Outcomes Following Staged Bilateral Total Knee Replacements: The Influence of First-Side Surgery on Results of the Second Side

Background In the UK, the vast majority of bilateral total knee replacements (BTKRs) are performed as staged procedures. Historically, the second-operated knee, in patients undergoing staged BTKRs, has poorer outcomes compared with the first-operated knee. The aim was to review patient-reported outcome measures (PROMs) for staged BTKRs. To further assess if outcomes from the first side of surgery can predict results on the second side. Methods A retrospective analysis was conducted on a consecutive cohort of staged BTKRs using the same approach and technique from August 2009 to January 2020. PROMs were recorded by means of Oxford Knee Scores (OKS) preoperatively, at six weeks postoperatively, and at one year. The minimal important change (MIC) in PROMs was set at ≥5. Results A total of 186 consecutive staged BTKRs were carried out in 93 patients. The average interval between surgeries was 28 months, ranging from 3 to 100 months. The mean age was 65.3 years for the first side and 67.7 years for the second side, with 58.1% of the patients (54/93) being female. The mean body mass index (BMI) was 35.1 for the first side and increased to 35.8 for the second side (p=0.503). One-year follow-up PROMs were available for 97.8% of the first-side surgeries and 89.2% of the second-side surgeries. The average improvement in PROMs at one year was 18.3 for the first side and 15.8 for the second side (p=0.108). A total of 95.6% of patients achieved the MIC for the first side, while 87.9% achieved it for the second side (p=0.340). Fourteen TKRs performed in 13 patients did not achieve MIC at one year. Among these 13 patients, three (23.1%) did not reach MIC after the first-side surgery, compared to nine (61.5%) after the second-side surgery. One patient did not achieve MIC for either side. Of the 14 TKRs that failed to reach MIC in one year, 10 eventually met MIC in two years. The four TKRs that did not achieve MIC at two years were performed on females with high BMIs. Conclusion This study found no significant difference in PROMs improvements between the first and second sides of staged BTKRs at one-year follow-up. A failure to reach the MIC on one side does not affect the success of the other side. Most patients who do not achieve MIC in one year are likely to reach it in two years. Persistent poor scores were associated with high BMI and female sex.