Evaluation of a new stress CT base-plate for 3D measurements of hindfoot kinematics and its pre-operative use in patients with primary osteochondral defects of the talus

The hindfoot complex, existing of the ankle and the subtalar joint, is prone to
a variety of disorders. There are a number of hindfoot joint affections, such
as degenerative joint disease after calcaneal fractures, foot deformities,
subtalar dislocation or instability, that cause severe pain and limit the
patient*s foot function. The wide range of values for injured and uninjured
ankles makes differentiation between normal and abnormal outcome difficult, and
differentiation at joint level is even more difficult. The high incidence of
chronic ankle instability after ankle ligament injury necessitates the
existence of effective diagnostic and treatment methods. In order to asses the
range of motion of the subtalar and talocrural joints independently, a
diagnostic tool was developed to perform a 3-dimensional stress CT (MEC
04/132). This CT-base-plate study proved to be a reliable method for analysing
joint mobility in extreme foot positions with little variation between the
testing subjects. Despite these positive results this device cannot be applied
in a clinical setting. Thereto, a new base-plate as designed that is smaller
and more ergonomic, has increased user friendliness, and does not require
assembling. Once validated, the new base-plate is used to measure the angle of
the maximum plantar flexion in patients with primary osteochondral defects of
the talus (OCD). This measure, combined with the position of the osteochondral
defect may be useful to decide the arthroscopic approach to be used in the
subsequent surgical procedure.

First part of the study: evaluation of the new CT base-plate
Compare the results obtained with the original base-plate to the results
obtained with the newly developed prototype platform and validate its use for
future clinical applications.
Second part of the study: clinical use of the new CT base-plate
Investigate whether the operative procedure can be planned more accurately with
the clinically measured maximal plantarflexion angle and the CT both in healthy
volunteers as in patients with an OCD that need surgical intervention.

First part of the study: evaluation of the new CT base-plate
We will analyse CT data of the ankles and hindfeet of a group of twenty healthy
individuals following a protocol similar to MEC 04/132, but with the addition
that their maximum plantarflexion angle in their right ankle is first measured
clinically by the surgeon. The subjects included in this project will be
volunteers of equally distributed to both sexes. Besides a CT scna in de
neutralposition, tn each subject four extreme foot positions will be measured
with both platforms: maximum dorsiflexion (DF), maximum plantarflexion (PF),
maximum anterolateral (AL) and maximum posteromedial (PM) position.

Second part of the study: clinical use of the new CT base-plate
In a subsequent period, twenty patients with an osteochondral defect who are
scheduled for a CT-scan of the ankle for preoperative planning of arthroscopic
treatment will be included. Their ankles are first measured clinically by the
surgeon. When routine CT-scans of the ankles for preoperative planning are
obtained, an additional low-dose CT-scan in the extreme plantarflexed positions
is also obtained, using the validated CT base-plate.

The research has no direct advantages for the twenty healthy individuals. As
opposed to the previous protocol the time required for the acquisition of
CT-scans will be reduced due to the use of the new base-plate. Disadvantage for
the volunteers is the radiation dose of the CT-scans, which is kept as low as
possible. Each subject will undergo one CT scan with a standard dosage (120 kV;
150 mAs) and 8 CT scans with a low dosage (120 kV; 26 mAs). Total exposure per
subject is 358 mAs, equal to ~ 0.3 mSv.
The research could potentially give a direct advantage for the twenty patients
participating. The results of the scans may provide the surgeon very detailed
information to decide which surgical approach would be the best for a patient.
Disadvantage for the patients is the extra (low) radiation dose of the
additional CT-scan.
The patients will undergo one CT scan with a standard dosage (120 kV; 150 mAs)
and one additional CT-scan with a low dosage (120 kV; 26mAs). Total exposure
per patient is 176 mAs, equal to ~ 0.15 mSv.