Loss to follow-up after total hip replacement: a source of bias in patient reported outcome measures and registry datasets?

Patient reported outcome measures (PROMs) are used to gauge clinical performance. The PROMs outcome programme at our centre achieves a preoperative data capture rate of 99%. This falls to 90.6%, 89%, 83% and 79% at the six-week, six-month, one-year and two-year time points, respectively. The study aims were to determine factors associated with patients who did not respond to outcome questionnaires following total hip replacement (THR), and the potential implications this may have when assessing patients following THRs. During the first year of the PROMs programme, 1,322 patients underwent unilateral primary THR at our institution. Of these, 1,311 completed preoperative questionnaires. Thirty-eight patients (2.9%) died within two years of surgery and have been excluded. For the remaining 1,273 patients, we identified those who did not return postoperative questionnaires at each of our review time points. Younger age, lower baseline EQ5D and Oxford Hip scores (OHS) were significantly associated with non-response (p<0.001). Patients with lower satisfaction scores, OHS and EQ5D scores, were less likely to respond to subsequent questionnaires. A significant association between non-response and deprivation (p<0.001) was demonstrated. Our findings suggest that the more satisfied patients are over-represented and our reported outcome results are better than they would have been if all patients had responded. This phenomenon may apply to studies where those categorised as "lost to follow-up" represent a subset of patients who have disengaged due to poor outcome or satisfaction.