PubMed · 9801229
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N F Friederich. 1998. Duplicate publication?. https://pubmed.ncbi.nlm.nih.gov/9801229/
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OBJECTIVE: A spring network can be used to represent the load transfer from a prosthetic stem into its surrounding bone. The study seeks to test the hypothesis that clinical patterns of bone remodelling can be simulated using a feedback that modifies the properties of the network depending on the load transfer. DESIGN: A mathematical model is used to simulate the initial properties of the linear system and its subsequent remodelling behaviour. BACKGROUND: A stable and pain-free transfer of physiological forces is essential for a clinically successful arthroplasty. Following surgery, bone remodelling and osteolysis can modify this load transfer. METHODS: The combined effect of all factors that influence prosthesis-bone load transfer are summarised in the properties of 'inter-link' springs that connect springs representing the prosthesis and bone in the linear network. It is on these inter-links that a remodelling feedback operates, and their properties can be varied with time in response to deformation or force values. RESULTS: Reducing inter-link stiffness leads to a broad distribution of load transfer, whilst an iso-elastic stem concentrates this transfer through the proximal and distal portions of a prosthesis. Physiological patterns of bone resorption and osteolysis become apparent in a time-series analysis of the feedback in the linear system. Specifically, osseo-integration requires a fixation of sufficient stiffness otherwise loosening will occur. Simulated osteolysis following osseo-integration loosens the implant from a distal to a proximal direction. CONCLUSIONS: Complex physiological bone remodelling patterns can emerge from a simple feedback within a linear system. Relevance. Implant loosening is presented here as an adverse response of a stable dynamic system caused by mechanical or biological stimuli.
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A new hybrid fixation stem, named cemented-locked uncemented (CLU), for total hip arthroplasty was developed to achieve good initial stability. Primary stability is guaranteed by the cement which is injected into two pockets in the lateral area. This leaves a large surface available for long-term biologic fixation (direct bone attachment on implant). This study evaluates in vitro the initial stability of the CLU prototype under torsional load, in comparison with cemented and cementless stems. The results show that the CLU stem is very stable in simulated stair climbing. Its micromotions are comparable to those of a cemented prosthesis, and significantly less (80-90% lower) than those for a cementless stem. These findings confirm the optimal initial stability expected from the CLU prototype. This new design, which employs hybrid fixation, should improve bone formation on the implant and reduce the risk of stem loosening.