One of the most common areas for any ribcage protrusion is the subcostal margin. This is were the cartilaginous portions of ribs 8, 9 and 10 merge to form the bottom part of the lower ribcage below the anterior chest wall. It has a defined edge in which most non-obese people can grab its lower region and get around to the other side. Most people on doing so will feel a rib ‘slip’ which is the unattached cartilaginous rib #9 sliding up over the more fixed rib #8. The subcostal margin has a curved shape which normally is aligned in a relatively smooth contour with the chest wall above and below it.
Some people do have a subcostal rib margin which sticks out…which means it has an excessive curve or convexity compared to the chest wall above it. This is often due to the combination of rib #8, 9 and 10. Medially it is due more to rib #8 but as one moves laterally the protrusion is more likely due to ribs #9 and/or #10. Such subcostal protrusions can be reduced or eliminated based on how much they stick out and the surface area of the ribs involved. In some cases portions of the rib are removed while in others they are shaved down.
In approaching subcostal rib protrusions that can benefit by a shaving reduction technique, a small direct incision is used. The major structure that exists between the skin and the subcostal rib margin is the rectus abdominus muscle. Most people think of the paired rectus muscles as inserting along the subcostal rib margin but it actually inserts much higher at the rib #5 and 6 levels. It covers the subcostal rib margin in its entirety. Rather than cutting across it perpendicular to the direction of the muscle fibers, it is better to split it longitudinally. This not offers a more efficient and bloodless dissection but will spare the patient the postoperative pain of transection of the muscle. Once the muscle is split the subcostal ribs come into view.
If the patient is young enough the rib cartilages are soft and can be shaved with a scalpel…but the angle is bad for a flat scalpel blade so it is easier and safer for the surrounding skin edges to do so with a high speed rotary burr. In older patients the rib cartilages are partially calcified so this becomes necessary anyway. The ribs are shaved down as much as needed, usually the small incision like a mobile window, but a thin layer of its inner surface is always preserved. This avoids potentially creating the opposite problem…an indentation or contour defect.
The subcostal rib shave site is closed with a few sutures to close the muscle which is injected with either Marcaine or Exparel for postoperative pain control. The skin is then closed with dermal and subcuticular sutures.
The incision and scar for a subcostal rib prominence reduction is in a fairly exposed area that offers no natural relaxed skin tension line for placement. For this reason it is important to keep its length as small as possible and be sure that the patient considers the scar tradeoff a worthy aesthetic exchange.
Dr. Barry Eppley
Indianapolis, Indiana