Dynamic response in an orthosis can be described as the ability to store energy and dissipate energy in the gait cycle to achieve smooth efficient walking. A device that is too rigid will provide for stability but will not provide for mobility. A device that is too soft or has joints that allow for excessive motion will provide mobility without stability. The orthotic response must coincide with the weak or missing muscles of each individual. The orthosis must replace the function of these muscles. Motion must be assisted and resisted at the appropriate time in the gait cycle.
This is an ambitious task for an orthosis. Dynamic response is the ultimate characteristic that will improve function; however, there are conditions that must be met for dynamic response to have an effect on efficient walking. The following criteria must be met:
- triplanar control of the foot and limb
- skeletal realignment of the ankle, knee and hip
- triplanar support of weak or missing muscles
- control of rotary forces from above that cause deformity and balance problems
Extraneous or unwanted motion causing deviations or compensations must be eliminated. Motion must be directed in the line of progression in order to achieve efficiency in walking. The orthosis must redirect the abnormal forces causing movement in the wrong direction to more normal movement patterns. Energy is wasted in compensations for balance and security that decrease efficiency.
Dynamic response will provide for optimal outcomes if the preceding criteria are met. Static balance and stability precede dynamic stability. Once proper alignment is restored and weak or missing muscles are supported, design and materials will determine the effectiveness of dynamic response.