Controversy persists concerning around posterior cruciate ligament (PCL) retention in total knee arthroplasty (TKA) for patients with rheumatoid arthritis (RA). This study investigated factors affecting anteroposterior (AP) instability following cruciate-retaining (CR)-TKA. In a consecutive series of 70 knees from 52 RA patients, total displacement (TD) was measured using a KT-2000 arthrometer before and after CR-TKA under anesthesia, and changes in TD were defined as DeltaTD. TD was also measured under anesthesia in 65 knees from 48 RA patients at a mean of 7.5 years after CR-TKA. Mean postoperative TD was 9.4+/-0.95 mm, representing an increase of about 1.5-1.8 mm compared to preoperative TD, and possibly reflecting resection of the anterior cruciate ligament. Correlation analysis revealed significant negative correlations between DeltaTD and both preoperative flexion angle (r=-0.67, p<0.001) and preoperative extension angle (r=-0.63, p<0.001), suggesting that TD in knees with flexion contracture increased postoperatively. At medium-term follow-up, no patients displayed AP instability, and mean TD was 8.3+/-0.48 mm. A significant correlation was found between TD and permissible flexion angle (r=0.61, p<0.001). These results indicate that TD is basically maintained during the course of CR-TKA in RA, but may be slightly affected by factors other than the PCL itself.