Background: Mail survey questionnaires are increasingly being used
for follow-up evaluations to gauge satisfaction and performance after total
joint arthroplasty. Responses to questionnaires are subject to a variety of
possible biases. We evaluated response behavior in a mail survey of patients
who had had a total knee arthroplasty.
Methods: A ten-question survey that evaluated satisfaction, general
health, and Knee Society knee function and clinical scores was mailed to 472
patients who had undergone consecutive primary total knee arthroplasties from
1996 to 1998. The 83% who responded were stratified as early, late, and
repeat-mailing responders. The 17% who failed to respond after two mailings
were considered nonresponders. All of the nonresponders were eventually
contacted. The groups were compared with regard to their scores at the
preoperative office visit, at the most recent office visit, and on the mail
survey.
Results: In the mail survey, the patients who responded earliest
gave the highest satisfaction ratings and the nonresponders gave the poorest
ratings (p < 0.001). Similarly, the mean Knee Society knee score (and
standard deviation) was significantly higher for the early responders (82.7
± 19.0) than for the nonresponders (66.9 ± 16.0), as was the
mean function score (68.8 ± 24.1 compared with 48.4 ± 12.5) and
the mean pain score (39.8 ± 13.9 compared with 27.0 ± 9.7) (all
p < 0.0001). The change between the preoperative and mail survey Knee
Society knee scores was significantly higher for the early responders (46.12
± 25.71) than for the nonresponders (28.45 ± 23.62), as was the
change in the mean function scores (18.87 ± 22.52 compared with 5.34
± 20.05) and the change in the mean pain scores (23.57 ± 17.76
compared with 10.67 ± 12.93) (all p < 0.0001).
Conclusions: Patients who do not respond to mail surveys used for
follow-up are unique in that they report significantly poorer outcomes than do
responders. This potential response bias should be considered in all follow-up
analyses. Because it may be difficult to attain 100% response rates in very
large series of patients, division of the study cohort into more manageable
segments is advised to achieve a more complete response rate. The assessment
of patients who are lost to follow-up is an important and necessary component
in the accurate analysis of outcomes after arthroplasty.