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Knee News

When No News Seems Like Good News after Total Knee Replacement

There's one big problem with follow-up studies in medicine: patients who are "lost to follow-up." These patients are included in the study at the outset. But then they stop returning letters or phone calls, or just generally make themselves scarce. These "lost" patients can sway the results of studies if, as a group, their outcomes are not like the patients who stayed in the study. Luckily, most studies lose few patients to follow-up.

However, patients who don't respond are more of a problem in mail surveys. And mail surveys are being used more and more by hospitals and doctors. After total knee replacement (TKR), mail surveys are often used to rate patient satisfaction and knee function. In this study, mail surveys were sent to 472 TKR patients. The survey included 10 simple questions. The answers were compared to the doctors' records from the patients' clinic visits. But the focus of the study was not so much on the answers. These researchers wanted to know if the nonresponders would in any way have changed the outcomes.

To do this, the researchers needed to make sure that all 472 patients answered the survey questions. For 83 percent of the patients, this was not a big problem. They returned their surveys after one or two mailings. The remaining 17 percent took some nagging. These 80 nonresponders got up to four further mailings and then phone calls until they answered the questions.

When the results were all in, the data was sorted by how quickly patients had responded. There were important differences between early responders and nonresponders. Early responders generally had:

  • Better knee function.
  • Less pain and swelling.
  • Higher satisfaction with their treatment.
  • Higher activity levels.
  • Better knee motion and stability.
  • Better ability to walk.

    In a normal study, the nonresponders would not have been hounded until they answered the survey. In this case, that means the survey would have shown much more positive results than were actually true. The patients "lost to follow-up" would definitely have swayed the survey results to make the outcomes of TKR look better.

    The study also showed that the clinical scores recorded by doctors during clinic visits looked better than patients' reports. The authors recommend that studies should allow patients to report their own levels of subjective items such as pain. The authors also recommend that all surveys should make every effort to get all patients to answer surveys. It could make a big difference in the final data.


    Jane Kim, BA, et al. Response Bias: Effect on Outcomes Evaluation by Mail Surveys after Total Knee Arthroplasty. In The Journal of Bone and Joint Surgery. January 2004. Vol. 86-A. No. 1. Pp. 15-21.

    03/15/2004

    *Disclaimer:* The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic.
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