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Functional analysis of the effect of the posterior stabilising cam in two total knee replacements

A COMPARISON OF THE INSALL/BURSTEIN AND BISURFACE PROSTHESES

¹ Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho Shogoin, Sakyo-ku, Kyoto City 606-8507, Japan.
² Bioceram Division, Kyocera Corporation, 6 Takeda Tobadono-cho Fushimi-ku, Kyoto City 612 8501, Japan.

Correspondence should be sent to Dr M. Akagi at the Department of Orthopaedic Surgery, Kinki University School of Medicine, 377-2 Ohno-Higashi, Osaka-Sayama City, Osaka 589-8511, Japan.

The Bisurface knee prosthesis (BP) has a posterior stabilising cam (ball-and-socket joint) in the mid-posterior region of the femorotibial joint in an attempt to improve the range of movement. Based on an in vitro weight-bearing study contact areas of the Insall/Burstein 2 (IB2) and the BP knee were compared using pressure-sensitive films. The stability afforded by the cam was evaluated by means of dislocation distances in the vertical and horizontal planes.

Significant adverse anterior translation in mid-flexion was not observed with the BP knee since the cam was effective above 60° of flexion. At flexion of 60° or more, the total contact areas were larger, as the cam represented a weight-bearing surface. The dislocation distances for the BP knee compared favourably with those for the IB2 knee. We conclude that the cam of the BP knee allows good movement, stability and wear.