In vivo anterior tibial post contact after posterior stabilizing total knee arthroplasty

Anterior polyethylene post failure in posterior stabilizing total knee arthroplasty (TKA) has been reported in recent patient follow‐up studies. However, no data have been reported on the biomechanic interaction between the anterior tibial post and femoral component in posterior stabilizing TKA patients under physiological conditions. The objective of this study was to measure the in vivo anterior tibial post contact area at full knee extension using a dual‐orthogonal fluoroscopic imaging technique. Eleven osteoarthritic patients were investigated after posterior stabilizing TKA to measure the contact between the femoral component box and anterior aspect of the tibial post. Anterior tibial post contact, ranging between 0.5 and 80.9 mm2, was detected in 63% of the healthy patients (seven out of the eleven patients) at weight‐bearing full extension of the knee. The patients with anterior tibial post contact had significantly higher hyperextension angles (−8.4 ± 4.3°) than those without contact (1.4 ± 7.2°). A statistically significant difference was also detected in the femoral component flexion with respect to the femoral shaft between the patients with anterior post contact (2.7 ± 2.7°) and without anterior post contact (−1.3 ± 2.2°). These data indicated that anterior post contact did occur in hyperextension within posterior stabilizing TKA patients. While excessive anterior tibial post contact may cause polyethylene wear and potentially lead to post failure, the tibial post may also act as a substitute for the ACL at low flexion, thus providing stability to the joint after posterior stabilizing TKA. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1447–1453, 2007