DOS 2019

174 · DOS Abstracts The osteoarthritic knee is worse in retrospective: recall bias in Oxford Knee Score and patient- reported range of motion 1 year after knee replacement Anne Mørup-Petersen, Sofia Mitropolskaya, Anders Odgaard Ortopædkirurgisk Afdeling, Herlev og Gentofte Hospital Background: Patient-reported outcome measures (PROMs) concern patients’ symptom states either currently or in the preceding e.g. four weeks, as in the case of Oxford Knee Score (OKS). Symptoms recorded retrospectively are gen- erally perceived as less reliable, but, to our knowledge, no studies have reported recall bias in Danish knee arthroplasty patients Purpose / Aim of Study: We sought to explore how well patients were able to remember their preoperative knee status one year after primary knee arthro- plasty (pKA). Also, we aimed to find factors influencing recollection error. Materials and Methods: 128 pKA patients, who had provided electronic pre- operative PROM answers as part of a large prospective cohort study, were con- tacted by email two weeks after completion of their 1-year follow-up PROM set. An email titled, “Do you remember how your knee was before the opera- tion?” contained OKS (0-48) along with Copenhagen Knee ROM Scale and a question regarding use of analgesics, all in past-time wording. Findings / Results: 95 patients (74.2%) responded. Recalled OKS was 22.3 [CI: 20.9; 23.6] (SD 6.8, range 7-37), whereas true preoperative OKS was 24.4 [23.1; 25.7] (SD 6.5, range 8-41). The majority of patients (n=58, 61.1%) recalled a score worse than the actual score, and 9 (9.5%) reported the same overall score. The mean recall difference was -2.1 OKS points [-3.2; -1.1] (SD 4.9, range -16 to 10, P<0.001). This was more pronounced in females (insig- nificant in males) and in patients with high preoperative OKS level (P<0.03), but independent of age and OKS result at 1 year. Knee flexion was 1 score worse (median) at recall (corresponding to 10-20°, P<0.001). Knee extension and frequency of analgesics use did not differ significantly between the two tests. Conclusions: One year after knee replacement, patients recalled their preop- erative knee symptoms worse than originally reported. Though the reported difference in OKS is lower than the smallest possible detectable change (4 points), this should be kept in mind whenever recall OKS is used to replace real- time data. 130.