The medial collateral ligament connects the end of the femur (thigh) to the top of the tibia (shin bone)

Smoking is a well-known contributor to heart disease, cancer and emphysema. But it also might cause you to limp a little longer after knee surgery. A research team at the Washington University School of Medicine in St. Louis studied mice with injuries to the medial collateral ligament, or MCL. Tearing of this knee ligament is one of the most common injuries among human athletes.

Orthopedic surgery researcher Linda Sandell explains that mice in the study smoked the equivalent of four packs of cigarettes a day, before and after their MCL surgery. "The mice are put in a tube, and they're exposed directly to cigarette smoke … and [we] know the levels of certain marker toxins in the bloodstream for these animals over a certain time. So we know those physiological effects of smoking."

The mice exposed to cigarette smoke did not heal as well - or as quickly - after MCL surgery as non-smoking mice.

Orthopedic surgery researcher Linda Sandell

Sandell reports, "The primary effect of smoking in our healing models is that we have less recruitment of cells to the healing process." Researchers suspect that smoking somehow interferes with the body's communication system that signals the healing macrophage cells to move to the injury site. Previous studies have shown that smoking hurts the body's ability to heal surgical wounds, but this is the first evidence that it also interferes with ligament healing.

Co-investigator and sports medicine specialist Rick Wright says he's counseling

Co-Investigator and sports medicine specialist Rick Wright

patients to try to quit smoking well before surgery. "We do have clear data that it will impact their ability to heal the surgical wounds. And now, I've started counseling patients with ligament injuries that I believe - while I can't tell them how much a difference it makes right now - decreasing or stopping smoking improves their ability to heal ligaments."

Wright and Sandell are continuing their studies, withdrawing mice from smoking at the time of surgery to see whether that speeds up ligament healing. They reported their findings in the Journal of Orthopaedic Research.