An evaluation of retrospective SF-12 and Foot Function Index (FFI) outcome scores in elective foot and ankle surgery

J. Widnall, P. Ralte, D. Selvan, A. Molloy

Introduction: Patient reported outcome measures are becoming more popular in their use. Retrospective scoring is not yet a validated method of data collection but one that could greatly decrease the complexity of research projects. We aim to compare preoperative and retrospective scores in order to assess their correlation and accuracy.

Methods: 36 patients underwent elective foot and ankle surgery. All patients were scored preoperatively using the SF-12 and FFI. Patients then recorded both PROMs retrospectively at the three month follow up (av. 139 days). Results were then analyzed for statistical significance.

Results: 36 patients (av. age 54.6 years) completed both sets of questionnaires. There were 15 hindfoot and 21 forefoot procedures. Two patients (5.6%) recalled their identical preoperative SF12 score. No retrospective FFI scores were identical. The mean percentage difference between the two preoperative scores was; -0.9% (-5.8 to 4.0%, 95% CI) for SF12 and 40.7% (25.3 to 56.1%, 95% CI) for FFI. This retrospective accuracy was statistically significant (p< 0.001). When both scores were plotted against each other, the outcome measurements showed positive correlations (SF 12 p 0.31, FFI p 0.81). With both PROMs mean percentage differences combined, patients undergoing hindfoot procedures (13.5%; 5.8 to 21.3%, 95% CI) were more accurate with retrospective scoring than their forefoot counterparts (26.8%; 10.4 to 43.1%, 95% CI). This was not statistically significant.

Conclusion: Retrospective scoring appears to lack accuracy when compared to prospective methods. However, our data shows the SF12 is recalled more accurately than the FFI (p< 0.001) and to an average discrepancy of < 1% when compared to the original preoperative result. These results show patients tend to recall their symptoms at a worse level preoperatively than originally described, especially those with forefoot problems.