II 5 Non-Surgical Risk Factors for Recurrence of Hernia L.T. Sorensen, L.N. Jorgensen Introduction Abdominal wall hernias may recur as long as 15 years after herniotomy. Recurrences which appear within 6 months following surgery are regarded as technical failures due to inadequate surgical technique. Recurrences which appear later than 6–9 months after the primary surgical procedure may be considered as a result of the abnormal collagen metabolism, which originally led to herniation [1, 2]. The pathological mechanisms for the non-surgical risk factors associated with recurrence of inguinal hernia or formation of abdominal wall hernia, for that matter, are not fully understood. Roughly, these risk factors may be divided into non-modifiable and potentially modifiable risk factors. The aim of this study is to review the literature regard- ing non-surgical physiological and biochemical mecha- nisms involved in both primary development and recur- rence of abdominal wall hernia. Non-Modifiable Risk Factors for Hernia Formation and Recurrence A higher prevalence of inguinal hernia is well known among patients suffering from congenital connective tissue disorders like osteogenesis imperfecta, cutis laxa, Ehlers-Danlos syndrome, Hurler-Hunter’s and Marfan’s syndrome [3–5]. In children with congenital hip dislocation, inguinal hernia occurs more frequently [6], and patients with Ehlers-Danlos syndrome exhibit a higher incidence of recurrent incisional hernia [7]. There is no evidence, however, to suggest that other ge- netically predisposed patients undergoing hernia repair are more likely to experience recurrent hernia form- ation. The prevalence of inguinal hernia increases sig- nificantly with patient age [8]. Experimental studies show that the activity of collagen-degrading enzymes is higher in elder patients, presumably due to a reduced inhibition of collagenase [9, 10]. It is not clear whether patient age is associated with recurrence of inguinal hernia. In a study of 544 patients undergoing inguinal hernia repair, a multivariate analysis showed that patient age was not an independent risk factor for recurrence within 2 years postoperatively [11]. In a recent study of incisional hernia, patient age was inversely associated with recurrence [12]. The incidence of inguinal hernia is higher in males, a difference partly due to embryological characteristics of each gender. It is puzzling, however, that one fifth of men pass into adulthood with a patent processus vaginalis, but less than half develop clinical herniation [1, 13]. In addition, indirect inguinal hernia may appear first in a man over 40 years of age [1]. These observa- tions suggest that other factors may play a role in the development of an indirect hernia including structural abnormalities of the internal ring, acquired attenuation of transversalis fascia or abnormal muscle function ac-