Patient-reported outcomes unbiased by length of follow-up after lumbar degenerative spine surgery: Do we need 2 years of follow-up?

Publication date: Available online 5 October 2018

Source: The Spine Journal

Author(s): Victor E. Staartjes, Alessandro Siccoli, Marlies P. de Wispelaere, Marc L. Schröder

Abstract

Background

In modern clinical research, the accepted minimum follow-up for patient-reported outcome measures (PROMs) after lumbar spine surgery is 24 months, particularly after fusion. Recently, this minimum requirement has been called into question.

Purpose

We aim to quantify the concordance of 1- and 2-year PROMs to evaluate the importance of long-term follow-up after elective lumbar spine surgery.

Study Design

Retrospective analysis of data from a prospective registry.

Patient Sample

We identified all patients in our prospective institutional registry who underwent degenerative lumbar spine surgery with complete baseline, 12-month, and 24-month follow-up for ODI and NRS back and leg pain.

Outcome Measures

Oswestry Disability Index (ODI) and numeric rating scales for back and leg pain at 1 year and at 2 years.

Methods

We evaluated concordance of 1- and 2-year change scores by means of Pearson's product-moment correlation and performed logistic regression to assess if achieving the minimum clinically important difference (MCID) at 12 months predicted 24-month MCID. Odds ratios (OR) and their 95% confidence intervals (CI), as well as model areas-under-the-curve (AUC) were obtained.

Results

A total of 210 patients were included. We observed excellent correlation among 12- and 24-month ODI (r = 0.88), NRS-LP (r = 0.76) and NRS-BP (r = 0.72, all p < 0.001). Equal results were obtained when stratifying for discectomy, decompression, or fusion. Patients achieving 12-month MCID were likely to achieve 24-month MCID for ODI (OR: 3.3, 95% CI: 2.4 to 4.1), NRS-LP (OR: 2.99, 95% CI: 2.2 to 4.2) and NRS-BP (OR: 3.4, 95% CI: 2.7 to 4.2, all p < 0.001) with excellent AUC values of 0.81, 0.77, and 0.84, respectively. Concordance rates between MCID at both follow-ups were 87.2%, 83.8%, and 84.2%. A post-hoc power analysis demonstrated sufficient statistical power.

Conclusions

Irrespective of the surgical procedure, 12-month PROMs for functional disability and pain severity accurately reflect those at 24 months. In support of previous literature, our results suggest that 12 months of follow-up may be sufficient for evaluating spinal patient care in clinical practice as well as in research.

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