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Minor effect of loss to follow-up on outcome interpretation in the Swedish spine register

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Abstract

Background and purpose

Loss to follow-up in observational studies may skew results and hamper study reliability. We evaluated the importance of loss to follow-up in the Swedish spine register.

Patients

Patients operated in the lumbar spine and scheduled for a postal questionnaire follow-up during part of 2016 were identified. Out of the 351 patients, 203 had responded. After multiple attempts, 115 of the 148 non-responders were reached; 68 returned the complete questionnaire; and 47 answered a brief questionnaire by phone. Analyses were made with the Chi-square test, analysis of covariance or logistic regression. Some analyses were adjusted.

Results

At baseline, the non-responders were younger than the responders (55 vs 61 years, p < 0.001) and had higher Oswestry Disability Index (ODI) (54 vs 48, p = 0.003), lower SF-36 physical component summary score (PCS) (36 vs 40, p = 0.011) and lower EQ-5D (0.17 vs 0.27, p = 0.018). Mean back pain, leg pain, ODI, EQ-5D, SF-36 mental component summary score (MCS) improved significantly in both groups (all p < 0.001). SF-36 PCS did not improve in the non-responder group (p = 0.063). Non-responders perceived less improvement in back pain (global assessment back 60% vs 72%, p = 0.002). At follow-up, there were no differences in patient-reported outcome measures between the groups (all p ≥ 0.06), with the exception of a lower SF-36 MCS among the non-responders (p = 0.015).

Interpretation

After surgery for lumbar spine degenerative disorders, non-responders achieve similar outcome as responders in the Swedish spine register, with the exception of a lower mental health and less perceived improvement in back pain.

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Funding

This study was financially supported by funds from the Swedish Society of Spinal Surgeons. The funding body had no role in the analysis, the interpretation of data or the writing of the manuscript.

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Authors and Affiliations

  1. Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Huddinge, Sweden

    P. Endler, F. Hellström, H. Möller & P. Gerdhem

  2. Department of Orthopaedics, Karolinska University Hospital, Stockholm, Sweden

    P. Endler, F. Hellström, H. Möller & P. Gerdhem

  3. Department of Clinical Science, Karolinska Institutet, Södersjukhuset, Stockholm, Sweden

    P. Ekman

  4. Department of Orthopaedics, Södersjukhuset, Stockholm, Sweden

    P. Ekman

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  1. P. Endler
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  2. P. Ekman
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  4. H. Möller
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  5. P. Gerdhem
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Correspondence to P. Endler.

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Endler, P., Ekman, P., Hellström, F. et al. Minor effect of loss to follow-up on outcome interpretation in the Swedish spine register. Eur Spine J 29, 213–220 (2020). https://doi.org/10.1007/s00586-019-06181-0

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  • DOI: https://doi.org/10.1007/s00586-019-06181-0

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