[Developments in hip hemi-arthroplasty and theory of the link-chain dimeric hip prosthesis]

Aim of the study was to analyze the developments of hemiarthroplasties from the femur prosthesis to the bicentric bipolar prosthesis of today. Using the theories published 1990 by Nägerl about "dimeric link chains", nineteen bipolar-head systems were analyzed and biomechanically explained. Clinical findings, such as the problems of luxation and varus positioning of the monocentric bipolars, as well as the valgus, "self-centric" positioning of the bicentric prosthesis are discussed and explained correctly by physics. The hemiarthoplasty with the bicentric bipolar system of today has realized the principles of the dimeric link chains and is superior concept. Eleven of the sixteen today available systems work like this concept which was reached by try and error. The function of a bicentric system is solved now and explained by physics.