Can we find the optimal Ankle Foot Orthoses (AFO)?

Energy storing carbon composite Ankle Foot Orthoses (AFO) are frequently
prescribed to compensate for a reduced push off power in patients with Stroke,
Multiple Sclerosis (MS) and partial Spinal Cord Injury (SCI). From a mechanical
point of view it can be reasoned that the amount of energy that can be stored
and returned by the AFO, and thereby the functional benefit of the AFO, depends
on the mechanical characteristics of the AFO, particularly the AFO stiffness.
However, this remains to be proven because the mechanical AFO characteristics
have rarely been quantified. Ahead of this study we developed a measurement
device to reliably quantify the mechanical AFO stiffness. By varying the AFO
stiffness, the effect of AFO stiffness on gait performance can be investigated,
which is likely to result in an optimal AFO stiffness. Furthermore, evaluation
of the walking patterns with biomechanical gait analysis, will reveal how the
stiffness of the AFO must interact with the impaired ankle function in order to
result in an optimal walking performance. In addition, the current AFO
prescription process can be evaluated by comparing an AFO for which the
stiffness is determined by the rehabilitation physician and orthothist, to the
measured most optimal AFO stiffness.

1. To determine whether AFO stiffness can be optimized for individual patients
in terms of minimizing the energy cost of walking.
2. To asses whether the optimal AFO in terms of energy cost of walking matches
the AFO at which the most energy can be stored in the AFO, and at which the
highest peak push off power around the ankle joint during the pre-swing phase
of gait is obtained.
3. To evaluate how the stiffness of an AFO prescribed by a rehabilitation
physician relates to the objectively measured most optimal AFO stiffness.

1. To determine whether AFO stiffness can be optimized for individual patients
in terms of minimizing the energy cost of walking.
Controlled intervention study in which the functional benefit of walking with 5
different AFOs is compared to walking without an AFO.
2. To asses whether the optimal AFO in terms of energy cost of walking matches
the AFO at which the most energy can be stored in the AFO, and at which the
highest peak push off power around the ankle joint during the pre-swing phase
of gait is obtained.
Observational study in which it will be determined whether the benefit of
walking with 5 AFOs can be related to the biomechanical aspects of walking with
each of these 5 AFOs.
3. To evaluate how the stiffness of an AFO prescribed by a rehabilitation
physician relates to the objectively measured most optimal AFO stiffness.
Comparative study in which the regular (subjective) manner of AFO prescription
is compared to the objectively measured most optimal AFO prescription.

All 12 patients will walk with five AFOs with different stiffnesses. The gait
whilst wearing each of these AFOs will be compared to the control condition,
i.e. walking without an AFO. Subsequently, these results will be compared to
walking with a 6th AFO, that is prescribed according to the regular procedures.

Patients are measured during intake at the VUmc movement laboratory. This takes
approximately 3 hours. After the intake, the patients will visit the VUmc on
three separate days. The measurements during each of these days will take
approximately 2 hours per day. The risk for the patients in this study is
negligible. The load for patients is slightly higher than in a common gait
analysis that is regularly performed at our department to support clinical
decision making. With the current protocol the patients* gait can be studied in
a more reliable and objective manner, which will result in the best AFO
prescription for the patient. In order to make the load for patients as low as
possible, bouts of (seated) rest periods are planned in between the different
parts of the experiment and between the trials. The patients may benefit from
the study, because the optimal AFO will be prescribed to the patient after the
study. (If this AFO differs form the regularly prescribed AFO).