Two studies presented at the 2012 annual meeting of the American Academy of Orthopaedic Surgeon highlight the dangers that smoking poses to patients receiving total knee or hip implants.

The first study looked at more than 600 total knee replacements (in patients with an average age of 62), performed between 2005 and 2009 at the Center for Joint Preservation and Replacement at Sinai Hospital of Baltimore, and the Bonutti Clinic of Effingham, Illinois. Among the patients, approximately 115 were smokers.

The researchers found that the overall revision rate – meaning the number of surgeries that had to be redone – was 10 times higher for smokers compared with nonsmokers: 10 percent vs. 1 percent. Smokers also had a significantly higher rate of complications compared with non-smokers (21 percent vs. 12 percent), including blood clots, abnormal heartbeat, irregular heartbeat, urinary tract infection and kidney failure.

The second study used data from 535 hip replacements surgeries (in 500 patients) performed by Joint Implant Surgeons Inc., a private practice in New Albany, Ohio between 1999 and 2009. Of the surgeries, 160 were first time hip implants, and 375 were revision surgery. Among the patients, 17 percent were smokers, 29.5 percent past smokers, 49 percent nonsmokers and the smoking status of 4.5 percent of patients was unknown.

The results show there were 33 failures at an average of 18 months after surgery, which translates into a 6.2 percent failure rate. When broken down into smoking status, failure rates were 11 percent in smokers, 5.3 percent in previous smokers and 3.8 percent in nonsmokers.

The study looked at a specific type of hip surgery that reconstructed the cup-shaped cavity at the base of the hip bone – called the acetabulum – using porous metal. The idea is that bone grows into and around the porous implant, which secures it.

The researchers considered failures due to infection, an inability of the bone to grow into the porous metal or hip fractures as possibly related to smoking (non smoking-related failures included dislocation and implant breakage).  When taking into account only smoking-related failures, the failure rate was 9 percent in smokers and 3.6 percent in nonsmokers.

Why this differences in failure rates between smokers and nonsmokers?