Abstract
BackgroundOne of the main goals in total hip replacement is to preserve the integrity of the hip kinematics, by well positioning the cup and to make sure its initial stability is congruent and attained. Achieving the latter is not trivial. MethodsA finite element model of the cup–bone interface simulating a realistic insertion and analysis of different scenarios of cup penetration, insertion, under-reaming and loading is investigated to determine certain measurable factors sensitivity to stress–strain outcome. The insertion force during hammering and its relation to the cup penetration during implantation is also investigated with the goal of determining the initial stability of the acetabular cup during total hip arthroplasty. The mathematical model was run in various configurations to simulate 1 and 2mm of under-reaming at various imposed insertion distances to mimic hammering and insertion of cup insertion into the pelvis. Surface contact and micromotion at the cup–bone interface were evaluated after simulated cup insertion and post-operative loading conditions. FindingsThe results suggest a direct correlation between under-reaming and insertion force used to insert the acetabular cup on the micromotion and fixation at the cup–bone interface. InterpretationWhile increased under-reaming and insertion force result in an increase amount of stability at the interface, approximately the same percentage of surface contact and micromotion reduction can be achieved with less insertion force. We need to exercise caution to determine the optimal configuration which achieves a good conformity without approaching the yield strength for bone.
Highlights
Each year, as many as 200,000 total hip replacements (THR) are performed in the UnitedStates [1], and approximately 7% of those require revision arthroplasty within 8 years of the initial procedure [2]
Following the first phase of cup insertion, the insertion force of the cup was evaluated to observe the influence of the force needed to insert under-reamed cups set to varying target locations, as specified by the hammering distance imposed on each cup
The results show that insertion force increases as a function of the amount of underreaming, as well as increasing target insertion distances Figure 7
Summary
As many as 200,000 total hip replacements (THR) are performed in the UnitedStates [1], and approximately 7% of those require revision arthroplasty within 8 years of the initial procedure [2]. As many as 200,000 total hip replacements (THR) are performed in the United. Risk factors for THR revision are patient-related (e.g., gender, neuromuscular disorder status, bone quality) or surgery-related (e.g., surgical approach of primary THA, orientation of the cup, component malpositioning, femoral head size, neck head offset, and surgeon experience) [14–. One of the main goals in total hip replacement is to preserve the integrity of the hip kinematics, by well positioning the cup and to make sure its initial stability is congruent and attained.
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