Referral Bias in Primary Total Knee Arthroplasty: Retrospective Analysis of 22,614 Surgeries in a Tertiary Referral Center

Background Patients who travel a significant distance to obtain surgical treatment typically experience better outcomes. This is called the referral bias and can limit the generalizability of studies performed at large tertiary care centers. We explored the influence of referral bias by comparing the clinical characteristics and outcomes of total knee arthroplasty (TKA) at a large tertiary care hospital in the United States. Methods The study cohort included 22,614 primary TKA procedures performed between 1985 and 2010. Patients were stratified into 5 groups using home address zip codes and according to travel distance from the hospital. Clinical characteristics and the risk of TKA complications and surgical outcomes (instability, surgical-site infections, and thrombovascular complications within the first year, reoperations, revisions, and mortality) were compared across the 5 groups. Results Compared with local patients, patients who traveled from other parts of the United States were significantly younger (mean age 67.8 vs 68.5 years; P <.05), were more likely to be male (47% vs 38%, P <.001), had lower body mass index (mean 30.4 vs 31.8 kg/m²; P <.001), were more likely to have inflammatory arthritis or neoplasms as surgical indications (P <.05), and were more likely to have a history of prior surgeries on the same knee (20% vs 14%; P <.001). Referral patients also had significantly higher American Society of Anesthesiologists scores and longer operative times (mean 173 vs 156 minutes P <.001). Despite these differences, the risk of instability, surgical-site infections, thrombovascular complications, reoperations, and revision surgeries were similar across the 5 groups. Conclusion Although referral patients differ from local patients, the groups seem to experience largely similar complication and revision rates after TKA.