The Journal of Bone and Joint Surgery (American). 2010;92:1765-1773.
doi:10.2106/JBJS.I.00479
© 2010 The Journal of Bone and Joint Surgery, Inc.
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Contact Stress at the Anterior Aspect of the Tibial Post in Posterior-Stabilized Total Knee Replacement

Satoshi Hamai, MD, PhD1, Hiromasa Miura, MD, PhD1, Shuichi Matsuda, MD, PhD1, Takeshi Shimoto, PhD2, Hidehiko Higaki, PhD2 and Yukihide Iwamoto, MD, PhD1

1 Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. E-mail address for H. Miura: miura{at}ortho.med.kyushu-u.ac.jp
2 Department of Mechanical Engineering, Faculty of Engineering, Kyushu Sangyo University, 2-3-1 Matsugadai, Higashi-ku, Fukuoka 813-8503, Japan

Investigation performed at the Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan

Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

Background Retrieval studies have demonstrated polyethylene wear and deformation of the anterior aspect of the tibial post of posterior-stabilized total knee replacements. We are not aware of any study that has analyzed the effects of the design of the femoral notch and the anterior aspect of the tibial post of posterior-stabilized total knee replacements on contact area, stress, and location. The purpose of the present study was to determine the levels of contact stress generated in three posterior-stabilized total knee replacement designs when the femoral intercondylar notch impinges on the anterior aspect of the tibial post.

Methods The contact area, mean and peak contact stresses, and contact location at the anterior aspect of the tibial post were determined when a posterior force of 100 N was applied to a NexGen LPS Flex, Genesis II, and Scorpio NRG total knee replacement. Measurements were performed at –15°, –10°, –5°, 0°, and 5° of flexion of the femoral component both in neutral and with 5° of rotation of the tibial component. Each measurement was sequentially performed five times, and the data were compared within and between the designs with use of analysis of variance and a post-hoc Scheffé F test.

Results The NexGen LPS Flex exhibited two contact areas on the medial and lateral corners of the anterior aspect of the post, whereas both the Genesis II and Scorpio NRG exhibited a single horizontal band. The NexGen LPS Flex showed the largest total contact area of the three designs at –15°, –10°, and 5° of flexion. The NexGen LPS showed the lowest mean contact stress at –15° and 5° but showed the highest peak contact stress at –5° and 0°. The Scorpio NRG showed the highest mean contact stress under all conditions and showed the highest peak contact stress at –15°, –10°, and 5°. With 5° of rotation of the tibial component, peak contact stress increased, relative to neutral, 1.2 to twofold (depending on the flexion angle) in the Genesis II design.

Conclusions The mean and peak contact stresses were variable for all three designs and the test conditions, approaching and in some cases exceeding the compressive yield stress for polyethylene. The geometry of the metal femoral notch and polyethylene tibial post in the axial and sagittal planes significantly affected contact area, mean and peak stresses, and contact location at the anterior aspect of the tibial post.

Clinical Relevance This study helps the surgeon to be more aware that high contact stresses under some conditions could lead to deformation and damage of the anterior aspect of the post in these three common designs of cruciate-sparing total knee replacements.


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