MRC/FNR Returning Safely to high-impact activities after JOINT replacements (SafeJOINTs)

Hip and knee replacements are very commonly performed surgeries. Joint replacements involve removing the painful portion of bone and replacing it with an implant. More and more patients wish to return to high-impact activities, like running, after a joint replacement. However, high-impact activities are discouraged by surgeons, for fear that they will harm the new joint implant and the surrounding bones - thus, requiring a second surgery. A second surgery is more expensive than the first and riskier for the patient.
This project will be the first to quantify the loads experienced by the implants and surrounding bones in high-impact activities after a joint replacement. It is very hard to conduct a 5 to 25-year study following patients over time and precisely measuring how many activities they are doing over these periods. However, computer models can allow us to precisely and efficiently measure the short- and long-term safety of high- and low-impact activities. Our three sub-projects will address this.
In our first sub-project, we will recruit individuals with hip and knee replacement who have successfully returned to high-impact activities. All participants will attend a single session of testing. Participants will complete a survey to gather information about their health and activity levels. We will capture motion and force measures and muscle activation patterns, while they will perform short bouts of walking, running, jumping, landing, hopping, and change of direction running. Lastly, participants will wear a small sensor for a week, to measure how much walking and running is done. The objective of this first sub-project is to understand how people move during high- and low-impact activities following a joint replacement. We also want to determine the volume of high- and low-impact activities undertaken by people after a joint replacement in their daily lives.
The second sub-project's objective is to determine how different types of activities (high-impact alone, lower-impact alone, or a mixture), different volumes and different movement techniques influence the amount that the new joint implant will wear out. This is crucial to understanding the safety of returning to running, because even though running exerts a higher impact than walking, it is done less frequently, and different running techniques can be used to potentially maximise its long-term safety. We will create computer models of the joints using information from the first sub-project, and create models that mimic many years of performing walking and running, and study the speed and amount of wear on the implants.
The objective of the final sub-project is to determine how different types of activities and movement techniques, influence the load experienced by the bone surrounding the new joint implant. By knowing how much load is applied and where it is concentrated, we can determine if these loads can result in bone breaking, or potentially be beneficial to build stronger bones. We will create another set of computer models of the joints to determine if the loads exerted by different activities will exceed the strength of the bone, causing breakage.
As joint replacements become more common and people live longer, more patients receiving a joint replacement will wish to return to some form of high-impact activities. High-impact activities have many physical and mental health benefits, like making bones stronger, which cannot easily be achieved by low-impact activities. Additionally younger patients are now receiving joint replacements. Not knowing if and by how much, high-impact activities are harmful, automatically removes the possibility to reap many health benefits from such activities. This will reduce patient satisfaction with the surgery. This project will provide crucial information that clinicians and patients can use to make informed healthcare decisions about the safety of returning to different activities after a joint replacement.

High-impact activities provide many superior health benefits over low-impact activities. However, high-impact activities are discouraged after a hip or knee joint replacement. High-impact activities may not automatically be harmful as these activities are performed less frequently than low-impact activities. Also, there are movement techniques that can make high-impact activities safer. SafeJOINTs will quantify and rank implant wear and bone loads across high- and low-impact activities, of varying volume and technique, with the goal that such information can be used for patient counselling.
In work package (WP) 1, we will recruit individuals who have successfully returned to high-impact activities after a hip or knee replacement. Using a custom survey, we will collect self-reported health, surgical, and activity outcomes. Biomechanics analysis will be undertaken during walking, running, jumping, drop-landing, hopping, and cutting. This will be followed up by a seven-day activity monitoring, to quantify the volume of walking and running performed. We will extract kinematic and kinetic hip and knee variables and compare them across activities. In WP2, we will perform musculoskeletal modelling to quantify joint contact forces, and conduct wear modelling of the hip and knee implants. We will quantify the wear volume, depth, rate, and location, and compare them across different activity types, volumes, and movement techniques. In WP3, finite element (FE) modelling will be used to quantify and compare the regional stress and strains of the bones surrounding the implants between different activities and movement techniques.
Without SafeJOINTs, many beneficial activity options will be removed from the lives of patients after a joint replacement, which will reduce surgical satisfaction. With SafeJOINTs, clinicians and patients can expect to know the risk associated with different activities, and how such risks can be managed by modifying activity volume and technique.