Page 50 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

50
Chapter III
aBStract
The effectiveness of an ankle foot orthosis-footwear combination (AFO-FC) may be partly dependent on the alignment of the ground reaction force with respect to lower limb joint rotation centers, reflected by joint angles and moments. Adjusting (i.e. tuning) the AFO-FC’s properties could affect this alignment, which may be guided by monitoring the shank-to-vertical angle (SVA). This study aimed to investigate whether the SVA during walking responds to variations in heel height and footplate stiffness, and if this would reflect changes in joint angles and net moments in healthy adults. Ten subjects walked on an instrumented treadmill and performed six trials while walking with bilateral rigid AFOs. The AFO-FC heel height was increased, aiming to impose a SVA of 5°, 11° and 20°, and combined with a flexible or stiff footplate. For each trial, the SVA, joint flexion-extension angles and net joint moments of the right leg at midstance were averaged over 25 gait cycles. The SVA significantly increased with increasing heel height (p<0.001), resulting in an increase in knee flexion angle and internal knee extensor moment (p<0.001). The stiff footplate reduced the effect of heel height on the internal knee extensor moment (p=0.030), while the internal ankle plantar flexion moment increased (p=0.035). Effects of heel height and footplate stiffness on the hip joint were limited. Our results support the potential to use the SVA as a parameter to evaluate AFO-FC tuning, as it is responsive to changes in heel height and reflects concomitant changes in the lower limb angles and moments.