Design and numerical modelling of a cryogenic medical device which facilitates the extraction of an uncemented femoral stem in a revision total hip arthroplasty procedure

Abstract

Total hip arthroplasty is a surgical technique which restores the movement and removes the pain of a hip joint suffering from a different set of pathologies such as osteoarthritis. The long term stability of the artificial joint largely depends on the adequate fixation of the femoral stem and thus, a lot of effort has been made in ensuring its fixation. Because of this, the removal of well-fixed femoral stems typically occurring in uncemented stems is a challenging and time consuming pro- cedure. The set of tools and approaches the surgeons use for the removal of an uncemented stem are quite varied, but the technique is essentially a planned and controlled femoral fracture. Because of this reasons, a new technique which relies on the thermally induced disruption of the bone-stem interface was proposed and is studied in detail. The technique involves the quenching of the femoral stem with liquid nitrogen until the temperature gradient within the stem reaches a certain depth and disrupts the interface. In order to study the novel technique, several finite element models were developed using different concepts from linear elastic mechanics, damage mechanics and heat transfer. The first numerical model developed aimed to replicate a controlled experimental setup performed previously, and analyse the data which was not possible to analyse experimentally, such as the interfacial stresses and displacements, and the temper- ature field within the body. The results obtained suggest that the technique in fact hinders the stiffness of the bond due to the miss-match of thermomechanical properties between the adjoining materials in the interface. Since the controlled experiments were undertaken in simple custom-made geometries and considered a cemented fixation method, the next part of this work focused on creating a nu- merical simulation considering now a real femur and a size 10 stem fixed by an uncemented interface. The results obtained from this model suggest that the un- derlying mechanism is still the same although the technique requires longer times of exposure than in the experimental test with the simple geometries. With these results, several conceptual designs of a medical device were developed and are presented.

Date of Award	1 Aug 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	M.T. Alonso-Rasgado (Supervisor) & Colin Bailey (Supervisor)