Adequately Diagnosing Total Knee Arthroplasty Loosening: a Randomized Controlled Trial Evaluating the AtMoves Knee System in a Routine Clinical Setting

Rationale:
Total Knee Arthroplasty (TKA) is a highly effective treatment for pain and loss
of function caused by rheumatoid arthritis or osteoarthritis of the knee. The
use of TKA has increased dramatically in recent years. Although TKA is a very
successful surgical procedure with satisfactory results, failure occurs and
results in persistent knee pain, reducing function. The main cause for revision
of a TKA is aseptic loosening, mainly of the tibial component. Current
diagnostic procedures are not completely adequate to determine TKA loosening.
This results in approximately 25-30% unnecessary revision surgeries, where at
the time of surgery the TKA is found not to be loose.

The AtMoves Knee System is a new technique developed to diagnose TKA release by
measuring the motion between the prosthetic component and adjacent bone as
caused by external loading of the knee. The measurement is performed on CT
scans of the loaded knee with a TKA. Using the AtMoves Knee System hardware
component, the loading device, the knee with the TKA is loaded with a bending
moment in the frontal plane, first in varus and second in valgus. With each
load, a CT scan of the bones and prosthetic components is taken. Using the
AtMoves Knee System software, the relative motion of the prosthetic component
to the bone is reconstructed and calculated from the three-dimensional CT scan
data.

AtMoves Knee System is expected to be a cheaper alternative to currently used
nuclear imaging techniques, such as bone scintigraphy and PET-CT scan. This
nuclear imaging only reveals biological activity in the bone surrounding the
prosthetic components. Therefore, nuclear imaging provides only indirect
evidence of prosthetic loosening and the outcome is often inconclusive, unlike
AtMoves Knee System, which provides actual data on the degree of TKA loosening.

The primary hypothesis is that the number of *failed outcomes* is lower after
using AtMoves Knee System in the diagnostic process, as opposed to using
standard imaging in the diagnostic process.

The primary objective of this study is to evaluate the efficacy of the AtMoves
Knee System in the clinical diagnostic process of aseptic knee loosening in
knee prostheses. This will be measured by the number of *failed outcomes*
resulting from incorrect diagnosis.

The study is a prospective, randomized, controlled, national diagnostic
multicenter trial.

The subject in the intervention group receives the AtMoves Knee System
evaluation, which includes both diagnostic reprocessing according to the
standard protocol along with two CT scans of the affected knee with opposing
varus and valgus loads as applied by the AtMoves Knee System loading device.
The AtMoves Knee System software calculates the relative motion between the
knee prosthetic component and the surrounding bone.

According to the initial routine reprocessing, the medical history is taken,
the physical examination is performed and a series of X-rays are taken
regularly. Only if the attending surgeons feel that an additional examination
is necessary, the subject is randomized into the intervention group or control
group. In the intervention group, the subject undergoes AtMoves Knee System
examination, i.e., CT imaging of the loaded knee.

The AtMoves Knee System examination consists of loading the knee and a
simultaneous CT scan of the knee and lower leg. The loads applied to the knee
by the AtMoves Knee System loading device are two bending moments in the
frontal plane of up to 20 Nm, in the varus and valgus directions. A CT scan is
taken at each loading. The loading of 20 Nm is less than the varus and valgus
load on the knee with a knee prosthesis during normal daily activities. The
total radiation does