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Thursday, March 1, 2001

Restoration of normal knee function depends on load sharing

Restoration of normal knee joint function through surgical reconstruction is dependent upon load sharing between the implant and surrounding soft tissue structures. Mobile bearing knee designs offer the advantage of maximum conformal geometry while diminishing constraint forces to fixation interfaces through plateau mobility, said researchers in scientific study 26. The degree of mobility afforded by these designs in anterior-posterior, medial-lateral and rotational directions, they said, defines the interaction necessary to maintain a stable articulation.

A study characterizes mobile bearing knee designs in terms of displacement under simulated in vivo loading and provides implant selection criteria for specific patient pathologies.

To conduct the study, a dynamic testing system was utilized to measure intrinsic directional constraint. Force-displacement curves were obtained and analyzed to establish the extent of tibial insert sliding as well as the shear forces generated by each tibial-femoral geometry.

All of the designs evaluated permitted rotation without the engagement of mechanical stops. In contrast, none of the designs accommodated medial-lateral translation without being coupled with internal/external rotation. There were substantial differences in the degree of mobility offered by these designs in the anterior-posterior direction due to the utilization of mechanical stops on the tibial tray to avoid component subluxation.

The researchers found that although differences in the degree of mobility offered by these mobile bearing knee designs were recorded, all displacements occurred within normal, anticipated in vivo ranges. This points out the absolute importance of soft tissue reconstruction during TKA to ensure a stable articulation in a given patient, the researchers said.

Coauthors of the study are Christine S. Heim, BSc; Paul D. Postak, BSc; Nicholas A. Plaxton, MS; and A. Seth Greenwald, D.Phil. (Oxon), all of Orthopaedic Research Laboratories, Lutheran Hospital, Cleveland Clinic Health System, Cleveland, Ohio.

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Last modified 14/February/2001 by IS