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

• Published in: Acta orthopaedica 2011-02, Vol.82 (1), p.56-63
• Main Authors: Solberg, Tore K, Sørlie, Andreas, Sjaavik, Kristin, Nygaard, Øystein P, Ingebrigtsen, Tor
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged; Aged, 80 and over; Bias; Cohort Studies; Community medicine, Social medicine: 801; Follow-Up Studies; Health sciences: 800; Health service and health administration research: 806; Helsefag: 800; Helsetjeneste- og helseadministrasjonsforskning: 806; Humans; Intervertebral Disc Displacement - surgery; Lost to Follow-Up; Lumbar Vertebrae - surgery; Medical disciplines: 700; Medisinske Fag: 700; Middle Aged; Outcome Assessment (Health Care); Prospective Studies; Registries; Risk Factors; Samfunnsmedisin, sosialmedisin: 801; Socioeconomic Factors; Spinal Stenosis - surgery; Surveys and Questionnaires; VDP; Young Adult
• ISSN: 1745-3674; 1745-3682
• DOI: 10.3109/17453674.2010.548024

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.