Would loss to follow-up bias the outcome evaluation of patients operated for degenerative disorders of the lumbar spine?

Abstract

Background and purpose Loss to follow-up may bias the outcome assessments of clinical registries. In this study, we wanted to determine whether outcomes were different in responding and non-responding patients who were included in a clinical spine surgery registry, at two years of follow-up. In addition, we wanted to identify risk factors for failure to respond.Methods 633 patients who were operated for degenerative disorders of the lumbar spine were followed for 2 years using a local clinical spine registry. Those who did not attend the clinic and those who did not answer a postal questionnaire—for whom 2 years of outcome data were missing—and who would be lost to follow-up according to the standard procedures of the registry protocols, were defined as non-respondents. They were traced and interviewed by telephone. Outcome measures were: improvement in health-related quality of life (EQ-5D), leg pain, and back pain; and also general state of health, employment status, and perceived benefits of the operation.Results We found no statistically significant differences in outcome between respondents (78% of the patients) and non-respondents (22%). Receipt of postal questionnaires (not being summoned for a follow-up visit) was the strongest risk factor for failure to respond. Forgetfulness appeared to be an important cause. Older patients and those who had complications were more likely to respond.Interpretation A loss to follow-up of 22% would not bias conclusions about overall treatment effects and, importantly, there were no indications of worse outcomes in non-respondents.

Factors Associated With Survey Response in Hand Surgery Research

“…The factors associated with not returning the survey were younger age, male sex, and more pain. Our finding that older patients are more likely to return the survey is in line with previous studies [7,21,26]. Smoking, marital status, and working status were not associated with returning surveys in our study, in contrast to earlier studies that did find differences in these demographic factors [8,13,21].…”

“…[1,15,17,21,[25][26][27]. Previous studies suggest that nonresponders to mailed surveys might differ in important ways from responders [7,8,13,21].…”

“…This is an important unresolved question that requires a different study design to address. Related to this, many survey studies in orthopaedic surgery evaluate the effects of major surgical interventions [2,5,10,15,17,23,26,27,33]; ours evaluated a mixed cohort of patients, many of whom had minor interventions or no intervention apart from the office visit. It is difficult to estimate what influence this difference might introduce on our results.…”

“…Solberg et al sent their patients a survey containing the European Quality Of Life-5 Dimensions (EQ-5D), a question regarding perceived benefit of the operation, and VAS for leg pain, back pain, and state of health after spine surgery [26]. The patients who did not respond were considered to be nonresponders and they received a phone call to find out why they did not return the survey [26].…”

“…One weakness of research that relies on mailed surveys for followup is a low response rate [26]. Response rates after mailings in medical research average approximately 60% [1].…”