The rectus abdominis has multiple proximal tendinous insertions onto the ribs and costal cartilages: the medial tendinous fibres insert into the fifth, sixth, and seventh costal cartilages, while the lateral fibres may reach the third and fourth costal cartilages. Three to four tendinous intersections within the muscle belly are adherent to the anterior rectus sheath. The muscle is enclosed by the rectus sheath formed by the aponeuroses of the three abdominal wall muscles.
The proximal rectus abdominis attachments are relevant in the TRAM and DIEP free flap donor site. The TRAM flap harvests the rectus muscle with its deep inferior epigastric pedicle; the DIEP flap harvests only the skin and fat via the epigastric perforators without the muscle. Post-harvest abdominal wall weakness is greater after TRAM than DIEP. Costal chondritis (Tietze syndrome) at the fifth and sixth costal cartilage insertions may mimic cardiac pain and responds to local injection. Rectus abdominis tears during intense abdominal exercise produce supraumbilical pain and palpable defect.
Violent eccentric contraction during situps or explosive sports tears the rectus abdominis at or near its proximal costal cartilage insertion, producing acute epigastric pain and local tenderness with visible bruising that extends inferiorly into the flank as haematoma tracks in the rectus sheath; MRI confirms the partial or complete tear and management is conservative with early return to activity.
