Table 2.

Possible etiological factors.

	Lateral hernia	Medial hernia	Results	Reference
External risk factors
High intraabdominal pressure	+	−	Increase cumulative occupational mechanical exposure increase the risk of lateral hernia repairs, but not lateral re-operations	(11, 12, 24)
Smoking	?	?	May theoretically increase herniation, but this has not been confirmed	(10, 12, 20, 21)
Patient risk factors
Age	+	+	Increasing age increase the risk of both lateral- and medial repairs	(9, 10, 12)
Connective tissue alteration	+	+	Both medial and lateral hernias have altered connective tissue compared with controls. Medial hernias seem to have a more profound alteration	(50–61)
Connective tissue disorders	+	+	This is a shown risk factor for inguinal hernias, but studies have not subdivided the results on hernia type	(13, 14)
Constipation	−	−	Does not appear to be a risk factor	(17)
Genetics	+	+	Gene mutations are reported for both hernia types, and generalizable mutations for inguinal hernias are possibly identified	(82–90)
Low body mass index (BMI)	+	+	A higher BMI is a protective factor	(10, 12, 15)
Male gender	+	+	Studies report male gender as a risk factor for inguinal hernias, without subdividing the results on hernia type	(9, 10)
Patent processus vaginalis	+	−	A risk factor, but not all patients with a patent processus vaginalis develop a lateral hernia. The exact mechanism why processus vaginalis fails to obliterate is not established	(7, 25–32, 34, 36–38)
Prostatic hypertrophy	?	?	A weak association has been found	(17–19)

+, a risk factor; −, not a risk factor; ?, unknown if it is a risk factor.