Mechanisms of the inguinal canal
Mechanisims which maintain the integrity of the inguinal canal during increases in intra-abdominal pressure can fail and an indirect (congenital) inguinal hernia or a direct (acquired) inguinal hernia can ensue. To maintain the intergrity of the inguinal canal these mechanisms must work efficiently and include a series of shutter mechanisms or musculoaponeurotic arcades, seen in Figure 15 (Moore et al. 2010).
1. The inner shutter mechanism is the movement between transversus abdominis and the transversalis fascia. It is located at the deep inguinal ring at the layer of transversus abdominis, which works alongside the transversalis fascia and is thought to be the most significant in maintaining the canals integrity.
A U-shaped edge of the transversalis fascia; the transversalis fascia sling is an opening in this layer, which acts as a tension mechanism. The medial crus of the transversalis fascia sling is attached to the aponeurosis and the lateral crus is attached to the posterior aspect of transversus abdominis. During muscle contraction the sling, which is inferior to the spermatic cord, is pulled in a supero-lateral direction closing the deep inguinal ring. |
2. The outer shutter operates through the contraction of internal oblique and transversus abdominis inferiorly, which aids in closing the inguinal canal. The contraction of internal oblique closes the deep inguinal ring anteriorly which pulls the medial part of the transversus abdominis arch in an infero-lateral direction towards the inguinal ligament acting as a partial shutter.
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The integrity of the inguinal canal is further jeopardised by a weakness in transversalis fascia of the posterior wall in the inguinal canal caused by weakness in the conjoint tendon. This also reduces support of the superficial inguinal ring.
Enlargement of the deep and superficial inguinal rings can also cause the oblique passage of the canal to be lost increasing further the opportunity for inguinal hernias to occur.
Enlargement of the deep and superficial inguinal rings can also cause the oblique passage of the canal to be lost increasing further the opportunity for inguinal hernias to occur.