Total knee arthroplasty (TKA), a knee implant surgery, is a treatment for end-stage knee osteoarthritis. In some cases, patients suffer an associated periprosthetic fracture, a broken bone that occurs around the implant of a TKA, they may not receive excellent care due to a lack of a trustworthy assessments for fracture healing in the research world. The prevalence of TKA surgeries is increasing annually and is expected to increase further due to an ageing population and obesity issue. By extension to this primary surgery, more Canadians will require an invasive revision surgery that risks patient morbidity and mortality. Thus, it is important to set a standard for fracture stabilization and bone healing assessments to lessen revision burdens and improve patient outcomes. CT imaging is the main clinical tool to evaluate implant stabilization in TKA, which can effectively visualize areas of incomplete bone ingrowth, bone growing into the implant, that may be hidden from overlapping bone and muscle tissue on plain x-rays. The purpose of this prospective study is to examine the efficacy of weight-bearing CT as a diagnostic tool for 21 participants who experienced a distal femur periprosthetic fracture and have underwent revision surgery using a fracture fixation plate and screws, internal splints that hold the bone pieces together. Participants will be scanned under loaded (applying weight on limb) and unloaded conditions. Radiographic outcomes, x-ray imaging from the weight-bearing CT, will be evaluated, including any movement of the bone segments and how they would relate to participants' reports of pain.

Total knee arthroplasty is the most cost-effective and successful treatment for knee joints with end-stage osteoarthritis, with more than 58,000 TKA surgeries in Canada in 2021-2022.1 The prevalence of TKA surgeries is increasing per year and is projected to rise due to an ageing population and obesity problems.1 In addition to the primary surgery, more than 4,000 Canadians require revision TKA surgery per year; the TKA revision burden is estimated to reach $13 billion by 2030 as a consequence of a substantial increase of 149% in primary surgeries by 2030 in the United States.1-3 Revision surgery is more invasive than primary surgery and poses the risk of increasing patient mortality rates, especially for older adults.3 Thus, it is imperative for surgeons to make an appropriate radiographic diagnosis of implant fixation and/or fracture healing, but many cases remain challenging to diagnose.4

In the orthopaedic literature, there is no consensus on a reliable definition criterion for long-bone non-unions, making the standardization of diagnoses difficult; the lack of a trustworthy assessment for component fixation and fracture healing can lead to patients receiving sub-optimal care.5 This can also limit the collection of evidence supporting the use of specific implant components, surgical techniques, and post-operative activity guidelines. Moreover, comparing healing results of different clinical studies for long-bone non-unions can become problematic due to different criteria being used.5 Radiographic features associated with loosening such as radiolucencies are often only appreciable for the cement-bone interface, rather than the cement-implant interface which is the most common site of failure causing loosening.4 Failure to properly diagnose fracture non-union leaves patients in pain with substantial morbidity, while unnecessary surgery risks significant complication. Given the increasing rates of TKA and associated predictions of increasing revision burden,6 along with ongoing debates over the superiority of certain implants or surgical techniques, there is an unmet need for better fixation and bone healing assessment.

Historically, radiostereometric analysis (RSA) has been the gold standard for measuring implant fixation.7 However, it remains a niche tool limited to clinical research because of its requirement for implanted marker beads and specialized equipment being accessible for a handful of labs in North America.7-8 Recently, multiple groups have developed approaches to perform RSA-like measurements using clinical CT scans for shoulder, hip, and knee replacements.9 The accuracy and precision of the "CT-RSA" methods are on par with conventional RSA and acceptable for clinical studies.10-15 It is predicted that there will be a greater uptake of CT-RSA than conventional RSA, but the technology is still in its infancy.9 The application of CT-RSA will undoubtedly be more inclusive as examinations can now be performed on patients who did not have marker beads implanted at the time of their original surgery, and CAD models of implants are not needed.16 Using a weight-bearing CT scanner is the most similar implementation of CT-RSA to conventional RSA, as exams can be acquired in unloaded and loaded positions.

Additionally, in the field of microbiome research, the gut microbiome is being investigated for its potential impacts on bone health and recovery. There are currently a few studies that have linked the intestinal microbiome having a beneficiary effect to fracture healing with a new concept referred to as the gut-bone axis.17 Moreover, the gut microbiome of patients with poor bone quality has previously been found to be altered.18 We will use stool samples to assess gut microbiome composition to see if patients with markers for poor bone quality could have increased migration.

The results of this proposed study will demonstrate the ability to precisely measure displacements between bone segments under loading following periprosthetic fracture repair with weight-bearing. These will be the first-ever measurements of distal femur periprosthetic fracture healing with weight-bearing CT-RSA. Demonstration of this will enable us to pursue future studies that are prospective in nature and may evaluate topics such as time to weight-bearing activities, different types of surgical reconstructions, and relationship between healing and bone quality/bone health. Other centres with access to weight-bearing CT will also benefit from this work. Usage of the weight-bearing CT may improve the generalizability of this approach and support it as a clinical diagnostic tool. For example, surgeons may better understand bone fragment motion over time and recommend appropriate postoperative activities for patients' weight-bearing tolerance. Therefore, the proposed study design will evaluate the ability to perform inducible displacement measurements following the surgical repair of distal femur periprosthetic fractures using weight-bearing CT.

Inclusion Criteria:

• Recently underwent revision surgery for repair of a distal femur fracture surgery for total knee arthroplasty femoral component using a fracture fixation plate. Due to the study requiring the potential participant to be scanned <1-week post-operation, the duration of "recently" will be defined as <1 week post-operation.
• Age 50-90 years
• Body mass index up to 40kg/m2
• Able to provide informed consent
• Able and willing to do study assessments and follow instructions

Exclusion Criteria:

• Prior revision surgery on the targeted knee
• Does not understand English
• Undergoing and/or have undergone revision surgery for any other indication
• Received intramedullary nail or distal femur replacement
• Cannot independently stand on one leg in the weight-bearing CT during the inducible displacement exam