Study design:

Follow-up study OBJECTIVE.: To determine whether minimally invasive lumbar spine surgery outcomes are different between those who are lost to follow-up and those who are not.

Summary of background data:

Lost to follow-up patients are a common source of selection bias for clinical outcomes research. Currently, there are no US based studies that evaluate the differences in outcomes of lost to follow-up patients after spine surgeries.

Methods:

A retrospective review of prospectively collected data of 289 patients who underwent minimally invasive lumbar surgery and were at least 1 year post-surgery was performed. Patients were divided into two groups: (1) Lost to follow-up (LTF), defined as patients who had missed >2 consecutive follow-up visits and had not attended their 1-year follow-up appointment; and (2) Not lost to follow-up. For the not-LTF cohort, PROMs (ODI, VAS back/leg, SF-12 Physical/Mental, PROMIS) and return to activities data were collected prospectively at each follow-up. For LTF patients, data were collected through emailed surveys or telephone interviews. PROMs and return to activities data of the two groups were compared. Sub-group analysis by type of surgery (decompression or fusion) was also performed.

Results:

For the entire cohort, independent t-test analysis showed LTF patients had greater improvement in PROMIS Physical Function scores than those who were not-LTF (15.08 vs 10.38, p = 0.026). For fusion surgeries, LTF patients showed a greater improvement in ODI (-30.94 vs -16.23, p = 0.003) VAS back (-4.92 vs -2.99, p = 0.044), and PROMIS-PF (16.09 vs 10.38, p = 0.049). There were no significant differences in complication rates between LTF and not LTF patients.

Conclusion:

Patients undergoing minimally invasive lumbar surgery – in particular lumbar fusions – who are lost to follow-up and responded to subsequent email and phone interviews showed greater improvements in self-reported outcomes than those who continued to follow-up. Thus, our results suggest that a substantial subset of patients who are lost to follow-up do not fare worse than those who do follow-up. However, an opposite response cannot be excluded in those who did not respond to email and phone interviews.

Level of evidence:

3.