Weight-bearing CT for musculoskeletal disorders

In patients with ankle osteoarthritis, cartilage wears over time at certain
critical locations in the joints. To correctly identify these stress locations
and assess their morphology, radiography is currently used in standard care.
Radiography is also the standard in patients with osteochondral defects, acute
ankle and foot trauma, neuropathic foot with or without Charcot and deformities
where severe deformities in case of claw toes or in case of amputation of (a
part of) the foot result in a change of anatomy, stability and loading
patterns.

The 2D nature of radiography limits the evaluation of morphological changes due
to over-projection of the complex three-dimensional (3D) structures in the foot
and ankle. Second, disorders with accompanying deformities may only be visible
in a weight-bearing situation. Furthermore, the foot is a structure that
continuously experiences weight-bearing, and pain is usually present during
load.

In a novel so-called weight-bearing computed tomography (CT) scanner, which is
installed this January 2019, 3D imaging of lower extremities takes place under
natural load in the upright position. This type of functional imaging, during
weight-bearing and simulated non-weight-bearing, may reveal problems that would
otherwise be non-discernable, such as the displacement and rotation of bone
fragments in patients with deformities and a diminished joint space in patients
with osteoarthritis. This perfectly fits in line with the goals and aims of the
Medical Image Quantification Centre (MIQC) of the Amsterdam University Medical
Centre.

By better understanding the morphology and by identifying locations of wear, or
impingement in 3D space, clinical decision-making and treatment plans may be
enhanced in patients with acute foot and ankle trauma, pathology or
instability, wear of the ankle, osteoarthritis, gait or deformities. In
patients treated for intra-articular dislocated calcaneal fractures, two groups
will be investigated. In the first group, the fracture is treated with primary
arthrodesis, where fracture fixation is used in the second group. Patient
outcomes in terms of stability, pressure distribution, pain due to impingement
and joint space can be compared between both groups in natural loading
conditions. In patients with Charcot foot, diabetic or neuropathic foot and
patients with claw toes or hallux valgus, imaging both with and without natural
loading enables to determine load induced pressure distribution under the foot
and its association with altered rotation and displacement of bones due to an
abnormal anatomy.

In the specified patient groups, quantitative outcomes will be compared in both
weight-bearing images and non-weight-bearing images. In detail, the location,
displacement and rotation of individual bone fragments in the foot will be
measured in 6 degrees of freedom (DOF) using dedicated Articulus software,
developed at the AMC. Measuring in 6 DOF enables to determine the actual
position of the foot, movement of bone fragments and condition of ligaments.
Also, the joint space can be visualized and measured at relevant wear
locations.

Primary Objective: The main objective is to determine the location,
displacement and rotation of individual bone fragments in the foot in 6 degrees
of freedom (DOF). A diminished joint space will be visualized and measured at
relevant wear locations.

Secondary Objective(s): The secondary objectives are:
- To measure pressure at multiple points under the foot using pressure plates
or soles currently used in a rehabilitation setting, and link this data to
functional image data.
- To compare location, displacement and rotational components of bone fragments
between weight-bearing and non-weight-bearing CT images.
- To link image data to patient reported outcome measures (PROMs):the Eurogol
5D questionnaire (EQ-5D) and the Functional Foot Index (FFI).

Acquisition:
Weight-bearing and non-weight-bearing images will be acquired on the Planmed
Verity® CT system of both ankles. This system uses cone beam CT (CBCT)
technology to provide 3D images of the extremities at a particularly low dose
similar to repeated plain radiographs. Patients stand on one leg in the small
bore of the weight-bearing CT scanner, with a field-of-view of approximately
13x16 cm. Forefoot and hindfoot images are acquired in order to image the
entire foot.


Analyses:
Articulus software will be used to measure the location, displacement and
rotation of individual bone fragments in 6 DOF. The software program will also
be used to investigate the possibilities to stitch forefoot and hindfoot
images. Diminished joint space can be measured using joint space maps, which
has previously been done in the wrist. Furthermore, relevant angle measurements
such as the hallux valgus angle (HVA), first intermetatarsal angle (IMA) and
calcaneal pitch angle (CPA) can be measured. Image metrics such as CT values
(measured in Hounsfield Units) and noise (measured as the standard deviation)
will be measured in relevant soft tissue and bone areas.

The patient does not have benefit from participating in this study and will
receive routine care. For research purposes additional weight-bearing and
non-weight-bearing CT-scans are obtained for each patient. This project will
yield a wealth of information on the applicability and added value of weight
bearing CT in a clinical setting. Results of functional image acquisition and
analysis may facilitate treating physicians in whether for example orthopaedic
surgery is indicated, if personal modified soles need to be created and if the
use of soles actually result in the intended position changes of the foot.