Total joint replacements have transformed millions of lives, but their success demands rigorous assessment of long-term safety, durability, and performance.
Professors Alice Roberts and Richard M Hall at the opening of the University of Birmingham's Advanced Medical Simulation and Testing laboratories.
Total joint replacements of the hip, knee, and increasingly, the shoulder and spine, have transformed the lives of millions, alleviating pain and restoring mobility. Their success has driven wider use, including in younger, more active individuals and patients with complex conditions. As the demands on these implants grow, so too does the need for more rigorous assessment of their long-term safety, durability, and clinical performance. This is no small task as human joints are complex, load-bearing systems, and the implants we design today are more advanced than ever.
At the University of Birmingham, we are working across engineering, healthcare, and regulatory science to improve how these critical technologies are evaluated. For decades, mechanical simulators have played a central role in these assessments. The machines replicate millions of walking cycles in the hip, for instance, to assess how implants wear and how generated debris might trigger adverse biological responses. However, despite these capabilities, questions persist about how well lab-based testing reflects the realities of human movement and joint function.
The challenge of representing the real world
Simulators are designed to balance reproducibility with clinical relevance. Most operate under idealised, standardised conditions – for example, fixed motions and controlled loads. Yet real-world patients vary widely in body weight, gait, muscular strength, and so on. Our laboratories at the University house unique simulators capable of recreating walking, running, and stair climbing in these patients. However, even with these advanced rigs significant challenges remain; for instance, a single test replicating five million walking cycles, roughly five years of use, can take up to four months. Additionally, implant technologies are progressing rapidly, with patient-specific designs, new biomaterials, and additive manufacturing becoming commonplace. Testing every possible configuration through physical trials alone is unfeasible. The pace of innovation is simply outstripping the capacity of conventional testing infrastructure.
One of the most promising advances in this space is the emergence of in silico trials; computer-based simulations that model how implants perform within virtual patient populations. These digital models can account for variations in, for instance, anatomy, movement, surgical approach, and disease status, offering insight into how devices might behave across a broad clinical spectrum.
International standards such as ISO 14242 (for hip wear) have improved the confidence in medical devices, but these standards often reflect only a narrow slice of clinical experience. The effects of conditions such as edge-loading, impingement, or inflammation are typically evaluated in supplementary, non-standard tests or not all. Critically, standards are often reactive. Many are introduced or updated only after long-term clinical use or when failures emerge. This lag can leave regulators and patients exposed to risks that were not well-characterised before the device entered the market. A prominent example is the metal-on-metal implant crisis of the 2010s. Devices were released with inadequate scrutiny, leading to high failure rates, tissue damage, and systemic metal ion exposure.
In Silico trials: A digital shift
One of the most promising advances in this space is the emergence of in silico trials; computer-based simulations that model how implants perform within virtual patient populations. These digital models can account for variations in, for instance, anatomy, movement, surgical approach, and disease status, offering insight into how devices might behave across a broad clinical spectrum. The advantages within these proposed models are significant - including the facts that simulations can assess hundreds of virtual patients in a fraction of the time needed for physical tests and the models can provide data not available in experimental assessments. Encouragingly, both the European Commission and US FDA are beginning to actively integrate in silico approaches into regulatory science within healthcare. These models are increasingly accepted in support of preclinical evaluation, performance prediction, and safety assessment.
Not replacement, but rethinking
It is important to be clear: in silico models are not a substitute for physical testing but are complementary. These virtual models must be built on robust experimental data and validated against clinical outcomes. Physical simulators still provide the empirical ‘ground truth’ against which digital models are refined. Similarly, retrieval analysis, the study of implants removed from patients, remains essential, especially when incorporating data from both successful and failed cases.
The future lies in hybrid frameworks. At Birmingham, we are in the early stages of developing integrated platforms that combine digital patient models with wear simulators and advanced imaging. These systems allow iterative testing of implant designs, failure scenarios, and surgical techniques. Crucially, they provide a more holistic, patient-centred view of device performance.
The broader implications
This shift in testing is part of a larger change in how we approach medical innovation. In silico trials enable adaptive testing strategies and earlier patient stratification, offering faster, safer access to life-enhancing technologies. For regulators and policymakers, this represents an opportunity to modernise evaluation frameworks without compromising on public trust.
Ultimately, we must ensure that our methods for assessing implants evolve alongside the devices themselves. That means embracing better models, smarter testing, and more responsive regulation. At the University of Birmingham, we believe the future lies in combining the power of simulation with the rigour of physical testing, in ways that are transparent, evidence-based, and focused on patient outcomes.
Professor of Biomechanical and Oncological Engineering
Profile of Professor Richard M Hall, University of Birmingham
