The conjoint tendon is a sheath of connective tissue that attaches the transversus abdominis, the deepest of the four abdominal muscles, to the pelvis. It gets its name from the fact that it is often continuous or conjoined with the tendon of the internal oblique, another of the abdominal muscles. As the abdominal muscles end a short distance above the pubic crest of the pelvis, the conjoint tendon along with the tendons of the rectus abdominis and external oblique muscles represent a continuation of fibrous tissue that links the abdominal wall to the pelvis and protects the organs contained within. It also makes up the upper border of the inguinal canal.
Previously referred to as the inguinal aponeurotic falx, the conjoint tendon is a paired structure that originates at the bottom of the transversus abdominis muscle on either side of the lower abdomen. It runs roughly parallel to and is found just to the inside of the inguinal ligament, the band of connective tissue that extends diagonally from the iliac crest at the top of either hipbone to the center of the pubic bone. This tendon was formerly identified as aponeurotic because all of the fibers of the transversus abdominis, which wraps anteriorly around the abdomen from either side, end in a sheet of connective tissue called an aponeurosis. Running down the midline of the abdomen, this aponeurosis forms the muscle’s medial or inside border and tapers where the muscle ends at the pelvis to insert into the tendon.
This tendon also was formerly identified by the term falx, a Latin word meaning “sickle,” for its curved shape. Combining with fibers from the bottom of the internal oblique muscle, the conjoint tendon curves inward as it descends, crossing obliquely toward the pubic bone. It inserts along the crest of the pubis, the forward-protruding curve found on either pubic bone where they meet in the middle to form a joint known as the pubic symphysis. Additionally, the tendon attaches to a ridge along the upper border of the pubic bone called the pectineal line.
While the conjoint tendon is one of several fibrous tissues filling the space in the anterior wall of the pelvis and whose purpose is to protect the organs and soft tissue within, it also coincides with a weak spot in this wall. This spot, known as Hesselbech’s triangle, is a small gap formed by the borders of the rectus abdominis muscle to the inside, the inferior epigastric artery and vein above and to the outside, and the conjoint tendon below. As a result of this weakness, a direct inguinal hernia can occur here, meaning that a portion of the intestinal wall or other tissue from the abdominal cavity protrudes through this triangle.