A team of researchers conducted a study to examine how AFO stiffness affects gait in patients who have undergone lower-limb salvage surgery; AFOs are commonly prescribed during rehabilitation from the surgery. They concluded that the patients were able to adapt to different dynamic AFO stiffnesses and demonstrated few biomechanical differences while walking. Further, none of the stiffness conditions normalized patients’ gait to that of the controls.
Spc. Michael Krapels, uses an IDEO during physical therapy at the Center for the Intrepid. Photograph courtesy of Steven Galvan, U. S. Army Medicine.
The study, published online before print in Clinical Orthopaedics and Related Research, describes the research team’s use of the Intrepid Dynamic Exoskeletal Orthosis (IDEO) to examine AFO stiffness in relation to gait parameters and whether AFO stiffness can normalize gait mechanics when compared to noninjured control subjects. Thirteen patients with lower-limb salvage after major lower-limb trauma (including ankle arthrodesis, neuropathy, or foot/ankle reconstruction) and 13 control subjects (no lower-limb trauma and no orthosis) underwent gait analysis at a standardized speed. Members of the patient group each wore a custom IDEO with posterior struts of three different stiffnesses: nominal (clinically prescribed stiffness), compliant (20 percent less stiff), and stiff (20 percent stiffer). Joint angles, moments, powers, and ground reaction forces were measured and compared across the varying stiffnesses and between the patient and control groups. An increase in AFO compliance resulted in 20-26 percent less knee flexion relative to the nominal and stiff conditions, respectively. Ankle range of motion and power generation were less than controls as a result of the relatively fixed ankle position; on average, ankle range of motion was 56 percent less and power generation was 63 percent less.
The data led the researchers to state that the general lack of difference across a 40 percent range of strut stiffness suggests that orthotists do not need to invest large amounts of time identifying optimal AFO stiffness for patients who use dynamic AFOs for low-impact activities. However, the researchers said, choosing a stiffer AFO strut may be beneficial in higher-impact activities and offer less chance of mechanical failure.
