Development of an instrumented hammer for the estimation of the stability of implants used in orthopedic surgery – OrthoMat

We have worked on the measurement protocol and on the hardware (size and weight of the hammer, data processing, sensors, etc...). In order to reduce the number of experimental tests with anatomical subjects, numerical simulations have been used to calibrate the model in order to improve the accuracy of the device. We have developed a reliable in silico model of the impact procedure for the femoral stem and for the acetabular cup implant, which allows the development of a signal processing algorithm that may be tested in silico. Signal processing techniques have been refined.

1. WP1 : Coordination of OrthoMat
No particular problem was met on WP1. The coordination is relatively easy due to the low number of partners.

2. WP2 : Development of a final protoype for CE Marking
We have already explored the regulatory environment of the future medical device, inclulding the cclass (Im) and the regulatory environment. The main step that will need to be performed will be to validate the sterilization, the electric safety and the CEM as well as the biocompatibility. We will also need to set up a SMQ.
We are now working on the final conception of the hammer and we have chosen to use stress sensors that must be included in the hammer.

3. WP3 : Modeling, simulation, signal processing
_We have studied the determinants of the primary stability of cementless acetabular cup implants using a 3D isogeometric finite element study [1]
_We have developed a stiction model to understand the long-term stability and debonding of cementless implants [2].
_We have studied the influence of the biomechanical environment on the femoral stem insertion and its vibrational behavior using a 3-D finite element study [5]
_We have developed an optimization model of a smart beam for monitoring a connected inaccessible mechanical system and applied it to bone-implant coupling [6]

4. WP4 : In vitro experiments
_We have validated the use of an instrumented hammer to monitor the femoral stem insertion [3]
_We have shown that it can be used to determine the occurrence of fractures around the femoral stem [8]

5. WP5 : Validation on anatomical subjects.
Here, we have focused on the validation of the instrumented in the context of rhinoplasty because it had not been done previously [4].

6. WP6 : Transfer strategy and industrial development.
We have studied the feasibility of the creation of a start-up and this solution is currently preferred.
The IP has been strengthened by the application of a patent for soft tissues.

7. WP7 : Preparation of other applications
Two new applications have been developed.
_The use of the instrumented hammer in the context of osteotomies [7].
_ The use of the instrumented hammer in the context of soft tissues characterization [9].

The translational character of the project is proven by the fact that its main objective is to bring this technique into the medical field. The approach introduced in the project presents the following advantages. First, it leads to an integration of the device in the operating room. Second, the device is not in direct contact with the implant, minimizing risks of infection. Third, the method does not require any modification of the surgical procedure, which makes it easy-to-use for surgeons, thus maximizing the chances of massive adoption by the surgeons.
Findings obtained in OrthoMat will to develop new medical devices for other applications such as other arthroplasty or osteotomy.

1. Immel, K., Nguyen, VH, Dubory, A, Flouzat-Lachaniette CH, Sauer, R, and Haiat G “Determinants of the primary stability of cementless acetabular cup implants: A 3D finite element study” Computers in Biology and Medicine 135 (2021), pp. 104607.
2. Immel, K., Nguyen, VH, Haiat G and Sauer, R, “Long-term stability and debonding of cementless implants” Proceedings in Applied Mathematics and Mechanics 21(1) (2021), pp. e202100118.
3. Poudrel, AS., Nguyen, VH, Rosi, G, and Haiat G “Modal Analysis of the Ancillary During Femoral Stem Insertion: A Study on Bone Mimicking Phantoms” Ann Biomed Eng, 50(1) (2022), pp. 16-28.
4. Giunta, J, Lamassoure, L, Rosi, G, Poudrel, AS, Meningaud, JP, Haiat G and Bosc, R, “Validation of an Instrumented Hammer for Rhinoplasty Osteotomies: A Cadaveric Study”, Facial Plast Surg Aesthet Med 24(5) (2022), pp. 369-374.
5. Poudrel, AS., Nguyen, VH, Rosi, G and Haiat G “Influence of the biomechanical environment on the femoral stem insertion and vibrational behavior: a 3-D finite element study” Biomech. Model. Mechanobiol 22(2) (2023), pp. 611-628
6. Poudrel, AS., Nguyen, VH, Haiat G and Rosi, G, “Optimization of a smart beam for monitoring a connected inaccessible mechanical system: application to bone-implant coupling” Mechanical Systems and Signal Processing 192(1) (2023), pp. 110188.
7. Bas dit Nugues, M., Rosi, G, Heriveaux, Y and Haiat G “Using an instrumented hammer to predict the rupture of bone samples subject to an osteotomy” Sensors 23(4) (2023), pp. 2304.
8. Poudrel, AS., Rosi, G, Nguyen, VH, Housset V, Flouzat-Lachaniette CH and Haiat G “Detection of periprosthetic fractures around the femoral stem by resonance frequency analysis: an in vitro study” Part H: Journal of Engineering in Medicine 237(5) (2023), pp. 585-596
9. Poudrel, AS., Bouffandeau, A, Le Demeet, O, Rosi, G, Nguyen, VH and Haiat G “Characterization of the concentration of agar-based soft tissue” J Mech Behav Biomed Mater 152 (2024), pp. 106465

Total hip replacement (THR) surgery is the second most common surgery in France with a total number of around 150,000 patients per year. However, there remain risks of failure which may have dramatic consequences and which depend on the implant primary stability. An increasing number of THR is performed using the press-fit procedure, which consists in impacting the slightly oversized implants within bone tissue using an orthopaedic hammer. OrthoMat aims at developing and validating a market-ready medical device to provide a decision support system helping the surgeons adapting their surgical protocol in a patient-specific manner. This medical device will allow to assess the implant stability and the amount of bone in contact with the implant and to minimize the impact energy, thus leading to a decrease of per operative fracture risk. It consists in a hammer instrumented with piezoelectric sensors to be used during surgery without any modification of the surgical protocol. OrthoMat is based on feasibility studies performed on acetabular cup implants and on the femoral stem. We aim at developing a prototype ready for the CE marking and to test it under various conditions (in silico, in vitro, ex vivo and in anatomical subjects).
The originality of OrthoMat lies in the development of a medical device bringing quantification into a field where the surgeon proprioception is still widely employed in the operating room. We will develop a final prototype respecting all regulatory issues and adapted to the requirements of a use in a clinical environment. To do so, we will work on the measurement protocol and on the hardware (size and weight of the hammer, data processing, sensors, etc...). In order to reduce the number of experimental tests with anatomical subjects, numerical simulations will be used to calibrate the model in order to improve the accuracy of the device. To do so, we will develop a reliable in silico model of the impact procedure for the femoral stem and for the acetabular cup implant, which will allow the development of a signal processing algorithm that may be tested in silico. Signal processing techniques will be refined, involving machine learning algorithms to perform the inversion.
The technological breakthrough consists in the development of a standalone decision-support system that will be made available to orthopedic surgeons to help them insert the implant used in THR in a patient-specific manner (both the femoral stem and the acetabular cup implant). The innovation is based on the possibility to i) obtain a quantitative assessment of the implant stability, which is especially interesting for the acetabular cup implant; and ii) minimize the number and amplitude of impacts, leading to a reduction of intraoperative bone fractures, which is especially interesting for the femoral stem. These advances have been made possible thanks to the work of fundamental nature carried out in the MSME laboratory, which consists in understanding the biomechanical properties of newly formed bone tissue.
The translational character of the project is proven by the fact that its main objective is to bring this technique into the medical field. The approach introduced in the project presents the following advantages. First, it leads to an integration of the device in the operating room. Second, the device is not in direct contact with the implant, minimizing risks of infection. Third, the method does not require any modification of the surgical procedure, which makes it easy-to-use for surgeons, thus maximizing the chances of massive adoption by the surgeons.
The transfer strategy will be done through the start-up WaveImplant working in the domain of medical device or on the implant manufacturer Groupe Lépine who are both interested in the project. Findings obtained in OrthoMat will to develop new medical devices for other applications such as other arthroplasty or osteotomy.