Ask the Doctors June 2013 Issue

Ask The Doctors: June 2013

Gender-specific knee implants...Biologic response modifier drugs for RA...

Q. My doctor has explained that a total knee replacement is the best treatment option for my osteoarthritis. As a petite woman, Iíve read that itís important that my surgeon uses a ďgender-specificĒ implant for a successful outcome. Is this true?

A. Total knee arthroplasty (TKA) is one of the most successful surgical procedures, with more than 600,000 knee replacements performed each year in the United States. As the procedure evolves, there has been a lot of attention on gender-specific knee implant sizing. Undeniably, there are small differences that occur in the shape of a womanís knee compared with that of a man. However, recent study results suggest that the differences are very small and not likely clinically significant.

A recent Korean study reviewed 30 female patients (average age 69.5 years) with a diagnosis of bilateral knee osteoarthritis. During bilateral TKA, a conventional implant was used in one knee and a gender-specific design was used in the opposite knee. Assignment of implant was both random and blinded to the surgeon and the patient, with all patients followed for a minimum of one year. The researchers found no significant difference between the two groups preoperatively, and at the most recent follow-up after surgery. The study also found no overwhelming patient preference for the gender-specific implant.

For clinical success, a total joint prosthesis must fit the bones of the knee it is implanted. While the size of the knee bone is, on average, smaller in women than in men, many men fall into the smaller size range and many women fall into the larger size range. This suggests that the physical build of the individual, not the gender, is the important factor. Overall, reported total knee replacement for women are equal to or better than those for men when traditional, non-sex-specific implants are used.

Q. Iíve been taking methotrexate for my rheumatoid arthritis for over a year, but itís not helping my symptoms. My doctor has suggested adding a biologic response modifier (BRM) drug to my treatment plan, but Iíve heard that BRMs can increase my risk of cancer. Is this true?

A. Rheumatoid arthritis has been treated with traditional or synthetic disease-modifying antirheumatic drugs (DMARDs) for many years. However, some patients arenít able to tolerate DMARDs well, or the drugs are not helpful for their condition. For these patients, agents known as biologic response modifiers (BRMs), also referred to as ďthe new or biologic DMARDsĒ have proven to significantly improve control of RAís symptoms.

Some studies have suggested BRMs are associated with an increased risk of infection and malignancy. A large observational study published in the journal Arthritis & Rheumatism that reviewed 13,000 patients with RA found a small but significant increase in skin cancer in patients taking BRMs.

The most recent study on BRM use specifically in RA patients showed no statistically significant increased risk of any type of cancer with the use of the drugs for at least six months as compared to controls. The study, published in the Journal of the American Medical Association (September 2012), suggests a small but significant increase in risk of malignancy at 52 weeks for patients on a combination of tumor necrosis factor (TNF) inhibitors and methotrexate, but this was not found at other time points during the study. Although this study did not find an increased cancer risk from BRMs used in the short term, future studies may help guide use of the drugs. Currently, BRMs are greatly beneficial for many RA patients, especially when used in combination with traditional DMARDs in early, moderately active RA.