Non-invasive Ultrasound Measurement Method for the Early Diagnosis of Loosening in Hip Prostheses

Germany leads the way in artificial hip replacement surgery. In 2020, 294.1 procedures were performed per 100,000 inhabitants, and the trend is rising. Loosening of artificial joints is one of the most common complications in orthopedics, with a prevalence of 10% within the first 15 years after surgery. When loosening occurs, a demineralized interlayer forms between the bone and the implant due to bone resorption; the thickness of this layer correlates with the stage of loosening. In the early stages, such loosening cannot be reliably diagnosed using conventional diagnostic methods, such as projection radiography. Nor can it be determined whether this is associated with the formation of a bacterial biofilm at the bone-implant interface, which can lead to infections. At the same time, promising ultrasound measurement principles exist in the technical context for determining the thickness and physical properties of a thin layer between two solid materials. Based on this, we developed a non-invasive ultrasound-based interferometric measurement method in collaboration with orthopedic surgeons from the regional Regiomed hospital network, which enables the characterization of the bone-implant interface. The method was successfully tested on simplified bone-implant systems for determining the interlayer thickness in the range of 200 µm to 2 mm. These results were presented at the MedtecSUMMIT 2023 conference and published in the journal “Sensors.” (https://doi.org/10.3390/s23135942).
To date, the method has been tested exclusively on idealized experimental setups, including the use of a pig bone with a prosthetic stem in a water bath. In real-world applications, many additional factors come into play that can affect the quality of the measurement results and place high demands on the robustness and accuracy of the method. These include the presence of periosteum, muscle, skin, and adipose tissue, as well as the individual characteristics of the bone tissue itself. An experimental validation of the method’s suitability—as expected by theory—for biofilm detection on the implant and thus for differentiating between mechanically and bacterially induced loosening is still pending.

The core of the project lies in the development of a non-invasive ultrasound measurement method for the early detection of hip prosthesis loosening. The goal is to characterize the interface layer that forms between the bone and the implant during loosening, so that the degree of loosening and its cause (e.g., bacterial infection) can be determined. This offers an advantage over conventional diagnostic methods, which do not allow for reliable early detection.

The project aims to further develop the method so that it delivers reliable results under the challenging conditions of real-world application. Additionally, the method’s suitability for detecting biofilm formation at the bone-implant interface will be evaluated. The ultimate goal is to develop a method that, by simply placing an ultrasound transducer on the skin of the thigh—in conjunction with the appropriate measurement electronics and evaluation algorithms—allows for reliable determinations of the type (determination of the physical properties of the interlayer) and stage (layer thickness) of existing prosthesis loosening.

Funding Program

DATIpilot Innovation Sprints

Project Title

Non-invasive Ultrasound Measurement Method for the Early Diagnosis of Loosening in Hip Prostheses (UltraHip)

Duration

October 1, 2024 – March 31, 2026

Funding Reference Number

03DPS1094

ISAT Funding Amount

€179,157.28