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. However, the
availability of weight- bearing CT will always be lesser than conventional clinical CT
scanners, even as more and more high volume orthopaedic centres are acquiring
weight-bearing CT scanners. While some groups have implemented specialized loading
devices to perform such scans with conventional CT,17 a more generalizable approach of
simple internal-external leg rotations held in place with tape would ultimately offer the
greatest potential uptake across centres.
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 CT and conventional CT scanners. 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.
Consideration for the ability to perform similar measurements with conventional CT in
place of weight-bearing CT will 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 both weight-bearing CT and conventional
CT.