Response rate does not affect patient-reported outcome after lumbar discectomy

Quality registers give unique possibilities to achieve information from large groups of patients, but outcome must be interpreted carefully due to less stringent data collection and lower follow-up rates than in research projects. We tried to quantify any outcome differences between a national spine quality register and a prospective observational study.

Adult patients treated with lumbar discectomy between 2004 and 2010 were retrieved from the Swedish Spine register (Swespine) (n = 7791) and from the single center lumbar disc herniation study (LDHS) in Stockholm (n = 177). The mean follow-up rates at 1 and 2 years were 73 and 62%, compared to 98 and 99%, respectively. Patient-reported outcome measurements included VAS for back and leg pain, ODI, EQ-5D, patient satisfaction, and global assessment.

When comparing the two cohorts at baseline, there were minor differences in the patient-reported outcome measurements, all within reported minimal clinical important differences (MCID). Mean outcome improved significantly in both groups after surgery. All outcomes at 1 and 2 years were similar and within the reported MCID in both groups. Complications and reoperations were similar, except for more surgical site infections in the LDHS group.

Higher response rates than seen in Swespine are not needed to achieve reasonably representative data on patient-reported outcome for large cohorts. Two-year data do not seem to add additional information. These slides can be retrieved under Electronic Supplementary Material.