. Hernia. 2009;13(4):407-14.
7. Docimo SP, EM. Treatment of Atypical Hernias. 1st ed: Springer; 2017 2017.
8. Bouillot JB, A; Alexandre, JH. Incisional abdominal hernia after median sternotomy. Repair with the use of Dacron mesh. Hernia. 1997;1:129-30.
9. Cohen MJ, Starling JR. Repair of subxiphoid incisional hernias with Marlex mesh after median sternotomy. Arch Surg. 1985;120(11):1270-1.
10. Eisenberg D, Popescu WM, Duffy AJ, Bell RL. Laparoscopic treatment of subxiphoid incisional hernias in cardiac transplant patients. Jsls. 2008;12(3):262-6.
11. Conze J, Prescher A, Kisielinski K, Klinge U, Schumpelick V. Technical consideration for subxiphoidal incisional hernia repair. Hernia. 2005;9(1):84-7.
12. Davidson BR, Bailey JS. Repair of incisional hernia after median sternotomy. Thorax. 1987;42(7):549-50.
13. Read RC, Yoder G. Recent trends in the management of incisional herniation. Arch Surg. 1989;124(4):485-8.
14. Vennarecci G, Guglielmo N, Pelle F, Felli E, Ettorre GM. The use of Permacol surgical implant for subxiphoid incisional hernia repair in cardiac transplant patients. Int J Surg. 2015;21:68-9.
15. Barner HB. A technical modification of median sternotomy to eliminate subxiphoid incisional hernias. Arch Surg. 1987;122(7):843.
16. Wells CA. Hernia: incisional and umbilical. Ann R Coll Surg Engl. 1956;19(5):316-8.
17. Losanoff JE, Basson MD, Laker S, Weiner M, Webber JD, Gruber SA. Subxiphoid incisional hernias after median sternotomy. Hernia. 2007;11(6):473-9.